explanation blue bibcodes open ADS page with paths to full text
Author name code: cao
ADS astronomy entries on 2022-09-14
author:"Cao, Wenda"
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Title: High-precision Multichannel Solar Image Registration Using
Image Intensity
Authors: Liang, Bo; Chen, Xi; Yu, Lan; Feng, Song; Guo, Yangfan; Cao,
Wenda; Dai, Wei; Yang, Yunfei; Yuan, Ding
2022ApJS..261...10L Altcode:
Solar images observed in different channels with different instruments
are crucial to the study of solar activity. However, the images
have different fields of view, causing them to be misaligned. It
is essential to accurately register the images for studying solar
activity from multiple perspectives. Image registration is described
as an optimizing problem from an image to be registered to a reference
image. In this paper, we proposed a novel coarse-to-fine solar image
registration method to register the multichannel solar images. In the
coarse registration step, we used the regular step gradient descent
algorithm as an optimizer to maximize the normalized cross correlation
metric. The fine registration step uses the Powell-Brent algorithms
as an optimizer and brings the Mattes mutual information similarity
metric to the minimum. We selected five pairs of images with different
resolutions, rotation angles, and shifts to compare and evaluate
our results to those obtained by scale-invariant feature transform
and phase correlation. The images are observed by the 1.6 m Goode
Solar Telescope at Big Bear Solar Observatory and the Helioseismic and
Magnetic Imager on board the Solar Dynamics Observatory. Furthermore, we
used the mutual information and registration time criteria to quantify
the registration results. The results prove that the proposed method
not only reaches better registration precision but also has better
robustness. Meanwhile, we want to highlight that the method can also
work well for the time-series solar image registration.
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Title: Solar Chromospheric Network as a Source for Solar Wind
Switchbacks
Authors: Lee, Jeongwoo; Yurchyshyn, Vasyl; Wang, Haimin; Yang, Xu;
Cao, Wenda; Carlos Martínez Oliveros, Juan
2022ApJ...935L..27L Altcode:
Recent studies suggest that the magnetic switchbacks (SBs) detected
by the Parker Solar Probe carry information on the scales of solar
supergranulation (large scale) and granulation (medium scale). We test
this claim using high-resolution Hα images obtained with the visible
spectropolarimeters of the Goode Solar Telescope in Big Bear Solar
Observatory. As possible solar sources, we count all the spicule-like
features standing along the chromospheric networks near the coronal
hole boundary visible in the Hα blue-wing but absent in the red-wing
images and measure the geometric parameters of dense sections of
individual flux tubes. Intervals between adjacent spicules located
along the chromospheric networks are found in the range of 0.4-1.5
Mm (0.°03-0.°12) tending to be smaller than the medium scale of
SBs. Interdistances between all pairs of the flux tubes are also counted
and they appear in a single peak distribution around 0.7 Mm (0.°06)
unlike the waiting-time distribution of SBs in a scale-free single
power-law form. The length-to-diameter ratio of the dense section
of flux tubes is as high as 6-40, similar to the aspect ratio of
SBs. The number of spicules along a network can be as high as 40-100,
consistent with numerous SBs within a patch. With these numbers, it is
argued that the medium scale of SBs can be understood as an equilibrium
distance resulting from a random walk within each diverging magnetic
field funnel connected to the chromospheric networks.
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Title: Fan-shaped jet close to a light bridge
Authors: Liu, Y.; Ruan, G. P.; Schmieder, B.; Masson, S.; Chen, Y.;
Su, J. T.; Wang, B.; Bai, X. Y.; Su, Y.; Cao, Wenda
2022arXiv220713246L Altcode:
On the Sun,jets in light bridges are frequently observed with
high-resolution instruments.The respective roles played by convection
and the magnetic field in triggering such jets are not yet clear.We
report a small fan-shaped jet along a LB observed by the 1.6m Goode
Solar Telescope(GST) with the TiO Broadband Filter Imager(BFI),the
Visible Imaging Spectrometer(VIS) in H{\alpha},and the Near-InfraRed
Imaging Spectropolarimeter(NIRIS),along with the Stokes parameters.The
high spatial and temporal resolution of those instruments allowed us to
analyze the features identified during the jet event.By constructing
the H{\alpha} Dopplergrams,we found that the plasma is first moving
upward,whereas during the second phase of the jet,the plasma is
flowing back.Working with time slice diagrams,we investigated
the propagation-projected speed of the fan and its bright base.The
fan-shaped jet developed within a few minutes,with diverging beams. At
its base,a bright point was slipping along the LB and ultimately invaded
the umbra of the sunspot.The H{\alpha} profiles of the bright points
enhanced the intensity in the wings, similarly to the case of Ellerman
bombs.Co-temporally,the extreme ultraviolet brightenings developed at
the front of the dark material jet and moved at the same speed as the
fan, leading us to propose that the fan-shaped jet material compressed
and heated the ambient plasma at its extremities in the corona.Our
multi-wavelength analysis indicates that the fan-shaped jet could result
from magnetic reconnection across the highly diverging field low in the
chromosphere,leading to an apparent slipping motion of the jet material
along the LB.However,we did not find any opposite magnetic polarity at
the jet base,as would typically be expected in such a configuration.We
therefore discuss other plausible physical mechanisms,based on waves
and convection, that may have triggered the event.
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Title: Chromospheric Recurrent Jets in a Sunspot Group and Their
Intergranular Origin
Authors: Zhao, Jie; Su, Jiangtao; Yang, Xu; Li, Hui; Schmieder,
Brigitte; Ahn, Kwangsu; Cao, Wenda
2022ApJ...932...95Z Altcode: 2022arXiv220506981Z
We report on high-resolution observations of recurrent fan-like jets
by the Goode Solar Telescope in multiple wavelengths inside a sunspot
group. The dynamics behavior of the jets is derived from the Hα line
profiles. Quantitative values for one well-identified event have been
obtained, showing a maximum projected velocity of 42 km s<SUP>-1</SUP>
and a Doppler shift of the order of 20 km s<SUP>-1</SUP>. The
footpoints/roots of the jets have a lifted center on the Hα line
profile compared to the quiet Sun, suggesting a long-lasting heating at
these locations. The magnetic field between the small sunspots in the
group shows a very high resolution pattern with parasitic polarities
along the intergranular lanes accompanied by high-velocity converging
flows (4 km s<SUP>-1</SUP>) in the photosphere. Magnetic cancellations
between the opposite polarities are observed in the vicinity of
the footpoints of the jets. Along the intergranular lanes horizontal
magnetic field around 1000 G is generated impulsively. Overall, all the
kinetic features at the different layers through the photosphere and
chromosphere favor a convection-driven reconnection scenario for the
recurrent fan-like jets and evidence a site of reconnection between the
photosphere and chromosphere corresponding to the intergranular lanes.
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Title: Magnetic Field Re-configuration Associated With a Slow Rise
Eruptive X1.2 Flare in NOAA Active Region 11944
Authors: Yurchyshyn, Vasyl; Yang, Xu; Nita, Gelu; Fleishman, Gregory;
Abramenko, Valentina; Inoue, Satoshi; Lim, Eun-Kyung; Cao, Wenda
2022FrASS...916523Y Altcode:
Using multi-wavelength observations, we analysed magnetic field
variations associated with a gradual X1.2 flare that erupted on
January 7, 2014 in active region (AR) NOAA 11944 located near the disk
center. A fast coronal mass ejection (CME) was observed following the
flare, which was noticeably deflected in the south-west direction. A
chromospheric filament was observed at the eruption site prior to and
after the flare. We used SDO/HMI data to perform non-linear force-free
field extrapolation of coronal magnetic fields above the AR and to
study the evolution of AR magnetic fields prior to the eruption. The
extrapolated data allowed us to detect signatures of several magnetic
flux ropes present at the eruption site several hours before the
event. The eruption site was located under slanted sunspot fields
with a varying decay index of 1.0-1.5. That might have caused the
erupting fields to slide along this slanted magnetic boundary rather
than vertically erupt, thus explaining the slow rise of the flare
as well as the observed direction of the resulting CME. We employed
sign-singularity tools to quantify the evolutionary changes in the
model twist and observed current helicity data, and found rapid and
coordinated variations of current systems in both data sets prior to
the event as well as their rapid exhaustion after the event onset.
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Title: Design and expected performances of the large acceptance
calorimeter for the HERD space mission.
Authors: Pacini, L.; Adriani, O.; Bai, Y. l.; Bao, T. w.; Berti, E.;
Bottai, S.; Cao, W. w.; Casaus, J.; Cui, X. z.; D'Alessandro, R.;
Formato, V.; Gao, J. r.; Li, R.; Liu, X.; Lorusso, L.; Lyu, L. w.;
Marín, J.; Martínez, G.; Pizzolotto, C.; Qin, J. j.; Quan, Z.; Shi,
D. l.; Starodubtsev, O.; Tang, Z. c.; Tiberio, A.; Vagelli, V.; Wang,
B.; Wang, R. j.; Wang, Z. g.; Xu, M.; Yang, Y.; Zhang, L.; Zheng,
J. k.; Velasco, M. A.
2022icrc.confE..66P Altcode: 2022PoS...395E..66P
No abstract at ADS
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Title: Abyssal Manganese Nodule Recording of Global Cooling and
Tibetan Plateau Uplift Impacts on Asian Aridification
Authors: Jiang, X. D.; Zhao, X.; Zhao, X. Y.; Chou, Y. -M.; Roberts,
A. P.; Hein, J. R.; Yu, J. M.; Sun, X. M.; Shi, X. F.; Cao, W.; Liu,
Q. S.
2022GeoRL..4996624J Altcode:
The impact of central Asian aridification on the low latitude North
Pacific Ocean since the late Miocene remains unclear. To address this
question, we systematically studied an abyssal manganese nodule from
the northwestern Pacific Ocean, which is expected to be sensitive to
eolian dust sourced from central Asia. Geochemical variations and the
fossilized remains of magnetotactic bacteria within the studied nodule
manifest two prominent Asian aridification events at ∼8-7 Ma and 3.6-0
Ma. These results suggest that central Asian aridification impacted both
primary productivity and abyssal microbial activity in the NW Pacific
Ocean via eolian dust inputs. In contrast to the Pliocene aridification
event, the late Miocene event was associated with a primary productivity
bloom that is not evident in coeval global primary productivity records,
which indicates that the ∼8-7 Asian aridification event was likely
due to NE Tibetan Plateau uplift rather than to global cooling.
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Title: A High-resolution Study of Magnetic Field Evolution and
Spicular Activity around the Boundary of a Coronal Hole
Authors: Wang, Jiasheng; Lee, Jeongwoo; Liu, Chang; Cao, Wenda;
Wang, Haimin
2022ApJ...924..137W Altcode:
In this study, we analyze high-spatial-resolution (0.″24)
magnetograms and high-spatial-resolution (0.″10) Hα off-band (±
0.8 Å) images taken by the 1.6 m Goode Solar Telescope to investigate
the magnetic properties associated with small-scale ejections in a
coronal hole boundary region from a statistical perspective. With one
and a half hours of optical observations under excellent seeing, we
focus on the magnetic structure and evolution by tracking the magnetic
features with the Southwest Automatic Magnetic Identification Suite
(SWAMIS). The magnetic field at the studied coronal hole boundary is
dominated by negative polarity with flux cancellations at the edges
of the negative unipolar cluster. In a total of 1250 SWAMIS-detected
magnetic cancellation events, ~39% are located inside the coronal
hole with an average flux cancellation rate of 2.0 × 10<SUP>18</SUP>
Mx Mm<SUP>-2</SUP> hr<SUP>-1</SUP>, and ~49% are located outside
the coronal hole with an average flux cancellation rate of 8.8 ×
10<SUP>17</SUP> Mx Mm<SUP>-2</SUP> hr<SUP>-1</SUP>. We estimated
that the magnetic energy released due to flux cancellation inside the
coronal hole is six times more than that outside the coronal hole. Flux
cancellation accounts for ~9.5% of the total disappearance of magnetic
flux. Other forms of its disappearance are mainly due to fragmentation
of unipolar clusters or merging with elements of the same polarity. We
also observed a number of significant small-scale ejections associated
with magnetic cancellations at the coronal hole boundary that have
corresponding EUV brightenings.
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Title: Multi-passband Observations of a Solar Flare over the He I
10830 Å line
Authors: Xu, Yan; Yang, Xu; Kerr, Graham S.; Polito, Vanessa; Sadykov,
Viacheslav M.; Jing, Ju; Cao, Wenda; Wang, Haimin
2022ApJ...924L..18X Altcode: 2021arXiv211209949X
This study presents a C3.0 flare observed by the Big Bear Solar
Observatory/Goode Solar Telescope (GST) and Interface Region Imaging
Spectrograph (IRIS) on 2018 May 28 around 17:10 UT. The Near-Infrared
Imaging Spectropolarimeter of GST was set to spectral imaging mode to
scan five spectral positions at ±0.8, ±0.4 Å and line center of He I
10830 Å. At the flare ribbon's leading edge, the line is observed to
undergo enhanced absorption, while the rest of the ribbon is observed
to be in emission. When in emission, the contrast compared to the
preflare ranges from about 30% to nearly 100% at different spectral
positions. Two types of spectra, "convex" shape with higher intensity at
line core and "concave" shape with higher emission in the line wings,
are found at the trailing and peak flaring areas, respectively. On the
ribbon front, negative contrasts, or enhanced absorption, of about
~10%-20% appear in all five wavelengths. This observation strongly
suggests that the negative flares observed in He I 10830 Å with
mono-filtergram previously were not caused by pure Doppler shifts of
this spectral line. Instead, the enhanced absorption appears to be a
consequence of flare-energy injection, namely nonthermal collisional
ionization of helium caused by the precipitation of high-energy
electrons, as found in our recent numerical modeling results. In
addition, though not strictly simultaneous, observations of Mg II
from the IRIS spacecraft, show an obvious central reversal pattern
at the locations where enhanced absorption of He I 10830 Å is seen,
which is consistent with previous observations.
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Title: Stokes Inversion with Stacked Deep Neural Networks
Authors: Jiang, Haodi; Li, Qin; Xu, Yan; Ahn, Kwangsu; Cao, Wenda;
Wang, Jason T. L.; Wang, Haimin
2021AGUFMNG45B0583J Altcode:
Prediction of solar eruptive events is an important topic in space
weather research. Acquiring high-quality magnetic and velocity fields
through Stokes inversion is crucial for accurate solar eruption
prediction. We present here a new deep learning method, dubbed Stacked
Deep Neural Networks (SDNN), for Stokes inversion. We apply SDNN to
inferring line-of-sight (LOS) velocities and Doppler widths in addition
to vector magnetic fields from Stokes profiles of the Near InfraRed
Imaging Spectropolarimeter on the 1.6 m Goode Solar Telescope at the Big
Bear Solar Observatory. Experimental results show that SDNN is faster,
while producing smoother and cleaner LOS velocity maps and Doppler
width maps, than the widely used Milne-Eddington method. Furthermore,
SDNN outperforms three related machine learning algorithms, including
a convolutional neural network, multiple support vector regression
model, and multilayer perceptrons model, on different datasets. Thus,
the proposed deep learning based SDNN tool can be considered as an
alternative and efficient method for Stokes inversion.
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Title: Possible Signature of Sausage Waves in Photospheric Bright
Points
Authors: Gao, Yuhang; Li, Fuyu; Li, Bo; Cao, Wenda; Song, Yongliang;
Tian, Hui; Guo, Mingzhe
2021SoPh..296..184G Altcode: 2021arXiv211211756G
Sausage waves have been frequently reported in solar magnetic structures
such as sunspots, pores, and coronal loops. However, they have not been
unambiguously identified in photospheric bright points (BPs). Using
high-resolution TiO image sequences obtained with the Goode Solar
Telescope at the Big Bear Solar Observatory, we analyzed four isolated
BPs. It was found that their area and average intensity oscillate
for several cycles in an in-phase fashion. The oscillation periods
range from 100 to 200 seconds. We interpreted the phase relation as a
signature of sausage waves, particularly slow waves, after discussing
sausage-wave theory and the opacity effect.
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Title: Investigations of Sizes and Dynamical Motions of Solar
Photospheric Granules by a Novel Granular Segmenting Algorithm
Authors: Liu, Yanxiao; Jiang, Chaowei; Yuan, Ding; Zuo, Pingbing;
Wang, Yi; Cao, Wenda
2021ApJ...923..133L Altcode: 2021ApJ...923..133Y; 2021arXiv211003951Y
Granules observed in the solar photosphere are believed to be
convective and turbulent, but the physical picture of the granular
dynamical process remains unclear. Here we performed an investigation
of granular dynamical motions of full length scales based on data
obtained by the 1 m New Vacuum Solar Telescope and the 1.6 m Goode
Solar Telescope. We developed a new granule segmenting method, which
can detect both small faint and large bright granules. A large number
of granules were detected, and two critical sizes, 265 and 1420 km,
were found to separate the granules into three length ranges. The
granules with sizes above 1420 km follow Gaussian distribution,
and demonstrate flat in flatness function, which shows that they are
non-intermittent and thus are dominated by convective motions. Small
granules with sizes between 265 and 1420 km are fitted by a combination
of power-law function and Gauss function, and exhibit nonlinearity in
flatness function, which reveals that they are in the mixing motions
of convection and turbulence. Mini granules with sizes below 265
km follow the power-law distribution and demonstrate linearity in
flatness function, indicating that they are intermittent and strongly
turbulent. These results suggest that a cascade process occurs: large
granules break down due to convective instability, which transports
energy into small ones; then turbulence is induced and grows, which
competes with convection and further causes the small granules to
continuously split. Eventually, the motions in even smaller scales
enter in a turbulence-dominated regime.
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Title: A deep learning method to estimate magnetic fields in solar
active regions from photospheric continuum images
Authors: Bai, Xianyong; Liu, Hui; Deng, Yuanyong; Jiang, Jie; Guo,
Jingjing; Bi, Yi; Feng, Tao; Jin, Zhenyu; Cao, Wenda; Su, Jiangtao;
Ji, Kaifan
2021A&A...652A.143B Altcode:
Context. The magnetic field is the underlying cause of solar
activities. Spectropolarimetric Stokes inversions have been routinely
used to extract the vector magnetic field from observations for
about 40 years. In contrast, the photospheric continuum images have
an observational history of more than 100 years. <BR /> Aims: We
suggest a new method to quickly estimate the unsigned radial component
of the magnetic field, |B<SUB>r</SUB>|, and the transverse field,
B<SUB>t</SUB>, just from photospheric continuum images (I) using deep
convolutional neural networks (CNN). <BR /> Methods: Two independent
models, that is, I versus |B<SUB>r</SUB>| and I versus B<SUB>t</SUB>,
are trained by the CNN with a residual architecture. A total of
7800 sets of data (I, B<SUB>r</SUB> and B<SUB>t</SUB>) covering 17
active region patches from 2011 to 2015 from the Helioseismic and
Magnetic Imager are used to train and validate the models. <BR />
Results: The CNN models can successfully estimate |B<SUB>r</SUB>|
as well as B<SUB>t</SUB> maps in sunspot umbra, penumbra, pore, and
strong network regions based on the evaluation of four active regions
(test datasets). From a series of continuum images, we can also detect
the emergence of a transverse magnetic field quantitatively with the
trained CNN model. The three-day evolution of the averaged value of
the estimated |B<SUB>r</SUB>| and B<SUB>t</SUB> from continuum images
follows that from Stokes inversions well. Furthermore, our models can
reproduce the nonlinear relationships between I and |B<SUB>r</SUB>|
as well as B<SUB>t</SUB>, explaining why we can estimate these
relationships just from continuum images. <BR /> Conclusions: Our
method provides an effective way to quickly estimate |B<SUB>r</SUB>|
and B<SUB>t</SUB> maps from photospheric continuum images. The
method can be applied to the reconstruction of the historical
magnetic fields and to future observations for providing the quick
look data of the magnetic fields. <P />Movie is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140374/olm">https://www.aanda.org</A>
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Title: Magneto-acoustic oscillations observed in a solar plage region
Authors: Ji, Haisheng; Hashim, Parida; Hong, Zhenxiang; Xu, Zhe;
Shen, Jinhua; Ji, Kaifan; Cao, Wenda
2021RAA....21..179J Altcode: 2021arXiv210111998J
We gave an extensive study for the quasi-periodic perturbations on
the time profiles of the line of sight (LOS) magnetic field in 10
× 10 sub-areas in a solar plage region (corresponds to a facula
on the photosphere). The perturbations are found to be associated
with the enhancement of He I 10830 Å absorption in a moss region,
which is connected to loops with million-degree plasma. FFT analysis
to the perturbations gives a kind of spectrum similar to that of
Doppler velocity: a number of discrete periods around 5 minutes. The
amplitudes of the magnetic perturbations are found to be proportional
to magnetic field strength over these sub-areas. In addition, magnetic
perturbations lag behind a quarter of the cycle in the phase with
respect to the p-mode Doppler velocity. We show that the relationships
can be well explained with an MHD solution for the magneto-acoustic
oscillations in high-β plasma. Observational analysis also shows
that, for the two regions with the stronger and weaker magnetic field,
the perturbations are always anti-phased. All findings show that the
magnetic perturbations are actually magneto-acoustic oscillations on the
solar surface, the photosphere, powered by p-mode oscillations. The
findings may provide a new diagnostic tool for exploring the
relationship between magneto-acoustic oscillations and the heating of
the solar upper atmosphere, as well as their role in helioseismology.
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Title: Multi-passband Observations Of A Negative Flare Near He I
10830 Å
Authors: Xu, Y.; Yang, X.; Kerr, G.; Polito, V.; Jing, J.; Cao, W.;
Wang, H.
2021AAS...23830305X Altcode:
This study presents a C3.0 flare observed by the BBSO/GST and
IRIS, on 2018-May-28 around 17:10 UT. The Near Infrared Imaging
Spectropolarimeter (NIRIS) was set to spectral imaging mode to scan
five spectral positions at ±0.8 Å, ±0.4 Å and line center of He I
10830 Å. Negative contrasts of around 10%, appear in all of the five
wavelengths, with a weak dependence of these wavelengths. This means
that the line is undergoing enhanced absorption at these times. The
observations confirm that the negative flares observed in He I 10830 Å
with mono-filtergram previously were not caused by pure Doppler shifts
of this spectral line. Instead, the enhanced absorption is a consequence
of nonthermal ionization of helium following precipitation of high
energy electrons, as found in recent numerical modeling results. In
addition, though not strictly simultaneously, the IRIS observations show
clear central reversals in Mg II lines and strong Doppler shifts in C
II and Mg II lines at the locations where enhanced absorption in He I
10830 Å is occurring, consistent with previous observations and the
modeling. In other locations the Mg II profiles appear as single peaked.
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Title: Magnetic Field Configuration Associated With A Slow Rise
Eruptive X1.2 Flare In Active Region 11944
Authors: Yang, X.; Yurchyshyn, V.; Nita, G.; Abramenko, V.; Lim, E.;
Cao, W.
2021AAS...23812707Y Altcode:
Using multi-wavelength observations, we studied a gradual X1.2 flare
that erupted on January 7, 2014, in active region (AR) NOAA 11944
located near the disk center. A fast coronal mass ejection (CME) was
observed following the flare; however, it was strongly deflected in the
south-west direction. We used SDO/HMI data to perform extrapolation of
coronal magnetic fields and to study the evolution of AR magnetic fields
before the eruption. Extrapolated data allowed us to detect a flux rope
(FR) present at the eruption site several hours before the event. That
was the only well-defined FR present in the AR. Although the strapping
and core fields in the model have significantly changed after the flare,
the model FR did not erupt. We note that a chromospheric filament
was observed at the eruption site prior to and after the flare. The
eruption site was located under sunspot canopy fields with a decay
index of about 0.5, which is not favorable for torus instability to
develop. That might have caused the erupting fields to slide along the
canopy rather than vertically erupt, thus explaining the slow rise of
the flare as well as the observed direction of the resulting CME. We
employed sign-singularity tools to quantify the evolutionary changes
in a model twist and observed current helicity data, and found rapid
enhancements in the current systems in both data sets prior to the
event as well as their rapid exhaustion after the event onset.
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Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
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Title: Research on Multiwavelength Isolated Bright Points Based on
Deep Learning
Authors: Xu, Li; Yang, Yunfei; Yan, Yihua; Zhang, Yin; Bai, Xianyong;
Liang, Bo; Dai, Wei; Feng, Song; Cao, Wenda
2021ApJ...911...32X Altcode:
Multiwavelength bright points (BPs) are taken to be cross sections
of magnetic flux tubes extending from the surface of the photosphere
upward to the higher photosphere. We aim to study the characteristics
of isolated multiwavelength BPs using the cotemporal and cospatial
TiO band and Hα line wings from the Goode Solar Telescope at Big Bear
Solar Observatory. A deep-learning method, based on Track Region-based
Convolutional Neural Networks, is proposed to detect, segment, and match
the BPs across multiple wavelength observations, including the TiO, Hα
+ 1 Å, Hα - 1 Å, Hα + 0.8 Å, and Hα - 0.8 Å line wings. Based on
the efficient detection and matching result with a precision of 0.98,
1283 groups of BPs matched in all five wavelengths are selected for
statistics analysis. The characteristic values of the BPs observed
at the same red and blue line wings are averaged. For the BPs of the
TiO, averaged Hα ± 1 Å, and averaged Hα ± 0.8 Å line wings, the
mean equivalent diameters are 162 ± 32, 254 ± 33, and 284 ± 28 km,
respectively. The maximum intensity contrasts are 1.11 ± 0.09, 1.05 ±
0.03, and 1.05 ± 0.02 $\left\langle {I}_{\mathrm{QS}}\right\rangle $
, respectively. The mean eccentricities are 0.65 ± 0.14, 0.63 ± 0.11,
and 0.65 ± 0.11, respectively. Moreover, the characteristic ratios of
each Hα ± 1 Å and Hα ± 0.8 Å BP to its corresponding TiO BP are
derived. Hα ± 1 Å and Hα ± 0.8 Å line wings BPs show 60% and 80%
increases compared to TiO BPs, respectively. With increasing height,
most BPs almost keep their shapes. This work is helpful for modeling
the three-dimensional structure of flux tubes.
---------------------------------------------------------
Title: Failed Eruption Caused by Interacting Multi-current System
in the Solar Corona
Authors: Yang, Kai; Cao, Wenda; Wheatland, Michael S.
2021cosp...43E1780Y Altcode:
Solar flares are one of the most energetic activities of the Sun,
and are caused by current systems in the solar corona. Sometimes the
eruption of a current system is confined in the solar corona and fails
to trigger a coronal mass ejection or jet. A multi-current system
(multi-flux rope system) makes the confined/failed eruption process
more complex. To further investigate this phenomenon, we conduct a
data-driven zero-beta magnetohydrodynamics (MHD) simulation using the
Message Passing Interface Adaptive Mesh Refinement Versatile Advection
Code (MPI-AMRVAC). The initial condition is obtained by applying the
three-dimensional nonlinear force-free model to an observed vector
magnetogram from HMI. From the force-free magnetic field, three
flux ropes are identified in the active region, and the results are
compared with H$\alpha$ observation by the Goode Solar Telescope at
Big Bear Solar Observatory. The MHD simulation is driven by the time
series of the observed magnetogram and the inferred photospheric plasma
velocity. The simulation and observation confirm an interaction between
the three flux ropes, which leads to the initial eruption. With the
development of the interaction, magnetic reconnection mixes the flux
ropes and leads the system to a new stable state.
---------------------------------------------------------
Title: High-resolution He I 10830 Å Narrowband Imaging for an
M-class Flare. III. EUV Late Phase
Authors: Wang, Ya; Ji, Haisheng; Warmuth, Alexander; Li, Ying;
Cao, Wenda
2020ApJ...905..126W Altcode:
In this paper, we report the EUV late phase for the M1.8 class
flare on 2012 July 5 in the active region (AR) 11515. The late phase
is shown by the prominent appearance of EUV emission at 131 Å of
two additional flare loop systems (flare arcades 2 and 3, as named
in this paper) other than the main flare loop (flare arcade 1), as
observed by the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamic Observatory (SDO). Three sets of flare arcades connect four
flare ribbons, which forms an asymmetric quadrupole magnetic field
configuration. While the emission from flare arcade 2, linking the
pair of secondary flare ribbons, and arcade 3, linking one of the
main flare ribbons and one of the secondary flare ribbons, conjointly
contributes to the EUV late phase, their heating mechanisms are quite
different. While the brightening of flare arcade 2 is the result
of disturbance created by the eruption of EUV hot channels to the
overlying coronal magnetic field, the heating of flare arcade 3 was
closely associated with two rapid contractions of the overlying filament
threads during the partial eruption of the filament. The contractions
are discernible in He I 10830 Å images and have signatures in the
EUV wavelengths of AIA. The two rapid contractions are the result
of a sudden drop in magnetic pressure after the eruption of two hot
channels. Clear evidence suggests that magnetic reconnection may
occur between the contracting filament threads and the low-lying
magnetic field.
---------------------------------------------------------
Title: CYRA: the cryogenic infrared spectrograph for the Goode Solar
Telescope in Big Bear
Authors: Yang, Xu; Cao, Wenda; Gorceix, Nicolas; Plymate, Claude;
Shumoko, Sergey; Bai, XianYong; Penn, Matt; Ayres, Thomas; Coulter,
Roy; Goode, Philip R.
2020SPIE11447E..AGY Altcode: 2020arXiv200811320Y
CYRA (CrYogenic solar spectrogRAph) is a facility instrument of the
1.6-meter Goode Solar Telescope (GST) at the Big Bear Solar Observatory
(BBSO). CYRA focuses on the study of the near-infrared solar spectrum
between 1 and 5 microns, an under-explored region which is not only
fertile ground for photospheric magnetic diagnostics but also allows a
unique window into the chromosphere lying atop the photosphere. CYRA is
the first-ever fully cryogenic spectrograph in any solar observatory
with its two predecessors, on the McMath-Pierce and Mees Telescopes,
being based on warm optics except for the detectors and order
sorting filters. CYRA is used to probe magnetic fields in various
solar features and the quiet photosphere. CYRA measurements will
allow new and better 3D extrapolations of the solar magnetic field
and will provide more accurate boundary conditions for solar activity
models. The superior spectral resolution of 150,000 and better allows
enhanced observations of the chromosphere in the carbon monoxide (CO)
spectral bands and will yield a better understanding of energy transport
in the solar atmosphere. CYRA is divided into two optical sub-systems:
The Fore-Optics Module and the Spectrograph. The Spectrograph is
the heart of the instrument and contains the IR detector, grating,
slits, filters, and imaging optics all in a cryogenically cooled
Dewar (cryostat). The sensor is a 2048 by 2048 pixel HAWAII 2 array
produced by Teledyne Scientific and Imaging, LLC. The cryostat interior
and the readout electronics are maintained at 90 Kelvin by helium
refrigerant-based cryo-coolers, while the IR array is cooled to 30
Kelvin. The Fore-Optics Module de-rotates and stabilizes the solar
image, provides scanning capabilities and transfers the GST image
to the Spectrograph. CYRA has been installed and is undergoing its
commissioning phase. This paper reports on the design, implementation,
and operation of CYRA in detail. The preliminary scientific results
have been highlighted as well.
---------------------------------------------------------
Title: Doppler shift oscillations of a sunspot detected by CYRA
and IRIS
Authors: Li, D.; Yang, X.; Bai, X. Y.; Su, J. T.; Ning, Z. J.; Cao,
W.; Deng, Y. Y.
2020A&A...642A.231L Altcode: 2020arXiv200906942L
Context. The carbon monoxide (CO) molecular line at around 46655 Å in
solar infrared spectra is often used to investigate the dynamic behavior
of the cold heart of the solar atmosphere, i.e., sunspot oscillation,
especially at the sunspot umbra. <BR /> Aims: We investigated sunspot
oscillation at Doppler velocities of the CO 7-6 R67 and 3-2 R14 lines
that were measured by the Cryogenic Infrared Spectrograph (CYRA),
as well as the line profile of Mg II k line that was detected by the
Interface Region Imaging Spectrograph (IRIS). <BR /> Methods: A single
Gaussian function is applied to each CO line profile to extract the
line shift, while the moment analysis method is used for the Mg II k
line. Then the sunspot oscillation can be found in the time-distance
image of Doppler velocities, and the quasi-periodicity at the sunspot
umbra are determined from the wavelet power spectrum. Finally, the
cross-correlation method is used to analyze the phase relation between
different atmospheric levels. <BR /> Results: At the sunspot umbra,
a periodicity of roughly 5 min is detected at the Doppler velocity
range of the CO 7-6 R67 line that formed in the photosphere, while a
periodicity of around 3 min is discovered at the Doppler velocities
of CO 3-2 R14 and Mg II k lines that formed in the upper photosphere
or the temperature minimum region and the chromosphere. A time delay
of about 2 min is measured between the strong CO 3-2 R14 line and
the Mg II k line. <BR /> Conclusions: Based on the spectroscopic
observations from the CYRA and IRIS, the 3 min sunspot oscillation
can be spatially resolved in the Doppler shifts. It may come from the
upper photosphere or the temperature minimum region and then propagate
to the chromosphere, which might be regarded as a propagating slow
magnetoacoustic wave.
---------------------------------------------------------
Title: Formation of a tiny flux rope in the center of an active region
driven by magnetic flux emergence, convergence, and cancellation
Authors: Zheng, Ruisheng; Chen, Yao; Wang, Bing; Song, Hongqiang;
Cao, Wenda
2020A&A...642A.199Z Altcode: 2020arXiv200904082Z
<BR /> Aims: Flux ropes are generally believed to be core structures
of solar eruptions that are significant for the space weather, but
their formation mechanism remains intensely debated. We report on
the formation of a tiny flux rope beneath clusters of active region
loops on 2018 August 24. <BR /> Methods: Combining the high-quality
multiwavelength observations from multiple instruments, we studied
the event in detail in the photosphere, chromosphere, and corona. <BR
/> Results: In the source region, the continual emergence of two
positive polarities (P1 and P2) that appeared as two pores (A and
B) is unambiguous. Interestingly, P2 and Pore B slowly approached
P1 and Pore A, implying a magnetic flux convergence. During the
emergence and convergence, P1 and P2 successively interacted with a
minor negative polarity (N3) that emerged, which led to a continuous
magnetic flux cancellation. As a result, the overlying loops became
much sheared and finally evolved into a tiny twisted flux rope
that was evidenced by a transient inverse S-shaped sigmoid, the
twisted filament threads with blueshift and redshift signatures,
and a hot channel. <BR /> Conclusions: All the results show that
the formation of the tiny flux rope in the center of the active
region was closely associated with the continuous magnetic flux
emergence, convergence, and cancellation in the photosphere. Hence,
we suggest that the magnetic flux emergence, convergence,
and cancellation are crucial for the formation of the tiny flux
rope. <P />Movies associated to Figs. 2, 4, and 7 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202037475/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: High-resolution Observations of Small-scale Flux Emergence
by GST
Authors: Wang, Jiasheng; Liu, Chang; Cao, Wenda; Wang, Haimin
2020ApJ...900...84W Altcode: 2020arXiv200906717W
Recent observations demonstrated that emerging flux regions, which
constitute the early stage of solar active regions, consist of
emergence of numerous small-scale magnetic elements. They in turn
interact, merge, and form mature sunspots. However, observations of
fine magnetic structures on photosphere with subarcsecond resolution
are very rare due to limitations of observing facilities. In this
work, taking advantage of the high resolution of the 1.6 m Goode Solar
Telescope, we jointly analyze vector magnetic fields, continuum images,
and Hα observations of NOAA AR 12665 on 2017 July 13, with the goal
of understanding the signatures of small-scale flux emergence, as well
as their atmospheric responses as they emerge through multiple heights
in the photosphere and chromosphere. Under such a high resolution of
0"1-0"2, our results confirm two kinds of small-scale flux emergence:
magnetic flux sheet emergence associated with the newly forming
granules, and the traditional magnetic flux loop emergence. With
direct imaging in the broadband TiO, we observe that both types of
flux emergence are associated with darkening of granular boundaries,
while only flux sheets elongate granules along the direction of
emerging magnetic fields and expand laterally. With a life span of
10 ∼ 15 minutes, the total emerged vertical flux is on the order
of 10<SUP>18</SUP> Mx for both types of emergence. The magnitudes of
the vertical and horizontal fields are comparable in the flux sheets,
while the former is stronger in flux loops. Hα observations reveal
transient brightenings in the wings in the events of magnetic loop
emergence, which are most probably the signatures of Ellerman bombs.
---------------------------------------------------------
Title: Spectral Diagnostics of Solar Photospheric Bright Points
Authors: Hao, Q.; Fang, C.; Ding, M. D.; Li, Z.; Cao, Wenda
2020ApJ...900..130H Altcode: 2020arXiv200709675H
Through the use of the high-resolution spectral data and the broadband
imaging obtained with the Goode Solar Telescope at the Big Bear Solar
Observatory on 2013 June 6, the spectra of three typical photospheric
bright points (PBPs) have been analyzed. Based on the Hα and Ca II
8542 Å line profiles, as well as the TiO continuum emission, for
the first time, the non-LTE semiempirical atmospheric models for the
PBPs are computed. The attractive characteristic is the temperature
enhancement in the lower photosphere. The temperature enhancement is
about 200-500 K at the same column mass density as in the atmospheric
model of the quiet-Sun. The total excess radiative energy of a typical
PBP is estimated to be 1 × 10<SUP>27</SUP>-2 × 10<SUP>27</SUP> erg,
which can be regarded as the lower limit energy of the PBPs. The
radiation flux in the visible continuum for the PBPs is about 5.5
× 10<SUP>10</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>. Our result
also indicates that the temperature in the atmosphere above PBPs
is close to that of a plage. It gives clear evidence that PBPs may
contribute significantly to the heating of the plage atmosphere. Using
our semiempirical atmospheric models, we estimate self-consistently
the average magnetic flux density B in the PBPs. It is shown that the
maximum value is about 1 kG, and it decreases toward both higher and
lower layers, reminding us of the structure of a flux tube between
photospheric granules.
---------------------------------------------------------
Title: Date Co-alignment for Ground-Based High-Resolution Solar
Imaging
Authors: Yang, X.; Ji, K.; Cao, W.; Yurchyshyn, V.; Xu, Z.
2020SPD....5120501Y Altcode:
The multi-wavelength analysis is a well-spread method in solar
physics studies, and the community increasingly relies on coordinated
observations involving multiple instruments. The calibration of
heliographic coordinates is therefore vital for the co-alignment
of such multi-instrument, multi-wavelength data. However, this is
particularly difficult for ground-based high-resolution observations
because of the limited field of view. Manually co-aligning data with
low-contrast features (e.g., photospheric observations of quiet Sun
regions) between different telescopes requires exceptional efforts
and patience. Here, we developed a technique to accurately determine
coordinates of high-resolution images acquired by the Goode Solar
Telescope (GST) at the Big Bear Solar Observatory. The technique employs
a scale-invariant feature transform (SIFT) method, which performs
without human interference. With this new approach, we co-aligned
multi-wavelength GST data sets to the continuum intensity data from
the Helioseismic and Magnetic Imager (HMI) precisely. The inferred
heliographic coordinates are saved in each FITS file header, which
is compatible with the common mapping methods available in the Solar
SoftWare (SSW) package. GST data are fully open to the scientific
community, and a substantial portion of observing time on the GST
opens to the community as well.
---------------------------------------------------------
Title: Mare Deposits Identification and Feature Analysis in Mare
Australe Based on CE-2 CELMS Data
Authors: Meng, Z. G.; Chen, S. B.; Zheng, Y. C.; Cheng, W. M.; Zhu,
Y. Q.; Cai, Z. C.; Zhang, Y. Z.; Cao, W.; Hou, L. L.
2020JGRE..12506330M Altcode:
The microwave signal has the penetration capability, which provides
a potential chance to improve understanding of the mare deposits and
the formation process of Mare Australe, a complex, extensive, and
poorly understood region on the Moon. In this paper, the Chang'E-2
microwave radiometer (CELMS) data were selected and processed to
evaluate the microwave thermal emission features of the mare deposits
in Mare Australe. After comparison, the dT<SUB>B</SUB> map at 3.0 GHz
is employed. The results are as follows. (a) The possible cryptomare
is much more extensive in Australe region than that identified with
optical data. (b) The basaltic volcanism is re-understood as three
major episodes. (c) The high dT<SUB>B</SUB> anomaly is interpreted as
the location of the vent areas in the mare patches. (d) The K-means
algorithm was first used to process the CELMS data, and the identified
linear and ring structures indicate some important information about
the formation processes of Mare Australe. These special findings will be
of fundamental significance to better understand the basaltic volcanism
and the evolution of the lunar surface.
---------------------------------------------------------
Title: Astronomical Massive Data Processing Technology
Authors: Wang, Feng; Cao, Wenda; Bastieri, Denis; Fan, Junhui; Cui,
Chenzhou
2020AdAst2020E...5W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rapid Evolution of Type II Spicules Observed in Goode Solar
Telescope On-disk H<SUB>α</SUB> Images
Authors: Yurchyshyn, Vasyl; Cao, Wenda; Abramenko, Valentina; Yang,
Xu; Cho, Kyung-Suk
2020ApJ...891L..21Y Altcode: 2020arXiv200504253Y
We analyze ground-based chromospheric data acquired at a high temporal
cadence of 2 s in wings of the H<SUB>α</SUB> spectral line using the
Goode Solar Telescope operating at the Big Bear Solar Observatory. We
inspected a 30 minute long H<SUB>α</SUB>-0.08 nm data set to find
that rapid blueshifted H<SUB>α</SUB> excursions (RBEs), which are a
cool component of type II spicules, experience very rapid morphological
changes on timescales of the order of 1 s. Unlike typical reconnection
jets, RBEs very frequently appear in situ without any clear evidence
of H<SUB>α</SUB> material being injected from below. Their evolution
includes inverted "Y," "V," "N," and parallel splitting (doubling)
patterns as well as sudden formation of a diffuse region followed
by branching. We also find that the same feature may undergo several
splitting episodes within about a 1 minute time interval.
---------------------------------------------------------
Title: Generation of solar spicules and subsequent atmospheric heating
Authors: Samanta, Tanmoy; Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi;
Cao, Wenda; Sterling, Alphonse; Erdélyi, Robertus; Ahn, Kwangsu;
Feng, Song; Utz, Dominik; Banerjee, Dipankar; Chen, Yajie
2019Sci...366..890S Altcode: 2020arXiv200602571S
Spicules are rapidly evolving fine-scale jets of magnetized plasma in
the solar chromosphere. It remains unclear how these prevalent jets
originate from the solar surface and what role they play in heating
the solar atmosphere. Using the Goode Solar Telescope at the Big Bear
Solar Observatory, we observed spicules emerging within minutes of the
appearance of opposite-polarity magnetic flux around dominant-polarity
magnetic field concentrations. Data from the Solar Dynamics Observatory
showed subsequent heating of the adjacent corona. The dynamic
interaction of magnetic fields (likely due to magnetic reconnection)
in the partially ionized lower solar atmosphere appears to generate
these spicules and heat the upper solar atmosphere.
---------------------------------------------------------
Title: Light Bridge Brightening and Plasma Ejection Driven by a
Magnetic Flux Emergence Event
Authors: Yang, Xu; Yurchyshyn, Vasyl; Ahn, Kwangsu; Penn, Matt;
Cao, Wenda
2019ApJ...886...64Y Altcode:
Observations with the Goode Solar Telescope (GST) are presented
here showing that the emergence of 1.91 × 10<SUP>18</SUP> Mx of
new magnetic flux occurred at the edge of a filamentary light bridge
(LB). This emergence was accompanied by brightness enhancement of a
photospheric overturning convection cell (OCC) at the endpoints of the
emerging magnetic structure. We present an analysis of the origin and
the dynamics of this event using high-resolution GST Fe I 1564.85 nm
vector magnetic field data, TiO photospheric, and Hα chromospheric
images. The emerged structure was 1.5 × 0.3 Mm in size at the peak
of development and lasted for 17 minutes. Doppler observations showed
presence of systematic upflows before the appearance of the magnetic
field signal and downflows during the decay phase. Changes in the
orientation of the associated transverse fields, determined from
the differential angle, suggest the emergence of a twisted magnetic
structure. A fan-shaped jet was observed to be spatially and temporally
correlated with the endpoint of the OCC intruding into the LB. Our data
suggest that the emerging fields may have reconnected with the magnetic
fields in the vicinity of the LB, which could lead to the formation of
the jet. Our observation is the first report of flux emergence within
a granular LB with evidence in the evolution of vector magnetic field,
as well as photosphere convection motions, and supports the idea that
the impulsive jets above the LB are caused by magnetic reconnection.
---------------------------------------------------------
Title: High-resolution Observations of Dynamics of Superpenumbral
Hα Fibrils
Authors: Jing, Ju; Li, Qin; Liu, Chang; Lee, Jeongwoo; Xu, Yan; Cao,
Wenda; Wang, Haimin
2019ApJ...880..143J Altcode:
We present high-resolution Hα observations of a small solar pore in
NOAA active region 12661, using the 1.6 m Goode Solar Telescope equipped
with high-order adaptive optics at Big Bear Solar Observatory. The
observations reveal copious fine-scale chromospheric superpenumbral
fibrils (with an average cross-sectional width of ∼0.″17 ±
0.″03), along with associated transit and intermittent flows with
apparent speeds of 5-14 km s<SUP>-1</SUP>. Wavelet analysis and
the spatio-temporal pattern of superpenumbral fibrils suggest that
the observed flows along fibrils are not likely an oscillation/wave
phenomenon. Based on our pseudo-Dopplergrams, we suggest that the
observed flows may be a phenomenon similar to inverse Evershed flows in
the chromosphere. The three-dimensional potential field model indicates
that the pore and the surrounding fibrils are enclosed by fan-field
lines forming a separatrix dome configuration. Such a magnetically
confined configuration may help to maintain the steadfastness of the
superpenumbral fibril dynamics.
---------------------------------------------------------
Title: High-resolution Spectroscopic Imaging of Counter-streaming
Motions in Solar Active Region Magnetic Loops
Authors: Yang, Xu; Cao, Wenda; Ji, Haisheng; Hashim, Parida; Shen,
Jinhua
2019ApJ...881L..25Y Altcode:
We carried out high-resolution spectroscopic imaging in He I 10830 Å
and H<SUB> α </SUB> for a set of active region (NOAA 12569) magnetic
loops of different sizes (classified into short and long loops)
with the Goode Solar Telescope at the Big Bear Solar Observatory on
2016 July 18. The long loops take the form of an chromospheric arch
filament system, yet their extreme ultraviolet (EUV) counterparts
are observed by the Atmospheric Imaging Assembly on board the Solar
Dynamics Observatory. Animations of blue- and red-wing images give
counter-streaming motions; i.e., chromospheric absorption features in
blue- and red-wing images move in opposite directions at different
strands. The moving pattern is detected with the local correlation
tracking method and confirmed by Doppler shifts. We speculate that,
combined with the results of wavelet analysis that gives obvious 4
minute oscillation along trailing polarity, counter-streaming motions
for short loops could be powered by p-mode leakage. However, for
counter-streaming motions in long loops, we show that unidirectional
mass flows in two opposite directions are accompanied with simultaneous
weak EUV brightenings. Heating processes, probably by magnetic
reconnection at footpoints, may have occurred. In addition, plasma
flows along the magnetic loops, tracked with absorption features
in He I 10830 Å, are found to be ejected from and drained out into
inter-granule lane areas at different ends of the loop system.
---------------------------------------------------------
Title: Counter-streaming motions in active region magnetic arches
observed by Helium I 10830Å spectroscopy
Authors: Yang, Xu; Ya, Wang; Ji, Haisheng; Cao, Wenda
2019AAS...23421706Y Altcode:
We report the first high-resolution observations of counter-streaming
motions in the active region magnetic arches with Helium I 10830
Å spectroscopy, achieved by the Goode Solar Telescope at Big Bear
Solar Observatory. Our observations reveal that the counter-streaming
motions are due to unidirectional mass flows along alternative arches,
rather than the longitudinal oscillations of filament threads as in some
solar filaments. Mass flow, rooting in the magnetic network region, are
pumped up from and down to the inter-granulation lanes. The apparent
speed of the flow is around 15-50 km s<SUP>-1</SUP> in the He I 10830
Å blue wing and 5-15 km s<SUP>-1</SUP> in the red wing. Co-spatial
brightenings in Atmospheric Imaging Assembly 304 Å and 171 Å images
are witnessed at the same time, indicating the possible corresponding
heating process. The oscillation power peaks around 4 minutes in the
roots region of the arches, however, the mass flows inside the long
arches seem to be continuous.
---------------------------------------------------------
Title: High-resolution Observations of Dynamics of Superpenumbral
Hα Fibrils
Authors: Jing, Ju; Li, Qin; Liu, Chang; Lee, Jeongwoo; Xu, Yan; Cao,
Wenda; Wang, Haimin
2019AAS...23430502J Altcode:
We present unprecedented high-resolution Hα observations of a small
solar pore in NOAA Active Region 12661, using the 1.6 m Goode Solar
Telescope (GST) equipped with high-order adaptive optics at Big Bear
Solar Observatory (BBSO). The observations reveal copious fine-scale
chromospheric superpenumbral fibrils (with a cross-sectional width of
0.15") around the pore, along with associated transit and intermittent
flows with apparent speeds of 5-20 km s<SUP>-1</SUP>. The wavelet
analysis suggests that the observed flows along fibrils are not likely
a manifestation of oscillations, but rather collections of actual
counterstreaming mass motions. The observed flow is interpreted as
siphon flow. In addition, the three-dimensional potential field model
indicates that the pore and the surrounding fibrils are enclosed by
fan field lines forming a separatrix dome configuration. We suggest
that such a magnetically confined configuration may help to maintain
the steadfastness of the superpenumbral fibril dynamics.
---------------------------------------------------------
Title: Multi-wavelength Multi-height Study of Super Strong Surface
and Coronal Magnetic Fields in Active Region 12673
Authors: Wang, Haimin; Chen, Bin; Jing, Ju; Yu, Sijie; Liu, Chang;
Yurchyshyn, Vasyl B.; Ahn, Kwangsu; Okamoto, Takenori; Toriumi, Shin;
Cao, Wenda; Gary, Dale E.
2019AAS...23440205W Altcode:
Using the joint observations of Goode Solar telescope (GST), Expanded
Owens Valley Solar Array (EOVSA), Solar Dynamics Observatory (SDO)
and Hinode, we study the Solar Active Region (AR) 12673 in September
2017, which is the most flare productive AR in the solar cycle 24. GST
observations show the strong photospheric magnetic fields (nearly
6000 G) in polarity inversion line (PIL) and apparent photospheric
twist. Consistent upward flows are also observed in Dopplergrams
of Hinode, HMI and GST at the center part of that section of PIL,
while the down flows are observed in two ends, indicating that the
structure was rising from subsurface. Combining Non-Linear Force Free
Extrapolation and EOVSA microwave imaging spectroscopy, we also look
into the coronal structure of magnetic fields in this unusual AR,
including the evolution before and after the X9.3 flare on September
6, 2017. Coronal fields between 1000 and 2000 gauss are found above
the flaring PIL at the height range between 8 and 4Mm, outlining the
structure of a fluxrope or sheared arcade.
---------------------------------------------------------
Title: Calibration of the Instrumental Crosstalk for the Near-IR
Imaging Spectropolarimeter at the NST
Authors: Ahn, K.; Cao, W.
2019ASPC..526..317A Altcode: 2019arXiv190912970A
The Near-IR Imaging Spectropolarimeter (NIRIS) is a polarimeter that is
installed at the New Solar Telescope at Big Bear Solar Observatory. This
instrument takes advantage of the highest spatial resolution and
flux. The primary mirror is an off-axis type, so it was our interest to
evaluate its contribution to the crosstalk among the Stokes parameters
since we could not put our calibration optics before the mirror. We
would like to present our efforts to compensate for the crosstalk among
Stokes profiles caused by the relay optics from the telescope to the
detector. The overall data processing pipeline is also introduced.
---------------------------------------------------------
Title: Flame-like Ellerman Bombs and Their Connection to Solar
Ultraviolet Bursts
Authors: Chen, Yajie; Tian, Hui; Peter, Hardi; Samanta, Tanmoy;
Yurchyshyn, Vasyl; Wang, Haimin; Cao, Wenda; Wang, Linghua; He, Jiansen
2019ApJ...875L..30C Altcode: 2019arXiv190301981C
Ellerman bombs (EBs) are small-scale intense brightenings in Hα
wing images, which are generally believed to be signatures of
magnetic reconnection around the temperature minimum region of the
solar atmosphere. They have a flame-like morphology when observed
near the solar limb. Recent observations from the Interface Region
Imaging Spectrograph (IRIS) reveal another type of small-scale
reconnection event called an ultraviolet (UV) burst, in the lower solar
atmosphere. Though previous observations have shown a clear coincidence
between the occurrence of some UV bursts and EBs, the exact relationship
between these two phenomena is still debated. We investigate the spatial
and temporal relationship between flame-like EBs and UV bursts using
joint near-limb observations between the 1.6 m Goode Solar Telescope
(GST) and IRIS. In total, 161 EBs have been identified from the GST
observations, and ∼20 of them reveal signatures of UV bursts in
the IRIS images. Interestingly, we find that these UV bursts have a
tendency to appear at the upper parts of their associated flame-like
EBs. The intensity variations of most EB-related UV bursts and their
corresponding EBs match well. Our results suggest that some of these
UV bursts and EBs likely form at different heights during a common
reconnection process.
---------------------------------------------------------
Title: Signatures of Magnetic Reconnection at the Footpoints of
Fan-shaped Jets on a Light Bridge Driven by Photospheric Convective
Motions
Authors: Bai, Xianyong; Socas-Navarro, Hector; Nóbrega-Siverio,
Daniel; Su, Jiangtao; Deng, Yuanyong; Li, Dong; Cao, Wenda; Ji, Kaifan
2019ApJ...870...90B Altcode: 2018arXiv181103723B
Dynamical jets are generally found on light bridges (LBs), which are
key to studying sunspot decay. So far, their formation mechanism
is not fully understood. In this paper, we used state-of-the-art
observations from the Goode Solar Telescope, the Interface Region
Imaging Spectrograph, the Spectro-polarimeter on board Hinode, and
the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory to analyze the fan-shaped jets on LBs in detail. A
continuous upward motion of the jets in the ascending phase is found
from the Hα velocity that lasts for 12 minutes and is associated
with the Hα line wing enhancements. Two mini jets appear on the
bright fronts of the fan-shaped jets visible in the AIA 171 and 193
Å channels, with a time interval as short as 1 minute. Two kinds of
small-scale convective motions are identified in the photospheric
images, along with the Hα line wing enhancements. One seems to be
associated with the formation of a new convection cell, and the other
manifests as the motion of a dark lane passing through the convection
cell. The finding of three-lobe Stokes V profiles and their inversion
with the NICOLE code indicate that there are magnetic field lines
with opposite polarities in LBs. From the Hα -0.8 Å images, we found
ribbon-like brightenings propagating along the LBs, possibly indicating
slipping reconnection. Our observation supports the idea that the
fan-shaped jets under study are caused by magnetic reconnection, and
photospheric convective motions play an important role in triggering
the magnetic reconnection.
---------------------------------------------------------
Title: Evolution of Photospheric Vector Magnetic Field Associated
with Moving Flare Ribbons as Seen by GST
Authors: Liu, Chang; Cao, Wenda; Chae, Jongchul; Ahn, Kwangsu; Prasad
Choudhary, Debi; Lee, Jeongwoo; Liu, Rui; Deng, Na; Wang, Jiasheng;
Wang, Haimin
2018ApJ...869...21L Altcode: 2018arXiv181011733L
The photospheric response to solar flares, also known as coronal
back reaction, is often observed as sudden flare-induced changes in
the vector magnetic field and sunspot motions. However, it remains
obscure whether evolving flare ribbons, the flare signature closest to
the photosphere, are accompanied by changes in vector magnetic field
therein. Here we explore the relationship between the dynamics of
flare ribbons in the chromosphere and variations of magnetic fields
in the underlying photosphere, using high-resolution off-band Hα
images and near-infrared vector magnetograms of the M6.5 flare on 2015
June 22 observed with the 1.6 m Goode Solar Telescope. We find that
changes of photospheric fields occur at the arrival of the flare ribbon
front, thus propagating analogously to flare ribbons. In general, the
horizontal field increases and the field lines become more inclined
to the surface. When ribbons sweep through regions that undergo a
rotational motion, the fields transiently become more vertical with
decreased horizontal field and inclination angle, and then restore
and/or become more horizontal than before the ribbon arrival. The
ribbon propagation decelerates near the sunspot rotation center,
where the vertical field becomes permanently enhanced. Similar magnetic
field changes are discernible in magnetograms from the Helioseismic and
Magnetic Imager (HMI), and an inward collapse of coronal magnetic fields
is inferred from the time sequence of nonlinear force-free field models
extrapolated from HMI magnetograms. We conclude that photospheric fields
respond nearly instantaneously to magnetic reconnection in the corona.
---------------------------------------------------------
Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
2018arXiv181008728N Altcode:
The authors of this report met on 28-30 March 2018 at the New Jersey
Institute of Technology, Newark, New Jersey, for a 3-day workshop
that brought together a group of data providers, expert modelers, and
computer and data scientists, in the solar discipline. Their objective
was to identify challenges in the path towards building an effective
framework to achieve transformative advances in the understanding
and forecasting of the Sun-Earth system from the upper convection
zone of the Sun to the Earth's magnetosphere. The workshop aimed to
develop a research roadmap that targets the scientific challenge
of coupling observations and modeling with emerging data-science
research to extract knowledge from the large volumes of data (observed
and simulated) while stimulating computer science with new research
applications. The desire among the attendees was to promote future
trans-disciplinary collaborations and identify areas of convergence
across disciplines. The workshop combined a set of plenary sessions
featuring invited introductory talks and workshop progress reports,
interleaved with a set of breakout sessions focused on specific topics
of interest. Each breakout group generated short documents, listing
the challenges identified during their discussions in addition to
possible ways of attacking them collectively. These documents were
combined into this report-wherein a list of prioritized activities
have been collated, shared and endorsed.
---------------------------------------------------------
Title: Dark Structures in Sunspot Light Bridges
Authors: Zhang, Jingwen; Tian, Hui; Solanki, Sami K.; Wang, Haimin;
Peter, Hardi; Ahn, Kwangsu; Xu, Yan; Zhu, Yingjie; Cao, Wenda; He,
Jiansen; Wang, Linghua
2018ApJ...865...29Z Altcode: 2018arXiv180900146Z
We present unprecedented high-resolution TiO images and Fe I 1565
nm spectropolarimetric data of two light bridges taken by the 1.6
m Goode Solar Telescope at Big Bear Solar Observatory. In the first
light bridge (LB1), we find striking knot-like dark structures within
the central dark lane. Many dark knots show migration away from the
penumbra along the light bridge. The sizes, intensity depressions,
and apparent speeds of their proper motion along the light bridges of
33 dark knots identified from the TiO images are mainly in the ranges
of 80 ∼ 200 km, 30% ∼ 50%, and 0.3 ∼ 1.2 km s<SUP>-1</SUP>,
respectively. In the second light bridge (LB2), a faint central dark
lane and striking transverse intergranular lanes were observed. These
intergranular lanes have sizes and intensity depressions comparable
to those of the dark knots in LB1 and also migrate away from the
penumbra at similar speeds. Our observations reveal that LB2 is made
up of a chain of evolving convection cells, as indicated by patches of
blueshift surrounded by narrow lanes of redshift. The central dark lane
generally corresponds to blueshifts, supporting the previous suggestion
of central dark lanes being the top parts of convection upflows. In
contrast, the intergranular lanes are associated with redshifts and
located at two sides of each convection cell. The magnetic fields are
stronger in intergranular lanes than in the central dark lane. These
results suggest that these intergranular lanes are manifestations of
convergent convective downflows in the light bridge. We also provide
evidence that the dark knots observed in LB1 may have a similar origin.
---------------------------------------------------------
Title: Formation of an Active Region Filament Driven By a Series
of Jets
Authors: Wang, Jincheng; Yan, Xiaoli; Qu, Zhongquan; UeNo, Satoru;
Ichimoto, Kiyoshi; Deng, Linhua; Cao, Wenda; Liu, Zhong
2018ApJ...863..180W Altcode: 2018arXiv180700992W
We present a formation process of a filament in active region NOAA
12574 during the period from 2016 August 11 to 12. Combining the
observations of the Global Oscillation Network Group Hα, the Hida
spectrum, and the Solar Dynamics Observatory/AIA 304 Å, the formation
process of the filament is studied. It is found that cool material (T
∼ 10<SUP>4</SUP> K) is ejected by a series of jets originating from
the western footpoint of the filament. Simultaneously, the magnetic flux
emerged from the photosphere in the vicinity of the western footpoint of
the filament. These observations suggest that cool material in the low
atmosphere can be directly injected into the upper atmosphere and the
jets are triggered by the magnetic reconnection between pre-existing
magnetic fields and new emerging magnetic fields. A detailed study of
a jet at 18:02 UT on August 11 with GST/BBSO TiO observations revealed
that some dark threads appeared in the vicinity of the western footpoint
after the jet and the projection velocity of plasma along the filament
axis was about 162.6 ± 5.4 km s<SUP>-1</SUP>. Using these observations
of the Domeless Solar Telescope/Hida, we find that the injected plasma
by a jet at 00:42 UT on August 12 was rotating. Therefore, we conclude
that the jets not only supplied the material for the filament, but also
injected the helicity into the filament simultaneously. Comparing the
quantity of mass injection by the jets with the mass of the filament,
we conclude that the estimated mass loading by the jets is sufficient
to account for the mass in the filament.
---------------------------------------------------------
Title: Magnetic Flux Emergence Triggered Light Bridge Brightening
and Reconnection Jets
Authors: Yang, Xu; Cao, Wenda; Yurchyshyn, Vasyl; Ahn, Kwangsu
2018cosp...42E3744Y Altcode:
Light bridges (LBs) are elongated, bright, granular structures that
divide the umbra of a large and complex sunspot into two or more umbral
regions with the same magnetic polarity. Surge-like activities are
common phenomenon appear above the LBs which always accompanied by the
magnetic flux emergence process. Former works tried to interpret the
triggering mechanism for them, however they often lacked the support of
high spatial and temporal resolution vector magnetic measurement. Our
recent Observation shows a strong magnetic flux emergence happened
at the edge of a filamentary Light Bridge (LB) and accompanied by
brightness enhancement of photospheric granulations at the endpoints
of the emerged magnetic structure. We study the origin and dynamics of
this magnetic flux emergence event with high resolution Fe I 1.56 μm
polarimetry magnetogram, TiO photosphere image and Hα chromosphere
image from the Goode Solar Telescope. The emerged magnetic structure
was 1.5 Mm × 0.3 Mm in size at its peak time and lasted for 17
minutes. Doppler map detected upflows before its formation and downflows
during the destruction. The magnetic orientation change was obtained by
calculating the shear angle and plotting the magnetic field vectors. The
result indicates that the new emerged more transverse magnetic field
reconnected with the pre-existing more vertical field, which triggered
the fan-shaped jets. The expanding fields at the endpoints due to the
flux emergence pushed and compressed the existing granulations and
led to their enhanced brightness.
---------------------------------------------------------
Title: Project of a New 2.5m Solar Telescope
Authors: Fang, Cheng; Chen, P. F.; Li, Zhen; Cao, Wenda; Hao, Qi;
Ding, Mingde; Gu, Baizhong; Yuan, Xiangyan
2018cosp...42E1042F Altcode:
A project of a 2.5m Solar Telescope has been worked out in China. It
is the first facility in the world with a special innovation design
and can conduct both high-resolution solar observations and the
large-field of view (FOV) night survey. Its scientific objectives
cover solar physics and time-domain astronomy, all of which are recent
hot topics in astronomy. As a large on-axis solar telescope in the
world with a larger FOV (7') than all the large solar telescopes
operating at present, it can provide unprecedented high-resolution
solar imaging and magnetic field data, which can help us obtain
breakthrough achievements on the study of solar active regions and
solar eruptions. The data are also very useful for the study of space
weather. As a large telescope in China, the telescope is very unique
in continuously monitoring short-time transient events by filling
the gap in the specific time-zone. Moreover, the telescope can make
essential contribution to training the graduate and undergraduate
students majoring in observational astronomy.
---------------------------------------------------------
Title: Project of a New 2.5m Solar Telescope
Authors: Fang, Cheng; Chen, P. F.; Li, Zhen; Cao, Wenda; Hao, Qi;
Ding, Mingde; Gu, Baizhong; Yuan, Xiangyan
2018cosp...42E1041F Altcode:
A project of a 2.5m Solar Telescope has been worked out in China. It
is the first facility in the world with a special innovation design
and can conduct both high-resolution solar observations and the
large-field of view (FOV) night survey. Its scientific objectives
cover solar physics and time-domain astronomy, all of which are recent
hot topics in astronomy. As a large on-axis solar telescope in the
world with a larger FOV (7') than all the large solar telescopes
operating at present, it can provide unprecedented high-resolution
solar imaging and magnetic field data, which can help us obtain
breakthrough achievements on the study of solar active regions and
solar eruptions. The data are also very useful for the study of space
weather. As a large telescope in China, the telescope is very unique
in continuously monitoring short-time transient events by filling
the gap in the specific time-zone. Moreover, the telescope can make
essential contribution to training the graduate and undergraduate
students majoring in observational astronomy.
---------------------------------------------------------
Title: High-resolution He I 10830 Å Narrowband Imaging for an
M-class Flare. II. Multiple Hot Channels: Their Origin and Destination
Authors: Wang, Ya; Su, Yingna; Shen, Jinhua; Yang, Xu; Cao, Wenda;
Ji, Haisheng
2018ApJ...859..148W Altcode:
In this paper, we report our second-part result for the M1.8 class
flare on 2012 July 5, with an emphasis on the initiation process
for the flare-associated filament eruption. The data set consists
of high-resolution narrowband images in He I 10830 Å and broadband
images in TiO 7057 Å taken at Big Bear Solar Observatory with
the 1.6 m aperture Goode Solar Telescope. EUV images in different
passbands observed by the Atmospheric Imaging Assembly on board the
Solar Dynamics Observatory are used to distinguish hot plasma from
cool plasma structures during the flare process. High-resolution
10830 Å images clearly show that, below the horizontal fibrils,
which correspond to the filament’s spine in full-disk Hα images,
a sheared arch filament system (AFS) lies across the penumbra and
surrounding satellite sunspots, between which continuous shearing
motion is observed. Before the eruption, three microflares occurred
successively and were followed by the appearance of three EUV hot
channels. Two hot channels erupted, producing two flaring sites and
two major peaks in GOES soft X-ray light curves; however, one hot
channel’s eruption failed. The 10830 Å imaging enables us to trace
the first two hot channels to their very early stage, which is signified
by the rising of the AFS after the first two precursors. Continuous flux
emergence and localized flare-associated cancellation are observed under
the AFS. In addition, EUV ejections were observed during the formation
of the EUV hot channels. These observations support the fact that the
hot channels are the result of magnetic reconnections during precursors.
---------------------------------------------------------
Title: Evolution of Photospheric Magnetic Field Associated with
Flare Ribbons as Seen by GST
Authors: Liu, Chang; Cao, Wenda; Xu, Yan; Ahn, Kwangsu; Wang, Haimin
2018tess.conf40803L Altcode:
Solar flares produce signatures at various wavelengths and heights,
among which the response of photospheric magnetic and flow fields
to flare reconnection has drawn increasing attention recently. Such
a response has been evidenced as sudden flare-induced photospheric
structural evolution, especially vector magnetic field changes
and sunspot rotations. However, previous studies on this coronal
back-reaction process focused on the magnetic polarity inversion line
region and/or the overall temporal relationship. Here we present
high-resolution H-alpha off-band images and near-infrared vector
magnetograms of a major flare observed with the 1.6 m Goode Solar
Telescope (GST), which allow us to probe the relationship between
motions of flare ribbons and variations of the underlying field. It
is found that changes of photospheric fields occur instantly in a
largely step-wise fashion at the arrival of the flare ribbon front,
thus exhibit a propagation analogous to flare ribbons. In general, the
fields become more inclined to the surface, with enhanced horizontal
field and magnetic shear. When ribbons sweep through regions that
undergo an apparent rotational motion, the fields transiently turn
more vertical with decreased horizontal field and inclination angel,
and then become more horizontal. Interestingly, the ribbon decelerates
as approaching the sunspot rotation center, where the vertical field
becomes persistently enhanced. Overall, NLFFF extrapolation models
based on HMI vector field data suggest an inward collapse of magnetic
fields. These results indicate that photospheric fields may respond
instantaneously and differentially to the coronal field restructuring
due to reconnection of individual flux bundles.
---------------------------------------------------------
Title: Observation of Light Bridge Brightening and Plasma Ejection
Triggered by a Magnetic Flux Emergence Event
Authors: Yang, Xu; Yurchyshyn, Vasyl; Ahn, Kwangsu; Cao, Wenda
2018tess.conf10906Y Altcode:
Light bridges (LBs) are elongated, bright, granular structures that
divide the umbra of a large and complex sunspot into two or more umbral
regions with the same magnetic polarity. Surge-like activities are
common phenomenon appear above the LBs which always accompanied by the
magnetic flux emergence process. Former works tried to interpret the
triggering mechanism for them, however they often lacked the support of
high spatial and temporal resolution vector magnetic measurement. Our
recent Observation shows a strong magnetic flux emergence happened
at the edge of a filamentary Light Bridge (LB) and accompanied by
brightness enhancement of photospheric granulations at the endpoints
of the emerged magnetic structure. We study the origin and dynamics of
this magnetic flux emergence event with high resolution Fe I 1.56 μm
polarimetry magnetogram, TiO photosphere image and Hα chromosphere
image from the Goode Solar Telescope. The emerged magnetic structure
was 1.5 Mm × 0.3 Mm in size at its peak time and lasted for 17
minutes. Doppler map detected upflows before its formation and downflows
during the destruction. The magnetic orientation change was obtained by
calculating the shear angle and plotting the magnetic field vectors. The
result indicates that the new emerged more transverse magnetic field
reconnected with the pre-existing more vertical field, which triggered
the fan-shaped jets. The expanding fields at the endpoints due to the
flux emergence pushed and compressed the existing granulations and
led to their enhanced brightness.
---------------------------------------------------------
Title: Study of 3D magnetic Structure Corresponding to Extremely
Strong Photospheric Magnetic Fields in Active Region 12673
Authors: Wang, Haimin; Yurchyshyn, Vasyl; Liu, Chang; Chen, Bin;
Jing, Ju; Ahn, Kwangsu; Toriumi, Shin; Cao, Wenda
2018tess.conf31902W Altcode:
Solar Active Region (AR) 12673 is the most flare productive AR in the
solar cycle 24. It produced four X-class flares including the X9.3 flare
on 06 September 2017 and the X8.2 limb event on 10 September. Sun and
Norton (2017) reported that this region had an unusual high rate of
flux emergence, while Huang et al. (2018) reported that the X9.3 flare
had extremely strong white-light flare emission. Yang et al. (2017)
described the detailed morphological evolution of this AR. In this work,
we first study the unusual behaviors of the light bridge (LB) dividing
the delta configuration of this AR, namely the strong magnetic fields
(above 5500 G) in the LB and the apparent photospheric twist as seen in
observations with a 0.1 arcsec spatial resolution obtained by the 1.6m
Goode Solar Telescope (GST) at the Big Bear Solar Observatory. Using the
newly commissioned Expanded Owens Valley Solar Array (EOVSA), we carried
out diagnoses of magnetic fields in this AR with microwave imaging
spectroscopy from 2.5 to 18 GHz. Finally, we utilized Non-Linear Force
Free Field (NLFFF) extrapolation to reveal 3-D magnetic structure to
gain a physical understanding of GST and EOVSA observations of this AR.
---------------------------------------------------------
Title: Milne-Eddington Stokes Inversion of the NIRIS Magnetogram
Data Achieved by Machine Learning Technique
Authors: Ahn, Kwangsu; Cao, Wenda
2018tess.conf30818A Altcode:
The Near InfraRed Imaging Spectrograph (NIRIS) at the Goode Solar
Telescope produces Stokes I, Q, U, and V polarimetric profiles at
a spectral resolution of 0.01 nm in 1564.8 nm band, with a typical
range of -0.25 to +0.25 nm from the line center. This narrow band
is achieved with a combination of a pre-filter and dual Fabry-Perot
(F-P) etalon system. Typical line scan takes about 30 seconds. We
use Milne-Eddington (ME) inversion technique to deduce physical
parameters of an image pixel - such as total magnetic field strength,
vertical/horizontal component of the magnetic field, Doppler shift of
the line center and so on. However, due to many noise factors such
inversion attempts are not always reasonable, especially when the
profiles are complicated. Most of the ME fitting errors come from
the initial guess of the longitudinal field strenghth calcuated from
the center-of-gravity method. <P />We present our result of a new
approach of inversion by using machine learning technique. Sagemaker,
a new platform from Amazon Web Services, was adopted for training and
modeling of the line profiles. We used principal component analysis
(PCA) algorithm to deduce several physical parameters out of a trained
model. This method not only reduces the dimension of the data but also
enhances the speed of data processing. The result indicates that our
model well fits into the actual measured line profiles as well as
saving processing time. We present comparison of our new method to
the ME inversion method in terms of accuracy and processing time.
---------------------------------------------------------
Title: The Formation of a Sunspot Penumbra Sector in Active Region
NOAA 12574
Authors: Li, Qiaoling; Yan, Xiaoli; Wang, Jincheng; Kong, DeFang;
Xue, Zhike; Yang, Liheng; Cao, Wenda
2018ApJ...857...21L Altcode:
We present a particular case of the formation of a penumbra sector
around a developing sunspot in the active region NOAA 12574 on 2016
August 11 by using the high-resolution data observed by the New Solar
Telescope at the Big Bear Solar Observatory and the data acquired
by the Helioseismic and Magnetic Imager and the Atmospheric Imaging
Assembly on board the Solar Dynamics Observatory satellite. Before the
new penumbra sector formed, the developing sunspot already had two
umbrae with some penumbral filaments. The penumbra sector gradually
formed at the junction of two umbrae. We found that the formation of
the penumbra sector can be divided into two stages. First, during the
initial stage of penumbral formation, the region where the penumbra
sector formed always appeared blueshifted in a Dopplergram. The area,
mean transverse magnetic field strength, and total magnetic flux of
the umbra and penumbra sector all increased with time. The initial
penumbral formation was associated with magnetic emergence. Second,
when the penumbra sector appeared, the magnetic flux and area of the
penumbra sector increased after the umbra’s magnetic flux and area
decreased. These results indicate that the umbra provided magnetic flux
for penumbral development after the penumbra sector appeared. We also
found that the newly formed penumbra sector was associated with sunspot
rotation. Based on these findings, we suggest that the penumbra sector
was the result of the emerging flux that was trapped in the photosphere
at the initial stage of penumbral formation, and when the rudimentary
penumbra formed, the penumbra sector developed at the cost of the umbra.
---------------------------------------------------------
Title: High-resolution Observations of Flares in an Arch Filament
System
Authors: Su, Yingna; Liu, Rui; Li, Shangwei; Cao, Wenda; Ahn, Kwangsu;
Ji, Haisheng
2018ApJ...855...77S Altcode: 2018arXiv180306085S
We study five sequential solar flares (SOL2015-08-07) occurring in
Active Region 12396 observed with the Goode Solar Telescope (GST) at the
Big Bear Solar Observatory, complemented by Interface Region Imaging
Spectrograph and SDO observations. The main flaring region is an arch
filament system (AFS) consisting of multiple bundles of dark filament
threads enclosed by semicircular flare ribbons. We study the magnetic
configuration and evolution of the active region by constructing
coronal magnetic field models based on SDO/HMI magnetograms using
two independent methods, i.e., the nonlinear force-free field (NLFFF)
extrapolation and the flux rope insertion method. The models consist
of multiple flux ropes with mixed signs of helicity, i.e., positive
(negative) in the northern (southern) region, which is consistent with
the GST observations of multiple filament bundles. The footprints of
quasi-separatrix layers (QSLs) derived from the extrapolated NLFFF
compare favorably with the observed flare ribbons. An interesting
double-ribbon fine structure located at the east border of the AFS is
consistent with the fine structure of the QSL’s footprint. Moreover,
magnetic field lines traced along the semicircular footprint of a
dome-like QSL surrounding the AFS are connected to the regions of
significant helicity and Poynting flux injection. The maps of magnetic
twist show that positive twist became dominant as time progressed,
which is consistent with the injection of positive helicity before
the flares. We hence conclude that these circular shaped flares are
caused by 3D magnetic reconnection at the QSLs associated with the
AFS possessing mixed signs of helicity.
---------------------------------------------------------
Title: Frequently Occurring Reconnection Jets from Sunspot Light
Bridges
Authors: Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi; Solanki, Sami
K.; Young, Peter R.; Ni, Lei; Cao, Wenda; Ji, Kaifan; Zhu, Yingjie;
Zhang, Jingwen; Samanta, Tanmoy; Song, Yongliang; He, Jiansen; Wang,
Linghua; Chen, Yajie
2018ApJ...854...92T Altcode: 2018arXiv180106802T
Solid evidence of magnetic reconnection is rarely reported within
sunspots, the darkest regions with the strongest magnetic fields
and lowest temperatures in the solar atmosphere. Using the world’s
largest solar telescope, the 1.6 m Goode Solar Telescope, we detect
prevalent reconnection through frequently occurring fine-scale jets
in the Hα line wings at light bridges, the bright lanes that may
divide the dark sunspot core into multiple parts. Many jets have an
inverted Y-shape, shown by models to be typical of reconnection in a
unipolar field environment. Simultaneous spectral imaging data from
the Interface Region Imaging Spectrograph show that the reconnection
drives bidirectional flows up to 200 km s<SUP>-1</SUP>, and that the
weakly ionized plasma is heated by at least an order of magnitude up
to ∼80,000 K. Such highly dynamic reconnection jets and efficient
heating should be properly accounted for in future modeling efforts
of sunspots. Our observations also reveal that the surge-like activity
previously reported above light bridges in some chromospheric passbands
such as the Hα core has two components: the ever-present short surges
likely to be related to the upward leakage of magnetoacoustic waves
from the photosphere, and the occasionally occurring long and fast
surges that are obviously caused by the intermittent reconnection jets.
---------------------------------------------------------
Title: Extending Counter-streaming Motion from an Active Region
Filament to a Sunspot Light Bridge
Authors: Wang, Haimin; Liu, Rui; Li, Qin; Liu, Chang; Deng, Na; Xu,
Yan; Jing, Ju; Wang, Yuming; Cao, Wenda
2018ApJ...852L..18W Altcode: 2017arXiv171206783W
We analyze high-resolution observations from the 1.6 m telescope
at Big Bear Solar Observatory that cover an active region
filament. Counter-streaming motions are clearly observed in the
filament. The northern end of the counter-streaming motions extends
to a light bridge, forming a spectacular circulation pattern around a
sunspot, with clockwise motion in the blue wing and counterclockwise
motion in the red wing, as observed in the Hα off-bands. The apparent
speed of the flow is around 10-60 km s<SUP>-1</SUP> in the filament,
decreasing to 5-20 km s<SUP>-1</SUP> in the light bridge. The most
intriguing results are the magnetic structure and the counter-streaming
motions in the light bridge. Similar to those in the filament, the
magnetic fields show a dominant transverse component in the light
bridge. However, the filament is located between opposed magnetic
polarities, while the light bridge is between strong fields of
the same polarity. We analyze the power of oscillations with the
image sequences of constructed Dopplergrams, and find that the
filament’s counter-streaming motion is due to physical mass motion
along fibrils, while the light bridge’s counter-streaming motion
is due to oscillation in the direction along the line-of-sight. The
oscillation power peaks around 4 minutes. However, the section of
the light bridge next to the filament also contains a component of
the extension of the filament in combination with the oscillation,
indicating that some strands of the filament are extended to and rooted
in that part of the light bridge.
---------------------------------------------------------
Title: Strong Transverse Photosphere Magnetic Fields and Twist in
Light Bridge Dividing Delta Sunspot of Active Region 12673
Authors: Wang, Haimin; Yurchyshyn, Vasyl; Liu, Chang; Ahn, Kwangsu;
Toriumi, Shin; Cao, Wenda
2018RNAAS...2....8W Altcode: 2018RNAAS...2a...8W; 2018arXiv180102928W
Solar Active Region (AR) 12673 is the most flare productive AR in the
solar cycle 24. It produced four X-class flares including the X9.3 flare
on 06 September 2017 and the X8.2 limb event on 10 September. Sun and
Norton (2017) reported that this region had an unusual high rate of
flux emergence, while Huang et al. (2018) reported that the X9.3 flare
had extremely strong white-light flare emissions. Yang at al. (2017)
described the detailed morphological evolution of this AR. In this
report, we focus on usual behaviors of the light bridge (LB) dividing
the delta configuration of this AR, namely the strong magnetic fields
(above 5500 G) in the LB and apparent photospheric twist as shown in
observations with a 0.1 arcsec spatial resolution obtained by the 1.6m
telescope at Big Bear Solar Observatory.
---------------------------------------------------------
Title: Transient rotation of photospheric vector magnetic fields
associated with a solar flare
Authors: Xu, Yan; Cao, Wenda; Ahn, Kwangsu; Jing, Ju; Liu, Chang;
Chae, Jongchul; Huang, Nengyi; Deng, Na; Gary, Dale E.; Wang, Haimin
2018NatCo...9...46X Altcode: 2018arXiv180103171X
As one of the most violent eruptions on the Sun, flares are believed to
be powered by magnetic reconnection. The fundamental physics involving
the release, transfer, and deposition of energy have been studied
extensively. Taking advantage of the unprecedented resolution provided
by the 1.6 m Goode Solar Telescope, here, we show a sudden rotation of
vector magnetic fields, about 12-20° counterclockwise, associated
with a flare. Unlike the permanent changes reported previously,
the azimuth-angle change is transient and cospatial/temporal with
Hα emission. The measured azimuth angle becomes closer to that in
potential fields suggesting untwist of flare loops. The magnetograms
were obtained in the near infrared at 1.56 μm, which is minimally
affected by flare emission and no intensity profile change was
detected. We believe that these transient changes are real and discuss
the possible explanations in which the high-energy electron beams or
Alfve'n waves play a crucial role.
---------------------------------------------------------
Title: 1.56 Micron Spectropolarimetry of Umbral Dots and Their
Evolution Associated with a Major Flare
Authors: Deng, Na; Liu, Chang; Xu, Yan; Ahn, Kwangsu; Jing, Ju; Cao,
Wenda; Wang, Haimin
2017SPD....4830003D Altcode:
We present unprecedented high-resolution and high magnetic
sensitivity spectropolarimetric characterization of umbral dots
(UDs), the prevailing fine scale brightness structure manifesting
magneto-convection inside sunspot umbrae where the magnetic fields
are strongest and nearly vertical. This is made available by recent
development of the Near InfraRed Imaging Spectropolarimeter (NIRIS)
using the 1.56 micron FeI line at the 1.6 meter New Solar Telescope
of Big Bear Solar Observatory. Vector magnetograms are obtained after
Milne-Eddington Stokes inversions, 180-degree azimuthal ambiguity
resolution, and correction of projection effects. A βγδ spot in NOAA
AR 12371 was observed for six hours on June 22, 2015 with a cadence of
87 s, which covered an M6.6 flare. The overall umbra is separated into
several smaller umbrae by light bridges. The umbrae are close to the
flaring polarity inversion line and show an average inclination of about
17° and field strength of about 2100 Gauss. The UDs are resolvable in
NIRIS vector magnetograms, especially for peripheral UDs. The measured
field strength is about 3% lower in UDs comparing to umbral cores (UCs)
where the continuum intensity is below the threshold of UDs. The field
is more inclined in UDs by 5% ( ≈ 1°) than that in UCs. One of the
umbrae showed rapid evolution associated with the flare. Its overall
intensity and the number of UDs decrease by at least 7% within two
hours after being swept by the flare ribbon. NIRIS vector magnetograms
indicate that the average field strength of that umbra has a rapid
stepwise increase for about 100 Gauss while the inclination almost
has no change. The decreases of the umbral brightness and the number
of UDs are thus attributed to the increase of the field strength. The
results suggest that the field strength plays the most important role
in constraining convective heat transport in umbra.
---------------------------------------------------------
Title: High-resolution Observations of Photospheric Structural
Evolution Associated with a Flare
Authors: Liu, Chang; Xu, Yan; Ahn, Kwangsu; Jing, Ju; Deng, Na; Cao,
Wenda; Wang, Haimin
2017SPD....4810101L Altcode:
The structural evolution of the photosphere not only play an important
role in contributing to the accumulation of free energy in the corona
that powers solar flares, but also may response to the restructuring
of coronal field as a result of flare energy release. A better
understanding of these issues may be achieved by high-resolution
observations of the photospheric structure covering the entire
flaring period, which are, however, still rare. Here we present
photospheric vector magnetograms and TiO images (at 0.2" and 0.09"
resolution, respectively) from before to after a major flare, taken
by the 1.6 m New Solar Telescope at Big Bear Solar Observatory. In the
pre-flare state, a small-scale magnetic structure of opposite-polarity
configuration is seen near the footpoints of sheared magnetic loops;
its magnetic fluxes and currents enhance till the flare start time and
decline afterwards. During the main phase, as one flare ribbon sweeps
across a sunspot, its different portions accelerate at different times
corresponding to peaks of flare hard X-ray emission. We suggest that
the small-scale flux emergence between the two sheared flux systems
triggers the flare reconnection, and that the sunspot rotation is driven
by the surface Lorentz-force change due to the coronal back reaction.
---------------------------------------------------------
Title: Magnetic vector rotation in response to the energetic electron
beam during a flare
Authors: Xu, Yan; Cao, Wenda; Kwangsu, Ahn; Jing, Ju; Liu, Chang;
Chae, Jongchul; Huang, Nengyi; Deng, Na; Gary, Dale E.; Wang, Haimin
2017SPD....4810001X Altcode:
As one of the most violent forms of eruption on the Sun, flares are
believed to be powered by magnetic reconnection, by which stored
magnetic energy is released. The fundamental physical processes
involving the release, transfer and deposition of energy in multiple
layers of the solar atmosphere have been studied extensively with
significant progress. Taking advantage of recent developments in
observing facilities, new phenomena are continually revealed, bringing
new understanding of solar flares. Here we report the discovery of
a transient rotation of vector magnetic fields associated with a
flare observed by the 1.6-m New Solar Telescope at Big Bear Solar
Observatory. After ruling out the possibility that the rotation is
caused by line profile changes due to flare heating, our observation
shows that the transverse field rotateded by about 12-20 degrees
counterclockwise, and returned quickly to previous values after the
flare ribbons swept through. More importantly, as a consequence of
the rotation, the flare loops untwisted and became more potential. The
vector magnetograms were obtained in the near infrared at 1560 nm, which
is minimally affected by flare emission and no intensity profile change
was detected. Therefore, we believe that these transient changes are
real, and conclude the high energy electron beams play an crucial role
in the field changes. A straightforward and instructive explanation is
that the induced magnetic field of the electron beam superimposed on
the pre-flare field leads to a transient rotation of the overall field.
---------------------------------------------------------
Title: The Eruption of a Small-scale Emerging Flux Rope as the Driver
of an M-class Flare and of a Coronal Mass Ejection
Authors: Yan, X. L.; Jiang, C. W.; Xue, Z. K.; Wang, J. C.; Priest,
E. R.; Yang, L. H.; Kong, D. F.; Cao, W. D.; Ji, H. S.
2017ApJ...845...18Y Altcode: 2017arXiv170700073Y
Solar flares and coronal mass ejections are the most powerful explosions
in the Sun. They are major sources of potentially destructive space
weather conditions. However, the possible causes of their initiation
remain controversial. Using high-resolution data observed by the New
Solar Telescope of Big Bear Solar Observaotry, supplemented by Solar
Dynamics Observatory observations, we present unusual observations of
a small-scale emerging flux rope near a large sunspot, whose eruption
produced an M-class flare and a coronal mass ejection. The presence of
the small-scale flux rope was indicated by static nonlinear force-free
field extrapolation as well as data-driven magnetohydrodynamics modeling
of the dynamic evolution of the coronal three-dimensional magnetic
field. During the emergence of the flux rope, rotation of satellite
sunspots at the footpoints of the flux rope was observed. Meanwhile,
the Lorentz force, magnetic energy, vertical current, and transverse
fields were increasing during this phase. The free energy from the
magnetic flux emergence and twisting magnetic fields is sufficient to
power the M-class flare. These observations present, for the first time,
the complete process, from the emergence of the small-scale flux rope,
to the production of solar eruptions.
---------------------------------------------------------
Title: Data processing pipeline of the Near-Infrared Imaging
Spectropolarimeter at the NST
Authors: Ahn, Kwangsu; Cao, Wenda
2017SPD....4811504A Altcode:
The Near-Infrared Imaging Spectropolarimeter (NIRIS) is made for imaging
magnetic field structures on the Sun. The data acquired undergoes
extensive post-processing to ensure high resolution, high signal to
noise ratio, and high accuracy. We would like to introduce how the data
are processed by demonstrating data processing pipeline. In this manner,
the capabilities and the limits in data analysis would be evaluated. The
NIRIS is dedicated to Fe I 15648 band observation for now, while it
has potential for expanding their choice of bands as well as improving
data quality. Such upgrade plans should be discussed and prioritized.
---------------------------------------------------------
Title: Extending Counter-Streaming Motion from an Active Region
Filament to Sunspot Light Bridge
Authors: Wang, Haimin; Liu, Rui; Deng, Na; Liu, Chang; Xu, Yan; Jing,
Ju; Wang, Yuming; Cao, Wenda
2017SPD....4810405W Altcode:
In this study, we analyze the high-resolution observations from the 1.6
m New Solar Telescope at Big Bear Solar Observatory that cover an entire
active region filament. The southern end of the filament is well defined
by a narrow lane situated in the negative magnetic polarity, while the
northern end lies in the positive polarity, extending to a much larger
area. Counter-streaming motions are clearly seen in the filament. The
northern end of the counter-streaming motions extends to a light
bridge, forming a spectacular circulation pattern around a sunspot,
with clockwise motion in the blue wing and counterclockwise motion in
the red wing as observed in H-alpha off-band. The apparent speed of the
flow is around 10 km/s. We show that the southern end of the filament
is consistent with that of a flux rope in a NLFFF extrapolation model,
but the northern ends of the modeled flux rope and observed H-alpha
footpoints have a significant spatial mismatch. The most intriguing
results are the magnetic structure and the counter-streaming motions
in the light bridge. Similar to those in the filament, magnetic fields
show a dominant transverse component in the light bridge. However,
the filament is located between opposite magnetic polarities, while
the light bridge is between strong fields of the same polarity. We
studied the correlation coefficients of image sequences of constructed
Dopplergrams, and found that the filament and the section of light
bridge next to it do not show oscillation motions, while a small section
of light bridge shows a prominent oscillation pattern. Therefore, we
conclude that the observed circulating counter-streaming motions are
largely collections of physical mass flows in the transverse direction
from the filament extending to a large section of the light bridge,
rather than a form of periodic oscillatory mass motions in line-of-sight
direction generated by perturbations omnipresent in the chromosphere.
---------------------------------------------------------
Title: High-Resolution Observations of Flares in an Arch Filament
System
Authors: Su, Yingna; Liu, Rui; Li, Shangwei; Cao, Wenda; Ji, Haisheng
2017SPD....4840604S Altcode:
We present high-resolution observations of five sequential solar flares
occurring in NOAA Active Region (AR) 12396 taken with the 1.6-m New
Solar Telescope at the Big Bear Solar Observatory, complemented by IRIS
and SDO observations. The main flaring region is an arch filament system
(AFS) consisting of multiple bundles of dark filament threads enclosed
by scattered flare brightenings. We study the magnetic configuration and
evolution of the active region by constructing coronal magnetic field
models based on SDO/HMI magnetograms using two independent methods,
i.e., the nonlinear force-free field (NLFFF) extrapolation and the
flux rope insertion method. We are able to identify multiple flux ropes
based on magnetic twist derived from the extrapolated NLFFF, which is
consistent with the NST observations of multiple filaments. Both models
suggest that the filament bundles may posses mixed signs of helicity,
i.e., positive (negative) in the north (south). The footprints of
quasi-separatrix layers (QSLs) derived from the extrapolated NLFFF
compare favorably with the observed flare ribbons. Moreover, magnetic
field lines traced along the semi-circular footprint of a dome-like
QSL surrounding the flaring region are connected to the regions of
significant helicity and Poynting flux injection. An interesting
double-ribbon fine structure located at the east border of the AFS is
consistent with the fine structure of the QSL's footprint. The maps
of magnetic twist show that positive twist became dominant as time
progressed, which is consistent with the injection of positive helicity
during a 26 hour interval before the flares. The trigger mechanisms
and detailed dynamics of the observed flares are also discussed.
---------------------------------------------------------
Title: Multi-wavelength Spectral Analysis of Ellerman Bombs Observed
by FISS and IRIS
Authors: Hong, Jie; Ding, M. D.; Cao, Wenda
2017ApJ...838..101H Altcode: 2017arXiv170304268H
Ellerman bombs (EBs) are a kind of solar activity that is suggested
to occur in the lower solar atmosphere. Recent observations using the
Interface Region Imaging Spectrograph (IRIS) show connections between
EBs and IRIS bombs (IBs), which imply that EBs might be heated to a much
higher temperature (8 × 10<SUP>4</SUP> K) than previous results. Here
we perform a spectral analysis of EBs simultaneously observed by the
Fast Imaging Solar Spectrograph and IRIS. The observational results
show clear evidence of heating in the lower atmosphere, indicated by
the wing enhancement in Hα, Ca II 8542 Å, and Mg II triplet lines and
also by brightenings in images of the 1700 Å and 2832 Å ultraviolet
continuum channels. Additionally, the intensity of the Mg II triplet
line is correlated with that of Hα when an EB occurs, suggesting the
possibility of using the triplet as an alternative way to identify
EBs. However, we do not find any signal in IRIS hotter lines (C II
and Si IV). For further analysis, we employ a two-cloud model to fit
the two chromospheric lines (Hα and Ca II 8542 Å) simultaneously,
and obtain a temperature enhancement of 2300 K for a strong EB. This
temperature is among the highest of previous modeling results, albeit
still insufficient to produce IB signatures at ultraviolet wavelengths.
---------------------------------------------------------
Title: High-resolution observations of flare precursors in the low
solar atmosphere
Authors: Wang, Haimin; Liu, Chang; Ahn, Kwangsu; Xu, Yan; Jing, Ju;
Deng, Na; Huang, Nengyi; Liu, Rui; Kusano, Kanya; Fleishman, Gregory
D.; Gary, Dale E.; Cao, Wenda
2017NatAs...1E..85W Altcode: 2017arXiv170309866W
Solar flares are generally believed to be powered by free magnetic
energy stored in the corona<SUP>1</SUP>, but the build up of
coronal energy alone may be insufficient to trigger the flare to
occur<SUP>2</SUP>. The flare onset mechanism is a critical but poorly
understood problem, insights into which could be gained from small-scale
energy releases known as precursors. These precursors are observed as
small pre-flare brightenings in various wavelengths<SUP>3-13</SUP>
and also from certain small-scale magnetic configurations such
as opposite-polarity fluxes<SUP>14-16</SUP>, where the magnetic
orientation of small bipoles is opposite to that of the ambient main
polarities. However, high-resolution observations of flare precursors
together with the associated photospheric magnetic field dynamics are
lacking. Here we study precursors of a flare using the unprecedented
spatiotemporal resolution of the 1.6-m New Solar Telescope, complemented
by new microwave data. Two episodes of precursor brightenings are
initiated at a small-scale magnetic channel<SUP>17-20</SUP> (a form of
opposite-polarity flux) with multiple polarity inversions and enhanced
magnetic fluxes and currents, lying near the footpoints of sheared
magnetic loops. Microwave spectra corroborate that these precursor
emissions originate in the atmosphere. These results provide evidence
of low-atmospheric small-scale energy release, possibly linked to the
onset of the main flare.
---------------------------------------------------------
Title: Magnetic Separatrix as the Source Region of the Plasma Supply
for an Active-region Filament
Authors: Zou, P.; Fang, C.; Chen, P. F.; Yang, K.; Cao, Wenda
2017ApJ...836..122Z Altcode: 2017arXiv170101526Z
Solar filaments can be formed via chromospheric evaporation followed
by condensation in the corona or by the direct injection of cool
plasma from the chromosphere to the corona. We here confirm with
high-resolution Hα data observed by the 1.6 m New Solar Telescope of
the Big Bear Solar Observatory on 2015 August 21 that an active-region
filament is maintained by the continuous injection of cold chromospheric
plasma. We find that the filament is rooted along a bright ridge in Hα,
which corresponds to the intersection of a magnetic quasi-separatrix
layer with the solar surface. This bright ridge consists of many
small patches whose sizes are comparable to the width of the filament
threads. It is found that upflows originate from the brighter patches
of the ridge, whereas the downflows move toward the weaker patches of
the ridge. The whole filament is composed of two opposite-direction
streams, implying that longitudinal oscillations are not the only
cause of the counterstreamings, and unidirectional siphon flows with
alternative directions are another possibility.
---------------------------------------------------------
Title: A novel 3-D calorimeter for the High Energy cosmic-Radiation
Detection (HERD) Facility onboard China's Future Space Station
Authors: Dong, Y.; HERD Collaboration; Xu, M.; Wang, Z.; Adriani, O.;
Albergo, S.; Ambrosi, G.; Azzarello, P.; Bai, Y.; Bao, T.; Bernardini,
P.; Bertucci, B.; Bi, X.; Bongi, M.; Bottai, S.; Cao, W.; Chai, J.;
Chen, Z.; D'Alessandro, R.; Santo, M. D.; Duranti, M.; Fang, K.;
Feng, H.; Formato, V.; Fusco, P.; Gao, J.; Gargano, F.; Giglietto,
N.; Hu, P.; Li, R.; Li, Y.; Lin, S.; Liu, H.; Liu, X.; Loparco, F.;
Lyu, J.; Marsella, G.; Mazziottai, M. N.; Mitri, I. D.; Mori, N.;
Papini, P.; Peng, W.; Pohl, M.; Quan, Z.; Shi, D.; Sun, X.; Surdo,
A.; Vannuccini, E.; Walter, R.; Wang, B.; Wang, B.; Wang, J.; Wang,
L.; Wang, R.; Wu, B.; Wu, Q.; Wu, X.; Zhang, L.; Zhang, S. N.
2017ICRC...35..253D Altcode: 2017PoS...301..253D
No abstract at ADS
---------------------------------------------------------
Title: Introduction to the High Energy cosmic-Radiation Detection
(HERD) Facility onboard China's Future Space Station
Authors: Zhang, S. N.; Adriani, O.; Consortium, H.; Albergo, S.;
Ambrosi, G.; An, Q.; Azzarello, P.; Bai, Y.; Bao, T.; Bernardini, P.;
Bertucci, B.; Bi, X.; Bongi, M.; Bottai, S.; Cao, W.; Cao, Z.; Chai,
J.; Chang, J.; Chen, G.; Chen, Y.; Chen, Z.; Cui, X. H.; Dai, Z. G.;
D'Alessandro, R.; Santo, M. D.; Dong, Y.; Duranti, M.; Fan, Y.; Fang,
K.; Feng, C. Q.; Feng, H.; Formato, V.; Fusco, P.; Gao, J.; Gargano,
F.; Giglietto, N.; Gou, Q.; Guo, Y. Q.; He, H. H.; Hu, H.; Hu, P.;
Huang, G. S.; Huang, J.; Huang, Y. F.; Li, H.; Li, R.; Li, Y.; Li,
Z.; Liang, E. W.; Lin, S.; Liu, H.; Liu, H.; Liu, J. B.; Liu, S. B.;
Liu, S. M.; Liu, X.; Loparco, F.; Lyu, J.; Marsella, G.; Mazziottai,
M. N.; Mitri, I. D.; Mori, N.; Papini, P.; Pearce, M.; Peng, W.; Pohl,
M.; Quan, Z.; Ryde, F.; Shi, D.; Su, M.; Sun, X. L.; Sun, X.; Surdo,
A.; Tang, Z. C.; Vannuccini, E.; Walter, R.; Wang, B.; Wang, B.; Wang,
J. C.; Wang, J. M.; Wang, J.; Wang, L.; Wang, R.; Wang, X. L.; Wang,
X. Y.; Wang, Z.; Wei, D. M.; Wu, B.; Wu, J.; Wu, Q.; Wu, X.; Wu,
X. F.; Xu, M.; Xu, Z. Z.; Yan, H. R.; Yin, P. F.; Yu, Y. W.; Yuan,
Q.; Zha, M.; Zhang, L.; Zhang, L.; Yi, Z.; Zhang, Y. L.; Zhao, Z. G.
2017ICRC...35.1077Z Altcode: 2017PoS...301.1077Z
No abstract at ADS
---------------------------------------------------------
Title: Objective Image Quality Assessment for High Resolution
Photospheric Images by Median Filter Gradient Similarity
Authors: Deng, Hui; Zhang, Dandan; Wang, Tianyu; Ji, Kaifan; Wang,
Feng; Liu, Zhong; Xiang, Yongyuan; Jin, Zhenyu; Cao, Wenda
2017arXiv170105300D Altcode:
All next generation ground-based and space-based solar telescopes
require a good quality assessment metric in order to evaluate their
imaging performance. In this paper, a new image quality metric, the
median filter gradient similarity (MFGS) is proposed for photospheric
images. MFGS is a no-reference/blind objective image quality metric
(IQM) by a measurement result between 0 and 1 and has been performed
on short-exposure photospheric images captured by the New Vacuum
Solar Telescope (NVST) of the Fuxian Solar Observatory and by
the Solar Optical Telescope (SOT) onboard the Hinode satellite,
respectively. The results show that: (1)the measured value of MFGS
changes monotonically from 1 to 0 with degradation of image quality;
(2)there exists a linear correlation between the measured values of
MFGS and root-mean-square-contrast (RMS-contrast) of granulation;
(3)MFGS is less affected by the image contents than the granular
RMS-contrast. Overall, MFGS is a good alternative for the quality
assessment of photospheric images.
---------------------------------------------------------
Title: Unprecedented Fine Structures during a Solar Eruptive
Event Observed by the 1.6-m New Solar Telescope at Big Bear Solar
Observatory
Authors: Xu, Y.; Jing, J.; Li, Q.; Cao, W.; Wang, H.
2016AGUFMSH41E..04X Altcode:
A solar eruptive event includes both large-scale and small-scale
structures. Flares, filament eruptions and CMEs are large-scale features
and have been studied extensively in the literature. On the other hand,
fine structures (below 500 km) are rarely observed and are accessible to
only a fewinstruments world-wide. Using the 1.6-m New Solar Telescope
(NST) at Big Bear Solar Observatory (BBSO), an M6.5 flare was captured
on June 22, 2015. This extraordinary observation reveals the process
of the magnetic energy release in unprecedented detail, including
the flare ribbon propagating across the sunspots, sunspot rotation,
magnetic channels (elongated structurescomprising alternating magnetic
polarity inversion lines), coronal rain (made of condensing plasma)
streaming down along the post-flare loops, and the chromosphere's
response to the impact of coronal rain, showing fine-scale brightenings
at the footpoints of the falling plasma. Here we present our analysis
of this event in a comprehensive manner covering the above phenomena.
---------------------------------------------------------
Title: High Resolution He I 10830 AA Narrow-band Imaging of an
M-class Flare. I - Analysis of Sunspot Dynamics during Flaring
Authors: Wang, Ya; Su, Yingna; Hong, Zhenxiang; Zeng, Zhicheng; Ji,
Kaifan; Goode, Philip R.; Cao, Wenda; Ji, Haisheng
2016ApJ...833..250W Altcode:
In this paper, we report our first-step results of high resolution
He I 10830 Å narrow-band imaging (bandpass: 0.5 Å) of an M1.8 class
two-ribbon flare on 2012 July 5. The flare was observed with the 1.6
m aperture New Solar Telescope at Big Bear Solar Observatory. For
this unique data set, sunspot dynamics during flaring were analyzed
for the first time. By directly imaging the upper chromosphere,
running penumbral waves are clearly seen as an outward extension
of umbral flashes; both take the form of absorption in the 10830 Å
narrow-band images. From a space-time image made of a slit cutting
across a flare ribbon and the sunspot, we find that the dark lanes
for umbral flashes and penumbral waves are obviously broadened after
the flare. The most prominent feature is the sudden appearance of an
oscillating absorption strip inside the ribbon when it sweeps into the
sunspot’s penumbral and umbral regions. During each oscillation,
outwardly propagating umbral flashes and subsequent penumbral waves
rush out into the inwardly sweeping ribbon, followed by a return
of the absorption strip with similar speed. We tentatively explain
the phenomena as the result of a sudden increase in the density
of ortho-helium atoms in the area of the sunspot being excited by
the flare’s extreme ultraviolet illumination. This explanation is
based on the observation that 10830 Å absorption around the sunspot
area gets enhanced during the flare. Nevertheless, questions are still
open and we need further well-devised observations to investigate the
behavior of sunspot dynamics during flares.
---------------------------------------------------------
Title: Material Supply and Magnetic Configuration of an Active
Region Filament
Authors: Zou, P.; Fang, C.; Chen, P. F.; Yang, K.; Hao, Q.; Cao, Wenda
2016ApJ...831..123Z Altcode: 2017arXiv170102407Z
It is important to study the fine structures of solar filaments
with high-resolution observations, since it can help us understand
the magnetic and thermal structures of the filaments and their
dynamics. In this paper, we study a newly formed filament located
inside the active region NOAA 11762, which was observed by the 1.6 m
New Solar Telescope at Big Bear Solar Observatory from 16:40:19 UT to
17:07:58 UT on 2013 June 5. As revealed by the Hα filtergrams, cool
material is seen to be injected into the filament spine with a speed of
5-10 km s<SUP>-1</SUP>. At the source of the injection, brightenings
are identified in the chromosphere, which are accompanied by magnetic
cancellation in the photosphere, implying the importance of magnetic
reconnection in replenishing the filament with plasmas from the lower
atmosphere. Counter-streamings are detected near one endpoint of the
filament, with the plane-of-the-sky speed being 7-9 km s<SUP>-1</SUP> in
the Hα red-wing filtergrams and 9-25 km s<SUP>-1</SUP> in the blue-wing
filtergrams. The observations are indicative that this active region
filament is supported by a sheared arcade without magnetic dips, and
the counter-streamings are due to unidirectional flows with alternative
directions, rather than due to the longitudinal oscillations of filament
threads as in many other filaments.
---------------------------------------------------------
Title: Spectropolarimetry of Atomic and Molecular Lines near 4135 nm
Authors: Penn, Matthew James; Uitenbroek, Han; Clark, Alan; Coulter,
Roy; Goode, Phil; Cao, Wenda
2016SoPh..291.2243P Altcode: 2015arXiv151204451P; 2016SoPh..tmp..142P
New spatially scanned spectropolarimetry sunspot observations are made
of photospheric atomic and molecular absorption lines near 4135 nm. The
relative splittings among several atomic lines are measured and shown
to agree with values calculated with configuration interaction and
intermediate coupling. Large splitting is seen in a line identified
with Fe I at 4137 nm, showing multiple Stokes V components and an
unusual linear polarization. This line will be a sensitive probe of
quiet-Sun magnetic fields, with a magnetic sensitivity of 2.5 times
higher than that of the well-known 1565 nm Fe I line.
---------------------------------------------------------
Title: High resolution He I 10830 angstrom narrow-band imaging of
an M-class flare.I-analysis of sunspot dynamics during flaring
Authors: Wang, Ya; Su, Yingna; Hong, Zhenxiang; Zeng, Zhicheng; Ji,
Kaifan; Goode, Philip R.; Cao, Wenda; Ji, Haisheng
2016usc..confE..38W Altcode: 2016arXiv161009227W
We report our first-step results of high resolution He I 1083
nm narrow-band imaging of an M 1.8 class two-ribbon flare on July
5,2012. The flare was observed with the 1.6 meter aperture New Solar
Telescope at Big Bear Solar Observatory. For this unique data set,
sunspot dynamics during flaring were analyzed for the first time. By
directly imaging the upper chromosphere, running penumbral waves
are clearly seen as an outward extention of umbral flashes, both
take the form of absorption in our 1083 nm narrow-band images. From
a space-time image made of a slit cutting across the ribbon and the
sunspot, we find that dark lanes for umbral flashes and penumbral waves
are obviously broadened after the flare. The most prominent feature
is the sudden appearance of an oscillating absorption strip inside
one ribbon of the flare when it sweeps into sunspot's penumbral and
umbral regions. During each oscillation, outwardly propagating umbral
flashes and subsequent penumbral waves rush out into the inwardly
sweeping ribbon, followed by a returning of the absorption strip with
similar speed. We tentatively explain the phenomenon as the result of
a sudden increase in the density of ortho-Helium atoms in the area of
the sunspot area being excited by the flare's EUV illumination. This
explanation is based on the obsevation that 1083 nm absorption in the
sunspot area gets enhanced during the flare. Nevertheless, questions are
still open and we need further well-devised observations to investigate
the behavior of sunspot dynamics during flares.
---------------------------------------------------------
Title: Flare differentially rotates sunspot on Sun's surface
Authors: Liu, Chang; Xu, Yan; Cao, Wenda; Deng, Na; Lee, Jeongwoo;
Hudson, Hugh S.; Gary, Dale E.; Wang, Jiasheng; Jing, Ju; Wang, Haimin
2016NatCo...713104L Altcode: 2016arXiv161002969L
Sunspots are concentrations of magnetic field visible on the solar
surface (photosphere). It was considered implausible that solar flares,
as resulted from magnetic reconnection in the tenuous corona, would
cause a direct perturbation of the dense photosphere involving bulk
motion. Here we report the sudden flare-induced rotation of a sunspot
using the unprecedented spatiotemporal resolution of the 1.6 m New
Solar Telescope, supplemented by magnetic data from the Solar Dynamics
Observatory. It is clearly observed that the rotation is non-uniform
over the sunspot: as the flare ribbon sweeps across, its different
portions accelerate (up to ~50° h<SUP>-1</SUP>) at different times
corresponding to peaks of flare hard X-ray emission. The rotation may be
driven by the surface Lorentz-force change due to the back reaction of
coronal magnetic restructuring and is accompanied by a downward Poynting
flux. These results have direct consequences for our understanding of
energy and momentum transportation in the flare-related phenomena.
---------------------------------------------------------
Title: High-resolution Observations of a Large Fan-shaped Surge
Authors: Li, Zhen; Fang, Cheng; Guo, Yang; Chen, P. F.; Zou, Peng;
Cao, Wenda
2016ApJ...826..217L Altcode:
We present high-resolution observations of a large fan-shaped
surge, which was observed on 2013 June 5 with the current largest
solar telescope, the 1.6 m New Solar Telescope (NST), at the
Big Bear Solar Observatory. The observations are made at TiO,
Hα, and 10830 Å wavebands with a spatial resolution better
than 0\buildrel{\prime\prime}\over{.} 1 and a full-run cadence of
∼30 s. The fan-shaped surge consists of many small-scale threads
with a typical width of 100 km and a length of up to 200 Mm at the
maximum. The threads come from material ejections, which start with a
velocity of several km s<SUP>-1</SUP>, and then accelerate up to 60-80
km s<SUP>-1</SUP> over six to seven minutes with an acceleration of
up to 0.2-0.3 km s<SUP>-2</SUP>. The threads can be observed in the
Hα band and in SDO/AIA 171 Å images as absorbed objects, implying
that they are cool material ejections. The surge is ejected along open
magnetic field lines in the extrapolated non-linear force-free field,
which might actually be a part of a large-scale magnetic loop stretching
back to the solar surface. After 10-20 minutes, the ejections gradually
decay and the surge eventually vanishes. The total lifetime is about 35
minutes. The Hα brightening at the root of the fan-shaped surge implies
that there is heating in the chromosphere, which could be produced
by low-atmosphere interchange magnetic reconnection. Our observation
provides evidence of the reconnection model for the fan-shaped surges,
which was proposed by Jiang et al.
---------------------------------------------------------
Title: Data Processing of the magnetograms for the Near InfraRed
Imaging Spectropolarimeter at Big Bear Solar Observatory
Authors: Ahn, Kwangsu; Cao, Wenda; Shumko, Sergiy; Chae, Jongchul
2016SPD....47.0207A Altcode:
We want to present the processing result of the vector magnetograms from
the Near InfraRed Imaging Spectropolarimeter (NIRIS) at Big Bear Solar
Observatory. The NIRIS is a successor of an old magnetograph system
at BBSO, which equips with the new infrared detector and the improved
Fabry-Perot filter system. While there are several upgrades to the new
hardware, there are also some challenges as the data acquisition rate
increases and we deal with the a larger detector array. The overall
process includes dark and flat correction, image alignment, de-stretch,
Stokes parameter selection, calibration of instrumental crosstalk,
and Milne-Eddington inversion.
---------------------------------------------------------
Title: Ultra-Narrow Negative Flare Front Observed in Helium-10830
Å Using the1.6m New Solar Telescope
Authors: Xu, Yan; Cao, Wenda; Ding, Mingde; Kleint, Lucia; Su,
Jiangtao; Liu, Chang; Ji, Haisheng; Chae, Jongchul; Jing, Ju; Cho,
Kyuhyoun; Cho, Kyung-Suk; Gary, Dale E.; Wang, Haimin
2016SPD....47.0633X Altcode:
Solar flares are sudden flashes of brightness on the Sun and are often
associated with coronal mass ejections and solar energetic particles
that have adverse effects on the near-Earth environment. By definition,
flares are usually referred to as bright features resulting from excess
emission. Using the newly commissioned 1.6-m New Solar Telescope at
Big Bear Solar Observatory, we show a striking “negative” flare
with a narrow but unambiguous “dark” moving front observed in He I
10830 Å, which is as narrow as 340 km and is associated with distinct
spectral characteristics in Hα and Mg II lines. Theoretically, such
negative contrast in He I 10830 Å can be produced under special
circumstances by nonthermal electron collisions or photoionization
followed by recombination. Our discovery, made possible due to
unprecedented spatial resolution, confirms the presence of the required
plasma conditions and provides unique information in understanding
the energy release and radiative transfer in solar flares.
---------------------------------------------------------
Title: BBSO/NST Observations of the Sudden Differential Rotation of
a Sunspot Caused by a Major Flare
Authors: Liu, Chang; Xu, Yan; Deng, Na; Cao, Wenda; Lee, Jeongwoo;
Hudson, Hugh S.; Gary, Dale E.; Wang, Jiasheng; Jing, Ju; Wang, Haimin
2016SPD....47.0615L Altcode:
Sunspots are concentrations of magnetic field visible on the solar
surface (photosphere), from which the field extends high into the
corona. Complex plasma motions that drag field in the photosphere can
build up free energy in the corona that powers solar eruptions. It
is known that solar flares and the often associated coronal ejections
(CMEs) can produce various radiations in the low atmosphere. However,
it was considered implausible that disturbances created in the tenuous
corona would cause a direct perturbation of the dense photosphere
involving bulk motion. Here we report the sudden rotational motion of
a sunspot clearly induced by a major solar flare (SOL2015-06-22T18:23
M6.6), using the unprecedented spatiotemporal resolution of the 1.6 m
New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO). It is
particularly striking that the rotation is not uniform over the sunspot:
as the flare ribbon sweeps across, its different portions accelerate
(up to ~50 degree per hour) at different times corresponding to peaks
of flare hard X-ray emission. The intensity and magnetic field of
the sunspot also change significantly associated with the flare. Our
results reveal an intrinsic relationship between the photospheric
plasma bulk motions and coronal energy release, with direct consequences
for our understanding of energy and momentum balance in the flare/CME
phenomenon. This work is mainly supported by NASA grants NNX13AF76G
and NNX13AG13G (LWS), and NNX16AF72G, and NSF grants AGS 1250818
and 1408703.
---------------------------------------------------------
Title: Multi-wavelength Observations of a Subarcsecond Penumbral
Transient Brightening Event
Authors: Bai, X. Y.; Su, J. T.; Cao, W. D.; Liu, S. Q.; Deng, Y. Y.;
Priya, T. G.
2016ApJ...823...60B Altcode:
We report a subarcsecond penumbral transient brightening event with the
high-spatial resolution observations from the 1.6 m New Solar Telescope
(NST), Interface Region Imaging Spectrograph (IRIS), and the Solar
Dynamics Observatory. The transient brightening, whose thermal energy
is in the range of nanoflares, has signatures in the chromosphere,
the transient region, and the corona. NST's Hα channel reveals the
fine structure of the event with a width as narrow as 101 km (0.″14),
which is much smaller than the width from the previous observation. The
transient brightening lasts for about 3 minutes. It is associated with
a redshift of about 17 km s<SUP>-1</SUP>, found in the Si IV 1402.77
Å line and exhibits an inward motion to the umbra with a speed of 87
km s<SUP>-1</SUP>. The small-scale energy released from the event has a
multi-temperature component. Spectral analysis of the brightening region
from IRIS shows that not only the transition region lines such as Si
IV 1402.77 Å and C II 1334.53 Å, but also the chromospheric Mg II k
2796.35 Å line are significantly enhanced and broadened. In addition,
the event can be found in all the extreme-ultraviolet passbands of
the Atmospheric Imaging Assembly and the derived differential emission
measure profile increases between 4 and 15 MK (or 6.6 ≤ log T ≤ 7.2)
in the transient brightening phase. It is possible that the penumbral
transient brightening event is caused by magnetic reconnection.
---------------------------------------------------------
Title: High-Resolution Observations of Flare Precursors and Their
Relationship with Magnetic Channels
Authors: Wang, Haimin; Xu, Yan; Ahn, Kwangsu; Jing, Ju; Liu, Chang;
Deng, Na; Huang, Nengyi; Gary, Dale E.; Cao, Wenda
2016SPD....4720501W Altcode:
The study of precursors of flares is important for understanding
the basic magnetic instability leading to solar flares, which can
aid the forecasting of eruptions potentially related to severe
space weather effects. Although literatures reported many important
clues, high-resolution observations of pre-flare activities before a
well-observed solar flare have been rare. Even rarely, the associated
magnetic structures in fine scale (below 1") were also observed. In
this study we take advantage of multiwavelength high-resolution
observations completely covering the 2015 June 22 M6.6 flare, which
were obtained under excellent seeing condition with the 1.6 m New Solar
Telescope (NST) at Big Bear Solar Observatory. The NST data includes
observations of the H-alpha line in five spectral positions at a spatial
resolution of 0.1" and magnetograms at a resolution of 0.25". These
are complemented by IRIS UV observations with a resolution of 0.25". We
find that there are two episodes of pre-flare brightenings (precursors),
which are spatially associated with magnetic channels, i.e., elongated
structures comprising alternating magnetic polarity inversion lines
(Zirin & Wang, 1993, Nature, 363, 426). The pre-flare chromospheric
and coronal features reflect an extremely sheared magnetic topology,
while the initiation of main flare brightenings correspond to a much
less sheared configuration. RHESSI HXR observations reveal that the
precursors have both thermal and nonthermal components, and the latter
is further evidenced by the microwave observations of the newly expanded
Solar Radio Array at Owens Valley.We further investigate the electric
current system above the magnetic channels using NLFFF extrapolations,
which show strong current sheets above the channel structure. This is
consistent with the MHD modeling of Kusano et al (2012, Ap.J., 760, 31),
who noted the importance of localized small-scale magnetic structure
in triggering the eruption of the whole active region. We suggest that
small-scale magnetic reconnection along the channels destabilizes the
magnetic structure of the active region and subsequently triggers the
main M6.6 flare and the associated halo CME.
---------------------------------------------------------
Title: Unprecedented Fine Structure of a Solar Flare Revealed by
the 1.6~m New Solar Telescope
Authors: Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale E.;
Wang, Haimin
2016SPD....47.0601J Altcode:
Solar flares signify the sudden release of magnetic energy and are
sources of so called space weather. The fine structures (below 500
km) of flares are rarely observed and are accessible to only a few
instruments world-wide. Here we present observation of a solar flare
using exceptionally high resolution images from the 1.6~m New Solar
Telescope (NST) equipped with high order adaptive optics at Big Bear
Solar Observatory (BBSO). The observation reveals the process of the
flare in unprecedented detail, including the flare ribbon propagating
across the sunspots, coronal rain (made of condensing plasma) streaming
down along the post-flare loops, and the chromosphere's response to
the impact of coronal rain, showing fine-scale brightenings at the
footpoints of the falling plasma. Taking advantage of the resolving
power of the NST, we measure the cross-sectional widths of flare
ribbons, post-flare loops and footpoint brighenings, which generally lie
in the range of 80-200 km, well below the resolution of most current
instruments used for flare studies. Confining the scale of such fine
structure provides an essential piece of information in modeling the
energy transport mechanism of flares, which is an important issue in
solar and plasma physics.
---------------------------------------------------------
Title: Unprecedented Fine Structure of a Solar Flare Revealed by
the 1.6 m New Solar Telescope
Authors: Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale;
Wang, Haimin
2016NatSR...624319J Altcode: 2016arXiv160408562J
Solar flares signify the sudden release of magnetic energy and
are sources of so called space weather. The fine structures (below
500 km) of flares are rarely observed and are accessible to only a few
instruments world-wide. Here we present observation of a solar flare
using exceptionally high resolution images from the 1.6 m New Solar
Telescope (NST) equipped with high order adaptive optics at Big Bear
Solar Observatory (BBSO). The observation reveals the process of the
flare in unprecedented detail, including the flare ribbon propagating
across the sunspots, coronal rain (made of condensing plasma) streaming
down along the post-flare loops, and the chromosphere’s response to
the impact of coronal rain, showing fine-scale brightenings at the
footpoints of the falling plasma. Taking advantage of the resolving
power of the NST, we measure the cross-sectional widths of flare
ribbons, post-flare loops and footpoint brighenings, which generally lie
in the range of 80-200 km, well below the resolution of most current
instruments used for flare studies. Confining the scale of such fine
structure provides an essential piece of information in modeling the
energy transport mechanism of flares, which is an important issue in
solar and plasma physics.
---------------------------------------------------------
Title: Resolving the Fan-spine Reconnection Geometry of a Small-scale
Chromospheric Jet Event with the New Solar Telescope
Authors: Zeng, Zhicheng; Chen, Bin; Ji, Haisheng; Goode, Philip R.;
Cao, Wenda
2016ApJ...819L...3Z Altcode: 2016arXiv160204237Z
Jets are ubiquitously present in both quiet and active regions on the
Sun. They are widely believed to be driven by magnetic reconnection. A
fan-spine structure has been frequently reported in some coronal jets
and flares, and has been regarded as a signature of ongoing magnetic
reconnection in a topology consisting of a magnetic null connected by
a fan-like separatrix surface and a spine. However, for small-scale
chromospheric jets, clear evidence of such structures is rather
rare, although it has been implied in earlier works that showed an
inverted-Y-shaped feature. Here we report high-resolution (0.″16)
observations of a small-scale chromospheric jet obtained by the New
Solar Telescope (NST) using 10830 Å filtergrams. Bi-directional flows
were observed across the separatrix regions in the 10830 Å images,
suggesting that the jet was produced due to magnetic reconnection. At
the base of the jet, a fan-spine structure was clearly resolved by
the NST, including the spine and the fan-like surface, as well as the
loops before and after the reconnection. A major part of this fan-spine
structure, with the exception of its bright footpoints and part of the
base arc, was invisible in the extreme ultraviolet and soft X-ray images
(observed by the Atmosphere Imaging Assembly and the X-Ray Telescope,
respectively), indicating that the reconnection occurred in the upper
chromosphere. Our observations suggest that the evolution of this
chromospheric jet is consistent with a two-step reconnection scenario
proposed by Török et al.
---------------------------------------------------------
Title: Bidirectional Outflows as Evidence of Magnetic Reconnection
Leading to a Solar Microflare
Authors: Hong, Jie; Ding, M. D.; Li, Ying; Yang, Kai; Cheng, Xin;
Chen, Feng; Fang, Cheng; Cao, Wenda
2016ApJ...820L..17H Altcode: 2016arXiv160300941H
Magnetic reconnection is a rapid energy release process that is believed
to be responsible for flares on the Sun and stars. Nevertheless, such
flare-related reconnection is mostly detected to occur in the corona,
while there have been few studies concerning the reconnection in the
chromosphere or photosphere. Here, we present both spectroscopic and
imaging observations of magnetic reconnection in the chromosphere
leading to a microflare. During the flare peak time, chromospheric
line profiles show significant blueshifted/redshifted components
on the two sides of the flaring site, corresponding to upflows and
downflows with velocities of ±(70-80) km s<SUP>-1</SUP>, comparable
with the local Alfvén speed as expected by the reconnection in
the chromosphere. The three-dimensional nonlinear force-free field
configuration further discloses twisted field lines (a flux rope)
at a low altitude, cospatial with the dark threads in He I 10830 Å
images. The instability of the flux rope may initiate the flare-related
reconnection. These observations provide clear evidence of magnetic
reconnection in the chromosphere and show the similar mechanisms of
a microflare to those of major flares.
---------------------------------------------------------
Title: Ultra-narrow Negative Flare Front Observed in Helium-10830
Å Using the 1.6 m New Solar Telescope
Authors: Xu, Yan; Cao, Wenda; Ding, Mingde; Kleint, Lucia; Su,
Jiangtao; Liu, Chang; Ji, Haisheng; Chae, Jongchul; Jing, Ju; Cho,
Kyuhyoun; Cho, Kyungsuk; Gary, Dale; Wang, Haimin
2016ApJ...819...89X Altcode: 2016arXiv160104729X
Solar flares are sudden flashes of brightness on the Sun and are often
associated with coronal mass ejections and solar energetic particles
that have adverse effects on the near-Earth environment. By definition,
flares are usually referred to as bright features resulting from excess
emission. Using the newly commissioned 1.6 m New Solar Telescope at
Big Bear Solar Observatory, we show a striking “negative” flare
with a narrow but unambiguous “dark” moving front observed in He I
10830 Å, which is as narrow as 340 km and is associated with distinct
spectral characteristics in Hα and Mg II lines. Theoretically, such
negative contrast in He I 10830 Å can be produced under special
circumstances by nonthermal electron collisions or photoionization
followed by recombination. Our discovery, made possible due to
unprecedented spatial resolution, confirms the presence of the required
plasma conditions and provides unique information in understanding
the energy release and radiative transfer in astronomical objects.
---------------------------------------------------------
Title: Observations of Oppositely Directed Umbral Wavefronts Rotating
in Sunspots Obtained from the New Solar Telescope of BBSO
Authors: Su, J. T.; Ji, K. F.; Cao, W.; Banerjee, D.; Priya, T. G.;
Zhao, J. S.; Bai, X. Y.; Chen, J.; Zhang, M.; Ji, H. S.
2016ApJ...817..117S Altcode:
We study the umbral waves as observed by chromospheric imaging
observations of two sunspots with the New Solar Telescope at the
Big Bear Solar Observatory. We find that the wavefronts (WFs) rotate
clockwise and form a one-armed spiral structure in the first sunspot,
whereas two- and three-armed structures arise in the second sunspot
where the WFs rotate anticlockwise and clockwise alternately. All the
spiral arms display propagation outwards and become running penumbral
waves once they cross the umbral boundaries, suggesting that the
umbral and penumbral waves propagate along the same inclined field
lines. We propose that the one-armed spiral structure may be produced
by the WF reflections at the chromospheric umbral light bridge, and the
multi-armed spirals may be related to the twist of the magnetic field
in the umbra. Additionally, the time lag of the umbral oscillations in
between the data of He I 10830 Å and {{H}}α -0.4 Å is ∼17 s, and
it is ∼60 s for that in between the data of 304 Å and {{H}}α -0.4
Å. This indicates that these disturbances are slow magnetoacoustic
waves in nature, and that they propagate upward along the inclined
lines with fast radial expansions causing horizontal velocities of
the running waves.
---------------------------------------------------------
Title: Interference of the Running Waves at Light Bridges of a Sunspot
Authors: Su, J. T.; Ji, K. F.; Banerjee, D.; Cao, W. D.; Priya, T. G.;
Zhao, J. S.; Yu, S. J.; Ji, H. S.; Zhang, M.
2016ApJ...816...30S Altcode:
The observations of chromospheric oscillations of two umbral light
bridges (LBs) within a sunspot from NOAA Active Region 12127 are
presented. It was found that the running umbral waves with periods
of 2.2-2.6 minutes underwent very fast damping before approaching
umbral boundaries, while those with higher periods (>2.6 minutes)
could propagate outside umbrae. On two sides of each LB adjacent to
umbrae, the cross-wavelet spectra displayed that the oscillations on
them had a common significant power region with dominant frequencies
of 2-6 minutes and phase differences of ∼90°. A counterstream of
two running umbral waves in the 2-6 minute frequency range propagated
toward the LBs, where they encountered each other and gave rise to
constructive or even destructive interference on the LBs. In addition,
the velocity and density perturbations on the LBs were found in opposite
phases suggesting that the perturbations were caused by the downward
propagating waves.
---------------------------------------------------------
Title: Statistical Analysis of Filament Features Based on the Hα
Solar Images from 1988 to 2013 by Computer Automated Detection Method
Authors: Hao, Q.; Fang, C.; Cao, W.; Chen, P. F.
2015ApJS..221...33H Altcode: 2015arXiv151104692H
We improve our filament automated detection method which was proposed
in our previous works. It is then applied to process the full disk
Hα data mainly obtained by the Big Bear Solar Observatory from 1988
to 2013, spanning nearly three solar cycles. The butterfly diagrams
of the filaments, showing the information of the filament area,
spine length, tilt angle, and the barb number, are obtained. The
variations of these features with the calendar year and the latitude
band are analyzed. The drift velocities of the filaments in different
latitude bands are calculated and studied. We also investigate the
north-south (N-S) asymmetries of the filament numbers in total and in
each subclass classified according to the filament area, spine length,
and tilt angle. The latitudinal distribution of the filament number
is found to be bimodal. About 80% of all the filaments have tilt
angles within [0°, 60°]. For the filaments within latitudes lower
(higher) than 50°, the northeast (northwest) direction is dominant
in the northern hemisphere and the southeast (southwest) direction is
dominant in the southern hemisphere. The latitudinal migrations of the
filaments experience three stages with declining drift velocities in
each of solar cycles 22 and 23, and it seems that the drift velocity
is faster in shorter solar cycles. Most filaments in latitudes lower
(higher) than 50° migrate toward the equator (polar region). The
N-S asymmetry indices indicate that the southern hemisphere is the
dominant hemisphere in solar cycle 22 and the northern hemisphere is
the dominant one in solar cycle 23.
---------------------------------------------------------
Title: Detection of a Fine-scale Discontinuity of Photospheric
Magnetic Fields Associated with Solar Coronal Loop Brightenings
Authors: Song, Donguk; Chae, Jongchul; Park, Soyoung; Cho, Kyung-Suk;
Lim, Eun-Kyung; Ahn, Kwangsu; Cao, Wenda
2015ApJ...810L..16S Altcode:
We present the transient brightening of a coronal loop and an associated
fine-scale magnetic discontinuity detected in the photosphere. Utilizing
the high-resolution data taken with the Fast Imaging Solar Spectrograph
and InfraRed Imaging Magnetograph of the New Solar Telescope at Big
Bear Solar Observatory, we detect a narrow lane of intense horizontal
magnetic field representing a magnetic discontinuity. It was visible
as a dark lane partially encircling a pore in the continuum image,
and was located near one of the footpoints of a small coronal loop
that experienced transient brightenings. The horizontal field strength
gradually increased before the loop brightening, and then rapidly
decreased in the impulsive phase of the brightening, suggesting the
increase of the magnetic non-potentiality at the loop footpoint and the
sudden release of magnetic energy via magnetic reconnection. Our results
support the nanoflare theory that coronal heating events are caused
by magnetic reconnection events at fine-scale magnetic discontinuities.
---------------------------------------------------------
Title: Objective Image-Quality Assessment for High-Resolution
Photospheric Images by Median Filter-Gradient Similarity
Authors: Deng, Hui; Zhang, Dandan; Wang, Tianyu; Ji, Kaifan; Wang,
Feng; Liu, Zhong; Xiang, Yongyuan; Jin, Zhenyu; Cao, Wenda
2015SoPh..290.1479D Altcode: 2015SoPh..tmp...34D
All next-generation ground-based and space-based solar telescopes
require a good quality-assessment metric to evaluate their imaging
performance. In this paper, a new image quality metric, the median
filter-gradient similarity (MFGS) is proposed for photospheric
images. MFGS is a no-reference/blind objective image-quality
metric (IQM) by a measurement result between 0 and 1 and has been
performed on short-exposure photospheric images captured by the New
Vacuum Solar Telescope (NVST) of the Fuxian Solar Observatory and
by the Solar Optical Telescope (SOT) onboard the Hinode satellite,
respectively. The results show that (1) the measured value of the MFGS
changes monotonically from 1 to 0 with degradation of image quality;
(2) there exists a linear correlation between the measured values
of the MFGS and the root-mean-square contrast (RMS-contrast) of the
granulation; (3) the MFGS is less affected by the image contents than
the granular RMS-contrast. Overall, the MFGS is a good alternative
for the quality assessment of photospheric images.
---------------------------------------------------------
Title: Negative Flare Emissions Observed in Euv By SDO/AIA
Authors: Xu, Y.; Liu, C.; Cao, W.; Jing, J.; Wang, H.
2014AGUFMSH51C4165X Altcode:
In this study, we present a large flare showing negative emissions
in the EUV passbands observed by SDO/AIA. Contrary to ordinary flare
emission represented by an increase of intensity, negative flare
emission refers to as a decrease of intensity during flares. In the
literature, negative flare emissions were usually reported by stellar
observations. Only a few negative solar flares were observed in He
I D3 in 1970s and one event observed in the near Infrared at 8542
Å in 2001. On 2014-Jan-07, an X1.2 flare occurred near the solar
disk center with a complex magnetic configuration, showing multiple
flare ribbons. Among them a remote flare ribbon is located to the
southwest from the flare core region. A small portion of the remote
ribbon became darkened from about 18:45 UT, while the rest of the
ribbon remained bright. This darkening lasted for more than one hour
and did not show obvious motion. Therefore, we exclude the possibility
of transient coronal hole associated with EUV waves. By comparing with
SDO/HMI LOS magnetograms, we find that the negative flare regions are
associated with weak magnetic fields, lower than 50 Gauss. In contrast,
the bright flare ribbons are co-spatial with strong magnetic fields
above 200 Gauss. Furthermore, we investigate the properties of the
negative emission by examining the temporal evolution of its intensity
and area. Finally, we discuss the possible mechanisms in generating
the negative emissions.
---------------------------------------------------------
Title: Active Region Coronal Rain Event Observed by the Fast Imaging
Solar Spectrograph on the NST
Authors: Ahn, Kwangsu; Chae, Jongchul; Cho, Kyung-Suk; Song, Donguk;
Yang, Heesu; Goode, Philip R.; Cao, Wenda; Park, Hyungmin; Nah,
Jakyung; Jang, Bi-Ho; Park, Young-Deuk
2014SoPh..289.4117A Altcode: 2014SoPh..tmp...98A
The Fast Imaging Solar Spectrograph (FISS) is being operated on the New
Solar Telescope of the Big Bear Solar Observatory. It simultaneously
records spectra of Hα and Ca II 8542 Å lines, and this dual-spectra
measurement provides an estimate of the temperature and nonthermal
speed components. We observed a loop structure in AR 11305 using the
FISS, SDO/AIA, and STEREO/EUVI in 304 Å, and found plasma material
falling along the loop from a coronal height into the umbra of a
sunspot, which accelerated up to 80 km s<SUP>−1</SUP>. We also
observed C2 and C7 flare events near the loop. The temperature of the
downflows was in the range of 10 000 - 33 000 K, increasing toward
the umbra. The temperature of the flow varied with time, and the
temperature near the footpoint rose immediately after the C7 flare,
but the temperature toward the umbra remained the same. There seemed
to be a temporal correlation between the amount of downflow material
and the observed C-class flares. The downflows decreased gradually soon
after the flares and then increased after a few hours. These high-speed
red-shift events occurred continuously during the observations. The
flows observed on-disk in Hα and Ca II 8542 Å appeared as fragmented,
fuzzy condensed material falling from the coronal heights when seen
off-limb with STEREO/EUVI at 304 Å. Based on these observations,
we propose that these flows were an on-disk signature of coronal rain.
---------------------------------------------------------
Title: A Flare Observed in Coronal, Transition Region, and Helium
I 10830 Å Emissions
Authors: Zeng, Zhicheng; Qiu, Jiong; Cao, Wenda; Judge, Philip G.
2014ApJ...793...87Z Altcode: 2014arXiv1408.0236Z
On 2012 June 17, we observed the evolution of a C-class flare associated
with the eruption of a filament near a large sunspot in the active
region NOAA 11504. We obtained high spatial resolution filtergrams
using the 1.6 m New Solar Telescope at the Big Bear Solar Observatory
in broadband TiO at 706 nm (bandpass: 10 Å) and He I 10830 Å narrow
band (bandpass: 0.5 Å, centered 0.25 Å to the blue). We analyze the
spatio-temporal behavior of the He I 10830 Å data, which were obtained
over a 90”×90” field of view with a cadence of 10 s. We also analyze
simultaneous data from the Atmospheric Imaging Assembly and Extreme
Ultraviolet Variability Experiment instruments on board the Solar
Dynamics Observatory spacecraft, and data from the Reuven Ramaty High
Energy Solar Spectroscopic Imager and GOES spacecrafts. Non-thermal
effects are ignored in this analysis. Several quantitative aspects
of the data, as well as models derived using the "0D" enthalpy-based
thermal evolution of loops model code, indicate that the triplet
states of the 10830 Å multiplet are populated by photoionization of
chromospheric plasma followed by radiative recombination. Surprisingly,
the He II 304 Å line is reasonably well matched by standard emission
measure calculations, along with the C IV emission which dominates
the Atmosphere Imaging Assembly 1600 Å channel during flares. This
work lends support to some of our previous work combining X-ray, EUV,
and UV data of flares to build models of energy transport from corona
to chromosphere.
---------------------------------------------------------
Title: Spectral Observations of Ellerman Bombs and Fitting with a
Two-cloud Model
Authors: Hong, Jie; Ding, M. D.; Li, Ying; Fang, Cheng; Cao, Wenda
2014ApJ...792...13H Altcode: 2014arXiv1407.3048H
We study the Hα and Ca II 8542 Å line spectra of four typical
Ellerman bombs (EBs) in the active region NOAA 11765 on 2013 June 6,
observed with the Fast Imaging Solar Spectrograph installed at the 1.6
m New Solar Telescope at Big Bear Solar Observatory. Considering that
EBs may occur in a restricted region in the lower atmosphere, and that
their spectral lines show particular features, we propose a two-cloud
model to fit the observed line profiles. The lower cloud can account
for the wing emission, and the upper cloud is mainly responsible for the
absorption at line center. After choosing carefully the free parameters,
we get satisfactory fitting results. As expected, the lower cloud shows
an increase of the source function, corresponding to a temperature
increase of 400-1000 K in EBs relative to the quiet Sun. This is
consistent with previous results deduced from semi-empirical models and
confirms that local heating occurs in the lower atmosphere during the
appearance of EBs. We also find that the optical depths can increase
to some extent in both the lower and upper clouds, which may result
from either direct heating in the lower cloud, or illumination by an
enhanced radiation on the upper cloud. The velocities derived from
this method, however, are different from those obtained using the
traditional bisector method, implying that one should be cautious when
interpreting this parameter. The two-cloud model can thus be used as
an efficient method to deduce the basic physical parameters of EBs.
---------------------------------------------------------
Title: AO-308: the high-order adaptive optics system at Big Bear
Solar Observatory
Authors: Shumko, Sergey; Gorceix, Nicolas; Choi, Seonghwan; Kellerer,
Aglaé; Cao, Wenda; Goode, Philip R.; Abramenko, Volodymyr; Richards,
Kit; Rimmele, Thomas R.; Marino, Jose
2014SPIE.9148E..35S Altcode:
In this paper we present Big Bear Solar Observatory's (BBSO) newest
adaptive optics system - AO-308. AO-308 is a result of collaboration
between BBSO and National Solar Observatory (NSO). AO-308 uses a 357
actuators deformable mirror (DM) from Xinetics and its wave front sensor
(WFS) has 308 sub-apertures. The WFS uses a Phantom V7.3 camera which
runs at 2000 Hz with the region of interest of 416×400 pixels. AO-308
utilizes digital signal processors (DSPs) for image processing. AO-308
has been successfully used during the 2013 observing season. The system
can correct up to 310 modes providing diffraction limited images at
all wavelengths of interest.
---------------------------------------------------------
Title: Control and operation of the 1.6 m New Solar Telescope in
Big Bear
Authors: Varsik, J.; Plymate, C.; Goode, P.; Kosovichev, A.; Cao,
W.; Coulter, R.; Ahn, K.; Gorceix, N.; Shumko, S.
2014SPIE.9147E..5DV Altcode:
The 1.6m New Solar Telescope (NST) has developed a modern and
comprehensive suite of instruments which allow high resolution
observations of the Sun. The current instrument package comprises
diffraction limited imaging, spectroscopic and polarimetric instruments
covering the wavelength range from 0.4 to 5.0 microns. The instruments
include broadband imaging, visible and near-infrared scanning
Fabry-Perot interferometers, an imaging spectropolarimeter,
a fast visible-light imaging spectrograph, and a unique new
scanning cryogenic infrared spectrometer/spectropolarimeter
that is nearing completion. Most instruments are operated with
a 308 subaperture adaptive optics system, while the thermal-IR
spectrometer has a correlation tracker. This paper reports on the
current observational programs and operational performance of the
telescope and instrumentation. The current control, data processing,
and archiving systems are also briefly discussed.
---------------------------------------------------------
Title: Optical design of the Big Bear Solar Observatory's
multi-conjugate adaptive optics system
Authors: Zhang, Xianyu; Gorceix, Nicolas; Schmidt, Dirk; Goode,
Philip R.; Cao, Wenda; Rimmele, Thomas R.; Coulter, Roy
2014SPIE.9148E..50Z Altcode:
A multi-conjugate adaptive optics (MCAO) system is being built for the
world's largest aperture 1.6m solar telescope, New Solar Telescope,
at the Big Bear Solar Observatory (BBSO). The BBSO MCAO system employs
three deformable mirrors to enlarge the corrected field of view. In
order to characterize the MCAO performance with different optical
configurations and DM conjugated altitudes, the BBSO MCAO setup also
needs to be flexible. In this paper, we present the optical design of
the BBSO MCAO system.
---------------------------------------------------------
Title: Study of Two Successive Three-ribbon Solar Flares Using
BBSO/NST Observations
Authors: Wang, Haimin; Liu, Chang; Deng, Na; Zeng, Zhicheng; Xu, Yan;
Jing, Ju; Cao, Wenda
2014AAS...22412304W Altcode:
We studied two rarely observed three-ribbon flares (M1.9 and C9.2) on
2012 July 6 in NOAA AR 11515, which we found using Hα observations
of 0.1 arcsec resolution from the New Solar Telescope and Ca II
H images from Hinode. The flaring site is characterized by an
intriguing "fish-bone-like" morphology evidenced by both Halpha
images and a nonlinear force-free field (NLFFF) extrapolation,
where two semi-parallel rows of low-lying, sheared loops connect an
elongated, parasitic negative field with the sandwiching positive
fields. The NLFFF model also shows that the two rows of loops are
asymmetric in height and have opposite twists, and are enveloped by
large-scale field lines including open fields. The two flares occurred
in succession within half an hour and are located at the two ends of
the flaring region. The three ribbons of each flare run parallel to
the magnetic polarity inversion line, with the outer two lying in the
positive field and the central one in the negative field. Both flares
show surge-like flows in Halpha apparently toward the remote region,
while the C9.2 flare is also accompanied by EUV jets possibly along
the open field lines. Interestingly, the 12-25 keV hard X-ray sources
of the C9.2 flare first line up with the central ribbon then shift to
concentrate on the top of the higher branch of loops. These results
are discussed in favor of reconnection along the coronal null line,
producing the three flare ribbons and the associated ejections.
---------------------------------------------------------
Title: A FLARE OBSERVED IN CORONAL, TRANSITION REGION AND HELIUM I
10830 Å EMISSIONS
Authors: Zeng, Zhicheng; Qiu, Jiong; Cao, Wenda; Judge, Philip G.
2014AAS...22412309Z Altcode:
On June 17, 2012, we observed the evolution of a C-class flare
associated with the eruption of a filament near a large sunspot in
the active region NOAA 11504. We obtained high spatial resolution
filtergrams using the 1.6 m New Solar Telescope at the Big Bear
Solar Observatory in TiO broad-band (bandpass: 10 Å)and He I 10830
Å narrow-band (bandpass: 0.5 Å, centered 0.25 Å to the blue). We
analyze the spatio-temporal behavior of the He I 10830 Å data, which
were obtained over a 90×90 arcsends field of view with a cadence
of 10 sec. We also analyze simultaneous data from the Atmospheric
Imaging Assembly and Extreme Ultraviolet Variability Experiment
instruments on board the Solar Dynamics Observatoryspacecraft, and
data from Reuven Ramaty High Energy Solar Spectroscopic Imager and
GOES spacecrafts. Several quantitative aspects of the data, as well as
models derived using the “0D” Enthalpy-Based Thermal Evolution of
Loops model (EBTEL: Klimchuk et al. 2008) code, indicate that the 10830
Å multiplet is formed primarily by photoionization of chromospheric
plasma followed by radiative recombination. Surprisingly, the He II
304 Å line is reasonably well matched by standard emission measure
calculations, along with the C IV emission which dominates the AIA
1600 Å channel during flares. This work lends support to some of our
previous work combining X-ray, EUV and UV data of flares to buildmodels
of energy transport from corona to chromosphere.
---------------------------------------------------------
Title: High-resolution Observation of the Smallest Ellerman Bombs
Authors: Fang, Cheng; Tang, Yu-hua; Li, Zhen; Xu, Zhi; Cao, Wenda;
Guo, Yang
2014cosp...40E.834F Altcode:
By use of the high-resolution spectral data obtained with the largest
solar telescope NST/BBSO in 2013 June, the characteristics of 3
well-observed smallest EBs have been analyzed. Their sizes are less
than 0.5 are second and their durations are only 2-3 minutes. The
most obvious characteristic of the EB spectra is the two emission
bumps at the two wings of both Hα and CaII 8542 Å lines. They are
located near the longitudinal magnetic polarity inversion lines and
accompanied by mass motions. The semi-empirical atmospheric models
for the EBs are computed. The common characteristic is the heating in
the upper photosphere. The temperature enhancement is about 400-500
K. These imply that the EBs can probably be produced by the magnetic
reconnection in the solar lower atmosphere. The radiative and kinetic
energies of the EBs are estimated, and the possible mechanism of
triggering the EBs is discussed.
---------------------------------------------------------
Title: Study of Two Successive Three-ribbon Solar Flares on 2012
July 6
Authors: Wang, Haimin; Liu, Chang; Deng, Na; Zeng, Zhicheng; Xu, Yan;
Jing, Ju; Cao, Wenda
2014ApJ...781L..23W Altcode: 2013arXiv1312.6649W
This Letter reports two rarely observed three-ribbon flares (M1.9
and C9.2) on 2012 July 6 in NOAA AR 11515, which we found using Hα
observations of 0.”1 resolution from the New Solar Telescope and
Ca II H images from Hinode. The flaring site is characterized by an
intriguing "fish-bone-like" morphology evidenced by both Hα images
and a nonlinear force-free field (NLFFF) extrapolation, where two
semi-parallel rows of low-lying, sheared loops connect an elongated,
parasitic negative field with the sandwiching positive fields. The
NLFFF model also shows that the two rows of loops are asymmetric in
height and have opposite twists, and are enveloped by large-scale field
lines including open fields. The two flares occurred in succession
within half an hour and are located at the two ends of the flaring
region. The three ribbons of each flare run parallel to the magnetic
polarity inversion line, with the outer two lying in the positive
field and the central one in the negative field. Both flares show
surge-like flows in Hα apparently toward the remote region, while
the C9.2 flare is also accompanied by EUV jets possibly along the
open field lines. Interestingly, the 12-25 keV hard X-ray sources of
the C9.2 flare first line up with the central ribbon then shift to
concentrate on the top of the higher branch of loops. These results
are discussed in favor of reconnection along the coronal null line,
producing the three flare ribbons and the associated ejections.
---------------------------------------------------------
Title: Temperature of Solar Prominences Obtained with the Fast Imaging
Solar Spectrograph on the 1.6 m New Solar Telescope at the Big Bear
Solar Observatory
Authors: Park, Hyungmin; Chae, Jongchul; Song, Donguk; Maurya, Ram
Ajor; Yang, Heesu; Park, Young-Deuk; Jang, Bi-Ho; Nah, Jakyoung; Cho,
Kyung-Suk; Kim, Yeon-Han; Ahn, Kwangsu; Cao, Wenda; Goode, Philip R.
2013SoPh..288..105P Altcode:
We observed solar prominences with the Fast Imaging Solar Spectrograph
(FISS) at the Big Bear Solar Observatory on 30 June 2010 and 15 August
2011. To determine the temperature of the prominence material, we
applied a nonlinear least-squares fitting of the radiative transfer
model. From the Doppler broadening of the Hα and Ca II lines, we
determined the temperature and nonthermal velocity separately. The
ranges of temperature and nonthermal velocity were 4000 - 20 000 K and
4 - 11 km s<SUP>−1</SUP>. We also found that the temperature varied
much from point to point within one prominence.
---------------------------------------------------------
Title: Fast Imaging Solar Spectrograph of the 1.6 Meter New Solar
Telescope at Big Bear Solar Observatory
Authors: Chae, Jongchul; Park, Hyung-Min; Ahn, Kwangsu; Yang, Heesu;
Park, Young-Deuk; Nah, Jakyoung; Jang, Bi Ho; Cho, Kyung-Suk; Cao,
Wenda; Goode, Philip R.
2013SoPh..288....1C Altcode: 2012SoPh..tmp..248C
For high resolution spectral observations of the Sun - particularly
its chromosphere, we have developed a dual-band echelle spectrograph
named Fast Imaging Solar Spectrograph (FISS), and installed it in a
vertical optical table in the Coudé Lab of the 1.6 meter New Solar
Telescope at Big Bear Solar Observatory. This instrument can cover any
part of the visible and near-infrared spectrum, but it usually records
the Hα band and the Ca II 8542 Å band simultaneously using two CCD
cameras, producing data well suited for the study of the structure and
dynamics of the chromosphere and filaments/prominences. The instrument
does imaging of high quality using a fast scan of the slit across the
field of view with the aid of adaptive optics. We describe its design,
specifics, and performance as well as data processing
---------------------------------------------------------
Title: Doppler Shifts of the Hα Line and the Ca II 854.2 nm Line
in a Quiet Region of the Sun Observed with the FISS/NST
Authors: Chae, Jongchul; Park, Hyung-Min; Ahn, Kwangsu; Yang, Heesu;
Park, Young-Deuk; Cho, Kyung-Suk; Cao, Wenda
2013SoPh..288...89C Altcode:
The characteristics of Doppler shifts in a quiet region of the Sun
are compared between the Hα line and the Ca II infrared line at 854.2
nm. A small area of 16″×40″ was observed for about half an hour
with the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New
Solar Telescope (NST) at Big Bear Solar Observatory. The observed area
contains a network region and an internetwork region, and identified
in the network region are fibrils and bright points. We infer Doppler
velocity v<SUB>m</SUB> from each line profile at each individual point
with the lambdameter method as a function of half wavelength separation
Δλ. It is confirmed that the bisector of the spatially averaged Ca II
line profile has an inverse C-shape with a significant peak redshift of
+ 1.8 km s<SUP>−1</SUP>. In contrast, the bisector of the spatially
averaged Hα line profile has a C-shape with a small peak blueshift of
− 0.5 km s<SUP>−1</SUP>. In both lines, the bisectors of bright
network points are significantly redshifted not only at the line
centers, but also at the wings. The Ca II Doppler shifts are found
to be correlated with the Hα ones with the strongest correlation
occurring in the internetwork region. Moreover, we find that here the
Doppler shifts in the two lines are essentially in phase. We discuss
the physical implications of our results in view of the formation of
the Hα line and Ca II 854.2 nm line in the quiet region chromosphere.
---------------------------------------------------------
Title: Connection Between Chromospheric Events and Photospheric
Dynamics
Authors: Anđić, A.; Chae, J.; Park, H.; Yang, H.; Ahn, K.; Cao,
W.; Park, Y. D.
2013SoPh..288...55A Altcode: 2012SoPh..tmp..232A
We analyzed chromospheric events and their connection to oscillation
phenomena and photospheric dynamics. The observations were done with the
New Solar Telescope of Big Bear Solar Observatory using a broad-band
imager at the wavelength of a TiO band and FISS spectrograph scanning
Ca II and Hα spectral lines. The event in Ca II showed strong plasma
flows and propagating waves in the chromosphere. The movement of
the footpoints of flux tubes in the photosphere indicated flux tube
entanglement and magnetic reconnection as a possible cause of the
observed brightening and waves propagating in the chromosphere. An
upward propagating train of waves was observed at the site of the
downflow event in Hα. There was no clear relationship between
photospheric waves and the Ca II and Hα events. Our observations
indicate that chromospheric waves that were previously thought to
originate from the photosphere may be generated by some events in the
chromosphere as well.
---------------------------------------------------------
Title: Infrared Observations from the New Solar Telescope at Big Bear
Authors: Goode, Philip R.; Cao, Wenda
2013SoPh..287..315G Altcode:
The 1.6 m clear aperture solar telescope in Big Bear is operational and
with its adaptive optics (AO) system it provides diffraction limited
solar imaging and polarimetry in the near-infrared (NIR). While the AO
system is being upgraded to provide diffraction limited imaging at bluer
wavelengths, the instrumentation and observations are concentrated in
the NIR. The New Solar Telescope (NST) operates in campaigns, making it
the ideal ground-based telescope to provide complementary/supplementary
data to SDO and Hinode. The NST makes photometric observations in Hα
(656.3 nm) and TiO (705.6 nm) among other lines. As well, the NST
collects vector magnetograms in the 1565 nm lines and is beginning
such observations in 1083.0 nm. Here we discuss the relevant NST
instruments, including AO, and present some results that are germane
to NASA solar missions.
---------------------------------------------------------
Title: Study of Rapid Formation of a δ Sunspot Associated with the
2012 July 2 C7.4 Flare Using High-resolution Observations of the
New Solar Telescope
Authors: Wang, Haimin; Liu, Chang; Wang, Shuo; Deng, Na; Xu, Yan;
Jing, Ju; Cao, Wenda
2013ApJ...774L..24W Altcode: 2013arXiv1308.2639W
Rapid, irreversible changes of magnetic topology and sunspot
structure associated with flares have been systematically observed
in recent years. The most striking features include the increase of
the horizontal field at the polarity inversion line (PIL) and the
co-spatial penumbral darkening. A likely explanation of the above
phenomenon is the back reaction to the coronal restructuring after
eruptions: a coronal mass ejection carries the upward momentum while
the downward momentum compresses the field lines near the PIL. Previous
studies could only use low-resolution (above 1”) magnetograms and
white-light images. Therefore, the changes are mostly observed for
X-class flares. Taking advantage of the 0.”1 spatial resolution
and 15 s temporal cadence of the New Solar Telescope at the Big Bear
Solar Observatory, we report in detail the rapid formation of sunspot
penumbra at the PIL associated with the C7.4 flare on 2012 July 2. It
is unambiguously shown that the solar granulation pattern evolves to
an alternating dark and bright fibril structure, the typical pattern
of penumbra. Interestingly, the appearance of such a penumbra creates
a new δ sunspot. The penumbral formation is also accompanied by the
enhancement of the horizontal field observed using vector magnetograms
from the Helioseismic and Magnetic Imager. We explain our observations
as being due to the eruption of a flux rope following magnetic
cancellation at the PIL. Subsequently, the re-closed arcade fields
are pushed down toward the surface to form the new penumbra. NLFFF
extrapolation clearly shows both the flux rope close to the surface
and the overlying fields.
---------------------------------------------------------
Title: Characteristic Length of Energy-containing Structures at the
Base of a Coronal Hole
Authors: Abramenko, V. I.; Zank, G. P.; Dosch, A.; Yurchyshyn, V. B.;
Goode, P. R.; Ahn, K.; Cao, W.
2013ApJ...773..167A Altcode: 2013arXiv1307.4421A
An essential parameter for models of coronal heating and fast solar
wind acceleration that rely on the dissipation of MHD turbulence is
the characteristic energy-containing length λ<SUB></SUB> of the
squared velocity and magnetic field fluctuations (u <SUP>2</SUP>
and b <SUP>2</SUP>) transverse to the mean magnetic field inside a
coronal hole (CH) at the base of the corona. The characteristic length
scale directly defines the heating rate. We use a time series analysis
of solar granulation and magnetic field measurements inside two CHs
obtained with the New Solar Telescope at Big Bear Solar Observatory. A
data set for transverse magnetic fields obtained with the Solar Optical
Telescope/Spectro-Polarimeter on board the Hinode spacecraft was
utilized to analyze the squared transverse magnetic field fluctuations
b_t^2. Local correlation tracking was applied to derive the squared
transverse velocity fluctuations u <SUP>2</SUP>. We find that for u
<SUP>2</SUP> structures, the Batchelor integral scale λ varies in
a range of 1800-2100 km, whereas the correlation length sigmav and
the e-folding length L vary between 660 and 1460 km. Structures for
b_t^2 yield λ ≈ 1600 km, sigmav ≈ 640 km, and L ≈ 620 km. An
averaged (over λ, sigmav, and L) value of the characteristic length
of u <SUP>2</SUP> fluctuations is 1260 ± 500 km, and that of b_t^2
is 950 ± 560 km. The characteristic length scale in the photosphere
is approximately 1.5-50 times smaller than that adopted in previous
models (3-30 × 10<SUP>3</SUP> km). Our results provide a critical
input parameter for current models of coronal heating and should yield
an improved understanding of fast solar wind acceleration.
---------------------------------------------------------
Title: The New Solar Telescope (NST): What’s Next ?
Authors: Cao, Wenda; Goode, P. R.; NST Team
2013SPD....4440006C Altcode:
The 1.6 m, off-axis, clear aperture New Solar Telescope (NST) has been
in regular operation in Big Bear Solar Observatory since 2009. The
NST is the first facility class solar telescope built in the U.S. in
a generation, which already offers a significant improvement in
ground-based high angular resolution capabilities. This presentation
reports the up-to-date progress on the NST and its 2nd generation
instruments including the AO system (AO-308), the Near-InfraRed Imaging
Spectro-polarimeter (NIRIS), the Visible Imaging Spectrometer (VIS),
and the Cryogenic Infrared Spectrograph (CYRA).
---------------------------------------------------------
Title: Observation of Magnetic Reconnection Driven by Granular
Scale Advection
Authors: Zeng, Zhichen; Cao, W.; Ji, H.
2013SPD....44...01Z Altcode:
We report the first evidence of magnetic reconnection driven by
advection in a rapidly developing large granule, using high spatial
resolution observations of a small surge event (base size 4‧‧
by 4‧‧) with the 1.6 meter aperture New Solar Telescope (NST)
at Big Bear Solar Observatory. The observations were carried out in
narrow-band (0.5 Å) Helium I 10830 Å and broad-band (10 Å) TiO
7057 Å. Since He I 10830 Å triplet has very high excitation level
and is optically thin, its filtergrams enable us to investigate the
surge from the photosphere through the chromosphere into the lower
corona. Simultaneous space data from Atmospheric Imaging Assembly
(AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar
Dynamics Observatory (SDO) were used in the analysis. It is shown that
the surge is spatio-temporally associated with magnetic flux emergence
in the rapidly developing large granule. During the development of
the granule, its advecting flow ( 2 km/ s) squeezed the magnetic flux
into an intergranular lane area, where a magnetic flux concentration
was formed and the neighboring flux with opposite magnetic polarity was
cancelled. During the cancellation, the surge was produced as absorption
in He I 10830 Å filtergrams while simultaneous EUV brightening occurred
at its base. The observations clearly indicate evidence of finest-scale
reconnection process driven by the granule’s motion.
---------------------------------------------------------
Title: Observation of Magnetic Reconnection Driven by Granular
Scale Advection
Authors: Zeng, Zhicheng; Cao, Wenda; Ji, Haisheng
2013ApJ...769L..33Z Altcode:
We report the first evidence of magnetic reconnection driven by
advection in a rapidly developing large granule using high spatial
resolution observations of a small surge event (base size ~ 4” ×
4”) with the 1.6 m aperture New Solar Telescope at the Big Bear Solar
Observatory. The observations were carried out in narrowband (0.5 Å)
He I 10830 Å and broadband (10 Å) TiO 7057 Å. Since He I 10830 Å
triplet has a very high excitation level and is optically thin, its
filtergrams enable us to investigate the surge from the photosphere
through the chromosphere into the lower corona. Simultaneous space
data from the Atmospheric Imaging Assembly and Helioseismic and
Magnetic Imager on board the Solar Dynamics Observatory were used
in the analysis. It is shown that the surge is spatio-temporally
associated with magnetic flux emergence in the rapidly developing large
granule. During the development of the granule, its advecting flow (~2
km s<SUP>-1</SUP>) squeezed the magnetic flux into an intergranular
lane area, where a magnetic flux concentration was formed and the
neighboring flux with opposite magnetic polarity was canceled. During
the cancellation, the surge was produced as absorption in He I 10830
Å filtergrams while simultaneous EUV brightening occurred at its
base. The observations clearly indicate evidence of a finest-scale
reconnection process driven by the granule's motion.
---------------------------------------------------------
Title: NIRIS: The Second Generation Near-Infrared Imaging
Spectro-polarimeter for the 1.6 Meter New Solar Telescope
Authors: Cao, W.; Goode, P. R.; Ahn, K.; Gorceix, N.; Schmidt, W.;
Lin, H.
2012ASPC..463..291C Altcode:
The largest aperture solar telescope, the 1.6 m New Solar Telescope
(NST) has been installed at the Big Bear Solar Observatory
(BBSO). To take full advantage of the NST's greatest potential, we
are upgrading the routinely operational InfraRed Imaging Magnetograph
(IRIM) to its second generation, the NIRIS (Near-InfraRed Imaging
Spectropolarimeter). NIRIS will offer unprecedented high resolution
spectroscopic and polarimetric imaging data of the solar atmosphere
from the deepest photosphere through the base of the corona. With the
aid of the BBSO adaptive optics (AO) system, the spatial resolution
will be close to the diffraction limit of the NST. The spectroscopic
cadence will reach one second, while polarimetric measurements,
including Stokes I, Q, U, V profiles, remain at a better than 10
s cadence. Polarization sensitivity is expected to be reach ∼
10<SUP>-4</SUP>I<SUB>c</SUB>. NIRIS will cover a broad spectral
range from 1.0 to 1.7μm, with particular attention to two unique
spectral lines: the Fe I 1565 nm doublet has already proven to be
the most sensitive to Zeeman effect for probing the magnetic field
in the deepest photosphere; the He I 1083 nm multiplet is one of the
best currently available diagnostic of upper chromospheric magnetic
fields that allows one to map the vector field at the base of the
corona. NIRIS will be built on dual Fabry-Pérot Interferometers (FPIs),
each of which has an aperture of 100 mm. The larger aperture of FPIs
allows the available field-of-view up to one and half minutes with a
spectral power of ∼ 10<SUP>5</SUP>.
---------------------------------------------------------
Title: The 1.6 m Off-Axis New Solar Telescope (NST) in Big Bear
Authors: Goode, P. R.; Cao, W.
2012ASPC..463..357G Altcode:
The New Solar Telescope (NST) in Big Bear is the first facility-class
solar telescope built in the US in a generation, and it has an
off-axis design as is planned for the Advanced Technology Solar
Telescope (ATST). The NST is in regular operation with adaptive optics
(AO) correcting the light currently feeding photometric and near-IR
polarimetric systems, as well as an imaging spectrograph. Here we show
the high resolution capabilities of the NST. As well, we sketch our
plans for, and reasoning behind the next generation NST instrumentation.
---------------------------------------------------------
Title: The 1.6 m New Solar Telescope (NST) in Big Bear
Authors: Cao, W.
2012IAUSS...6E.202C Altcode:
The 1.6 m clear aperture, off-axis New Solar Telescope (NST) is in
regular operation in Big Bear Solar Observatory. The NST is the first
facility-class solar telescope built in the U.S. in a generation. The
NST provides high resolution and high sensitivity observations of the
solar photosphere and chromosphere in the visible and near infrared
(NIR). A high order adaptive optics system delivers corrected light
to an ensemble of state-of-the-art scientific instruments in the coude
laboratory including the Broad-band Filter Imagers (BFIs), NIR Imaging
Spectro-polarimeter (NIRIS), Visible Imaging Spectro-polarimeter (VIS)
and Fast Imaging Solar Spectrograph (FISS). Some early scientific
results from the NST will be presented, followed by a progress report
on NST instrument development projects, as well as upgrades to existing
instruments.
---------------------------------------------------------
Title: The 1.6 m off-axis New Solar Telescope (NST) in Big Bear
Authors: Goode, Philip R.; Cao, Wenda
2012SPIE.8444E..03G Altcode:
The 1.6-m New Solar Telescope (NST) has been used to observe the Sun
for more than three years with ever increasing capabilities as its
commissioning phase winds down. The NST is the first facility-class
solar telescope built in the U.S. in a generation, and it has
an off-axis design as is planned for the 4 m Advanced Technology
Solar Telescope. Lessons learned will be discussed. Current NST
post-focus instrumentation includes adaptive optics (AO) feeding
photometric and near-IR polarimetric sytems, as well as an imaging
spectrograph. On-going instrumentation projects will be sketched,
including Multi-Conjugate AO (MCAO), next generation (dual Fabry-
Perot) visible light and near-IR polarimeters and a fully cryogenic
spectrograph. Finally, recent observational results illustrating the
high resolution capabilities of the NST will be shown.
---------------------------------------------------------
Title: Small Scale Field Emergence and Its Impact on Photospheric
Granulation
Authors: Yurchyshyn, V.; Ahn, K.; Abramenko, V.; Goode, P.; Cao, W.
2012arXiv1207.6418Y Altcode:
We used photospheric intensity images and magnetic field measurements
from the New Solar Telescope in Big Bear and Helioseismic Magnetic
Imager on board Solar Dynamics Observatory (SDO) to study the the effect
that the new small-scale emerging flux induces on solar granulation. We
report that emerging flux appears to leave different types of footprint
on solar granulation: i) diffuse irregular patches of increased
brightness, ii) well defined filament-like structures and accompanied
bright points, and iii) bright point-like features that appear inside
granules. We suggest that the type of the footprint depends on the
intensity of emerging fields. Stronger fields, emerging as a part of
large magnetic structure, create on the solar surface a well defined
filamentary pattern with bright points at the ends of the filaments,
while weak turbulent fields are associated with bright patches inside
the host granule.
---------------------------------------------------------
Title: Profiles of the daytime atmospheric turbulence above Big Bear
solar observatory
Authors: Kellerer, A.; Gorceix, N.; Marino, J.; Cao, W.; Goode, P. R.
2012A&A...542A...2K Altcode:
Context. Space weather has become acutely critical for today's
global communication networks. To understand its driving forces we
need to observe the Sun with high angular-resolution, and within
large fields-of-view, i.e. with multi-conjugate adaptive optics
correction. <BR /> Aims: The design of a multi-conjugate adaptive
optical system requires the knowledge of the altitude distribution of
atmospheric turbulence. We have therefore measured daytime turbulence
profiles above the New Solar Telescope (NST), on Big Bear Lake. <BR />
Methods: To this purpose, a wide-field wavefront sensor was installed
behind the NST. The variation of the wavefront distortions with
angular direction allows the reconstruction of the distribution of
turbulence. <BR /> Results: The turbulence is found to have three
origins: 1. a ground layer (<500 m) that contains 55-65% of the
turbulence, 2. a boundary layer between 1-7 km comprises 30-40% of
the turbulent energy, 3. and the remaining ~5% are generated in the
tropopause, which is above 12 km in summer and between 8 and 12 km in
winter. <BR /> Conclusions: A multi-conjugate adaptive optical system
should thus aim at correcting the ground turbulence, the center of
the boundary layer at roughly 3 km altitude and, eventually, the upper
boundary layer around 6 km altitude.
---------------------------------------------------------
Title: Characteristic Size of Flare Kernels in the Visible and
Near-infrared Continua
Authors: Xu, Yan; Cao, Wenda; Jing, Ju; Wang, Haimin
2012ApJ...750L...7X Altcode:
In this Letter, we present a new approach to estimate the formation
height of visible and near-infrared emission of an X10 flare. The sizes
of flare emission cores in three wavelengths are accurately measured
during the peak of the flare. The source size is the largest in the
G band at 4308 Å and shrinks toward longer wavelengths, namely the
green continuum at 5200 Å and NIR at 15600 Å, where the emission is
believed to originate from the deeper atmosphere. This size-wavelength
variation is likely explained by the direct heating model as electrons
need to move along converging field lines from the corona to the
photosphere. Therefore, one can observe the smallest source, which in
our case is 0farcs65 ± 0farcs02 in the bottom layer (represented by
NIR), and observe relatively larger kernels in upper layers of 1farcs03
± 0farcs14 and 1farcs96 ± 0farcs27, using the green continuum and
G band, respectively. We then compare the source sizes with a simple
magnetic geometry to derive the formation height of the white-light
sources and magnetic pressure in different layers inside the flare loop.
---------------------------------------------------------
Title: Observation of Ultrafine Channels of Solar Corona Heating
Authors: Ji, Haisheng; Cao, Wenda; Goode, Philip R.
2012ApJ...750L..25J Altcode:
We report the first direct observations of dynamical events
originating in the Sun's photosphere and subsequently lighting up the
corona. Continuous small-scale, impulsive events have been tracked from
their origin in the photosphere on through to their brightening of the
local corona. We achieve this by combining high-resolution ground-based
data from the 1.6 m aperture New Solar Telescope (NST) at Big Bear Solar
Observatory (BBSO), and satellite data from the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The
NST imaging observations in helium I 10830 Å reveal unexpected
complexes of ultrafine, hot magnetic loops seen to be reaching from the
photosphere to the base of the corona. Most of these ultrafine loops
are characterized by an apparently constant, but surprisingly narrow
diameter of about 100 km all along each loop, and the loops originate
on the solar surface from intense, compact magnetic field elements. The
NST observations detect the signature of upward injections of hot plasma
that excite the ultrafine loops from the photosphere to the base of the
corona. The ejecta have their individual footpoints in the intergranular
lanes between the Sun's ubiquitous, convectively driven granules. In
many cases, AIA/SDO detects cospatial and cotemporal brightenings
in the overlying, million degree coronal loops in conjunction with
the upward injections along the ultrafine loops. Segments of some
of the more intense upward injections are seen as rapid blueshifted
events in simultaneous Hα blue wing images observed at BBSO. In sum,
the observations unambiguously show impulsive coronal heating events
from upward energy flows originating from intergranular lanes on the
solar surface accompanied by cospatial mass flows.
---------------------------------------------------------
Title: Calibration of data from InfraRed Imaging Magnetograph for
the New Solar Telescope
Authors: Ahn, Kwangsu; Cao, W.; Gorceix, N.; Goode, P. R.
2012AAS...22020616A Altcode:
The InfraRed Imaging Magnetograph (IRIM) takes advantage of the
high spatial resolution of New Solar Telescope (NST). It adopts a
rotating birefringent polymer to modulate polarization signals and
two Wollaston prisms as analyzer. Dual beam setup is used to minimize
the effect of image motion caused by seeing. Its field of view is 50"
x 25" and the wavelengths of operation are Fe I 15648 A and He I 10830
A. Due to the off-axis shape of the NST primary and secondary mirrors,
multiple calibration techniques should be combined to reconstruct the
original Stokes parameters. Here, we would like to introduce current
status of our calibration efforts and discuss how IRIM data can be
used for scientific purposes.
---------------------------------------------------------
Title: Characteristic Size Of Flare Kernels In Visible And The
Near-infrared Continua
Authors: Xu, Yan; Cao, W.; Jing, J.; Wang, H.
2012AAS...22020413X Altcode:
In this study, we present a new approach to estimate the formation
height of visible and the near-infrared emission during an X10
flare. The sizes of flare cores in three wavelengths are accurately
measured during the peak time. The result shows that the source
size is the largest in G-band at 4308 Å and shrinks towards longer
wavelengths, namely the green continuum at 5200 Å and NIR at 15600 Å,
where the emission is believed to originate from deeper atmosphere. This
size-wavelength variation is likely explained by the direct heating
model as electrons need to move along converging field lines. In this
model, energetic electrons are confined by the magnetic field lines,
which converge from the corona to the photosphere. Therefore one
can observe the smallest source, which in our case is 0.65 ± 0".02
(radius by assuming a circular shape) in the bottom layer (represented
by NIR) and observe relatively large kernels in upper layers of 1".03
± 0".14 and 1".96 ± 0".27, using the green continuum and G-band
respectively. We then compare the source sizes with a simple magnetic
geometry to derived the formation height of the white-light sources
and magnetic pressure in different layers inside the flare loop.
---------------------------------------------------------
Title: Origin of Rapid Blueshifted Events in Coronal Holes
Authors: Yurchyshyn, Vasyl B.; Ahn, K.; Abramenko, V.; Goode, P.;
Cao, W.
2012AAS...22042304Y Altcode:
Clusters of photospheric bright points are surrounded by chromospheric
rosette-like structures. These rosettes, when observed in the far
off-band (-0.1nm) Halpha images often appear to consist of short living,
narrow rapid blueshifted events (RBEs). RBEs, in turn, are thought to
be disk counterparts of type II spicules (spicules II), detected in
Hinode data, which may be playing play an important role in coronal
heating since they are thought to supply mass to the solar corona. The
search for the origin of type II spicules was one of the main focus of
solar physics research in the recent years. <P />Here we present our
findings on the possible driving mechanism of spicules II, which are
based on high resolution photospheric, chromospheric and magnetic field
data from the New Solar Telescope (NST) collected in a coronal hole. We
report that the majority of RBEs, occurring around a network cluster,
are associated with appearance of opposite polarity features within
the unipolar cluster fields, suggesting that magnetic reconnection
may be the driving mechanism. We will present these observations in
details and discuss possible implications.
---------------------------------------------------------
Title: Observation of Hyperfine Channels of Solar Corona Heating
Authors: Cao, Wenda; Ji, H.; Goode, P. R.
2012AAS...22042301C Altcode:
We report here the first direct observations of dynamical events
originating in the sun’s cool photosphere and subsequently lighting
up the corona. Continuous impulsive events have been tracked from
their origin in the photosphere on through to their brightening
of the local corona. We achieve this by combining high resolution
ground-based data from the 1.6 meter aperture New Solar Telescope
(NST) at Big Bear Solar Observatory (BBSO),and satellite data from
the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics
Observatory (SDO). The NST observations in a narrow band absorption
line, Helium I 10830 Å, reveal unexpected complexes of hyperfine,
hot magnetic loops seen to be reaching from the photosphere to the
base of the corona. Most of these hyperfine loops are characterized
by an apparently constant, but surprisingly narrow diameter of about
100 km all along each loop, and the loops originate on the solar
surface from intense, small-scale magnetic field elements. The NST
observations detect upward injections of hot plasma that excite the
hyperfine loops from the photosphere to the base of the corona. The
ejecta have their individual footpoints in the intergranular lanes
between the sun’s ubiquitous, convectively driven granules. In
many cases, AIA/SDO detects co-spatial and co-temporal brightenings
in the overlying, million-degree coronal loops in conjunction with
the upward injections along the hyperfine loops. Segments of some
of the more intense upward injections are seen as rapid blue-shifted
events in simultaneous Hα blue wing images observed at BBSO. In sum,
the observations unambiguously show impulsive coronal heating events
from upward energy flows originating from intergranular lanes on the
solar surface accompanied by co-spatial mass flows.
---------------------------------------------------------
Title: Depth profiling of dopants implanted in Si using the
synchrotron radiation based high-resolution grazing emission technique
Authors: Kayser, Y.; Banaś, D.; Cao, W.; Dousse, J. -Cl.; Hoszowska,
J.; Jagodziński, P.; Kavčič, M.; Kubala-Kukuś, A.; Nowak, S.;
Pajek, M.; Szlachetko, J.
2012XRS....41...98K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Properties of Umbral Dots as Measured from the New Solar
Telescope Data and MHD Simulations
Authors: Kilcik, A.; Yurchyshyn, V. B.; Rempel, M.; Abramenko, V.;
Kitai, R.; Goode, P. R.; Cao, W.; Watanabe, H.
2012ApJ...745..163K Altcode: 2011arXiv1111.3997K
We studied bright umbral dots (UDs) detected in a moderate size sunspot
and compared their statistical properties to recent MHD models. The
study is based on high-resolution data recorded by the New Solar
Telescope at the Big Bear Solar Observatory and three-dimensional (3D)
MHD simulations of sunspots. Observed UDs, living longer than 150 s,
were detected and tracked in a 46 minute long data set, using an
automatic detection code. A total of 1553 (620) UDs were detected
in the photospheric (low chromospheric) data. Our main findings
are (1) none of the analyzed UDs is precisely circular, (2) the
diameter-intensity relationship only holds in bright umbral areas, and
(3) UD velocities are inversely related to their lifetime. While nearly
all photospheric UDs can be identified in the low chromospheric images,
some small closely spaced UDs appear in the low chromosphere as a single
cluster. Slow-moving and long-living UDs seem to exist in both the low
chromosphere and photosphere, while fast-moving and short-living UDs
are mainly detected in the photospheric images. Comparison to the 3D
MHD simulations showed that both types of UDs display, on average, very
similar statistical characteristics. However, (1) the average number
of observed UDs per unit area is smaller than that of the model UDs,
and (2) on average, the diameter of model UDs is slightly larger than
that of observed ones.
---------------------------------------------------------
Title: Properties of Umbral Dots as Measured from the New Solar
Telescope Data and MHD Simulations
Authors: Yurchyshyn, V.; Kilcik, A.; Rempel, M.; Abramenko, V.; Kitai,
R.; Goode, P. R.; Cao, W.; Watanabe, H.
2011sdmi.confE..86Y Altcode:
We studied bright umbral dots (UDs) detected in the main sunspot
of AR NOAA 11108 and compare their statistical properties to a
state-of-the-art MHD model of a sunspot. The study is based on
high resolution data recorded on September 20, 2010 by the New Solar
Telescope (NST) at Big Bear Solar Observatory and 3D MHD simulations of
sunspots. The 46 min data set included photospheric (0.3nm TiO filter
centered at 705.7 nm) and chromospheric (0.025nm Hα Lyot filter)
adaptive optics corrected and speckle reconstructed images. Bright
UDs, living longer than 150 s, were detected and tracked using an
automatic UD detection code. Total 1553 (620) UDs were detected
in the photospheric (chromospheric) data. Our main findings are:
i) none of the analyzed UDs is of an exact circular shape, ii) the
diameter-intensity relationship only works for bright umbral areas, and
iii) UD velocities inversely related to their life time. Comparison of
photospheric and chromospheric data showed that nearly all photospheric
UDs can be identified in the chromospheric images. However, it appears
that some small closely spaced UDs appear in the chromospheric images
as a single cluster, which may lead to the underestimation of the total
number of detected chromospheric UDs. Also, while slow moving and long
living UDs seem to exist in both chromosphere and photosphere, fast
moving and short living ones are detected mainly in the photospheric
images. Comparison of model and observed data shows that both types
of UDs display very similar statistical characteristics. The main
difference between parameters of model and observed UDs is that i)
the average number of observed UDs per unit area is smaller than that
of the model UDs, and ii) on average, the diameter of model UDs is
slightly larger than that of observed ones.
---------------------------------------------------------
Title: High-resolution observations of the solar dynamics and
magnetism
Authors: Goode, Phil; Cao, Wenda; Yurchyshyn, Vasyl
2011sdmi.confE..28G Altcode:
The NST is the first facility-class solar telescope built in the US
in a generation. Images and movies illustrating the high resolution
capabilities of the NST will be shown. In particular, high resolution
NST observations reveal vortices in the granular field that are
associated with newly discovered, but ubiquitous small-scale jets,
which are much smaller-scale than Hinode type-II jets. NST observations
have been used to probe the nature of the diffusion of magnetic bright
points, which seems consistent with the operation of small-scale
dynamos, while seeming to be sufficient on large-scales to support the
Wang-Sheeley dynamo picture. Other recent NST results correlated with
satellite observations will be shown and discussed.
---------------------------------------------------------
Title: Photospheric Signatures of Granular-scale Flux Emergence and
Cancellation at the Penumbral Boundary
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Abramenko, Valentyna;
Ahn, Kwangsu; Cao, Wenda; Goode, Philip
2011ApJ...740...82L Altcode: 2011arXiv1107.5254L
We studied flux emergence events of sub-granular scale in a solar
active region. The New Solar Telescope (NST) of the Big Bear Solar
Observatory made it possible to clearly observe the photospheric
signature of flux emergence with very high spatial (0farcs11 at 7057
Å) and temporal (15 s) resolution. From TiO observations with the
pixel scale of 0farcs0375, we found several elongated granule-like
features (GLFs) stretching from the penumbral filaments of a sunspot
at a relatively high speed of over 4 km s<SUP>-1</SUP>. After a
slender arched darkening appeared at the tip of a penumbral filament,
a bright point (BP) developed and quickly moved away from the filament,
forming and stretching a GLF. The size of a GLF was approximately
0farcs5 wide and 3” long. The moving BP encountered nearby structures
after several minutes of stretching, and the well-defined elongated
shape of the GLF faded away. Magnetograms from the Solar Dynamics
Observatory/Helioseismic and Magnetic Imager and NST/InfraRed Imaging
Magnetograph revealed that those GLFs are photospheric indicators of
small-scale flux emergence, and their disappearance is related to
magnetic cancellation. From two well-observed events, we describe
detailed development of the sub-structures of GLFs and different
cancellation processes that each of the two GLFs underwent.
---------------------------------------------------------
Title: Umbral Dynamics in the Near-infrared Continuum
Authors: Anđić, A.; Cao, W.; Goode, P. R.
2011ApJ...736...79A Altcode: 2011arXiv1105.1825A
We detected peaks of oscillatory power at 3 and ~6.5 minutes in the
umbra of the central sunspot of the active region NOAA AR 10707 in data
obtained in the near-infrared (NIR) continuum at 1565.7 nm. The NIR data
set captured umbral dynamics around 50 km below the τ<SUB>500</SUB> =
1 level. The umbra does not oscillate as a whole, but rather in distinct
parts that are distributed over the umbral surface. The most powerful
oscillations, close to a period of ~6.5, do not propagate upward. We
noted a plethora of large umbral dots (UDs) that persisted for >=30
minutes and stayed in the same locations. The peaks of oscillatory
power above the detected UDs are located at 3 and 5 minute oscillations,
but are very weak in comparison with the oscillations of ~6.5 minutes.
---------------------------------------------------------
Title: Near-infrared Imaging Spectropolarimeter For The Nst
Authors: Cao, Wenda; Ahn, K.; Gorceix, N.; Shumko, S.; Coulter, R.;
Goode, P.
2011SPD....42.0606C Altcode: 2011BAAS..43S.0606C
The NST Near-Infrared Imaging Spectropolarimeter is one of the first
imaging solar spectro-polarimeters working in the near infrared
(NIR). It has been installed and commissioned in the Coude Lab of the
1.6-meter NST at Big Bear Solar Observatory (BBSO). This innovative
system, which includes a 2.5 nm interference filter, a unique 0.25
nm birefringent Lyot filter, and a Fabry-Perot etalon, is capable of
providing a bandpass as low as 0.01 nm over a field-of-view (FOV) of 50"
in a telecentric configuration. An NIR waveplate rotates ahead of M3
in the NST as the polarimeter modulator, and ahead of it a calibration
unit is located to reduce polarization cross-talk induced by subsequent
oblique mirrors. Dual-beam differential polarimetry is employed to
minimize seeing-induced spurious polarization. Based on the unique
advantages in IR window, the very capable NST with adaptive optics, it
will provide unprecedented solar spectro-polarimetry with high Zeeman
sensitivity (10<SUP>-3</SUP>I<SUB>c</SUB>), high spatial resolution
(0.2"), and high cadence (15s). In this presentation, we discuss the
design, fabrication, and calibration, as well as showing the results
of the first light observations.
---------------------------------------------------------
Title: Sunspot Umbral Dots Detected with the New Solar Telescope
Authors: Kilcik, Ali; Yurchyshyn, V.; Abramenko, V.; Goode, P.; Cao, W.
2011SPD....42.1901K Altcode: 2011BAAS..43S.1901K
We present a study of bright umbral dots detected inside a large sunspot
of NOAA AR 11108. This study is based on high resolution data recorded
on September 20, 2010 with the New Solar Telescope (NST) at Big Bear
Solar Observatory. The data set, spanning 46 min, consists of a total
of 184 adaptive optics corrected and speckle reconstructed images
obtained with a 0.3 nm passband TiO filter centered on the 705.7 nm
spectral line. The image cadence is 15 s and the pixel size of 0.0375
arcsec. <P />Bright umbral dots (UDs) were detected and tracked using
an automatic routine. Here we only focus on long living UDs (>150
s in life time) and a total of 513 such features were detected during
the observed period. We found that the average lifetime of a UD is 7.4
min and an average size is 0.34 arcsec. There is a tendency for larger
UDs to be brighter (and more circular). Many UDs are not of circular
shape. We will also present probability distribution of various physical
parameters and compare the results to similar earlier studies.
---------------------------------------------------------
Title: Active Region High Velocity Events Observed by Fast Imaging
Solar Spectrograph on the NST
Authors: Ahn, Kwangsu; Chae, J.; Nah, J.; Park, H.; Jang, B.; Yang,
H.; Park, Y.; Cao, W.; Goode, P. R.
2011SPD....42.1904A Altcode: 2011BAAS..43S.1904A
The Fast Imaging Solar Spectrograph (FISS) is the only
spectrograph-based instrument on the NST that is currently
operational. With a high spectral resolution of 1.4 x 10<SUP>5</SUP>
and simultaneous dual spectral band imaging, this instrument can
accurately determine the physical parameters of chromospheric features
--- filaments, jets and so on. Initial observations captured several
peculiar dynamic events that showed high line-of-sight velocities
of the order of 20 km s<SUP>-1</SUP> in the vicinity of sunspots. We
expect that FISS will provide a better understanding of the physics
in the chromosphere with the aid of the unprecedentedly high spatial
resolution of NST.
---------------------------------------------------------
Title: Response of Granulation to Small-scale Bright Features in
the Quiet Sun
Authors: Anđić, A.; Chae, J.; Goode, P. R.; Cao, W.; Ahn, K.;
Yurchyshyn, V.; Abramenko, V.
2011ApJ...731...29A Altcode: 2011arXiv1102.3404A
We detected 2.8 bright points (BPs) per Mm<SUP>2</SUP> in the quiet
Sun with the New Solar Telescope at Big Bear Solar Observatory, using
the TiO 705.68 nm spectral line at an angular resolution ~0farcs1 to
obtain a 30 minute data sequence. Some BPs formed knots that were
stable in time and influenced the properties of the granulation
pattern around them. The observed granulation pattern within ~3”
of knots presents smaller granules than those observed in a normal
granulation pattern, i.e., around the knots a suppressed convection
is detected. Observed BPs covered ~5% of the solar surface and were
not homogeneously distributed. BPs had an average size of 0farcs22,
they were detectable for 4.28 minutes on average, and had an averaged
contrast of 0.1% in the deep red TiO spectral line.
---------------------------------------------------------
Title: The New Solar Telescope in Big Bear: Polarimetry II
Authors: Cao, W.; Ahn, K.; Goode, P. R.; Shumko, S.; Gorceix, N.;
Coulter, R.
2011ASPC..437..345C Altcode:
IRIM (Infrared Imaging Magnetograph) is one of the first imaging solar
spectro-polarimeters working in the near infrared (NIR). IRIM is being
installed and commissioned in the Coudé Lab of the 1.6-meter New Solar
Telescope (NST) at Big Bear Solar Observatory (BBSO). This innovative
system, which includes a 2.5 nm interference filter, a unique 0.25
nm birefringent Lyot filter, and a Fabry-Pérot etalon, is capable of
providing a bandpass as low as 0.01 nm over a field-of-view of 50" in a
telecentric configuration. An NIR waveplate rotates ahead of M3 in the
NST as the polarimeter modulator, and ahead of it locates a calibration
unit to reduce polarization cross-talk induced by subsequent oblique
mirrors. Dual-beam differential polarimetry is employed to minimize
seeing-induced spurious polarization. Based on the unique advantages
in IR window, the very capable NST with adaptive optics, IRIM will
provide unprecedented solar spectro-polarimetry with high Zeeman
sensitivity (10<SUP>-3</SUP>I<SUB>c</SUB>), high spatial resolution
(0.2"), and high cadence (15 s). In this paper, we discuss the design,
fabrication, and calibration of IRIM, as well as the results of the
first light observations.
---------------------------------------------------------
Title: Time Distributions of Large and Small Sunspot Groups Over
Four Solar Cycles
Authors: Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.;
Ozguc, A.; Rozelot, J. P.; Cao, W.
2011ApJ...731...30K Altcode: 2011arXiv1111.3999K
Here we analyze solar activity by focusing on time variations of
the number of sunspot groups (SGs) as a function of their modified
Zurich class. We analyzed data for solar cycles 20-23 by using Rome
(cycles 20 and 21) and Learmonth Solar Observatory (cycles 22 and 23)
SG numbers. All SGs recorded during these time intervals were separated
into two groups. The first group includes small SGs (A, B, C, H, and
J classes by Zurich classification), and the second group consists
of large SGs (D, E, F, and G classes). We then calculated small and
large SG numbers from their daily mean numbers as observed on the
solar disk during a given month. We report that the time variations
of small and large SG numbers are asymmetric except for solar cycle
22. In general, large SG numbers appear to reach their maximum in the
middle of the solar cycle (phases 0.45-0.5), while the international
sunspot numbers and the small SG numbers generally peak much earlier
(solar cycle phases 0.29-0.35). Moreover, the 10.7 cm solar radio
flux, the facular area, and the maximum coronal mass ejection speed
show better agreement with the large SG numbers than they do with
the small SG numbers. Our results suggest that the large SG numbers
are more likely to shed light on solar activity and its geophysical
implications. Our findings may also influence our understanding of
long-term variations of the total solar irradiance, which is thought
to be an important factor in the Sun-Earth climate relationship.
---------------------------------------------------------
Title: The New Solar Telescope in Big Bear: Polarimetry I
Authors: Goode, P. R.; Cao, W.; Ahn, K.; Gorceix, N.; Coulter, R.
2011ASPC..437..341G Altcode:
We present here the near-term polarimetry plans for the 1.6 m clear
aperture, off-axis telescope in Big Bear. The first scientific data
were taken in the Summer of 2009 at the Nasmyth focus, and first
observations corrected by adaptive optics were taken in the Summer
of 2010. The first polarimetry for this telescope will be done in the
near infrared at 1.56 μm, which is close to the photospheric opacity
minimum. We show and explain reasons for the general layout of the
polarimetric hardware for the telescope.
---------------------------------------------------------
Title: Hard X-ray Source Distributions on EUV Bright Kernels in a
Solar Flare
Authors: Ning, Zongjun; Cao, Wenda
2011SoPh..269..283N Altcode: 2010SoPh..tmp..247N
We explore the hard X-ray source distributions of an C1.1 flare
occurred on 14 December 2007. Both Hinode/EIS and RHESSI observations
are used. One of EIS rasters perfectly covers the double hard X-ray
footpoints, where the EUV emission appears strong from the cool line
of He II (log T=4.7) to the hot line of Fe XVI (log T=6.4). We analyze
RHESSI X-ray images at different energies and different times before
the hard X-ray maximum. The results show a similar topology for the
time-dependent source distribution (i.e. at 14:14:35 UT) as that for
energy-dependent source distribution (i.e. at a given energy band of 6 -
9 keV) overlapped on EUV bright kernels, which seems to be consistent
with the evaporation model.
---------------------------------------------------------
Title: Development of the Fast Imaging Solar Spectrograph for 1.6
m New Solar Telescope
Authors: Nah, Ja-Kyoung; Chae, Jong-Chul; Park, Young-Deuk; Park,
Hyung-Min; Jang, Bi-Ho; Ahn, Kwang-Su; Yang, Hee-Su; Cho, Kyung-Suk;
Kim, Yeon-Han; Kim, Kwang-Dong; Cao, Wenda; Gorceix, Nicolas; Goode,
Philip. R.
2011PKAS...26...45N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measurement of Sky Brightness and Suppression of Scattering
in Sky Brightness Monitor
Authors: Liu, N. P.; Liu, Y.; Shen, Y. D.; Zhang, X. F.; Cao, W. D.;
Arnaud, J.
2011AcASn..52..160L Altcode:
A modern Sky Brightness Monitor (SBM) was developed for the site survey
in West China for the future large solar equipment installation. The
performance of this new SBM was tested in the recent preliminary
experiments. A lot of sky brightness data had been obtained at a few
sites in Yunnan. The blue channel result shows that the sky brightness
near the noon time on Jiaozi Snow Mountain is as low as a few millionths
of the solar center intensity, indicating the low scattering level
inside our SBM instrument. The scattering is mainly from two parts:
the diffraction rings from the occulter edges, distributed in the inner
field of view but outside the occulter region containing the ND4 filter;
the diffraction from the baffle rings, distributed in the extreme edges
of the field of view. To suppress the scattering of the latter part,
experiments with different aperture sizes of baffle rings are made. The
result shows that, by mounting new baffle rings with proper aperture
size into the SBM telescope tube, diffraction in the extreme edges of
the field of view can be effectively reduced.
---------------------------------------------------------
Title: Ferroelectrics, Thermodynamic Phenomenology of
Authors: Cao, W.
2011emst.book.3074C Altcode:
Phenomenological theories of ferroelectrics, such as the
Landau-Ginzburg-Devonshire type models, are based on thermodynamic
principles and the structural symmetry relationship between the
paraelectric and ferroelectric phases. The primary order parameter for
describing a ferroelectric system is the electrical polarization, and
the elastic strain, as a secondary order parameter, almost always plays
a key role in the phase transition, domain formation, and other related
physical phenomena. Phenomenological theories are field theories;
however, they do reflect the discrete atomic displacement patterns and
the symmetry changes in the unit cell associated with the ferroelectric
phase transition. <ce:anchor
---------------------------------------------------------
Title: Chromospheric Signatures of Small-scale Flux Emergence as
Observed with New Solar Telescope and Hinode Instruments
Authors: Yurchyshyn, V. B.; Goode, P. R.; Abramenko, V. I.; Chae,
J.; Cao, W.; Andic, A.; Ahn, K.
2010ApJ...722.1970Y Altcode: 2011arXiv1102.1034Y
With the ever-increasing influx of high-resolution images of the solar
surface obtained at a multitude of wavelengths, various processes
occurring at small spatial scales have become a greater focus of our
attention. Complex small-scale magnetic fields have been reported that
appear to have enough stored energy to heat the chromosphere. While
significant progress has been made in understanding small-scale
phenomena, many specifics remain elusive. We present here a detailed
study of a single event of disappearance of a magnetic dipole and
associated chromospheric activity. Based on New Solar Telescope Hα
data and Hinode photospheric line-of-sight magnetograms and Ca II
H images, we report the following. (1) Our analysis indicates that
even very small dipoles (elements separated by about 0farcs5 or less)
may reach the chromosphere and trigger non-negligible chromospheric
activity. (2) Careful consideration of the magnetic environment where
the new flux is deposited may shed light on the details of magnetic
flux removal from the solar surface. We argue that the apparent
collision and disappearance of two opposite polarity elements may
not necessarily indicate their cancellation (i.e., reconnection,
emergence of a "U" tube, or submergence of Ω loops). In our case, the
magnetic dipole disappeared by reconnecting with overlying large-scale
inclined plage fields. (3) Bright points (BPs) seen in off-band Hα
images are very well correlated with the Ca II H BPs, which in turn
are cospatial with G-band BPs. We further speculate that, in general,
Hα BPs are expected to be cospatial with photospheric BPs; however,
a direct comparison is needed to refine their relationship.
---------------------------------------------------------
Title: Patterns of Flows in an Intermediate Prominence Observed
by Hinode
Authors: Ahn, Kwangsu; Chae, Jongchul; Cao, Wenda; Goode, Philip R.
2010ApJ...721...74A Altcode:
The investigation of plasma flows in filaments/prominences gives
us clues to understanding their magnetic structures. We studied
the patterns of flows in an intermediate prominence observed by
Hinode/SOT. By examining a time series of Hα images and Ca II H images,
we have found horizontal flows in the spine and vertical flows in
the barb. Both of these flows have a characteristic speed of 10-20 km
s<SUP>-1</SUP>. The horizontal flows displayed counterstreaming. Our
detailed investigation revealed that most of the moving fragments in
fact reversed direction at the end point of the spine near a footpoint
close to the associated active region. These returning flows may be
one possible explanation of the well-known counterstreaming flows
in prominences. In contrast, we have found vertical flows—downward
and upward—in the barb. Most of the horizontal flows in the spine
seem to switch into vertical flows when they approach the barb,
and vice versa. We propose that the net force resulting from a small
deviation from magnetohydrostatic equilibrium, where magnetic fields
are predominantly horizontal, may drive these patterns of flow. In the
prominence studied here, the supposed magnetohydrostatic configuration
is characterized by magnetic field lines sagging with angles of 13°
and 39° in the spine and the barb, respectively.
---------------------------------------------------------
Title: Evidence of Filament Upflows Originating from Intensity
Oscillations on the Solar Surface
Authors: Cao, Wenda; Ning, Zongjun; Goode, Philip R.; Yurchyshyn,
Vasyl; Ji, Haisheng
2010ApJ...719L..95C Altcode:
A filament footpoint rooted in an active region (NOAA 11032) was well
observed for about 78 minutes with the 1.6 m New Solar Telescope at the
Big Bear Solar Observatory on 2009 November 18 in Hα ±0.75 Å. This
data set had high cadence (~15 s) and high spatial resolution (~0farcs1)
and offered a unique opportunity to study filament dynamics. As in
previous findings from space observations, several dark intermittent
upflows were identified, and they behave in groups at isolated locations
along the filament. However, we have two new findings. First, we
find that the dark upflows propagating along the filament channel are
strongly associated with the intensity oscillations on the solar surface
around the filament footpoints. The upflows start at the same time as
the peak in the oscillations, illustrating that the upflow velocities
are well correlated with the oscillations. Second, the intensity of
one of the seven upflows detected in our data set exhibits a clear
periodicity when the upflow propagates along the filament. The periods
gradually vary from ~10 to ~5 minutes. Our results give observational
clues on the driving mechanism of the upflows in the filament.
---------------------------------------------------------
Title: Investigation of Chromospheric Evaporation in a Neupert-type
Solar Flare
Authors: Ning, Zongjun; Cao, Wenda
2010ApJ...717.1232N Altcode:
The Neupert effect implies a flare model in which the hard X-rays (HXRs)
are produced by energetic electrons via electron-ion bremsstrahlung as
they lose their energies in the chromosphere, while the soft X-rays
(SXRs) are produced by thermal bremsstrahlung from "chromospheric
evaporation" due to plasma being heated by those same electrons. Based
on this concept, we investigate the evidence for chromospheric
evaporation in a Neupert-type flare on 2004 October 30. First, we
demonstrate that this event is consistent with the Neupert effect. Using
the RHESSI data, both thermal and nonthermal energies are derived after
the onset of this flare. The high correlation between the derivative
of the SXRs and HXRs and between the derivative of the thermal energy
and nonthermal energy indicates that the 2004 October 30 flare is a
Neupert-type event. Second, chromospheric evaporation is necessarily
expected during the flare's rising phase. We analyze RHESSI images at
different energies and different times around the flare maximum. The
HXR emission tends to move the footpoints close to each other, finally
merging them into a single source with the same position as the loop-top
source. When the projection effect (due to this event being near the
disk center) is taken into account, this fact can be regarded as the
signature of chromospheric evaporation in the X-ray observations. RHESSI
observations show three kinds of evidence that are consistent with
the evaporation model. First, at a given instant, the higher energy
X-rays originate from the deeper layers of the atmosphere or further
away from the loop top. Second, in a given energy band, i.e., at 20-30
keV, the earlier X-rays originate from the deeper layers or further
away from the loop top. Third, the X-ray footpoint sources at higher
energies disappear at later times. Based on these characteristics,
chromospheric evaporation took about 100 s for the 2004 October 30
flare. X-rays at all energy bands do not show evidence of evaporation
probably because measurements are the most sensitive only between 12
and 30 keV. After measuring the source scale as a function of time,
we roughly estimate the shrinkage velocities at different energies, for
instance, 238 km s<SUP>-1</SUP> for 12-15 keV, 285 km s<SUP>-1</SUP> for
15-20 keV, and 846 km s<SUP>-1</SUP> for 20-30 keV. If the evaporation
processes primarily contribute to the source shrinkage, these values
are considered as the evaporation velocities, indicating that the
evaporation flow would be faster during the latter part of flare.
---------------------------------------------------------
Title: Oscillatory Behavior in the Quiet Sun Observed with the New
Solar Telescope
Authors: Anđić, A.; Goode, P. R.; Chae, J.; Cao, W.; Ahn, K.;
Yurchyshyn, V.; Abramenko, V.
2010ApJ...717L..79A Altcode: 2010arXiv1007.0272A
Surface photometry of the quiet Sun has achieved an angular resolution
of 0farcs1 with the New Solar Telescope at Big Bear Solar Observatory,
revealing that a disproportionate fraction of the oscillatory events
appear above observed bright point-like structures. During the tracking
of these structures, we noted that the more powerful oscillatory events
are cospatial with them, indicating that observed flux tubes may be
the source of many observed oscillatory events.
---------------------------------------------------------
Title: Repackaging and characterizing of a HgCdTe CMOS infrared
camera for the New Solar Telescope
Authors: Cao, Wenda; Coulter, Roy; Gorceix, Nicolas; Goode, Philip R.
2010SPIE.7742E..20C Altcode: 2010SPIE.7742E..55C
The 1.6-meter New Solar Telescope (NST) is currently the world's
largest aperture solar telescope. The NST is newly built at Big Bear
Solar Observatory (BBSO). Among other instruments, the NST is equipped
with several focal plane instruments operating in the near infrared
(NIR). In order to satisfy the diverse observational requirements of
these scientific instruments, a 1024 × 1024 HgCdTe TCM8600 CMOS camera
manufactured by Rockwell Scientific Company has been repackaged and
upgraded at Infrared Laboratories Inc. A new ND-5 dewar was designed to
house the TCM8600 array with a low background filter wheel, inverted
operation and at least 12 hours of hold time between fills. The
repackaged camera will be used for high-resolution NIR photometry
at the NST Nasmyth focus on the telescope and high-precision NIR
spectro-polarimetry in the NST Coudé Lab below. In March 2010, this
repackaged camera was characterized in the Coudé Lab at BBSO. This
paper presents the design of new dewar, the detailed process of
repackaging and characterizing the camera, and a series of test results.
---------------------------------------------------------
Title: Investigation of the Neupert Effect in the Various Intervals
of Solar Flares
Authors: Ning, Zongjun; Cao, Wenda
2010SoPh..264..329N Altcode: 2010SoPh..tmp..124N; 2010SoPh..tmp..112N
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
gives us a chance to investigate the theoretical Neupert effect
using the correlation between the thermal-energy derivative and
the nonthermal energy, or the thermal energy and the integral
nonthermal energy. Based on this concept, we analyze four M-class
RHESSI flares on 13 November 2003, 4 November 2004, 3 and 25 August
2005. According to the evolution of the temperature [T], emission
measure [EM], and thermal energy [E<SUB>th</SUB>], each event is
divided into three phases during the nonthermal-energy input [\frac
{dE_{nth}}{dt} in the units of erg s<SUP>−1</SUP>]. Phase 1 is
identified as the interval before the temperature maximum, while
after the thermal-energy maximum is phase 3, between them is phase
2. We find that these four flares show the Neupert effect in phase 1,
but not in phase 3. The Neupert effect still works well in the second
phase, although the cooling becomes slightly important. We define
the parameter μ in the relation of dE_{th}/dt=μdE_{nth}(t)/dt or
E_{th}(t<SUB>0</SUB>)=μ\int<SUB>0</SUB>^{t<SUB>0</SUB>}dE_{nth}(t)/dt
dt when the cooling is ignored in phase 1. Considering the uncertainties
in estimating the energy from the observations, it is not possible to
precisely determine the fraction of the known energy in the nonthermal
electrons transformed into the thermal energy of the hottest plasma
observed by RHESSI. After a rough estimate of the flare volume and the
assumption of the filling factor, we investigate the parameter μ in
these four events. Its value ranges from 0.02 to 0.20, indicating that
a small fraction (2% - 20%) of the nonthermal energy can be efficiently
transformed into thermal energy, which is traced by the soft X-ray
emission, and the bulk of the energy is lost possibly due to cooling.
---------------------------------------------------------
Title: Nasmyth focus instrumentation of the New Solar Telescope at
Big Bear Solar Observatory
Authors: Cao, Wenda; Gorceix, Nicolas; Coulter, Roy; Wöger, Friedrich;
Ahn, Kwangsu; Shumko, Sergiy; Varsik, John; Coulter, Aaron; Goode,
Philip R.
2010SPIE.7735E..5VC Altcode: 2010SPIE.7735E.194C
The largest solar telescope, the 1.6-m New Solar Telescope (NST) has
been installed and is being commissioned at Big Bear Solar Observatory
(BBSO). It has an off-axis Gregorian configuration with a focal ratio
of F/52. Early in 2009, first light scientific observations were
successfully made at the Nasmyth focus, which is located on the east
side of the telescope structure. As the first available scientific
instruments for routine observation, Nasmyth focus instrumentation
(NFI) consists of several filtergraphs offering high spatial resolution
photometry in G-band 430 nm, Ha 656 nm, TiO 706 nm, and covering the
near infrared 1083 nm, 1.6 μm, and 2.2 μm. With the assistance of
a local correlation tracker system, diffraction limited images were
obtained frequently over a field-of-view of 70 by 70 after processed
using a post-facto speckle reconstruction algorithm. These data sets
not only serve for scientific analysis with an unprecedented spatial
resolution, but also provide engineering feedback to the NST operation,
maintenance and optimization. This paper reports on the design and the
implementation of NFI in detail. First light scientific observations
are presented and discussed.
---------------------------------------------------------
Title: First light of the 1.6 meter off-axis New Solar Telescope at
Big Bear Solar Observatory
Authors: Cao, Wenda; Gorceix, Nicolas; Coulter, Roy; Coulter, Aaron;
Goode, Philip R.
2010SPIE.7733E..30C Altcode: 2010SPIE.7733E..93C
New Jersey Institute of Technology, in collaboration with the University
of Hawaii and the Korea Astronomy & Space Science Institute, has
successfully developed and installed a 1.6 m clear aperture, off-axis
New Solar Telescope (NST) at the Big Bear Solar Observatory. The NST
will be the largest aperture solar telescope in the world until the 4
m Advanced Technology Solar Telescope (ATST) and 4 m European Solar
Telescope (EST) begin operation in the next decade. Meanwhile, the
NST will be the largest off-axis telescope before the 8.4 m segmented
Giant Magellan Telescope (GMT) comes on-line. The NST is configured
as an off-axis Gregorian system consisting of a parabolic primary,
prime focus field stop and heat reflector, elliptical secondary and
diagonal flats. The primary mirror is made of Zerodur from Schott and
figured to a final residual error of 16 nm rms by Steward Observatory
Mirror Lab. The final focal ratio is f/52. The 180 circular opening in
the field stop defines the maximal square field-of-view. The working
wavelength range will cover 0.4 to 1.7 μm in the Coud´e Lab two
floors beneath the telescope, and all wavelengths including far infrared
at the Nasmyth focus on an optical bench attached to the side of the
telescope structure. First-light scientific observations have been
attained at the Nasmyth focus and in the Coud´e Lab. This paper
presents a detailed description of installation and alignment of the
NST. First-light observational results are also shown to demonstrate
the validity of the NST optical alignment.
---------------------------------------------------------
Title: High resolution observations of white-light emissions from
the opacity minimum during an X-class flare
Authors: Xu, Y.; Cao, W.; Jing, J.; Wang, H.
2010AN....331..596X Altcode:
Using high cadence, high resolution near infrared (NIR) observations of
the X10 white-light flare (WLF) on 2003 October 29, we investigated
the evolution of the core-halo structure of white-light emission
during the two-second period flare peak. We found that size and
intensity of the halo remained almost constant in the range of 10
Mm<SUP>2</SUP>. However, the core area was very compact and expanded
rapidly from about 1 Mm<SUP>2</SUP> to 4 Mm<SUP>2</SUP>. At the same
time, the total emission of the core increased nearly twenty times. This
distinct behavior indicates that different heating mechanisms might be
responsible for core and halo emissions. In addition to the temporal
analysis, we compared the intensity enhancements of the flare core and
halo. The result shows that the halo contrast increased by about 8%
compared to the flare-quiet region, which could be explained by a
combination of direct-heating and backwarming models.
---------------------------------------------------------
Title: The NST: First results and some lessons for ATST and EST
Authors: Goode, P. R.; Coulter, R.; Gorceix, N.; Yurchyshyn, V.;
Cao, W.
2010AN....331..620G Altcode:
In January 2009, first light observations with the NST (New Solar
Telescope) in Big Bear Solar Observatory (BBSO) were made. NST has a
1.7 m primary with a 1.6 m clear aperture. First observational results
in TiO and Hα are shown and discussed. The NST primary mirror is the
most aspheric telescope mirror deployed to date. The NST is early in its
commissioning, and the plans for this phase will be sketched. Lessons
learned in building and implementing the NST are germane for the ATST
and EST telescopes and will be discussed. The NST has an off-axis
Gregorian configuration consisting of a parabolic primary, heat-stop,
elliptical secondary and diagonal flats. The focal ratio of the
primary mirror is f/2.4. The working wavelength range covers from 0.4
to 1.7 μm in the Coudé Lab beneath the telescope and all wavelengths
including the far infrared at the Nasmyth focus on the dome floor.
---------------------------------------------------------
Title: Scientific instrumentation for the 1.6 m New Solar Telescope
in Big Bear
Authors: Cao, W.; Gorceix, N.; Coulter, R.; Ahn, K.; Rimmele, T. R.;
Goode, P. R.
2010AN....331..636C Altcode:
The NST (New Solar Telescope), a 1.6 m clear aperture, off-axis
telescope, is in its commissioning phase at Big Bear Solar Observatory
(BBSO). It will be the most capable, largest aperture solar telescope
in the US until the 4 m ATST (Advanced Technology Solar Telescope)
comes on-line late in the next decade. The NST will be outfitted with
state-of-the-art scientific instruments at the Nasmyth focus on the
telescope floor and in the Coudé Lab beneath the telescope. At the
Nasmyth focus, several filtergraphs already in routine operation
have offered high spatial resolution photometry in TiO 706 nm,
H\alpha 656 nm, G-band 430 nm and the near infrared (NIR), with the
aid of a correlation tracker and image reconstruction system. Also,
a Cryogenic Infrared Spectrograph (CYRA) is being developed to supply
high signal-to-noise-ratio spectrometry and polarimetry spanning
1.0 to 5.0 μm. The Coudé Lab instrumentation will include Adaptive
Optics (AO), InfraRed Imaging Magnetograph (IRIM), Visible Imaging
Magnetograph (VIM), and Fast Imaging Solar Spectrograph (FISS). A 308
sub-aperture (349-actuator deformable mirror) AO system will enable
nearly diffraction limited observations over the NST's principal
operating wavelengths from 0.4 μm through 1.7 μm. IRIM and VIM are
Fabry-Pérot based narrow-band tunable filters, which provide high
resolution two-dimensional spectroscopic and polarimetric imaging in
the NIR and visible respectively. FISS is a collaboration between BBSO
and Seoul National University focussing on chromosphere dynamics. This
paper reports the up-to-date progress on these instruments including an
overview of each instrument and details of the current state of design,
integration, calibration and setup/testing on the NST.
---------------------------------------------------------
Title: Highest Resolution Observations of the Quietest Sun
Authors: Goode, Philip R.; Yurchyshyn, Vasyl; Cao, Wenda; Abramenko,
Valentyna; Andic, Aleksandra; Ahn, Kwangsu; Chae, Jongchul
2010ApJ...714L..31G Altcode:
Highest resolution observations made with the new 1.6 m aperture solar
telescope in Big Bear Solar Observatory during this time of historic
inactivity on the Sun reveal new insights into the small-scale dynamics
of the Sun's photosphere. The telescope's unprecedented resolution
enabled us to observe that the smallest scale photospheric magnetic
field seems to come in isolated points in the dark intergranular lanes,
rather than the predicted continuous sheets confined to the lanes, and
the unexpected longevity of the bright points implies a deeper anchoring
than predicted. Further, we demonstrated for the first time that the
photospheric plasma motion and magnetic fields are in equipartition
over a wide dynamic range, and both cascade energy to ever-smaller
scales according to classical Kolmogorov turbulence theory. Finally,
we discovered tiny jet-like features originating in the dark lanes that
surround the ubiquitous granules that characterize the solar surface.
---------------------------------------------------------
Title: New Solar Telescope Observations of Magnetic Reconnection
Occurring in the Chromosphere of the Quiet Sun
Authors: Chae, Jongchul; Goode, P. R.; Ahn, K.; Yurchysyn, V.;
Abramenko, V.; Andic, A.; Cao, W.; Park, Y. D.
2010ApJ...713L...6C Altcode:
Magnetic reconnection is a process in which field-line connectivity
changes in a magnetized plasma. On the solar surface, it often
occurs with the cancellation of two magnetic fragments of opposite
polarity. Using the 1.6 m New Solar Telescope, we observed the
morphology and dynamics of plasma visible in the Hα line, which is
associated with a canceling magnetic feature (CMF) in the quiet Sun. The
region can be divided into four magnetic domains: two pre-reconnection
and two post-reconnection. In one post-reconnection domain, a small
cloud erupted, with a plane-of-sky speed of 10 km s<SUP>-1</SUP>,
while in the other one, brightening began at points and then tiny
bright loops appeared and subsequently shrank. These features support
the notion that magnetic reconnection taking place in the chromosphere
is responsible for CMFs.
---------------------------------------------------------
Title: Dual-Stage Reconnection During Solar Flares Observed in
Hard X-ray
Authors: Xu, Yan; Jing, Ju; Cao, Wenda; Wang, Haimin
2010ApJ...709L.142X Altcode:
In this Letter, we present hard X-ray (HXR) observation by the Reuven
Ramaty High Energy Solar Spectroscopic Imager of the 2003 October 29
X10 flare. Two pairs of HXR conjugate footpoints have been identified
during the early impulsive phase. This geometric configuration is very
much in the manner predicted by the "tether-cutting" scenario first
proposed by Moore & Roumeliotis. The HXR light curves show that
the outer pair of footpoints disappeared much faster than the other
pair. This temporal behavior further confirms that this event is a good
example of the "tether-cutting" model. In addition, we reconstructed
a three-dimensional magnetic field based on the nonlinear force-free
extrapolation and found that each pair of HXR footpoints were indeed
linked by corresponding magnetic field lines.
---------------------------------------------------------
Title: Scientific Instruments of 1.6 m New Solar Telescope in Big Bear
Authors: Cao, W.
2009AGUFMSH51A1261C Altcode:
The NST (New Solar Telescope) is in its commissioning phase at
Big Bear Solar Observatory (BBSO). It will be the most capable,
largest aperture solar telescope in the US until the 4 m ATST
(Advanced Technology Solar Telescope) comes on-line in the middle
of the next decade. The NST will be outfitted with state-of-the-art
post-focus instrumentations at the Nasmyth focus on the dome floor
and in the Coude Lab beneath the telescope. At the Nasmyth focus,
several filter-based systems already in routine operation offer high
spatial resolution photometry in TiO 704 nm, Hα 656 nm, G-band 430
nm and near infrared 1.56 μm & 2.2 μm, with the assistance
of local correlation tracking and image reconstruction. As well, a
Cryogenic InfraRed Spectrograph (CIRS) is being developed to supply
high signal-to-noise-ratio spectrometry and polarimetry spanning 1.0 to
5.0 μm. The Coudé-lab instrumentations will include Adaptive Optics
system (AO), InfraRed Imaging Magnetograph (IRIM), Visible Imaging
Magnetograph (VIM), Real-time Image Reconstruction System (RIRS), and
Fast Imaging Solar Spectrograph (FISS) -- most of these instruments
operated on the old 0.6 m BBSO telescope. AO is being upgraded to a 308
sub-aperture (349-actuator Deformable Mirror) AO system that will enable
diffraction limited observations over the NST's principal operating
wavelengths from 0.4 through 1.7 μm. IRIM and VIM are Fabry-Pérot
based narrow-band tunable filter, which provide high resolution
two-dimensional spectroscopic and polarimetric imaging in the near
infrared and visible respectively. Using a 32-node parallel computing
system, RIRS is capable of performing real-time image reconstruction
with one image every minute. FISS is a collaboration between BBSO and
Seoul National University to focus on chromosphere dynamics. Key tasks
including optical design, hardware/software integration and subsequent
setup/testing on the NST, will be presented here. Some preliminary
observation results in the near infrared will be shown.
---------------------------------------------------------
Title: A LATE BRITTLE COMPONENT OF MOTION WITHIN THE DUCTILE EASTERN
SIERRA CREST SHEAR ZONE (ESCSZ) ALONG THE EASTERN BOUNDARY OF THE
TOLUMNE BATHOLITH IN THE SADDLEBAG LAKE, CA AREA. WHITESIDES, Andrew1,
ENRIQUEZ, Marcus2 , HARDY, Jill1 , EHRET, Philip1, IANNONE, Monika1,
CULBERT, Kristan1 GROSS, Ben3, LODEWYK, Jessica3, CAO, Wenrong1 ,
ZHANG, Tao1, MEMETI, Valbone3, PATERSON, Scott1 SCHMIDT, Keegan4. (1)
Department of Earth Sciences, University of Southern California,
Los Angeles, CA 90089-0740, awhitesi@usc.edu , (2) Department of
Geological Sciences, Cal State L.A., 5151 State University Drive, Los
Angeles, CA 90032, (3) Department of Earth and Planetary Sciences,
Washington University, Campus Box 1169, 1 Brookings Dr, Saint
Louis, MO, 63130, (4) Division of Natural Science and Mathematics,
Lewis-Clark State College, 500 8th Ave., Lewiston, ID 83501
Authors: Whitesides, A. S.; Enriquez, M.; Hardy, J.; Ehret, P.;
Iannone, M.; Culbert, K. N.; Gross, M. B.; Lodewyk, J.; Cao, W.;
Zhang, T.; Memeti, V.; Paterson, S. R.; Schmidt, K. L.
2009AGUFM.T21D1862W Altcode:
During mapping (by the Undergraduate Team Research program, University
of Southern California) in the Saddlebag Lake pendant just along the
eastern margin of the Tuolumne batholith we have discovered a brittle
slip component in the ESCSZ that juxtaposes largely metasedimentary and
metavolcanic rock packages. The metasedimentary package is dominated
by bedded sandstones and siltstones and local conglomerates whereas
the metavolcanics show a large range of volcanic and volcaniclastic
units. All of the units dip steeply and have an average N-NW
strike. Dextral oblique ductile shear is distributed in domains in both
rock packages with varying width from ~2 km in the South to ~1 km in the
North. Shear sense in planes at high angles to a steep to SW plunging
mineral lineation include S-C structures, shear bands, asymmetrical
folding, sigma and delta clasts, and asymmetrical boudins. Partitioning
of shear is common with the metarhyolites and metasediments showing
higher non-coaxial strain than in the metaandesite and metadacite
units. Map-scale “z-shaped” asymmetrical folds within the shear
zone are also consistent with dextral shearing. Folded and sheared
dikes of the 88-85 Ma Cathedral Peak phase of the Tuolumne batholith are
common in the shear zone. A newly discovered brittle slip surface with
breccias, gouge, and local pseudotachylite and large quartz veins was
also mapped in the center of the ductile shear zone typically along the
contact between the western metasedimentary and eastern metavolcanics
(often a metarhyolite at the contact) on the east. Local slickenlines,
steps, and offset dikes indicate that the brittle fault also had oblique
dextral movement, similar to the ductile shear zone. In the mapped area
no dikes originating from the TB cross the brittle fault and some are
terminated at the brittle fault surface We interpret these observations
to indicate northward displacement of the metasedimentary package by
first ductile then brittle faulting during cooling and possibly uplift
of this region with the youngest motion post 82 Ma.
---------------------------------------------------------
Title: Behavior of the Spines in a Quiescent Prominence Observed
by Hinode/SOT
Authors: Ning, Z.; Cao, W.; Goode, P. R.
2009ApJ...707.1124N Altcode:
We report the behaviors of the spines in a quiescent prominence
from the observations on 2008 January 15 made with Hinode/SOT in
Hα +0.076 Å, Hα-0.34 Å, and Ca II H line filters. Two spines (1
and 2) are visible in this event. In the spacetime plots of the Hα
and Ca II intensities, the two spines seem to gradually move closer
together, and finally merge, then separate again. Their behaviors are
separated into two kinds of typical motions. On the Doppler diagrams,
the spine 1 has a dominant redshift, and spine 2 favors a blueshift,
which reveals that the spines 1 and 2 firstly display the drifting
motions in opposite directions. The former is drifting northward, while
the latter drifts southward. Second, both spines display large-scale
oscillating motions. Their oscillating velocities, amplitudes, and
periods have average values of 3 km s<SUP>-1</SUP>, ±5 Mm, and 98
minutes, respectively, indicating a small-amplitude oscillation with a
long period. After the sinusoidal fitting, both spines almost exhibit
an antiphase oscillating motions. The spine 2 oscillates 135° ahead
of the spine 1. Such antiphase oscillations would reflect the coupling
of the transverse oscillations of the spines in this prominence.
---------------------------------------------------------
Title: Evidence of Chromospheric Evaporation in the 2004 December
1 Solar Flare
Authors: Ning, Zongjun; Cao, Wenda; Huang, Jing; Huang, Guangli; Yan,
Yihua; Feng, Hengqiang
2009ApJ...699...15N Altcode:
In this paper, we present the radio and hard X-ray evidence of
chromospheric evaporation during an M1.0 flare which occurred on 2004
December 1. The radio emission was observed by the Solar Broadband
Radio Dynamic Spectrometer in China, which yielded dynamic spectra
of decimetric emission. The hard X-ray emission was observed by
RHESSI. In the radio spectra, the burst is characterized by two groups
of parallel-drifting structures, some of which change their drifting
rates from positive to negative. Based on the standard flare model,
we may explain these decimetric bursts in terms of chromospheric
evaporation. On the other hand, RHESSI observations show that the hard
X-ray emission in the energy range of 10-15 keV tends to rise from two
footpoints to the looptop and eventually merges into a single looptop
source, which is accepted as evidence of hard X-ray chromospheric
evaporation. Such processes happened twice in this event. The drifting
radio structures occurred between them, at the same time as the third
hard X-ray peak was observed at 25-50 keV.
---------------------------------------------------------
Title: Spatial and Spectral Behaviors of Solar Flares Observed
in Microwaves
Authors: Ning, Zongjun; Cao, Wenda
2009SoPh..257..335N Altcode:
The spatial and spectral behaviors of two solar flares observed by
the Nobeyama Radioheliograph (NoRH) on 24 August 2002 and 22 August
2005 are explored. They were observed with a single loop-top source
and double footpoint sources at the beginning, then with looplike
structures for the rest of the event. NoRH has high spatial and temporal
resolution at the two frequencies of 17 and 34 GHz where a nonthermal
radio source is often optically thin. Such capabilities give us an
opportunity to study the spatial and spectral behaviors of different
microwave sources. The 24 August 2002 flare displayed a soft - hard -
soft (SHS) spectral pattern in the rising - peak - decay phases at 34
GHz, which was also observed for the spectral behavior of both loop-top
and footpoint sources. In contrast, the 22 August 2005 flare showed a
soft - hard - harder (SHH) spectral pattern for its both loop-top and
footpoint sources. It is interesting that this event showed a harder
spectrum in the early rising phase. We found a positive correlation
between the spectral index and microwave flux in both the loop-top
source and the footpoint sources in both events. The conclusions drawn
from the flux index could apply to the electron index as well, because
of their simple linear relationship under the assumption of nonthermal
gyrosynchrotron mechanism. Such a property of spatial and spectral
behaviors of microwave sources gives an observational constraint on
the electron acceleration mechanism and electron propagation.
---------------------------------------------------------
Title: Periodicity of Twisting Motions in Sunspot Penumbral Filaments
Authors: Ning, Zongjun; Cao, Wenda; Goode, Philip R.
2009SoPh..257..251N Altcode:
We study the periodicity of twisting motions in sunspot penumbral
filaments, which were recently discovered from space (Hinode) and
ground-based (SST) observations. A sunspot was well observed for
97 minutes by Hinode/SOT in the G-band (4305 Å) on 12 November
2006. By the use of the time - space gradient applied to intensity
space - time plots, twisting structures can be identified in the
penumbral filaments. Consistent with previous findings, we find that
the twisting is oriented from the solar limb to disk center. Some of
them show a periodicity. The typical period is about ≈ four minutes,
and the twisting velocity is roughly 6 km s<SUP>−1</SUP>. However,
the penumbral filaments do not always show periodic twisting motions
during the time interval of the observations. Such behavior seems to
start and stop randomly with various penumbral filaments displaying
periodic twisting during different intervals. The maximum number of
periodic twists is 20 in our observations. Studying this periodicity can
help us to understand the physical nature of the twisting motions. The
present results enable us to determine observational constraints on
the twisting mechanism.
---------------------------------------------------------
Title: Post-focus Instrumentation Of The NST
Authors: Cao, Wenda; Gorceix, N.; Andic, A.; Ahn, K.; Coulter, R.;
Goode, P.
2009SPD....40.1803C Altcode:
The NST (New Solar Telescope), 1.6 m clear aperture, off-axis
telescope, is in its commissioning phase at Big Bear Solar Observatory
(BBSO). It will be the most capable, largest aperture solar telescope
in the US until the 4 m ATST (Advanced Technology Solar Telescope)
comes on-line in the middle of the next decade. The NST will be
outfitted with state-of-the-art post-focus instrumentation, which
currently include Adaptive Optics system (AO), InfraRed Imaging
Magnetograph (IRIM), Visible Imaging Magnetograph (VIM), Real-time
Image Reconstruction System (RIRS), and Fast Imaging Solar Spectrograph
(FISS). A 308 sub-aperture (349-actuator Deformable Mirror) AO system
will enable diffraction limited observations over the NST's principal
operating wavelengths from 0.4 µm through 1.7 µm. IRIM and VIM
are Fabry-Perot based narrow-band tunable filter, which provide high
resolution two-dimensional spectroscopic and polarimetric imaging in
the near infrared and visible respectively. Using a 32-node parallel
computing system, RIRS is capable of performing real-time image
reconstruction with one image every minute. FISS is a collaboration
between NJIT and Seoul National University to focus on chromosphere
dynamics. This instruments would be installed this Summer as a part
of the NST commissioning and the implementation of Nysmyth focus
instrumentation. Key tasks including optical design, hardware/software
integration and subsequent setup/testing on the NST, will be presented
in this poster. First light images from the NST will be shown.
---------------------------------------------------------
Title: Oscillatory Behavior and its Connection to Granulation
Authors: Andic, Aleksandra; Cao, W.; Goode, P. R.; Jess, D. B.
2009SPD....40.0933A Altcode:
Results are presented from two distinct sets of the observations to
further elucidate origin of, and the role of high frequency oscillations
in <P />atmospheric dynamics. One set was performed using IBIS that
Observatorio <P />Astrofisico di Arcetri developed. This 2D spectrograph
utilized the Fe I 709nm spectral line at the Dunn Solar telescope,
Sacramento Peak, of National Solar Observatory. This data set was
first speckle reconstructed. The second data set was obtained from
the same telescope using BBSO's IRIM with its Rockwell Near Infrared
Camera measuring the Fe 1565.7nm spectral line. <P />It was determined
that the magnetic field has a significant role in <P />propagation of
the oscillations, and our near infrared observations revealed <P />new
insights into the oscillatory dynamics of the deep photosphere. Detailed
results will be presented.
---------------------------------------------------------
Title: Small-scale oscillations in a quiescent prominence observed
by HINODE/SOT. Prominence oscillations
Authors: Ning, Z.; Cao, W.; Okamoto, T. J.; Ichimoto, K.; Qu, Z. Q.
2009A&A...499..595N Altcode:
Context: Investigations of the behavior of small-scale threads can
provide an alternative approach to studying prominence dynamics and
understanding its origin and nature. <BR />Aims: The behavior of
threads are analyzed in a quiescent prominence, including drifting
and both the horizontally and vertically oscillating motions. These
indicate waves in the solar prominence. <BR />Methods: We used the Hα
images at a setting wavelength of +0.076 Å. A quiescent prominence
was observed by HINODE/SOT on 2008 January 15 for about 3 h in
total. <BR />Results: Consistent with previous findings, prominences
show numerous thread-like structures. Some threads clearly exhibit both
vertically and horizontally oscillatory motions, while others are only
drifting. Complicated cases show both drifting and oscillatory motions
simultaneously. In the upper part of the prominence, the threads are
oscillating independently of each other. We find that three threads
oscillate with the same phase for at least two periods. The oscillations
seem to be strongly damped since they disappear after a few periods. The
maximum number of observed periods is 8 in our observations. In the
lower part of the prominence, however, the different threads have a
mixed character with the individual oscillatory motions unstable for
one entire period. Most oscillatory motions will disappear after a half
period or less, while the new oscillatory motions are excited nearby. A
5-min period is predominant, and the oscillating amplitudes show an
average value of ±3.5 km s<SUP>-1</SUP>. We find some upflows in the
spicule layer, and they appear to transport the mass from photosphere
(or spicules themselves) to the prominence. These upflows have an
average velocity amplitude of 0.8 km s<SUP>-1</SUP>. <BR />Conclusions:
The threads exhibit three distinct behaviors. The first is only
drifting, the second is typically oscillating, and the third shows
both characteristics. There are no substantial differences between
the periods of horizontally and vertically oscillating threads in
this prominence.
---------------------------------------------------------
Title: Early Abnormal Temperature Structure of X-Ray Loop-Top Source
of Solar Flares
Authors: Shen, Jinhua; Zhou, Tuanhui; Ji, Haisheng; Wang, Na; Cao,
Wenda; Wang, Haimin
2008ApJ...686L..37S Altcode: 2008arXiv0808.4047S
This Letter is to investigate the physics of a newly discovered
phenomenon—contracting flare loops in the early phase of solar
flares. In classical flare models, which were constructed based on
the phenomenon of the expansion of flare loops, an energy releasing
site is put above flare loops. These models can predict that there is
a vertical temperature gradient in the top of flare loops due to heat
conduction and cooling effects. Therefore, the centroid of an X-ray
loop-top source at higher energy bands will be higher in altitude,
which we can define as the normal temperature distribution. With
observations made by RHESSI, we analyzed 10 M- or X-class flares (9
limb flares). For all these flares, the movement of loop-top sources
shows an obvious U-shaped trajectory, which we take as the signature of
contraction-to-expansion of flare loops. We find that, for all these
flares, a normal temperature distribution does exist, but only along
the path of expansion. The temperature distribution along the path of
contraction is abnormal, showing no spatial order at all. The result
suggests that magnetic reconnection processes in the contraction and
expansion phases of these solar flares are different.
---------------------------------------------------------
Title: Magnetic Reconnection Rate and RHESSI Hard X-Ray Imaging
Spectroscopy of Well Resolved X-class Flares
Authors: Xu, Y.; Jing, J.; Cao, W.; Wang, H.
2008AGUSMSP51C..06X Altcode:
Three X-class white-light flares were captured by BBSO observing team
at NSO in 2003 and the Solar Optical Telescope (SOT) on board HINODE in
2006. They were all typical two-ribbon flares and the flare ribbons were
resolved to the diffraction limit in G-band observations. We measure
the velocities of ribbon-motion Vn for different flaring kernels and
the corresponding magnetic flux density Bn. We compare the correlation
between Vn and Bn with previous obtained empirical relationship. In
addition, we investigate the temporal evolution of shear-angle between
conjugate foot-points and magnetic neutral line using both Hard X-ray
(HXR) observation obtained by Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) and G-band data. The results show clear decrease
of shear-angles, indicating motion of flare kernels along the flare
ribbons in early stage of flares. The optical observations including
G-band show that some isolated HXR flare kernels are actually connected
by the optical flare ribbons. Using the high resolution cleaned HXR
images, we also present the spectral information obtained for all
the HXR kernels and discuss the difference of spectral index in the
different magnetic field environment.
---------------------------------------------------------
Title: Multiwavelength Study of Flow Fields in Flaring Super Active
Region NOAA 10486
Authors: Deng, N.; Xu, Y.; Yang, G.; Cao, W.; Liu, C.; Rimmele, T. R.;
Wang, H.; Denker, C.
2006AGUFMSH31B..06D Altcode:
We present high resolution observations of horizontal flow fields
measured by Local Correlation Tracking from intensity images in three
wavelengths, i.e., G-Band (GB), White-Light (WL), and Near InfraRed
(NIR). The observations were obtained on 2003 October~29 within
the flaring super active region NOAA~10486, which was the source of
several X-class flares, including an X10 flare that occurred near
the end of the observing run. The data were obtained at National
Solar Observatory/Sacramento Peak (NSO/SP) using the newly developed
high-order Adaptive Optics (AO) system. We also use Dopplergrams
and magnetograms from MDI on board SOHO to study the line-of-sight
flow and magnetic field. We observe persistent and long-lived (at
least 5 hours) strong horizontal and vertical shear flows (both in
the order of 1 km s-1) along the magnetic Neutral Line (NL) until
the X10 flare occurred. From lower photospheric level (NIR), the
direction of the flows does not change up to the upper photosphere
(GB), while the flow speeds in the shear motion regions decrease and
on the contrary those in regions without shear motions increase with
increasing altitude. Right after the X10 flare, the magnetic gradient
decreased, while both horizontal and vertical shear flows dramatically
enhanced near the flaring NL. Our results suggest that photospheric
shear flows and local magnetic shear near the NL can increase after
the flare, which may be the result of shear release in the overlying
large-scale magnetic system or the reflection of a twisted or sheared
flux emergence carrying enough energy from subphotosphere.
---------------------------------------------------------
Title: First Light of the Near-Infrared Narrow-Band Tunable
Birefringent Filter at Big Bear Solar Observatory
Authors: Cao, Wenda; Hartkorn, Klaus; Ma, Jun; Xu, Yan; Spirock, Tom;
Wang, Haimin; Goode, Philip R.
2006SoPh..238..207C Altcode: 2006SoPh..tmp...53C
We discuss a near-infrared (NIR) narrow-band tunable birefringent
filter system newly developed by the Big Bear Solar Observatory
(BBSO). This is one of the first narrow-bandpass NIR filter systems
working at 1.56 μm which is used for the observation of the deepest
solar photosphere. Four stages of calcite were used to obtain a bandpass
of 2.5 Å along with a free spectral range (FSR) of 40 Å. Some unique
techniques were implemented in the design, including liquid crystal
variable retarders (LCVRs) to tune the bandpass in a range of ±100 Å,
a wide field configuration to provide up to 2° incident angle, and
oil-free structure to make it more compact and handy. After performing
calibration and characteristic evaluation at the Evans Facility of
the National Solar Observatory at Sacramento Peak (NSO/SP), a series
of high-resolution filtergrams and imaging polarimetry observations
were carried out with the Dunn Solar Telescope of NSO/SP and the
65-cm telescope of BBSO, in conjunction with the high-order adaptive
optics system and the Fabry-Pérot Interferometer (FPI). In this
paper, we describe the optical design and discuss the calibration
method. Preliminary observations show that it is capable of serving as
either a stand-alone narrow-band filter for NIR filtergram observations
or an order-sorting filter of a FPI applied to NIR two-dimensional
imaging spectro-polarimetry.
---------------------------------------------------------
Title: Progress on the 1.6-meter New Solar Telescope at Big Bear
Solar Observatory
Authors: Denker, C.; Goode, P. R.; Ren, D.; Saadeghvaziri, M. A.;
Verdoni, A. P.; Wang, H.; Yang, G.; Abramenko, V.; Cao, W.; Coulter,
R.; Fear, R.; Nenow, J.; Shoumko, S.; Spirock, T. J.; Varsik, J. R.;
Chae, J.; Kuhn, J. R.; Moon, Y.; Park, Y. D.; Tritschler, A.
2006SPIE.6267E..0AD Altcode: 2006SPIE.6267E..10D
The New Solar Telescope (NST) project at Big Bear Solar Observatory
(BBSO) now has all major contracts for design and fabrication in place
and construction of components is well underway. NST is a collaboration
between BBSO, the Korean Astronomical Observatory (KAO) and Institute
for Astronomy (IfA) at the University of Hawaii. The project will
install a 1.6-meter, off-axis telescope at BBSO, replacing a number
of older solar telescopes. The NST will be located in a recently
refurbished dome on the BBSO causeway, which projects 300 meters into
the Big Bear Lake. Recent site surveys have confirmed that BBSO is
one of the premier solar observing sites in the world. NST will be
uniquely equipped to take advantage of the long periods of excellent
seeing common at the lake site. An up-to-date progress report will
be presented including an overview of the project and details on the
current state of the design. The report provides a detailed description
of the optical design, the thermal control of the new dome, the optical
support structure, the telescope control systems, active and adaptive
optics systems, and the post-focus instrumentation for high-resolution
spectro-polarimetry.
---------------------------------------------------------
Title: Diffraction-limited Polarimetry from the Infrared Imaging
Magnetograph at Big Bear Solar Observatory
Authors: Cao, Wenda; Jing, Ju; Ma, Jun; Xu, Yan; Wang, Haimin; Goode,
Philip R.
2006PASP..118..838C Altcode:
The Infrared Imaging Magnetograph (IRIM) system developed by Big Bear
Solar Observatory (BBSO) has been put into preliminary operation. It is
one of the first imaging spectropolarimeters working at 1565 nm and is
used for the observations of the Sun at its opacity minimum, exposing
the deepest photospheric layers. The tandem system, which includes a
4.2 nm interference filter, a unique 0.25 nm birefringent Lyot filter,
and a Fabry-Pérot etalon, is capable of providing a bandpass as low as
0.01 nm in a telecentric configuration. A fixed quarter-wave plate and
a nematic liquid crystal variable retarder are employed for analyzing
the circular polarization of the Zeeman components. The longitudinal
magnetic field is measured for the highly Zeeman-sensitive Fe I line
at 1564.85 nm (Landé factor g=3). The polarimetric data were taken
through a field of view of ~145<SUP>”</SUP>×145<SUP>”</SUP> and
were recorded by a 1024×1024 pixel, 14 bit HgCdTe CMOS focal plane
array camera. Benefiting from the correlation tracking system and a
newly developed adaptive optics system, the first imaging polarimetric
observations at 1565 nm were made at the diffraction limit on 2005 July
1 using BBSO's 65 cm telescope. After comparing the magnetograms from
IRIM with those taken by the Michelson Doppler Imager on board SOHO,
it was found that all the magnetic features matched very well in both
sets of magnetograms. In addition, Stokes V profiles obtained from the
Fabry-Pérot etalon scan data provide access to both the true magnetic
field strength and the filling factor of the small-scale magnetic
flux elements. In this paper, we present the design, fabrication, and
calibration of IRIM, as well as the results of the first scientific
observations.
---------------------------------------------------------
Title: High-Resolution Studies of Complex Solar Active Regions
Authors: Deng, Na; Wang, H.; Liu, C.; Yang, G.; Xu, Y.; Tritschler,
A.; Cao, W.; Rimmele, T. R.; Denker, C.
2006SPD....37.3401D Altcode: 2006BAAS...38..258D
Most Flares and CMEs occur or originate in solar active regions,
typically in sunspots with complex magnetic fields such as
delta-spots. Rapid and substantial changes of the sunspot structure have
been discovered to be associated with flares/CMEs. Rapid penumbral decay
and umbral enhancements are intensity changes, which are interpreted as
signatures of magnetic reconnection during the flare. The magnetic field
lines switch from an inclined to a more vertical orientation. Strong and
long-lived shear flows near the flaring magnetic inversion line have
been detected using Local Correlation Tracking (LCT) techniques based
on multi-wavelength high resolution observations. A newly observed and
important phenomenon is the increased local shear flow and magnetic
shear right after the flare in spite of theoretical models requiring
an overall decrease in the magnetic free energy. The emergence of a
twisted or pre-sheared flux rope near the neutral line is a possible
interpretation. Using high-order adaptive optics combined post-facto
speckle masking image reconstruction, we can obtain time-series with
highly improved image quality and spatial resolution in the order of
0.14" or about 100 km on the solar surface. We combine the observed
longitudinal Dopplergrams obtained with two-dimensional imaging
spectrometer and transverse LCT flow maps derived from time-series
of speckle reconstructed images to create real local 3D flow maps
(view from above). Using these precise 3D flow maps observed in a
typical sunspot in the course of its center to limb disc passage,
we observe distinct division line between radially inward and outward
flow in the penumbra and its evolution during the decaying phase of
the sunspot. The inclination angles of penumbral flow channels are
also calculated.Acknowledgments: This work is supported by NSF under
grant ATM 03-42560, ATM 03-13591, ATM 02-36945, ATM 05-48952, and MRI
AST 00-79482 and by NASA under grant NAG 5-13661.
---------------------------------------------------------
Title: Multiwavelength Study of Flow Fields in Flaring Super Active
Region NOAA 10486
Authors: Deng, Na; Xu, Yan; Yang, Guo; Cao, Wenda; Liu, Chang; Rimmele,
Thomas R.; Wang, Haimin; Denker, Carsten
2006ApJ...644.1278D Altcode:
We present high-resolution observations of horizontal flow fields
measured by local correlation tracking from intensity images in three
wavelengths, i.e., G band (GB), white light (WL), and near-infrared
(NIR). The observations were obtained on 2003 October 29 within
the flaring super active region NOAA 10486, which was the source of
several X-class flares, including an X10 flare that occurred near
the end of the observing run. The data were obtained at National
Solar Observatory/Sacramento Peak (NSO/SP) using the newly developed
high-order adaptive optics (AO) system. We also use Dopplergrams
and magnetograms from MDI on board SOHO to study the line-of-sight
flow and magnetic field. We observe persistent and long-lived (at
least 5 hr) strong horizontal and vertical shear flows (both in the
order of 1 km s<SUP>-1</SUP>) along the magnetic neutral line (NL)
until the X10 flare occurred. From lower photospheric level (NIR),
the direction of the flows does not change up to the upper photosphere
(GB), while the flow speeds in the shear motion regions decrease and,
on the contrary, those in regions without shear motions increase with
increasing altitude. Right after the X10 flare, the magnetic gradient
decreased, while both horizontal and vertical shear flows dramatically
enhanced near the flaring NL. Our results suggest that photospheric
shear flows and local magnetic shear near the NL can increase after
the flare, which may be the result of shear release in the overlying
large-scale magnetic system or the reflection of a twisted or sheared
flux emergence carrying enough energy from the subphotosphere.
---------------------------------------------------------
Title: The first light of the Infrared Imaging Magnetographat Big
Bear Solar Observatory
Authors: Cao, Wenda; Ma, J.; Jing, J.; Xu, Y.; Denker, C.; Wang, H.;
Goode, P.
2006SPD....37.0612C Altcode: 2006BAAS...38..227C
The InfraRed Imaging Magnetograph (IRIM) system developed by Big Bear
Solar Observatory (BBSO) has been put into preliminary operation. It
is one of the first imaging spectro-polarimeters working at 1565 nm,
and is used for the observations of the Sun at its opacity minimum,
exposing the deepest photospheric layers. The tandem system of a 4.2 nm
interference filter, an unique 0.25 nm birefringent Lyot filter and a
Fabry-Perot etalon is capable of providing a bandpass as low as 0.01
nm in a telecentric configuration. A fixed quarter wave plate and a
nematic liquid crystal variable retarder are employed for analyzing
the circular polarization of the Zeeman components. The longitudinal
magnetic field is measured for highly Zeeman-sensitive Fe I line at
1564.85 nm (Lande factor g = 3). The polarimetric data, with a field of
view (FOV) 145" × 145", were recorded by a 1024 × 1024 pixel, 14-bit
HgCdTe CMOS focal plane array camera. Benefiting from the Correlation
Tracking system (CT) and newly developed Adaptive Optics (AO) system,
the first imaging polarimetric observations at 1565 nm were made at the
diffraction limit on 1 July 2005 using BBSO's 65 cm telescope. After
comparing the magnetograms from IRIM with those taken by the Michelson
Doppler Imager (MDI) on board SOHO, it was found that all the magnetic
features matched very well in both sets of magnetograms. Also, Stokes
V profiles obtained from the Fabry-Perot etalon scanning data provide
access to both the true magnetic field strength and filling factor of
the small-scale magnetic flux elements. In this paper, we present the
design, fabrication, and calibration of IRIM, as well as the results
of the first scientific observations.
---------------------------------------------------------
Title: High-Resolution Observations of Multiwavelength Emissions
during Two X-Class White-Light Flares
Authors: Xu, Yan; Cao, Wenda; Liu, Chang; Yang, Guo; Jing, Ju; Denker,
Carsten; Emslie, A. Gordon; Wang, Haimin
2006ApJ...641.1210X Altcode:
We observed two X-class white-light flares (WLFs) on 2003 October 29
(~20:40 UT) and November 2 (~17:16 UT) using the Dunn Solar Telescope
(DST) and its High-Order Adaptive Optics (HOAO) system in several
wavelengths. The spatial resolution was close to the diffraction limit
of DST's 76 cm aperture, and the cadence was as high as 2 s. This
is the first time that WLFs have been observed in the near-infrared
(NIR) wavelength region. We present a detailed study in this paper
comparing photospheric continuum observations during the two events with
corresponding line-of-sight magnetograms from the Solar and Heliospheric
Observatory (SOHO) Michelson Doppler Imager (MDI) and hard X-ray (HXR)
data from the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). We
also discuss several models that provide possible mechanisms to explain
these continuum enhancements, especially in the NIR.
---------------------------------------------------------
Title: Properties of Small Dark Features Observed in the Pure
Near-Infrared and Visible Continua
Authors: Xu, Yan; Cao, Wenda; Ma, Jun; Hartkorn, Klaus; Jing, Ju;
Denker, Carsten; Wang, Haimin
2005ApJ...628L.167X Altcode:
High-resolution images in the visible and near-infrared (NIR) continua
at around 1560 nm were obtained of solar active regions NOAA AR 10707
and AR 10486 with the Dunn Solar Telescope (DST) at the National Solar
Observatory/Sacramento Peak (NSO/SP) on 2004 December 1 and 2 and
2003 October 29. The images were taken with the high-order adaptive
optics (HOAO) system, and the spatial resolution was close to the
diffraction limit of the 76 cm aperture DST in both wavelengths. For
the 2004 December run, the NIR observations were made with a newly
developed Lyot filter system, which was designed at the Center for
Solar-Terrestrial Research (CSTR)/New Jersey Institute of Technology
(NJIT). The filter has a bandpass of 2.5 Å that allows us to observe
the pure NIR continuum at the opacity minimum. Our data show that all
dark features in the NIR are also dark in the visible light. There
is no evidence showing the existence of so-called dark faculae, i.e.,
faculae that have negative contrasts in the NIR but positive contrasts
in the visible. The negative peak contrasts of these small pores are
about 50% in the visible and 25% in the NIR, and their dimensions are
in the range of 1"-4".
---------------------------------------------------------
Title: Near-infrared HeI 1083nm Stokes polarimeter based on liquid
crystal variable retarders
Authors: Zhang, Zhiyong; Deng, Yuanyong; Wong, Dongguang; Sun, Yingzi;
Cao, Wenda
2005SPIE.5901..377Z Altcode:
The spectral line of HeI 1083nm is important and potential to measure
the magnetic field of the solar upper chromosphere. In this paper, we
present a newly developed Stokes polarimeter for measuring the polarized
signals at this wavelength. In this device, two Liquid Crystal Variable
Retarders (LCVRs) were employed as electro-optical modulators and
a Wollaston prism as analyzer and polarized beam splitter. Compared
to the commonly used linear-polarized analyzer, the Wollaston prism
analyzer has main advantage to minimize the seeing-induced contamination
of earth's atmosphere, as it produces simultaneous images by the
two perpendicular polarization states. A novel optical design which
focuses the two beams on different detector areas is described. And
the accurate calibration methods are introduced too.
---------------------------------------------------------
Title: 1024 × 1024 HgCdTe CMOS camera for infrared imaging
magnetograph of Big Bear Solar Observatory
Authors: Cao, W.; Xu, Y.; Denker, C.; Wang, H.
2005SPIE.5881..245C Altcode:
The InfraRed Imaging Magnetograph (IRIM)<SUP>1,2</SUP> is a
two-dimensional narrow-band solar spectro-polarimeter currently being
developed at Big Bear Solar Observatory (BBSO). It works in the near
infrared (NIR) from 1.0 μm to 1.7 μm and possesses high temporal
resolution, high spatial resolution, high spectral resolving power, high
magnetic sensitivity. As the detector of IRIM, the 1024 × 1024 HgCdTe
TCM8600 CMOS camera manufactured by the Rockwell Scientific Company
plays a very important role in acquiring the high precision solar
spectropolarimetry data. In order to make the best use of it for solar
observation, the characteristic evaluation was carried out at BBSO and
National Solar Observatory (NSO), Sacramento Peak in October 2003. The
paper presents a series of measured performance parameters including
linearity, readout noise, gain, full well capacity, hot pixels, dark,
flat field, frame rate, vacuum, low temperature control, etc., and
shows some solar infrared narrow band imaging observation results.
---------------------------------------------------------
Title: Do Dark Faculae Exist?
Authors: Xu, Y.; Cao, W.; Ma, J.; Hartkon, K.; Jing, J.; Denker, C.;
Wang, H.
2005AGUSMSP31A..01X Altcode:
High-resolution images in visible light and the near infrared
(NIR) continuum around 1560~nm were obtained in solar active region
NOAA~10707 with the Dunn Solar Telescope (DST) at the National Solar
Observatory/Sacramento Peak (NSO/SP) on 2004 December~2 and 7. A
spatial resolution close to the diffraction limit of the 76~cm DST was
achieved with high-order adaptive optics system. The observation were
made with a near infrared tunable Lyot filter system newly developed
by Big Bear Solar Observatory (BBSO). The filter has a bandpass
of 2.5~Å. This allows us to observe the pure NIR continuum that
represents the opacity minimum. Our data show that the contrast of
faculae has the same sign in the visible and the NIR continua. There
is no evidence for the existence of so-called "dark faculae", faculae
that have negative contrasts in the NIR and positive contrasts in
visible light. We conclude that the previously observed "dark faculae"
are unresolved pores. <P />This work is supported by NSF under grants
ATM-0313591, ATM-0236945, ATM-0233931 and AST-0307676, by NASA under
grants NAG5-10910, NAG5-10212 and NAG5-12733, and by Air Force under
grant F49620-02-1-0265 and by NSFC-10103004.
---------------------------------------------------------
Title: The New Solar Telescope at Big Bear Solar Observatory -
A Progress Report
Authors: Denker, C.; Cao, W.; Chae, J.; Coulter, R.; Kuhn, J. R.;
Marquette, W. H.; Moon, Y.; Park, Y.; Ren, D.; Tritschler, A.; Varsik,
J. R.; Wang, H.; Yang, G.; Shoumko, S.; Goode, P. R.
2005AGUSMSP43A..07D Altcode:
The New Solar Telescope (NST) is a new 1.6-meter, off-axis telescope
for the Big Bear Solar Observatory (BBSO) in California. The NST is
collaboration between BBSO, the Korean Astronomical Observatory (KAO)
and Institute for Astronomy (IfA) at the University of Hawaii. BBSO
is an ideal site for high-spatial resolution observations, since this
mountain-lake site provides consistent seeing conditions with extended
periods of excellent seeing from sunrise to sunset. These unique seeing
characteristics make BBSO ideally suited for combined high-resolution
campaigns and synoptic observations, which are essential for studies
of solar activity and space weather. In this progress report, we
present the latest information on the optical design, the optical
support structure, the telescope control system and the requisite
instrumentation for the telescope. Acknowledgements: This work has been
supported by NSF under grants ATM-0236945, ATM-0342560, MRI-0320540,
and Air Force DURIP F-49620-03-1-0271.
---------------------------------------------------------
Title: Dissertation Talk: High Resolution Observations of
Multi-Wavelength Emissions During Two X-Class White-Light Flares
Authors: Xu, Y.; Cao, W.; Liu, C.; Yang, G.; Jing, J.; Denker, C.;
Wang, H.
2005AGUSMSP51C..01X Altcode:
We observed two X-class white-light flares (WLF) on 2003 October~29
(~20:40~UT) and November~2 (~17:16 UT) using the Dunn Solar Telescope
(DST) and its High-Order Adaptive Optics (HOAO) system in several
wavelengths. The spatial resolution was close to the diffraction limit
of DST's 76~cm aperture. The temporal resolution was as high as 2~s. It
is the first time that WLFs were observed in the Near Infrared (NIR)
wavelength region. We present a detailed study in this presentation
by comparing the photospheric continuum observations during these
two events with corresponding line-of-sight (LOS) magnetograms of the
Michelson Doppler Imager (MDI) and hard X-ray (HXR) data of the Ramaty
High Energy Solar Spectroscopic Imager (RHESSI). Our observations show
that: <P />Significant intensity enhancements were observed in the
visible and NIR continua and G-band during the impulsive phase of the
flares. The maximum intensity enhancements were 37% of white-light
and 25% of the NIR continuum during the first event, and 76% of
white-light and 66% of the NIR continuum for the second flare. The
flares were typical two ribbon flares. All ribbons showed a brighter
core surrounded by a halo structure. The ribbon separation speeds
were about 28~km/s in the first and 24~km/s in the second event based
on NIR observations. The derived electric fields in the reconnection
current sheet Ec are about 23~V~ cm-1 and 22~V~cm-1, respectively. The
NIR emission and the impulsive HXR emission up to 800~keV were well
correlated, not considering a small delay of less than two minutes. The
high resolution and high cadence images gave us the first chance to
measure the cooling time of flares close to the photosphere. We found
that the cooling process could be characterized by two steps. A quick
temperature drop, which is related to the cooling process of the bright
cores, and a relative slow decay related to the halo structures. The
fine scale is in the order of less than 30~s and a few minutes for these
two steps, respectively. <P />Based on these observational results,
we discuss several models that provide possible mechanisms to explain
these continuum enhancements, especially in the NIR. This work is
supported by NSF under grants ATM-0313591, ATM-0236945, ATM-0233931 and
AST-0307676, by NASA under grants NAG5-10910, NAG5-10212 and NAG5-12733,
and by Air Force under grant F49620-02-1-0265 and by NSFC-10103004.
---------------------------------------------------------
Title: First Light for the Near-Infrared Narrow-Band Tunable
Birefringent Filter of the Big Bear Solar Observatory
Authors: Cao, W.; Hartkorn, K.; Ma, J.; Wang, J.; Xu, Y.; Spirock,
T.; Denker, C.; Wang, H.
2005AGUSMSP43A..08C Altcode:
A new near-infrared, narrow-band tunable birefringent filter has
been developed by BBSO/NJIT. This filter, one of the first Lyot
filters in the near-infrared, has a FWHM of about 2.5 ~Å at the
design wavelength of 1.5648 μm and is used to observe the deepest
levels of the photosphere. New techniques were employed in the design,
including liquid crystal retarders to tune the center wavelength in
range of ± 100 ~Å. After finishing the calibration and evaluation of
the filter at the Evans Facility of the NSO at Sacramento Peak, high
spatial resolution filtergrams and imaging spectroscopy observations
were carried out at the Dunn Solar Telescope of NSO in December 2004
with the use of the high-order Adaptive Optics System. For some of
these observations, the Lyot filter was combined with a Fabry-Perot
Etalon to achieve a much higher spectral resolution. We discuss the
calibration methods and present some preliminary observation results.
---------------------------------------------------------
Title: On the Relation Between Flow Fields and Magnetic Field
Evolution in Flare Productive NOAA Active Region 10486
Authors: Deng, N.; Xu, Y.; Yang, G.; Cao, W.; Rimmele, T. R.; Wang,
H.; Denker, C.
2005AGUSMSP51C..05D Altcode:
We present high resolution observations of flow fields within solar NOAA
active region 10486 before an X10 flare on October 29, 2003. From 2003
October 28 to November 4, a complex δ-sunspot located in NOAA 10486
produced dramatic flare activities in the descending phase of the solar
cycle 23. The flow fields are measured by local correlation tracking
(LCT) based on speckle masking white-light images, near-infrared (NIR)
continuum images at 1.56 μm, and G-band images obtained with the Dunn
Solar Telescope (DST) of the National Solar Observatory/Sacramento Peak
(NSO/SP). NSO's newly developed high-order adaptive optics system at
the DST was used to achieve diffraction-limited imaging with a high
signal-to-noise ratio. The spatial resolution of the images approaches
the diffraction limit of the 76 cm aperture DST of about 0.14 ″ at
527 nm. In addtion, we use longitudinal magnetograms from the Michelson
Doppler Imager (MDI) on board the Solar and Heliospheric Observatory
(SoHO) to study the evolution of photospheric magnetic field and
its correlation with flow fields in this flare productive active
region. We link strong magnetic shear and fast emergence of magnetic
flux to photospheric flows, which might trigger the flares. Our result
suggests that the time-series analysis of the photospheric flow fields
is a critical observational diagnostic for the evolution of magnetic
fields in solar active regions. This work was supported by NSF under
grant ATM 03-42560, ATM 03-13591, ATM 02-36945, and MRI AST 00-79482
and by NASA under grant NAG 5-13661.
---------------------------------------------------------
Title: Narrow-band Near Infrared Filtergram Observation of Light
Bridges and Umbral Dots
Authors: Ma, J.; Cao, W.; Denker, C.; Wang, H.
2005AGUSMSP31A..03M Altcode:
We are presenting the observations of the active region NOAA 10709
on December, 2004 using 0.12Å~narrow band filter centered around
1.56μm. The observation run was carried out using Dunn Tower
Telescope of NSO (SacPeak) with high-order AO system. The averaged
angular resolution of this observation is 0.5" or better. These high
resolution data in near infrared offer a new view on the photospheric
structures of sunspot near opacity minimum. By using the tunable near
infrared narrow band filtergram, we are able to construct magnetic
field strength map of sunspot. In particular, we will show the magnetic
structure of light bridges and umbral dots.
---------------------------------------------------------
Title: Magnetic Helicity Change Rate Associated with an X10
White-Light Flare
Authors: Yang, G.; Xu, Y.; Cao, W.; Carsten, D.; Wang, H.
2005AGUSMSP23B..01Y Altcode:
Solar active region NOAA 10486 was very active during the descending
phase of solar cycle 23. Eight X-class flares and a multitude of M-class
flares were observed in this region from 2003 October 23 to November
6. In our previous study we presented the high resolution observations
of the flow fields associated with the X10 white-light flare in this
active region on 2003 October 29. We linked the strong photospheric
shear flow with the flare. In this paper, we further our study by
investigating the magnetic helicity injection rate of the active region
NOAA 10486 covering the time period of this X10 white-light flare. The
magnetic helicity injection rate due to horizontal photospheric
motions is determined by analyzing a set of 1 minute cadence full-disk
magnetograms taken by the Michelson Doppler Imager on board the Solar
and Heliospheric Observatory, in addition to the flow fields derived
previously. The results of this study will aid us to understand the
process of energy build-up and release associated with the flare.
---------------------------------------------------------
Title: High-Spatial-Resolution Imaging Combining High-Order Adaptive
Optics, Frame Selection, and Speckle Masking Reconstruction
Authors: Denker, Carsten; Mascarinas, Dulce; Xu, Yan; Cao, Wenda;
Yang, Guo; Wang, Haimin; Goode, Philip R.; Rimmele, Thomas
2005SoPh..227..217D Altcode:
We present, for the first time, high-spatial-resolution observations
combining high-order adaptive optics (AO), frame selection, and
post-facto image correction via speckle masking. The data analysis is
based on observations of solar active region NOAA 10486 taken with the
Dunn Solar Telescope (DST) at the Sacramento Peak Observatory (SPO) of
the National Solar Observatory (NSO) on 29 October 2003. The high Strehl
ratio encountered in AO corrected short-exposure images provides highly
improved signal-to-noise ratios leading to a superior recovery of the
object's Fourier phases. This allows reliable detection of small-scale
solar features near the diffraction limit of the telescope. Speckle
masking imaging provides access to high-order wavefront aberrations,
which predominantly originate at high atmospheric layers and are only
partially corrected by the AO system. In addition, the observations
provided qualitative measures of the image correction away from the
lock point of the AO system. We further present a brief inspection
of the underlying imaging theory discussing the limitations and
prospects of this multi-faceted image reconstruction approach in
terms of the recovery of spatial information, photometric accuracy,
and spectroscopic applications.
---------------------------------------------------------
Title: Photospheric Shear Flows along the Magnetic Neutral Line of
Active Region 10486 prior to an X10 Flare
Authors: Yang, Guo; Xu, Yan; Cao, Wenda; Wang, Haimin; Denker, Carsten;
Rimmele, Thomas R.
2004ApJ...617L.151Y Altcode:
We present high spatial resolution observations of proper motions in
the solar NOAA Active Region 10486 using a high-order adaptive optics
system, frame selection, and speckle-masking image reconstruction. The
data were obtained with the Dunn Solar Telescope of the National Solar
Observatory/Sacramento Peak on 2003 October 29. The resolution of the
images approaches the diffraction-limited resolution of the Dunn Solar
Telescope of about 0.14" at 527 nm. We analyzed a 2 hr time series with
a 1 minute cadence prior to an X10 white-light flare. Local correlation
tracking was used to measure the photospheric proper motions. We find
specific evidence of strong shear flows along the magnetic neutral line;
these shear flows are well defined and correlated with white-light
flare kernels in the visible and infrared. The speed along the flow
channels can reach up to 1.6 km s<SUP>-1</SUP>, and the separation of
channels with head-on flows can be less than 1". Counterstreaming and
complex flow patterns have been distinguishing characteristics of this
extraordinarily flare-productive active region.
---------------------------------------------------------
Title: Near infrared (NIR) achromatic phase retarder
Authors: Ma, Jun; Wang, Jingshan; Cao, W.; Denker, Carsten; Wang,
Haimin
2004SPIE.5523..139M Altcode:
The tunable near InfraRed Lyot filter (TNIRLF) is one of the focal plane
instruments for Advanced Technology Solar Telescope (ATST) project of
the National Solar Observatory (NSO). Achromatic half waveplate and
quarter waveplates working from 1000 nm to 1700 nm will be used in
this filter. In this paper, we give a description of the design and
development for the synthesized achromatic waveplates using quartz
plates. The retardance variation is within 1% over the full spectral
range and we discuss the variance of optical axis.
---------------------------------------------------------
Title: Near infrared waveplate
Authors: Wang, Dongguang; Deng, Yuanyong; Cao, Wenda
2004SPIE.5492.1786W Altcode:
The waveplate made of Polyvinyl Alcohol (PVA) plastic film has several
advantages compared with that of birefringent crystal in visible region,
such as its lower cost and insensitivity to temperature and incidence
angle. What are the performances when they are used in the near infrared
spectral region? In this paper, we provide some experimental results of
infrared PVA waveplates. To do this, we make some samples and measure
their polarization characteristics at several aspects. Firstly, we
measure the performance of these PVA waveplates by precise instruments
in laboratory. Secondly, we put the waveplates into a Stokes polarimeter
to observe the solar magnetic field at near infrared line FeI1.56μm. By
use of this polarimeter mounted on the vertical spectrograph of 2m
McMath telescope at Kitt Peak, the two-dimensional Stokes parameters, I,
Q, U, and V, of a sunspot were observed. From the results of laboratory
and observation, we get the conclusion that PVA waveplate has the fair
polarization performance to be used to observe the solar magnetic
fields in the near infrared spectral region. By these experiments,
we provide a design of an achromatic waveplate in infrared region,
which consists of five-element, to illustrate the PVA waveplate is
the best choice to it.
---------------------------------------------------------
Title: Near-Infrared Observations at 1.56 Microns of the 2003 October
29 X10 White-Light Flare
Authors: Xu, Yan; Cao, Wenda; Liu, Chang; Yang, Guo; Qiu, Jiong;
Jing, Ju; Denker, Carsten; Wang, Haimin
2004ApJ...607L.131X Altcode:
We present high-resolution observations of an X10 white-light flare in
solar NOAA Active Region 10486 obtained with the Dunn Solar Telescope
(DST) at the National Solar Observatory/Sacramento Peak on 2003
October 29. Our investigation focuses on flare dynamics observed
in the near-infrared (NIR) continuum at 1.56 μm. This is the first
report of a white-light flare observed at the opacity minimum. The
spatial resolution was close to the diffraction limit of the 76 cm
aperture DST. The data benefited from a newly developed high-order
adaptive optics system and a state-of-the-art NIR complex metal oxide
semiconductor focal plane array. In addition, we compared hard X-ray
(HXR) data of RHESSI and magnetograms of the Michelson Doppler Imager on
board SOHO with the NIR continuum images. Although it is still possible
that some high-energy electrons penetrate deep to this layer, a more
likely explanation of the observed emission is back-warming. During
the impulsive phase of the flare, two major flare ribbons moved apart,
which were both temporally and spatially correlated with RHESSI HXR
ribbons. The maximum intensity enhancement of the two flare ribbons is
18% and 25%, respectively, compared to the quiet-Sun NIR continuum. The
separation speed of the ribbons is about 38 km s<SUP>-1</SUP> in regions
with weak magnetic fields and decreases to about 19 km s<SUP>-1</SUP>,
where stronger magnetic fields are encountered. The derived electric
field in reconnection current sheet E<SUB>c</SUB> is of the order of
45 V cm<SUP>-1</SUP> during the flare maximum.
---------------------------------------------------------
Title: Near Infrared Obsevations at 1.56 μ m of the 2003 October
29 X10 White-Light Flare
Authors: Xu, Y.; Cao, W.; Liu, C.; Yang, G.; Qiu, J.; Jing, J.;
Denker, C.; Wang, H.
2004AAS...204.4712X Altcode: 2004BAAS...36..738X
We present high resolution observations of an X10 white-light flare in
solar active region NOAA 10486 obtained with the Dunn Solar Telescope
(DST) at the National Solar Observatory/Sacramento Peak (NSO/SP) on 2003
October 29. Our investigation focusses on flare dynamics observed in the
near-infrared (NIR) continuum at 1.56 μ m. This is the first report
of a white-light flare observed in the NIR. The spatial resolution
was close to the diffraction limit of the 76 cm aperture DST. The data
benefited from a newly developed high order adaptive optics (AO) system
and a state-of-the-art NIR complex metal oxide semiconductor (CMOS)
focal plane array (FPA). In addition, we compared hard X-ray (HXR)
data of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and
magnetograms of the Michelson Doppler Imager (MDI) onboard the Solar and
Heliospheric Observatory (SoHO) with the NIR continuum images. Since the
NIR data were observed at the opacity minimum, only the most energetic
electrons can penetrate to this layer in the deep photosphere. As a
consequence, the flare ribbons appear to be very thin (<2 arcseconds)
and well defined. During the impulsive phase of the flare, two major
flare ribbons moved apart, which were both temporally and spatially
correlated with RHESSI HXR ribbons. The two ribbons ranges are 18%
to 25% brighter than the quiet sun NIR continuum. The separation speed
of the ribbons is about 38 km/s in regions with weak magnetic fields
and decreases to about 19 km/s, where stronger magnetic fields are
encountered. The derived reconnection electric field E<SUB>c</SUB>
is of order 50 Vcm<SUP>-1</SUP> at the flare maximum.
---------------------------------------------------------
Title: The VIsible and InfraRed Imaging Magnetograph (VIM-IRIM)
at Big Bear Solar Observatory
Authors: Cao, W.; Tritschler, A.; Denker, C.; Wang, H.; Shumko, S.;
Ma, J.; Wang, J.; Marquette, B.
2004AAS...204.6907C Altcode: 2004BAAS...36..795C
The Visible-light and the InfraRed Imaging Magnetograph (VIM-IRIM) are
Fabry-Perot based filtergraphs working in a telecentric configuration,
planned to upgrade the capability for measuring solar magnetic fields
at BBSO. Both filtergraph instruments are designed to work with
the combination of a narrow-band prefilter and a single Fabry-Perot
etalon. VIM and IRIM will provide high temporal resolution, high spatial
resolution (< 0.2 "/pixel image scale), high spectral resolution
(< 0.1 Å) simultaneous observation at 600-700 nm and 1.0-1.6 μ
m with a substantial field of view 170", respectively. Modifications
in the setup allow also for scanning different spectral lines that
cover the height range from the solar photosphere up to the solar
chromopshere. Here we describe the optical setup and present first
observations to demonstrate the feasibility of the instrument. After
the instrument has proven to work as a 2D-spectrometer, the upgrade
to a 2D spectropolarimeter is planned.
---------------------------------------------------------
Title: Magnetic Helicity Change Rate Associated With X-Class and
M-Class Flares
Authors: Hartkorn, K.; Wang, H.; Cao, W.; Denker, C.; Xu, Y.
2004AAS...204.3901H Altcode: 2004BAAS...36..714H
We investigate the total helicity change rate of active regions
during the time period of five X-class and five M-class flares. The
X-class flares include the X17 flare on October 28 2003 and the X11
flare on October 29 2003. For the X11 flare we have high-resolution
IR and G-band data available which allows us to compare flow fields
derived from this high-resolution data with the flow fields derived
from MDI full disc magnetograms. <P />Four out of five regions with
X-class flares show a significant change in the helicity change rate,
while none of the five active regions with an associated M-class flare
shows this behavior. We determine the location of the helicity change
in the active regions and discuss possible causes. We also investigate
active regions with no flare activity to determine the fluctuations
of the helicity change rate due to instrumental effects.
---------------------------------------------------------
Title: High-Spatial Resolution Observations of Flow Fields in Solar
Active Region NOAA 10486
Authors: Yang, G.; Xu, Y.; Cao, W.; Wang, H.; Denker, C.; Rimmele,
T. R.
2004AAS...204.0210Y Altcode: 2004BAAS...36..669Y
We present high-spatial resolution observations of proper motions in
solar active region NOAA 10486 using the newly developed high-order
adaptive optics (AO) system at the Dunn Solar Telescope (DST) of the
National Solar Observatory/Sacramento Peak (NSO/SP) on 2003 October
29. The images were obtained with high-order AO, frame selection, and
speckle masking image reconstruction. We analyze a two hour time series
with 1-minute cadence in the context of an X10 white-light flare. Local
correlation tracking (LCT) was used to measure the horizontal proper
motions in the photosphere and relate them to the strong shear observed
in the magnetic field configuration.
---------------------------------------------------------
Title: Characteristic evaluation of a near-infrared Fabry-Perot
filter for the InfraRed Imaging Magnetograph (IRIM)
Authors: Cao, Wenda; Denker, Carsten J.; Wang, Haimin; Ma, J.; Qu,
M.; Wang, Jinshan; Goode, Philip R.
2004SPIE.5171..307C Altcode:
The InfraRed Imaging Magnetograph (IRIM) is a high temporal
resolution, high spatial resolution, high spectral resolving power,
and high magnetic sensitivity solar two-dimensional narrow-band
spectro-polarimeter working in the near infrared from 1.0 μm to
1.7 μm at Big Bear Solar Observatory (BBSO). It consists of an
interference filter, a polarization analyzer, a birefringent filter,
and a Fabry-Perot etalon. As the narrowest filter of IRIM, the infrared
Fabry-Perot plays a very important role in achieving the narrow band
transmission of ~ 10 pm and high throughput between 85% and 95% for
the full wavelength range, maintaining wavelength tuning ability
from 1.0 to 1.7 μm, and assuring stability and reliability. As
the third of a series of publications describing IRIM, this paper
outlines a set of methods to evaluate the near infrared Fabry-Perot
etalon. Two-dimensional characteristic maps of the near infrared
Fabry-Perot etalon, including the bandpass ▵λ, effective finesse
F<SUB>eff</SUB>, peak transmission τ<SUB>max</SUB>, along with a free
spectral range, flatness, roughness, and stability and repeatability
were obtained with laboratory equipment. These measured results will
benefit the optimization of IRIM design and observational mode of
the future.
---------------------------------------------------------
Title: Imaging Spectropolarimetry of Ti I 2231 nm in a Sunspot
Authors: Penn, M. J.; Cao, W. D.; Walton, S. R.; Chapman, G. A.;
Livingston, W.
2003SoPh..215...87P Altcode:
Spectro-polarimetric observations at 2231 nm were made of NOAA 10008
near the west solar limb on 29 June 2002 using the National Solar
Observatory McMath-Pierce Telescope at Kitt Peak and the California
State University Northridge - National Solar Observatory infrared
camera. Scans of spectra in both Stokes I and Stokes V were collected;
the intensity spectra were processed to remove strong telluric
absorption lines, and the Stokes V umbral spectra were corrected for
instrumental polarization. The sunspot temperature is computed using
the continuum contrast and umbral temperatures down to about 3700 K are
observed. A strong Ti i line at 2231.0 nm is used to probe the magnetic
and velocity fields in the spot umbra and penumbra. Measurements of the
Ti i equivalent width versus plasma temperature in the sunspot agree
with model predictions. Zeeman splitting measurements of the Stokes I
and Stokes V profiles show magnetic fields up to 3300 G in the umbra,
and a dependence of the magnetic field on the plasma temperature
similar to that which was seen using Fe i 1565 nm observations of the
same spot two days earlier. The umbral Doppler velocity measurements
are averaged in 16 azimuthal bins, and no radial flows are revealed to
a limit of ± 200 m s<SUP>−1</SUP>. A Stokes V magnetogram shows a
reversal of the line-of-sight magnetic component between the limb and
disk center sides of the penumbra. Because the Ti i line is weak in
the penumbra, individual spectra are averaged in azimuthal bins over
the entire penumbral radial extent. The averaged Stokes V spectra show
a magnetic reversal as a function of sunspot azimuthal angle. The mean
penumbral magnetic field as measured with the Stokes V Zeeman component
splitting is 1400 G. Several weak spectral lines are observed in the
sunspot and the variation of the equivalent width versus temperature
for four lines is examined. If these lines are from molecules, it is
possible that lines at 2230.67, 2230.77, and 2231.70 nm originate from
OH, while the line at 2232.21 nm may originate from CN.
---------------------------------------------------------
Title: Weak Infrared Molecular Lines Reveal Rapid Outflow in Cool
Magnetic Sunspot Penumbral Fibrils
Authors: Penn, M. J.; Cao, W. D.; Walton, S. R.; Chapman, G. A.;
Livingston, W.
2003ApJ...590L.119P Altcode:
New imaging spectropolarimetric observations of the Evershed flow
in sunspot penumbrae using weak infrared molecular absorption lines
are presented. A plane-polar coordinate system in the sunspot frame
is defined, allowing averaging of many raw spectra. Molecular lines
show Doppler shifts implying typical horizontal outflow speeds of 6
and up to 9 km s<SUP>-1</SUP>. The Ti I polarimetric spectra show the
same rapid outflow and suggest an average penumbral magnetic field
strength of 1400 G. While these observations show Doppler shifts of
the entire line profile, the velocities are in better agreement with
previous measurements from spectral line asymmetries.
---------------------------------------------------------
Title: Weak IR Lines Reveal Rapid Outflow in Cool Magnetic Penumbra
Authors: Penn, M. J.; Cao, W. D.; Walton, S. R.; Chapman, G. A.;
Livingston, W.
2003SPD....34.1106P Altcode: 2003BAAS...35..827P
New imaging spectropolarimetric observations of the Evershed flow in
sunspot penumbrae using weak infrared molecular absorption lines are
presented. A plane-polar coordinate system in the sunspot frame is
defined, allowing averaging of many raw spectra. Molecular lines show
Doppler shifts implying typical horizontal outflow speeds of 6 to 9
km/sec. The Ti I polarimetric spectra show the same rapid outflow
and suggest an average penumbral magnetic field strength of 1400
Gauss. While these observations show Doppler shifts of the entire
line profile the velocities are in better agreement with previous
measurements from spectral line asymmetries.
---------------------------------------------------------
Title: High-Resolution Infrared Filter System for Solar Spectroscopy
and Polarimetry
Authors: Cao, W.; Ma, J.; Wang, J.; Goode, P. R.; Wang, H.; Denker, C.
2003SPD....34.2013C Altcode: 2003BAAS...35..846C
We report on the design of an imaging filter system working at the
near infrared (NIR) of 1.56 μ m to obtain monochromatic images
and to probe weak magnetic fields in different layers of the deep
photosphere with high temporal resolution and spatial resolution at
Big Bear Solar Observatory (BBSO). This filter system consists of
an interference filter, a birefringent filter, and a Fabry-Pérot
etalon. As the narrowest filter system, the infrared Fabry-Pérot
plays an important role in achieving narrow band transmission and
high throughput, maintaining wavelength tuning ability, and assuring
stability and reliability. In this poster, we outline a set of methods
for the evaluation and calibration of the near infrared Fabry-Pérot
etalon. Two-dimensional characteristic maps of the near infrared
Fabry-Pérot etalon, including full-width-at-half-maximum (FWHM),
effective finesse, peak transmission, along with free spectral range,
flatness, roughness, stability and repeatability were obtained with lab
equipments. Finally, by utilizing these results, a detailed analysis
of the filter performance for the Fe I 1.5648 μ m and Fe I 1.5652 μ
m Zeeman sensitive lines is presented. These results will benefit the
design of NIR spectro-polarimeter of Advanced Technology Solar Telescope
(ATST).
---------------------------------------------------------
Title: Design of Achromatic Waveplates for ATST Near IR Filter System
Authors: Ma, J.; Wang, J.; Cao, W.; Denker, C.; Wang, H.
2003SPD....34.2024M Altcode: 2003BAAS...35R.848M
Achromatic waveplates play one of the central roles in constructing
universal birefringent filters (UBF). Although it's been developed
very well by several authors in the last decades, the mechanisms and
detailed techniques which can realize the achromatism are still not
clearly categorized. Such waveplates for Infrared do not exist yet. In
the recent development of a InfraRed High Resolution Magnetograph at
BBSO, it is realized that a standard approach of designing achromatic
waveplate is needed not only for the IRHRM, but more importantly, for
the Near IR Tunable Filter for ATST. <P />There are several theoretical
methods which are available to describe the behavior of waveplates and
polarization status of field, including algebraic tools (Jones Algebra,
Muler Matrix, Stokes Vector), and geometrical approach (Poincere Sphere,
which is Complex Analysis in fact). By using these methods, it can
be proved that a combination of waveplates could have much better
achromatic performance than a single component has. <P />Since the
simulation of the combination of waveplates gets more and more complex,
a computer program software package for designing achromatic waveplates
is developed. Compared to the most popular commercial software package,
such as ZEMAX which uses ray-tracing approach, the recently developed
software tools is based on Transfer Functions of Optical Systems,
which will be more efficient than ray-tracing approach.
---------------------------------------------------------
Title: Stokes polarimetry at near-infrared 1.56 um for solar
observation
Authors: Cao, Wenda; Ye, Binxun; Wang, Dongguang; Song, Qian
2002SPIE.4480..176C Altcode:
FeI 1.56 micrometers Zeeman-sensitive lines are very important and
potential to measure the magnetic field of the deepest layer of the
solar photosphere. The new generation polarimeter is designed and
manufactured in this wavelength range. By use of the polarimeter mounted
on the vertical spectrograph of the 2m solar telescope at Kitt Peak,
we can observe the Stokes I, Q, U, Vv parameters simultaneously. The
paper presents the introduction of the near infrared polarimeter and
the polarmetry of a sunspot group.
---------------------------------------------------------
Title: The Primary Design of A 1-Meter Infrared Solar Telescope
Authors: Cao, W. D.; Liu, Z.; Ye, B. X.
2002stma.conf...75C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Design concepts of EUV telescopes and the detectors boarded
on the Solar Space Telescope
Authors: Song, Qian; Ye, Binxun; Cao, Jianlin; Chen, Bo; Cao, Wenda
2001SPIE.4498..335S Altcode:
The Solar Space Telescope (SST) is the largest scientific space project
of China up to now. It engages to observe the transient and steady state
solar hydrodynamic and magneto-hydrodynamic process over 2-D real time
polarizing spectrum, UV, X-ray and H(alpha) image, and continuous time
evolution with high spatial and temporal resolution in order to achieve
a break through advance in solar physics. The EUV part of SST, the EUV
telescope (EUT), consists of four telescopes with their detectors, which
are parallel situated in a single telescope tube. Each telescope of the
EUT adopts the normal-incidence principle with help of the multilayer
technology and the primary mirror diameter is 12cm. The detectors of
the EUT are constructed with EUV sensitive phosphors, fiber tapers,
image intensifiers, CCDs, camera electronics and cooling blocks. Three
telescopes of EUT are designed to achieve a spatial resolution of 0.5
arcsecond with a field of view (FOV) of 8.5'x8.5' in order to get the
ever high-resolution image of the fine structure of the high temperature
activities in solar corona and the fourth one is 85'x85' to have the
full solar disk always in its field of view. In our presentation,
the scientific objectives and the configuration of EUT are introduced.
---------------------------------------------------------
Title: The Observation and Study of Two Prominence Events in the
Infrared
Authors: Cao, W. D.; Ye, B. X.; Livingston, W.
2001IAUS..203..257C Altcode:
This paper reports the infrared observation of two prominence events
on Jan. 8, 1999 and Feb. 9, 1999 at H Paschen β 12818Å, H Bracket
α 40512Å, and H Pfund β 46525Å using the McMath Telescope. We
scanned the spectrograph slit across the prominences parallel to
the solar limb to obtain three-dimensional data cubes (two spatial
dimensions and one spectral dimension). By fitting these observed
lines, we can directly determine some important physical parameters
such as Doppler width, the optical thickness at line center, and
the line displacement. Combined with simultaneous observation of
Balmer H<SUB>α</SUB>, H<SUB>β</SUB>, and K lines, the new results of
structure and dynamics of limb prominence are presented. These results
imply that these infrared lines can penetrate through the prominence
and become the potential probe and tool of them, while H<SUB>α</SUB>
and H<SUB>β</SUB> sense the prominence skin only.
---------------------------------------------------------
Title: Simulation and Observation of Solar FeI 1.56 μm Line using
PtSi Array Camera
Authors: Cao, W.; Song, Q.; Ye, B.
2001ASPC..236..281C Altcode: 2001aspt.conf..281C
No abstract at ADS
---------------------------------------------------------
Title: PtSi IRFPA camera and its application in infrared solar
spectrum observation
Authors: Cao, Wenda; Ye, Binxun; Song, Qian; He, J.; Zhou, X. D.;
Ji, Kaifan
2000SPIE.4008..806C Altcode:
Although the interest in PtSi IR focal pane array has waned due to
its low quantum efficiency compared with InSb and HgCdTe arrays,
it is very potential in observing brighter celestial objects. We
explored the possibility of applying it to the observation of IR solar
spectrum. In the paper, the methods of the simulation and calibration
in our observation are introduced and discussed in detail. Using this
kind of camera, a new observational band is added to the 2D Multi-band
Solar Spectrograph at Yunnan Observatory. The dispersion for FeI 1.56
micrometers of the new IR solar spectrograph is 0.0722 angstrom per
pixel, and each vertical pixel represents 0.51 inch of solar disk. It
is specially suitable for 2D spectroscopic observation of the deepest
solar photosphere. Some primary observation results are also presented.
---------------------------------------------------------
Title: Simultaneous remote observation from six sites organized at
the 1-m telescope of the Yunnan Observatory
Authors: Cao, Wenda; Song, Qian; Ji, Kaifan
2000SPIE.4011..117C Altcode:
On Mar. 6-7, 1997, a simultaneous remote observation from 6 sites
was successfully carried out with the cooperation of astronomers
and hobbyists in China, United States, Canada, and Great Britain. In
the paper, the process and technical methods in this observation are
introduced in detail. The present difficulties and brilliant prospects
in the observational method under the current circumstances of Internet
in China are shown as well.
---------------------------------------------------------
Title: A research on the detectors for solar spectrographs.
Authors: Cao, Wenda; Ji, Kaifan; Song, Qian
2000AcASn..41...93C Altcode:
The selection and application of detectors for a solar spectrograph
described in this paper are more or less different from those in
other works. For use at the solar spectrograph of Yunnan Observatory,
the authors have built a model to estimate the spectral fluxes
of solar spectrograph with computer and confirmed the result with
observations. The spectral fluxes in visible and near infrared bands
were calculated for the same spectrograph. Based on these results,
the authors have discussed the detectors in details and summed up the
processes in observation where some additional comments are needed.
---------------------------------------------------------
Title: Simulation and observation of near infrared solar Fe I 1.56
μm line.
Authors: Cao, Wenda; Song, Qian; Ji, Kaifan
1999ArBei..34...60C Altcode:
The infrared focal plane array (IRFPA) with large size and high
quantum efficiency is very difficult to acquire. On Jan. 29 - 30,
1999, the authors utilized PtSi IRFPA to observe the infrared solar
Fe I 1.56 μm line. The simulation and observation for this experiment
are introduced in detail.
---------------------------------------------------------
Title: Radiation damage on CCDs in space environment.
Authors: Song, Qian; Cao, Wenda; Ji, Kaifan
1999ArBei..34...67S Altcode:
The energetic radiation existing in the space natural radiation
environment may cause damages to charge-coupled devices (CCDs) working
in space and degrade their performance. In this paper, the mechanism
of the CCD's radiation damage is reviewed and an interpretation is
attempted for the radiation-caused performance defects of the Solar-A
SXT CCD with the flat-band shift resulted from the trapped holes within
the insulator layer between gates and silicon bulk.
---------------------------------------------------------
Title: Laboratory evaluation of CCD for astronomical application.
Authors: Song, Qian; Ji, Kaifan; Cao, Wenda
1999AcApS..19..333S Altcode:
The method of evaluating charge-coupled device for astronomical
application used in Yunnan Observatory CCD-testing Laboratory is
presented. The parameters evaluated include linearity, noise, gain
quantum efficiency and transfer efficiency.
---------------------------------------------------------
Title: Silicon CCD optimized for NIR wavelengths.
Authors: Song, Qian; Ji, Kaifan; Cao, Wenda
1999PYunO...4...60S Altcode:
CCDs processed on typical substrates exhibit low NIR QE. Because
the relatively thin epitaxial layer allows a high percentage of long
wavelength photons to pass through and the reflection loss of back
surface is high. A thick epitaxial layer allows the longer wavelength
photons to be absorbed into the epitaxial layer where the resultant
electrons generated will be collected in the potential wells. The
drawback of processing with this method is a resultant degradation
of carrier diffusion MTF. Increasing the depleted region under each
gate, which can be realized by using high resistivity substrates,
can enhance MTF. A new kind of CCD fabricated on high resisitivity
silicon at Lick Observatory has superior red performance beyond 800 nm
wavelength. The application of thin film AR coating directly on to the
CCD back surface can significantly reduce reflection loss from UV to
NIR and greatly decrease interference fringing on back illuminated CCDs.
---------------------------------------------------------
Title: Calculation of spectral fluxes for the solar spectrograph of
Yunnan Observatory.
Authors: Cao, Wenda; Ji, Kaifan; Song, Qian
1999PYunO...4...53C Altcode:
For the solar spectrograph of Yunnan Observatory, a computer model to
estimate the spectral fluxes is set up and is verified by the authors'
observations. The spectral fluxes are calculated. In view of these
results, the plan of the detectors for the Solar Spectrograph is
suggested.
---------------------------------------------------------
Title: An Interpretation of a Radiation Damage Phenomenon of the
solar-A CCD
Authors: Song, Qian; Cao, Wenda
1999oaaf.conf..139S Altcode:
: The Yohkoh satellite for the Japanese Solar-A Mission was launched
in 1991. There were some unexpected darkened spots on the recent images
took by the Soft X-ray Telescope (SXT) boarded on. The images were took
by a CCD camera utilized a 1024x1024 virtual phase CCD. CCDs used in
space are subjected to natural radiation environments that may cause
permanent damages on them and degrade their performance. In this paper,
an interpretation by CCD radiation damage theory was attempted and a
computer-simulated result was calculated.
---------------------------------------------------------
Title: Model of Spectral Fluxes for Solar Spectrograph
Authors: Cao, Wenda; Song, Qian
1999oaaf.conf..400C Altcode:
Taking use of the solar spectrograph in Yunnan Observatory, we built
a model to estimate the spectral fluxes of solar spectrograph with
computer and confirmed the result by observations. The spectral
fluxes in visible and near infrared bands were calculated for the
solar spectrograph of Yunnan Observatory. Based on the results, we
made a suggestion of the detectors for solar spectrograph and summed
out the processes in observation where the additional attention should
be needed.
---------------------------------------------------------
Title: Methods for blue enhancement of CCDs.
Authors: Ji, Kaifan; Song, Qian; Cao, Wenda
1999PYunO...3...50J Altcode:
CCDs have become the most important astronomical detector for UV,
visible and NIR imaging and spectroscopy at most observatories
throughout the world. But the quantum efficiencies (QE) in the blue
region of general CCDs are very low. Increasing the sensitivity in
this region is desirable when the CCDs are used in astronomy. There are
two ways to improve QEs of frontside illuminated CCDs. Deposition of a
very thin polysilicon gate allows transmittance of shorter wavelength
photons, and frontside coating a completed device with lumogen absorbs
lower wavelength photons and re-emits them near the peak sensitivity
of the CCD. After optimizing, 100% QE enhancement may be realized at
UV band.
---------------------------------------------------------
Title: Easy way to evaluate CCDs for astronomical use
Authors: Song, Qian; Ji, Kaifan; Cao, Wenda
1998SPIE.3553..291S Altcode:
The methods of evaluating the astronomy-using CCDs in Yunnan Observatory
CCD-testing Lab are introduced, concerning the evaluation of linearity,
noise, gain, quantum efficiency and transfer efficiency, etc.
---------------------------------------------------------
Title: Near infrared focal plane arrays for astronomy.
Authors: Cao, Wenda; Ye, Binxun
1998PABei..16..103C Altcode:
Developments in infrared focal plane arrays are summarized. InSb,
HgCdTe, and PtSi near-infrared focal plane arrays are introduced and
combined with the plan of the infrared solar tower in China, their
features are compared in detail.
---------------------------------------------------------
Title: Two remote-presence observations at the 1-m telescope of the
Yunnan Observatory in China
Authors: Ji, Kaifan; Cao, Wenda; Ye, Binxun; Song, Q.; Chu, Y.; Chen,
K.; Sun, J.; Sun, Y. S.
1998SPIE.3351...25J Altcode:
Two remote presence observations on Dec. 25, 1995 and Mar. 7, 1997 were
achieved at the 1-m telescope of Yunnan Observatory. In this paper,
the observations are introduced in detail. The technical methods in
the remote presence observation are also discussed under the current
circumstances of hardware and software in China. The brilliant prospects
of the observational method are shown as well.
---------------------------------------------------------
Title: Evidence for resonant absorption of VLF waves obtained at
Zhongshan Station, Antarctica
Authors: Tang, K. Y.; Peng, F. L.; Ning, Z. L.; Cao, W. Z.; Meng,
Q. F.; Yang, Y. H.; Jiao, C. M.
1998mrat.conf...37T Altcode:
Evidence for resonant absorption of VLF waves was obtained at Zhongshan
Station, Antarctica. The L value for Zhongshan Station is about 14. Due
to such high geomagnetic latitude, no whistlers were received, but a
lot of VLF emissions have been recorded since the station was founded
in 1990. The VLF emission recorded in Zhongshan Station are usually
wide-band emission, from a few hundred Hz to about 15kHz. In February
and June of 1993, we recorded two sets of VLF emissions never seen
before. The main feature for the emission is a blank curve around
5kHz cut from the wide-band emissions. We explain these observations
in term of resonant absorption of VLF waves by ions.
---------------------------------------------------------
Title: The test of the DALSA CA-D7-1024T CCD camera.
Authors: Song, Qian; Liu, Weiwei; Ji, Kaifan; Cao, Wenda
1998PYunO...2...72S Altcode:
From 2nd to 6th, Sep., 1996, the main detector of the balloon-borne
solar telescope of the Beijing Observatory, DALSA CA-D7-1024T camera,
was tested in the CCD - Testing Laboratory of Yunnan Observatory. The
test revealed that despite some problems on the image-collecting system,
the overall behavior of the camera is superb as a non-cooling detector.
---------------------------------------------------------
Title: International astronomical remote present observation on IRC.
Authors: Ji, Kaifan; Cao, Wenda; Song, Qian
1998PYunO...2...67J Altcode:
On March 6 - 7, 1997, an international astronomical remote present
observation (RPO) was made on Internet Relay Chat (IRC) for the first
time. Seven groups in four countries, China, United States, Canada and
Great Britain, used the 1 meter telescope of Yunnan observatory together
by the way of remote present observation. Within minutes, images were
"On-line" by FTP, and every one was able to get them by anonymous ftp
and discuss them on IRC from different widely separated sites.
---------------------------------------------------------
Title: Computer simulation for the observation of the 1.56 μm Fe
I spectral line of solar magnetic field.
Authors: Cao, Wenda; Ji, Kaifan; Song, Qian
1998PYunO...4...43C Altcode:
It makes an interesting idea and work to use the IRFPA made in China
and the solar spectrometer at Yunnan Observatory to probe into the
local magnetic field on solar surface by the observation of NIR Fe I
line at 1.56 μm. The computer simulation is presented. The influence
of the apparatus effects and noises in the observation results are
also discussed in detail.
---------------------------------------------------------
Title: RVC and Its Effect of Solar-terrestrial Physics
Authors: Ji, S. C.; Wei, F. S.; Cao, W. D.
1998asct.conf..125J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A remote-presenting observation at the 1 m telescope of
Yunnan Observatory.
Authors: Cao, Wenda; Ji, Kaifan; Song, Qian; Liu, Weiwei
1997PYunO...3...88C Altcode:
With the development of techniques of the computer, communication,
network, and data compress, the technique of remote-presenting
observation is achieved at the 1 m telescope of Yunnan
Observatory. Compared with the traditional observation, it has a
lot of advantages. In this paper, the remote-presenting observation
during Dec 26 - 27, 1995 is introduced in detail. Under the current
circumstances of hardware and software in China, the technical methods
and difficulties in the remote-presenting observation are discussed.
---------------------------------------------------------
Title: PI 1024 CCD of Yunnan Observatory.
Authors: Ji, Kaifan; Song, Qian; Cao, Wenda
1997PYunO...4...63J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: WinView software and an application to image processing.
Authors: Cao, Wenda; Huan, Zunxiang; Ji, Kaifan; Song, Qian
1997PYunO...2...75C Altcode:
WinView is a high performance software package written specifically
for the acquisition and analysis of images. Many sophisticated
postprocessing options are available. These options are introduced in
this paper.
---------------------------------------------------------
Title: Remote Real-Time Astronomical Observations on IRC
Authors: Kaifan, Ji; Cao, W.; Song, Q.; Ye, B.
1997IAUJD..20E..11K Altcode:
On March 6-7, 1997, remote real-time observations were successfully made
by the cooperation of seven groups in China, the United States, Canada
and Great Britain. BVy using the medium of FTP and the Internet Relay
Chat (IRC) network, we were able to make astronomicaal observations,
from widely separated geographical sites, with the 1m telescope of the
observatory in China's Yunnan Province. Within minutes, images were
on the Internet and everyone was able to view them and to communicate
with each other, discussing the objectives, making decisions and having
the team member at the observatory operate the controls to obtain the
images we needed for later study and analysis. The important adavntage
of this event is that all Internet connections were made through a local
phone line connection. The long-distance connections were then routed
through the free Internet communications, thus avoiding the extremely
high cost of transcontinental long-distance telephone connections.
---------------------------------------------------------
Title: Laboratory Evaluations of a CCD System For the Balloon-borne
Solar Telescope
Authors: Song, Q.; Liu, W.; Ji, K.; Cao, W.; Huan, Z.
1997IAUJD..19E..49S Altcode:
The CCD camera, DALSA/CA-D7-1024, which is a commercial CCD system,
is selected as the main detector for the BAO's Balloon-borne Solar
Telescope. The principal parameters were tested by the YNAO, CCD-Testing
Laboratory in the early September, 1996. The equipment of the lab and
the method of the evaluations are described in the Poster. Evaluations
show that the overall behavior of the camera is superb among the
non-cooling commercial CCD systems. Nevertheless, there are some flaws
in the image-collecting system which must be solved before launch.
---------------------------------------------------------
Title: Some infared focal panel arrays applying in near infrared
solar observation.
Authors: Cao, Wenda; Song, Qian; Ji, Kaifan
1997PYunO...4...73C Altcode:
The development course and structure of infrared focal plane arrays
are summarized. Near-infrared focal plane arrays are introduced
emphatically, and combined with the infrared solar tower plan at
present, their features are compared in detail.
---------------------------------------------------------
Title: The computer network and software system for 1 meter telescope.
Authors: Ji, Kaifan; Song, Qian; Cao, Wenda
1997PYunO...4...68J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: WinView and its usage on the 1 m telescope at Yunnan
Observatory.
Authors: Cao, Wenda; Ji, Kaifan; Song, Qian; Huan, Zunxiang
1997PYunO...1...76C Altcode:
The WinView is a highly-efficient software package for image collecting
and processing in astronomy. The essential functions and the usage of
this package in astronomy are described in detail.
---------------------------------------------------------
Title: FITS BMP and SCR image formats and the transformations.
Authors: Ji, Kaifan; Cao, Wenda; Song, Qian
1996PYunO...2...60J Altcode:
The image formats - FITS, BMP and SCR - are introduced in detail. The
FITS format has become a universal format in astronomy and can
be supported by almost all the software packages in astronomical
uses. Meanwhile the BMP format is widely used on personal computers
and is supported by a large amount of PC softwares in displaying,
progressing and printing. The SCR format is used in the Yunnan
Observatory to implement CCD image collection on PCs. Therefore, it
is important to realize the transformation among the three formats
so that CCD images head and image data, and the critical part is to
transform the high and low bits of the data.
---------------------------------------------------------
Title: The one-dimension centering algorithms of CCD image.
Authors: Kaifan, J.; Song, Qian; Cao, Wenda
1996PYunO...4...69K Altcode:
The digital centering algorithms with high resolution becomes more and
more important in astrometry. The marginal distribution method is used
to transform the two-dimensional stellar image to one-dimensional. From
comparisons among four kinds of one-dimensional centering algorithms
(Gaussian fit, modified moment, median and derivative search) it is
shown that Gaussian fit ranks highest in resolution, then the modified
moment, and derivative the lowest. But the Gaussian fit is too slow in
the view of calculating speed. Therefore, modified moment is the best
choise as a centering method which can meet both the high resolution
and high efficiency demands.
---------------------------------------------------------
Title: Development and test of an operation gain amplifier with the
solar radio telescope at 15 cm wavelengths.
Authors: Ghen, Guoqiang; Cao, Wenda; Yang, Kaiping
1995PYunO...1...47G Altcode:
The construction principle of the operation gain amplifier with the
solar radio telescope at 15 cm wavelengths is introduced. The adjustment
and the test for measurement results have been obtained.
---------------------------------------------------------
Title: Approaching to Internet.
Authors: Ji, Kaifan; Song, Qian; Cao, Wenda
1995PYunO...3...62J Altcode:
With help from Computer Network Center of Chinese Academy of Sciences
(CNC) and Telecommunication Office of Kunming, the authors have built
their e-mail system. The node computer named ROSE belonging to CNC is
linked to Internet.
---------------------------------------------------------
Title: Carbon dioxide interactions with irradiance and temperature
in potatoes
Authors: Cao, W.; Tibbitts, T. W.; Wheeler, R. M.
1994AdSpR..14k.243C Altcode: 1994AdSpR..14..243C
Separate controlled environment studies were conducted to determine
the interaction of CO<SUB>2</SUB> with irradiance and interaction of
CO<SUB>2</SUB> with temperature on growth of three potato cultivars. In
the first study, an elevated CO<SUB>2</SUB> concentration of 1000
μmol mol<SUP>-1</SUP> and an ambient CO<SUB>2</SUB> of 350 μmol
mol<SUP>-1</SUP> were maintained at the photosynthetic photon
fluxes (PPF) of 17 and 34 mol m<SUP>-2</SUP> d<SUP>-1</SUP> with
12 h photoperiod, and at the PPF of 34 and 68 mol m<SUP>-2</SUP>
d<SUP>-1</SUP> with 24 h photoperiod (400 and 800 μmol m<SUP>-2</SUP>
s<SUP>-1</SUP> PPF at each photoperiod). Tuber and total dry weights of
90-day old potatoes were significantly increased with CO<SUB>2</SUB>
enrichment, but the CO<SUB>2</SUB> stimulation was less with higher
PPF and longer photoperiod. Shoot dry weight was affected more
by photoperiod than by PPF and CO<SUB>2</SUB> concentrations. The
elevated CO<SUB>2</SUB> concentration increased leaf CO<SUB>2</SUB>
assimilation rates and decreased stomatal conductance with 12 h
photoperiod, but had only a marginal effect with 24 h photoperiod. In
the second study, four CO<SUB>2</SUB> concentrations of 500, 1000, 1500
and 2000 μmol mol<SUP>-1</SUP> were combined with two air temperature
regimes of 16 and 20°C under a 12 h photoperiod. At harvest, 35
days after transplanting, tuber and total dry weights of potatoes
reached a maximum with 1000 μmol mol<SUP>-1</SUP> CO<SUB>2</SUB>
at 16°C, but continued to increase up to 2000 μmol mol<SUP>-1</SUP>
CO<SUB>2</SUB> at 20°C. Plant growth was greater at 20°C than at 16°C
under all CO<SUB>2</SUB> concentrations. At 16°C specific leaf weight
increased substantially with increasing CO<SUB>2</SUB> concentrations
as compared to 500 μmol mol<SUP>-1</SUP> CO<SUB>2</SUB>, but increased
only slightly at 20°C. This suggests a carbohydrate build-up in the
leaves at 16°C temperature that reduces plant response to increased
CO<SUB>2</SUB> concentrations. The data in the two studies indicate
that a PPF of 34 mol m<SUP>-2</SUP> d<SUP>-1</SUP>, 20°C temperature,
and 1000-2000 μmol mol<SUP>-1</SUP> CO<SUB>2</SUB> produces optimal
tuber yield in potatoes. <P />Current address: MD-RES, Kennedy Space
Center, FL 32899.
---------------------------------------------------------
Title: Solid matrix and liquid culture procedures for growth of
potatoes
Authors: Tibbitts, T. W.; Cao, W.
1994AdSpR..14k.427T Altcode: 1994AdSpR..14..427T
This report discusses the advantages and limitations of several
different procedures for growth of potatoes for CELSS. Solution culture,
in which roots and stolons are submerged, and aeroponic culture
were not found useful for potatoes because stolons did not produce
tubers unless a severe stress was applied to the plants. In detailed
comparison studies, three selected culture systems were compared,
nutrient film technique (NFT), NFT with shallow media, and pot culture
with deep media. For the NFT and NFT plus shallow media, plants were
grown in 0.3 m<SUP>2</SUP> trays and for the deep medium culture,
in 20 liter pots. A 1 cm depth of arcillite, a baked montmorillonite
clay, was used as shallow media (NFT-arc). Peatvermiculite mixture was
used to fill the pots for the deep media. Nutrient solution, modified
half-strength Hoagland's was recirculated among the tray culture plants
with pH automatically controlled at 5.5, and conductivity maintained
~ 1100 μS cm<SUP>-1</SUP> by adding stock nutrients or renewing the
solution. A separate nutrient solution was used to water the pot plants
four times daily to excess and the excess was discarded. Plants of
Norland cv. were utilized and transplanted from sterile-propagated
stem cutting plantlets. The plants were grown for 66 days under
12 h photoperiod in a first study and grown for 54 days under 24 h
photoperiod in a second study. Under both photoperiods, total plant
growth was greater in NFT-arc than in either NFT or pot culture. Under
12 h photoperiod, tuber dry weight was 30% higher with NFT-arc, but
50% lower with NFT, than with pot culture. Under 24 h photoperiod,
however, tuber dry weight in both NFT and NFT-arc was only 20% of that
in pot culture. The NFT and NFT-arc produced a greater shoot growth
and larger number of small tubers than pot culture, especially with 24
h photoperiod. It is concluded that there are serious limitations to
the use of NFT alone for growth of potatoes in a CELSS system. These
limitations can be minimized by using a modified NFT with a shallow
layer of media, such as arcillite, yet additional work is needed to
ensure high tuber production with this system under long photoperiods.
---------------------------------------------------------
Title: Some common characteristics of the basic components of the
solar radio emission and confirmation of a fourth basic component.
Authors: Ji, S. C.; Cao, W. D.; Chen, G. Q.; Yang, K. P.
1994A&A...286..588J Altcode:
Our high time-resolution data observed with fast sampling radio
telescopes in three periods were processed. It is found that there
is a rapidly varying component (RVC) in the radio emission source
on the Sun. After investigating some common characteristics of the
basic components of the solar radio emission, we discover that RVC is
different in nature from the known three basic components: the quiet
Sun, the slowly varying component (SVC), and the radio burst. It
has a character superimposed on the radio burst: short duration,
high brightness temperature and small dimension. For this reason, it
is presented as a fourth basic component. Up to now, we have observed
five types of RVC. Among them four types can be confirmed, another
is yet in dispute. Finally, the five categories of observational
characteristics of RVC are given.
---------------------------------------------------------
Title: Solar radio type II burst in the corona and interplanetary
medium.
Authors: Cao, Wenda; Yang, Kaiping; Ghen, Guoqiang
1994PYunO...1...49C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The frequency splitting phenomenon in type II solar radio
bursts.
Authors: Cao, Wenda; Chen, Guoqing; Yang, Kaiping
1994PYunO...2...11C Altcode:
The frequency splitting phenomenon in type II solar radio bursts is
introduced and its observational features and theoretical explanation
are summarized. The numerous existing models on frequency splitting
are discussed in detail.
---------------------------------------------------------
Title: Test of the intermediate frequency amplifier of the solar
radio telescope at 2130 MHz.
Authors: Chen, Guoqing; Cao, Wenda; Yang, Kaiping
1994PYunO...2...19C Altcode:
The construction principle and the technical parameters of the
intermediate frequency amplifier of the solar radio telescope at 2130
MHz at Yunnan Observatory are introduced. Some measurement results
are presented.
---------------------------------------------------------
Title: Radio and soft X-ray investigation of the solar flares of
February 4, 1986
Authors: Ji, Shuchen; Ding, Youji; Chen, Guoqiang; Cao, Wenda
1993Ap&SS.203..241J Altcode:
In this paper, the 3B flare of February 4, 1986 is studied
comprehensively. The escape electrons accelerated to 10 100 keV at the
top of coronal loop are confirmed by III type bursts. The energetic
electron beams moved downward trigger the eruptions in the low layer
of solar atmosphere. The radio and soft X-ray bursts are interpreted,
respectively, by the maser mechanism and evaporation effect. Finally,
the important role of energetic electron beams in solar flares is
pointed out.
---------------------------------------------------------
Title: Duration of the solar radio spike radiation at decimetric
waves and milliseconds.
Authors: Cao, Wenda; Ghen, Guoqiang; Yang, Kaiping
1993PYunO...3...24C Altcode:
The duration of the solar radio milliseconds spike radiation is
shortened with increasing frequency, which has been a puzzling problem
for a long time. In this paper, according to the electron cyclotron
maser excited by the electron beams of the hollow beam distribution
associated with the type III bursts, the relation between the duration
of the spike radiation and the characteristic frequency ratio with the
wave growth rate is discussed in detail. It is concluded that at the
different wavelength of the decimetric wave, the spike radiations are
the different frequency harmonic waves and the correlative decrease
of the duration appears with increasing frequency.
---------------------------------------------------------
Title: Improvement and test of a microwave noise generator.
Authors: Ghen, Guoqiang; Yang, Kaiping; Cao, Wenda
1993PYunO...3...29G Altcode:
The improvement and test of the calibration source (or the noise
generator) of the solar radio telescope are briefly described. The
construction principle and measured results are also presented. It is
known through the operation that the improvement is a success and the
desired results are achieved.
---------------------------------------------------------
Title: Solar radio decimetric spike radiation and metric radio bursts.
Authors: Cao, Wenda
1992PYunO...3....8C Altcode:
The millisecond spike events from Jan 1990 to Mar 1991 observed and
recorded with the fast sampling radio telescopes at four frequencies
at the Yunnan Observatory are analysed. With the data combined with
those of the radio outbursts at the metric wave-band published by the
Solar-Geophysical Data during this time, the various features of the
millisecond spikes are given. The relation between the millisecond
spikes and the solar radio bursts of types III, II and IV is also
summarized.