Author name code: janvier
ADS astronomy entries on 2022-09-14
=author:"Janvier, Miho" OR =author:"Janvier, M."
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Title: ML pipeline for Solar Dynamics Observatory (SDO) data
Authors: Salvatelli, Valentina; Neuberg, Brad; Dos Santos, Luiz F. G.;
Bose, Souvik; Cheung, Mark C. M; Janvier, Miho; Jin, Meng; Gal, Yarin;
Güneş Baydın, Atılım
Bibcode: 2022zndo...6954828S
Altcode:
This software has been developed from the [FDL SDO
Team](https://frontierdevelopmentlab.org/2019-sdo). The
package contains: a configurable pipeline to train and
test ML models on data from the Solar Dynamics Observatory
some notebooks for data exploration and results analysis. It
contains all the code supporting the publications: [Multi-Channel
Auto-Calibration for the Atmospheric Imaging Assembly using Machine
Learning](https://arxiv.org/abs/2012.14023) "Exploring the Limits of
Synthetic Creation of Solar EUV Images via Image-to-Image Translation"
Accepted for publication on ApJ (July 2022)
Title: Exploring the Limits of Synthetic Creation of Solar EUV Images
via Image-to-Image Translation
Authors: Salvatelli, Valentina; dos Santos, Luiz F. G.; Bose, Souvik;
Neuberg, Brad; Cheung, Mark C. M.; Janvier, Miho; Jin, Meng; Gal,
Yarin; Gunes Baydin, Atilim
Bibcode: 2022arXiv220809512S
Altcode:
The Solar Dynamics Observatory (SDO), a NASA multi-spectral decade-long
mission that has been daily producing terabytes of observational data
from the Sun, has been recently used as a use-case to demonstrate the
potential of machine learning methodologies and to pave the way for
future deep-space mission planning. In particular, the idea of using
image-to-image translation to virtually produce extreme ultra-violet
channels has been proposed in several recent studies, as a way to
both enhance missions with less available channels and to alleviate
the challenges due to the low downlink rate in deep space. This
paper investigates the potential and the limitations of such a deep
learning approach by focusing on the permutation of four channels and
an encoder--decoder based architecture, with particular attention to
how morphological traits and brightness of the solar surface affect the
neural network predictions. In this work we want to answer the question:
can synthetic images of the solar corona produced via image-to-image
translation be used for scientific studies of the Sun? The analysis
highlights that the neural network produces high-quality images
over three orders of magnitude in count rate (pixel intensity)
and can generally reproduce the covariance across channels within
a 1% error. However the model performance drastically diminishes in
correspondence of extremely high energetic events like flares, and we
argue that the reason is related to the rareness of such events posing
a challenge to model training.
Title: Interpreting the Two-step Forbush Decrease with a closer
look at the two substructures modulating Galactic Cosmic Rays within
Coronal Mass Ejections
Authors: Janvier, Miho; Dasso, Sergio; Demoulin, Pascal; Guo, Jingnan;
Regnault, Florian; Perri, Barbara; Guttierez, Christian
Bibcode: 2022cosp...44.1272J
Altcode:
Interplanetary Coronal Mass Ejections (CMEs) are magnetic structures
emanating from the Sun. A consequence of their passage at planetary
bodies can be seen as the reduction of galactic cosmic rays (GCRs),
a phenomenon called a Forbush decrease. These decreases are routinely
monitored with neutron detectors around the world, while ICMEs are
measured directly in situ by spacecraft dedicated to the monitoring of
the solar wind. In particular, these detections show that ICMEs may or
not build a sheath of compressed solar wind at their front, preceded in
some cases by a shock. Then, the question remains which substructure
may, and how, drive the Forbush decrease. Here, we will discuss how
statistical analyses such as superposed epoch studies can be applied
to ICME-induced Forbush decreases. In particular, by selecting ICMEs
with or without a sheath, we will show that magnetic ejecta alone can
drive Forbush decreases as strong as those with a sheath. Different
from previous studies, we find with such a study that it is the magnetic
field intensity, rather than its fluctuations, that is the main driver
of Forbush decreases. Finally, we will show how the passage of isolated
magnetic ejecta reveal an anisotropy in the level of GCRs in the solar
wind at 1 au, a finding that we explain as related to the gradient of
the GCR flux found at different distances in the heliosphere, i.e.,
the GCR flux is slightly higher at a larger heliospheric distance.
Title: Magnetic field of interplanetary ejecta
Authors: Janvier, Miho
Bibcode: 2022cosp...44.2432J
Altcode:
Interplanetary ejecta transport solar plasma and magnetic field
from the Sun on large distances in the solar system. They can
originate from diverse solar locations, from active regions, to
quiescent filaments/prominences, to jets and streamers reconnected
flux ropes. In the interplanetary medium, they have been routinely
monitored at different helio-distances with the availability of
different instruments on board space missions. We will review how
statistical analyses of some properties point to different sources but
similar magnetic structures of these ejecta: from small flux ropes to
bigger ones found in magnetic clouds. We will also see in particular
how magnetic ejecta in interplanetary coronal mass ejections (ICMEs)
can differ one from another depending on the conditions of the ejection
and their interplay with the solar wind. By reviewing the numerous
data we now have, from long-term missions such as ACE or Wind, to more
recent missions such as Parker Solar Probe and Solar Orbiter close to
the Sun, and with the help of numerical simulations, we will discuss
how this wealth of data provides us with a better understanding of
the evolution of theses magnetic ejecta in the interplanetary medium.
Title: Forecasting the Kp index a few days ahead using solar imaging
and neural networks alone: is it achievable?
Authors: Bernoux, Guillerme; Sicard, Angelica; Buchlin, Eric; Janvier,
Miho; Brunet, Antoine
Bibcode: 2022cosp...44.3330B
Altcode:
Over the past decade, data-driven methods using near-Earth solar
wind parameters to forecast geomagnetic indices have shown very good
performance, mostly outperforming many empirical and physics-based
models in terms of accuracy. In addition, these forecasting models have
recently shown their relevance to drive various magnetospheric models
in space weather pipelines. However, these methods still suffer from
many limitations, among which their restriction to a short effective
forecasting horizon (often up to approximately 6 hours at best). This is
not surprising, as these lead-times are of the same order of magnitude
as the solar wind-magnetosphere coupling time-lags. Therefore, in order
to increase the forecasting horizon, one solution would be to use more
spatially remote data, such as solar imaging. In order to address this
issue, we introduce SERENADE, a deep learning-based model driven only
by Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA)
data that can provide probabilistic forecasts of geomagnetic indices
such as Kp up to a few days ahead. We evaluate the model and discuss its
advantages and drawbacks based on these first results. In particular,
we compare it with baseline models and assess the performance of our
model according to the solar cycle phase. We show that our method
is promising, especially since it is only a first model that can be
improved in many aspects.
Title: Magnetic field lines configuration inside magnetic clouds:
observations at 1 au
Authors: Dasso, Sergio; Demoulin, Pascal; Janvier, Miho; Lanabere,
Vanina
Bibcode: 2022cosp...44.2435D
Altcode:
Flux ropes, which are twisted magnetic flux tubes, are of major
interest in different space and astrophysical domains, such as the Sun,
planetary environments, and stellar physics. In particular, these
structures are observed in the solar photosphere, the corona, the
interplanetary medium, and also in planetary magnetospheres. Magnetic
flux ropes in the solar wind can reach huge sizes in the heliosphere,
storing significant amounts of magnetic energy and helicity. Thus,
interplanetary flux ropes (IFRs) transport these quantities from the
Sun to the outer heliosphere. A few analytical models provide the IFR
internal magnetic configuration, which can then be compared with in
situ observations at 1 au. This provides hints (or information) on the
associated coronal magnetic configuration at the origin of the event.The
derived magnetic structure of IFRs has also implications to improve
models for propagation of energetic particles inside IFRs. Finally,
magnetic clouds are the clearest observed sub-set of IFRs, so that a
detailed analysis and modelisation of the observed data can be performed
to derive their magnetic twist profile. In this review talk we will
present a summary of the state of the art about the quantification of
the magnetic twist
distribution in magnetic clouds from 'in-situ'
observations at 1 au.
Title: Evolution of Plasma Composition in an Eruptive Flux Rope
Authors: Baker, Deborah; Demoulin, Pascal; Long, David; Janvier, Miho;
Green, Lucie; Brooks, David; van Driel-Gesztelyi, Lidia; Mihailescu,
Teodora; To, Andy S. H.; Yardley, Stephanie; Valori, Gherardo
Bibcode: 2022cosp...44.1361B
Altcode:
Magnetic flux ropes are bundles of twisted magnetic field enveloping a
central axis. They harbor free magnetic energy and can be progenitors
of coronal mass ejections (CMEs). However, identifying flux ropes on
the Sun can be challenging. One of the key coronal observables that
has been shown to indicate the presence of a flux rope is a peculiar
bright coronal structure called a sigmoid. In this work, we show Hinode
EUV Imaging Spectrometer observations of sigmoidal active region (AR)
10977. We analyze the coronal plasma composition in the AR and its
evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma
with photospheric composition was observed in coronal loops close to
the main polarity inversion line during episodes of significant flux
cancellation, suggestive of the injection of photospheric plasma into
these loops driven by photospheric flux cancellation. Concurrently,
the increasingly sheared core field contained plasma with coronal
composition. As flux cancellation decreased and a sigmoid/flux
rope formed, the plasma evolved to an intermediate composition in
between photospheric and typical AR coronal compositions. Finally,
the flux rope contained predominantly photospheric plasma during and
after a failed eruption preceding the CME. Hence, plasma composition
observations of AR 10977 strongly support models of flux rope formation
by photospheric flux cancellation forcing magnetic reconnection first
at the photospheric level then at the coronal level.
Title: Abundance diagnostics in active regions with Solar
Orbiter/SPICE
Authors: Giunta, Alessandra; Peter, Hardi; Parenti, Susanna; Buchlin,
Eric; Thompson, William; Auchere, Frederic; Kucera, Therese; Carlsson,
Mats; Janvier, Miho; Fludra, Andrzej; Hassler, Donald M.; Grundy,
Timothy; Sidher, Sunil; Guest, Steve; Leeks, Sarah; Fredvik, Terje;
Young, Peter
Bibcode: 2022cosp...44.2583G
Altcode:
With the launch of Solar Orbiter in February 2020, we are now able to
fully explore the link between the solar activity on the Sun and the
inner heliosphere. Elemental abundance measurements provide a key tracer
to probe the source regions of the solar wind and to track it from the
solar surface and corona to the heliosphere. Abundances of elements
with low first ionisation potential (FIP) are enhanced in the corona
relative to high-FIP elements, with respect to the photosphere. This is
known as the FIP effect, which is measured as abundance bias (FIP bias)
of low and high FIP elements. This effect is vital for understanding the
flow of mass and energy through the solar atmosphere. The comparison
between in-situ and remote sensing composition data, coupled with
modelling, will allow us to trace back the source of heliospheric
plasma. Solar Orbiter has a unique combination of in-situ and remote
sensing instruments that will help to make such a comparison. In
particular, the SPICE (Spectral Imaging of the Coronal Environment)
EUV spectrometer records spectra in two wavelength bands, 70.4-79.0
nm and 97.3-104.9 nm. SPICE is designed to provide spectroheliograms
using a core set of emission lines arising from ions of both low-FIP
and high-FIP elements such as C, N, O, Ne, Mg, S and Fe. These lines
are formed over a wide range of temperatures from 20,000 K to over 1
million K, enabling the analysis of the different layers of the solar
atmosphere. SPICE spectroheliograms can be processed to produce FIP
bias maps, which can be compared to in-situ measurements of the solar
wind composition of the same elements. During the Solar Orbiter Cruise
Phase, SPICE observed several active regions. We will present some of
these observations and discuss the SPICE diagnostic potential to derive
relative abundances (e.g., Mg/Ne) and the FIP bias in those regions.
Title: The SPICE spectrograph on Solar Orbiter: an introduction and
results from the first Orbits
Authors: Auchère, Frédéric; Peter, Hardi; Parenti, Susanna; Buchlin,
Eric; Thompson, William; Auchere, Frederic; Teriaca, Luca; Kucera,
Therese; Carlsson, Mats; Janvier, Miho; Fludra, Andrzej; Giunta,
Alessandra; Schuehle, Udo; Hassler, Donald M.; Grundy, Timothy;
Sidher, Sunil; Fredvik, Terje; Plowman, Joseph; Aznar Cuadrado, Regina
Bibcode: 2022cosp...44.1338A
Altcode:
The Spectral Imaging of the Coronal Environment (SPICE) instrument is
the EUV imaging spectrometer on board the Solar Orbiter mission. With
its ability to derive physical properties of the coronal plasma,
SPICE is a key component of the payload to establish the connection
between the source regions and the in-situ measurements of the solar
wind. The spacecraft was successfully launched in February 2020 and
completed its cruise phase in December 2021. During this period,
the remote sensing instruments were mostly operated during limited
periods of time for 'checkout' engineering activities and synoptic
observations. Nonetheless, several of these periods provided enough
opportunities already to obtain new insights on coronal physics. During
the march 2022 perihelion - close to 0.3 AU - SPICE will provide
its highest spatial resolution data so far. Coordinated observations
between the remote sensing and in-situ instruments will provide the
first opportunity to use the full potential of the Solar Orbiter
mission. We will review the instrument characteristics and present
initial results from the cruise phase and first close encounter.
Title: Evolution of Plasma Composition in an Eruptive Flux Rope
Authors: Baker, D.; Green, L. M.; Brooks, D. H.; Démoulin, P.;
van Driel-Gesztelyi, L.; Mihailescu, T.; To, A. S. H.; Long, D. M.;
Yardley, S. L.; Janvier, M.; Valori, G.
Bibcode: 2022ApJ...924...17B
Altcode: 2021arXiv211011714B
Magnetic flux ropes are bundles of twisted magnetic field enveloping a
central axis. They harbor free magnetic energy and can be progenitors
of coronal mass ejections (CMEs). However, identifying flux ropes on
the Sun can be challenging. One of the key coronal observables that
has been shown to indicate the presence of a flux rope is a peculiar
bright coronal structure called a sigmoid. In this work, we show Hinode
EUV Imaging Spectrometer observations of sigmoidal active region (AR)
10977. We analyze the coronal plasma composition in the AR and its
evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma
with photospheric composition was observed in coronal loops close to
the main polarity inversion line during episodes of significant flux
cancellation, suggestive of the injection of photospheric plasma into
these loops driven by photospheric flux cancellation. Concurrently,
the increasingly sheared core field contained plasma with coronal
composition. As flux cancellation decreased and a sigmoid/flux
rope formed, the plasma evolved to an intermediate composition in
between photospheric and typical AR coronal compositions. Finally,
the flux rope contained predominantly photospheric plasma during and
after a failed eruption preceding the CME. Hence, plasma composition
observations of AR 10977 strongly support models of flux rope formation
by photospheric flux cancellation forcing magnetic reconnection first
at the photospheric level then at the coronal level.
Title: 3D modelling of Titov-Demoulin modified Flux Ropes propagation
in the Solar Wind
Authors: Regnault, Florian; Janvier, Miho; Strugarek, Antoine; Auchere,
F.; Al-Haddad, Nada
Bibcode: 2021AGUFMSH33A..04R
Altcode:
Interplanetary Coronal Mass Ejections (ICMEs) originate from the
eruption of complex magnetic structures occurring in our stars
atmosphere. They propagate in the interplanetary medium, where they
can be probed by spacecraft. ICMEs are known to generate geomagnetic
storms that can disturb our technologies on earth, this is why they
are a subject of interest. Studying ICMEs could, therefore, allow us to
predict and lower their impact in our technology. We present the results
of the propagation simulation of a set of Titov-Demoulin flux ropes
(Titov et al. 2014) with different magnetic fields and sizes at the
initiation. This is done with the 3D MHD module of the PLUTO code. Our
grid starts at the low corona and goes up to 2 astronomical units. This
allows us to study the effect of the magnetic field intensity or the
size of the flux rope at the initiation on its properties during the
propagation, highlighting then the physical processes happening during
their journey in the inner heliosphere. The evolution of the magnetic
field of the flux rope during the propagation agrees with evolution
laws deduced from in situ observations. We also simulate in situ
profiles that spacecraft would have measured at Mercury and at Earth,
and we compare with the results of Janvier et al. 2019 and Regnault et
al. 2020. We find a good match between simulated in situ profiles and
typical profiles obtained in these studies. The magnetic components
of the simulated flux rope match well with what we are expecting from
theory (Lundquist et al. 1950). This simulation helps us to have a
better understanding of the physical mechanisms that happen during
propagation of an ICME.
Title: The Two-step Forbush Decrease: A Tale of Two Substructures
Modulating Galactic Cosmic Rays within Coronal Mass Ejections
Authors: Janvier, Miho; Démoulin, Pascal; Guo, Jingnan; Dasso, Sergio;
Regnault, Florian; Topsi-Moutesidou, Sofia; Gutierrez, Christian;
Perri, Barbara
Bibcode: 2021ApJ...922..216J
Altcode: 2021arXiv210914469J
Interplanetary coronal mass ejections (ICMEs) are known to modify
the structure of the solar wind as well as interact with the space
environment of planetary systems. Their large magnetic structures have
been shown to interact with galactic cosmic rays (GCRs), leading to the
Forbush decrease (FD) phenomenon. We revisit in the present article
the 17 yr of Advanced Composition Explorer spacecraft ICME detection
along with two neutron monitors (McMurdo and Oulu) with a superposed
epoch analysis to further analyze the role of the magnetic ejecta in
driving FDs. We investigate in the following the role of the sheath and
the magnetic ejecta in driving FDs, and we further show that for ICMEs
without a sheath, a magnetic ejecta only is able to drive significant
FDs of comparable intensities. Furthermore, a comparison of samples with
and without a sheath with similar speed profiles enable us to show that
the magnetic field intensity, rather than its fluctuations, is the main
driver for the FD. Finally, the recovery phase of the FD for isolated
magnetic ejecta shows an anisotropy in the level of the GCRs. We relate
this finding at 1 au to the gradient of the GCR flux found at different
heliospheric distances from several interplanetary missions.
Title: First observations from the SPICE EUV spectrometer on Solar
Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A.; Grundy, T.; Guest,
S.; Leeks, S.; Sidher, S.; Auchère, F.; Carlsson, M.; Hassler, D.;
Peter, H.; Aznar Cuadrado, R.; Buchlin, É.; Caminade, S.; DeForest,
C.; Fredvik, T.; Haberreiter, M.; Harra, L.; Janvier, M.; Kucera, T.;
Müller, D.; Parenti, S.; Schmutz, W.; Schühle, U.; Solanki, S. K.;
Teriaca, L.; Thompson, W. T.; Tustain, S.; Williams, D.; Young, P. R.;
Chitta, L. P.
Bibcode: 2021A&A...656A..38F
Altcode: 2021arXiv211011252F
Aims: We present first science observations taken during the
commissioning activities of the Spectral Imaging of the Coronal
Environment (SPICE) instrument on the ESA/NASA Solar Orbiter
mission. SPICE is a high-resolution imaging spectrometer operating at
extreme ultraviolet (EUV) wavelengths. In this paper we illustrate
the possible types of observations to give prospective users a
better understanding of the science capabilities of SPICE.
Methods: We have reviewed the data obtained by SPICE between April
and June 2020 and selected representative results obtained with
different slits and a range of exposure times between 5 s and 180
s. Standard instrumental corrections have been applied to the raw
data.
Results: The paper discusses the first observations
of the Sun on different targets and presents an example of the full
spectra from the quiet Sun, identifying over 40 spectral lines from
neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur,
magnesium, and iron. These lines cover the temperature range between
20 000 K and 1 million K (10 MK in flares), providing slices of the
Sun's atmosphere in narrow temperature intervals. We provide a list
of count rates for the 23 brightest spectral lines. We show examples
of raster images of the quiet Sun in several strong transition region
lines, where we have found unusually bright, compact structures in the
quiet Sun network, with extreme intensities up to 25 times greater
than the average intensity across the image. The lifetimes of these
structures can exceed 2.5 hours. We identify them as a transition
region signature of coronal bright points and compare their areas and
intensity enhancements. We also show the first above-limb measurements
with SPICE above the polar limb in C III, O VI, and Ne VIII lines, and
far off limb measurements in the equatorial plane in Mg IX, Ne VIII,
and O VI lines. We discuss the potential to use abundance diagnostics
methods to study the variability of the elemental composition that can
be compared with in situ measurements to help confirm the magnetic
connection between the spacecraft location and the Sun's surface,
and locate the sources of the solar wind.
Conclusions: The
SPICE instrument successfully performs measurements of EUV spectra
and raster images that will make vital contributions to the scientific
success of the Solar Orbiter mission.
Title: An operational approach to forecast the Earth's radiation
belts dynamics
Authors: Bernoux, Guillerme; Brunet, Antoine; Buchlin, Éric; Janvier,
Miho; Sicard, Angélica
Bibcode: 2021JSWSC..11...60B
Altcode:
The Ca index is a time-integrated geomagnetic index that correlates
well with the dynamics of high-energy electron fluxes in the outer
radiation belts. Therefore, Ca can be used as an indicator for the state
of filling of the radiation belts for those electrons. Ca also has the
advantage of being a ground-based measurement with extensive historical
records. In this work, we propose a data-driven model to forecast Ca
up to 24 h in advance from near-Earth solar wind parameters. Our model
relies mainly on a recurrent neural network architecture called Long
Short Term Memory that has shown good performances in forecasting other
geomagnetic indices in previous papers. Most implementation choices
in this study were arbitrated from the point of view of a space system
operator, including the data selection and split, the definition of a
binary classification threshold, and the evaluation methodology. We
evaluate our model (against a linear baseline) using both classical
and novel (in the space weather field) measures. In particular, we use
the Temporal Distortion Mix (TDM) to assess the propensity of two time
series to exhibit time lags. We also evaluate the ability of our model
to detect storm onsets during quiet periods. It is shown that our model
has high overall accuracy, with evaluation measures deteriorating in
a smooth and slow trend over time. However, using the TDM and binary
classification forecast evaluation metrics, we show that the forecasts
lose some of their usefulness in an operational context even for time
horizons shorter than 6 h. This behaviour was not observable when
evaluating the model only with metrics such as the root-mean-square
error or the Pearson linear correlation. Considering the physics of
the problem, this result is not surprising and suggests that the use
of more spatially remote data (such as solar imaging) could improve
space weather forecasts.
Title: BepiColombo's cruise phase: unique opportunity for synergistic
observations
Authors: Hadid, L. Z.; Génot, V.; Aizawa, S.; Milillo, A.; Zender,
J.; Murakami, G.; Benkhoff, J.; Zouganelis, I.; Alberti, T.; André,
N.; Bebesi, Z.; Califano, F.; Dimmock, A. P.; Dosa, M.; Escoubet,
C. P.; Griton, L.; Ho, G. C.; Horbury, T. S.; Iwai, K.; Janvier, M.;
Kilpua, E.; Lavraud, B.; Madar, A.; Miyoshi, Y.; Müller, D.; Pinto,
R. F.; Rouillard, A. P.; Raines, J. M.; Raouafi, N.; Sahraoui, F.;
Sánchez-Cano, B.; Shiota, D.; Vainio, R.; Walsh, A.
Bibcode: 2021FrASS...8..154H
Altcode:
The investigation of multi-spacecraft coordinated observations
during the cruise phase of BepiColombo (ESA/JAXA) are reported,
with a particular emphasis on the recently launched missions,
Solar Orbiter (ESA/NASA) and Parker Solar Probe (NASA). Despite
some payload constraints, many instruments onboard BepiColombo
are operating during its cruise phase simultaneously covering a
wide range of heliocentric distances [0.28 AU - 0.5 AU]. Hence, the
various spacecraft configurations and the combined in-situ and remote
sensing measurements from the different spacecraft, offer unique
opportunities for BepiColombo to be part of these unprecedented
multipoint synergistic observations and for potential scientific
studies in the inner heliosphere, even before its orbit insertion
around Mercury in December 2025. The main goal of this report is to
present the coordinated observation opportunities during the cruise
phase of BepiColombo (excluding the planetary flybys). We summarize
the identified science topics, the operational instruments, the method
we have used to identify the windows of opportunity and discuss the
planning of joint observations in the future.
Title: Magnetic imaging of the outer solar atmosphere (MImOSA)
Authors: Peter, H.; Ballester, E. Alsina; Andretta, V.; Auchère, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; Alemán, T. del Pino; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Štěpán, J.; Teriaca, L.; Bueno, J. Trujillo
Bibcode: 2021ExA...tmp...95P
Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability of
planets orbiting these host stars. Although the magnetic field at the
surface of the Sun is reasonably well characterised by observations,
the information on the magnetic field in the higher atmospheric layers
is mainly indirect. This lack of information hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution
and high sensitivity. (b) An extreme-UV-to-IR coronagraph that is
designed to measure the large-scale magnetic field in the corona with
an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter
based on a 30 cm telescope that combines high throughput in the
extreme UV with polarimetry to connect the magnetic measurements
of the other two instruments. Placed in a near-Earth orbit, the data
downlink would be maximised, while a location at L4 or L5 would provide
stereoscopic observations of the Sun in combination with Earth-based
observatories. This mission to measure the magnetic field will finally
unlock the driver of the dynamics in the outer solar atmosphere and
thereby will greatly advance our understanding of the Sun and the
heliosphere.
Title: Plasma Upflows Induced by Magnetic Reconnection Above an
Eruptive Flux Rope
Authors: Baker, Deborah; Mihailescu, Teodora; Démoulin, Pascal;
Green, Lucie M.; van Driel-Gesztelyi, Lidia; Valori, Gherardo; Brooks,
David H.; Long, David M.; Janvier, Miho
Bibcode: 2021SoPh..296..103B
Altcode: 2021arXiv210616137B
One of the major discoveries of Hinode's Extreme-ultraviolet
Imaging Spectrometer (EIS) is the presence of upflows at the edges
of active regions. As active regions are magnetically connected
to the large-scale field of the corona, these upflows are a likely
contributor to the global mass cycle in the corona. Here we examine
the driving mechanism(s) of the very strong upflows with velocities
in excess of 70 km s−1, known as blue-wing asymmetries,
observed during the eruption of a flux rope in AR 10977 (eruptive flare
SOL2007-12-07T04:50). We use Hinode/EIS spectroscopic observations
combined with magnetic-field modeling to investigate the possible
link between the magnetic topology of the active region and the strong
upflows. A Potential Field Source Surface (PFSS) extrapolation of the
large-scale field shows a quadrupolar configuration with a separator
lying above the flux rope. Field lines formed by induced reconnection
along the separator before and during the flux-rope eruption are
spatially linked to the strongest blue-wing asymmetries in the upflow
regions. The flows are driven by the pressure gradient created when
the dense and hot arcade loops of the active region reconnect with
the extended and tenuous loops overlying it. In view of the fact
that separator reconnection is a specific form of the more general
quasi-separatrix (QSL) reconnection, we conclude that the mechanism
driving the strongest upflows is, in fact, the same as the one driving
the persistent upflows of ≈10 - 20 km s−1 observed in
all active regions.
Title: Multichannel autocalibration for the Atmospheric Imaging
Assembly using machine learning
Authors: Dos Santos, Luiz F. G.; Bose, Souvik; Salvatelli, Valentina;
Neuberg, Brad; Cheung, Mark C. M.; Janvier, Miho; Jin, Meng; Gal,
Yarin; Boerner, Paul; Baydin, Atılım Güneş
Bibcode: 2021A&A...648A..53D
Altcode: 2020arXiv201214023D
Context. Solar activity plays a quintessential role in affecting the
interplanetary medium and space weather around Earth. Remote-sensing
instruments on board heliophysics space missions provide a pool of
information about solar activity by measuring the solar magnetic
field and the emission of light from the multilayered, multithermal,
and dynamic solar atmosphere. Extreme-UV (EUV) wavelength observations
from space help in understanding the subtleties of the outer layers
of the Sun, that is, the chromosphere and the corona. Unfortunately,
instruments such as the Atmospheric Imaging Assembly (AIA) on board
the NASA Solar Dynamics Observatory (SDO), suffer from time-dependent
degradation that reduces their sensitivity. The current best calibration
techniques rely on flights of sounding rockets to maintain absolute
calibration. These flights are infrequent, complex, and limited to
a single vantage point, however.
Aims: We aim to develop a
novel method based on machine learning (ML) that exploits spatial
patterns on the solar surface across multiwavelength observations to
autocalibrate the instrument degradation.
Methods: We established
two convolutional neural network (CNN) architectures that take either
single-channel or multichannel input and trained the models using the
SDOML dataset. The dataset was further augmented by randomly degrading
images at each epoch, with the training dataset spanning nonoverlapping
months with the test dataset. We also developed a non-ML baseline model
to assess the gain of the CNN models. With the best trained models,
we reconstructed the AIA multichannel degradation curves of 2010-2020
and compared them with the degradation curves based on sounding-rocket
data.
Results: Our results indicate that the CNN-based models
significantly outperform the non-ML baseline model in calibrating
instrument degradation. Moreover, multichannel CNN outperforms
the single-channel CNN, which suggests that cross-channel relations
between different EUV channels are important to recover the degradation
profiles. The CNN-based models reproduce the degradation corrections
derived from the sounding-rocket cross-calibration measurements
within the experimental measurement uncertainty, indicating that
it performs equally well as current techniques.
Conclusions:
Our approach establishes the framework for a novel technique based
on CNNs to calibrate EUV instruments. We envision that this technique
can be adapted to other imaging or spectral instruments operating at
other wavelengths.
Title: Statistical analysis of magnetic field fluctuations in
CME-driven sheath regions
Authors: Kilpua, E. K. J.; Good, S. W.; Ala-Lahti, M.; Osmane, A.;
Fontaine, D.; Hadid, L.; Janvier, M.; Yordanova, E.
Bibcode: 2021FrASS...7..109K
Altcode:
We report a statistical analysis of magnetic field fluctuations in 79
coronal mass ejection (CME)-driven sheath regions that were observed
in the near-Earth solar wind. Wind high-resolution magnetic field
data are used to investigate 2-hour regions adjacent to the shock and
ejecta leading edge (Near-Shock and Near-LE regions, respectively)
and the results are compared to a 2-hour region upstream of the
shock. The inertial range spectral indices in the sheaths are found
to be mostly steeper than the Kolmogorov -5/3 index and steeper than
in the solar wind ahead. We did not find indications of a $f^{-1}$
spectrum, implying that magnetic fluctuation properties in CME
sheaths differ significantly from planetary magnetosheaths and
that CME-driven shocks do not reset the solar wind turbulence to a
similar extent as planetary bow shocks. However, our study suggests
that new compressible fluctuations are generated in the sheath for
a wide variety of shock/upstream conditions. Fluctuation properties
particularly differed between the Near-Shock region and the solar wind
ahead. A strong positive correlation was found between the mean magnetic
compressibility upstream and downstream regions, but the compressibility
values in sheaths were similar to that in the slow solar wind ($<
0.2$), regardless of the value in the preceding wind. Otherwise, we
did not find clear correlations between the inertial range spectral
indices in the sheaths and shock/preceding solar wind properties,
nor with the mean normalized fluctuation amplitudes. Correlations were
also considerably lower in the Near-LE region than in the Near-Shock
region. Intermittency was also considerably higher in the sheath than
in the upstream wind according to several proxies, particularly so
in the Near-Shock region. Fluctuations in the sheath exhibit larger
rotation than upstream, implying the presence of strong current sheets
in the sheath that can add to intermittency.
Title: Magnetic twist distribution inside interplanetary flux ropes
Authors: Dasso, Sergio; Rodriguez, Luciano; Demoulin, Pascal;
Masias-Meza, Jimmy J.; Janvier, Miho; Lanabere, Vanina
Bibcode: 2021cosp...43E1756D
Altcode:
Twisted magnetic flux tubes, also known as flux ropes, are ubiquitous
in solar, stellar, and planetary environments. They are present in the
photosphere of the Sun, the solar corona, the solar wind, and also in
different locations of planetary magnetospheres and ionospheres. In
particular, interplanetary flux ropes (IFRs) can store magnetic energy
and, because their magnetic field lines are twisted around the tube
axis, also can store important amounts of magnetic helicity. Thus, IFRs
can transport these quantities from the Sun to the outer space of the
heliosphere. The internal distribution of the magnetic twist forming
the flux rope (i.e., the number of turns per unit length), is a key
property to link IFRs with their solar origin and ejection processes,
to improve the knowledge of coronal structures in equilibrium, and
also to better understand the energetic particle propagation inside
these interplanetary structures. Quantifying the magnetic twist
distribution in IFRs from 'in-situ' observations of single events has
a major difficulty produced by the significant field fluctuations
in the interplanetary magnetic field. Magnetic clouds (MCs) are a
sub-set of Interplanetary Coronal Ejections (ICMEs), which present
clear signatures of flux ropes when 'in-situ' observed. In this work,
we apply a superposed epoch analysis to a significant sample of MCs
observed at 1 au, to extract their common features, and to remove the
peculiarity and eventual high level of noise present in individual
cases. From this analysis, we quantify the typical twist distribution
inside the flux ropes forming MCs. As one of the main results, we find
that the twist is nearly uniform in the core (central half part around
the flux rope axis), and it increases moderately, up to a factor two,
towards the MC boundaries. These results will allow to better understand
these magnetic structures and to link them with their solar origin.
Title: 20 years of ACE data: how superposed epoch analyses reveal
generic features in interplanetary CME profiles
Authors: Regnault, Florian; Dasso, Sergio; Auchere, Frederic; Demoulin,
Pascal; Janvier, Miho; Strugarek, Antoine
Bibcode: 2021cosp...43E1017R
Altcode:
Interplanetary Coronal Mass Ejections (ICMEs) result from solar flares
occurring in our star's atmosphere. These large-scale magnetized
structures propagate in the interplanetary medium where they can be
probed by spacecraft. Depending on their speed, ICMEs may accumulate
enough solar wind plasma to form a turbulent sheath ahead of them. They
therefore consist of two main substructures : a sheath and a magnetic
ejecta (ME). The magnetic ejecta is the main body of an ICME where
the magnetic field is more intense and with less variance than that
of the ambient solar wind. We present a statistical study using the
superposed epoch analysis technique on a catalog of around 400 ICMEs
where we consider the profiles of the physical parameters of the ICMEs
(the magnetic field intensity, the speed, temperature, ...) seen at
1 AU by the ACE spacecraft. In particular, we investigate different
possible classifications of ICMEs, for example based on their speeds,
the phase of the solar cycle when they are detected, and the detection
of an associated magnetic cloud (MCs, a subset of MEs with a clear
rotation of the magnetic field as well as a low plasma temperature
compared with the solar wind). We confirm that slow ICMEs have a
more symmetric profile than fast ICMEs, therefore generalizing the
work made on a sample of 44 ICMEs with clearly identified magnetic
clouds by Masias-Meza et al. (2016). We also find that fast ICMEs
show signs of compression in both their magnetic ejecta and in their
sheath. Furthermore, we do not find any impact of the solar cycle on the
generic features of ICMEs. However, more extreme events are observed
during the active parts of the cycle, widening the distributions of
all parameters. Finally, we find that ICMEs with or without a detected
magnetic cloud show similar profiles, which confirms the hypothesis
that both types of events correspond to similar ICMEs, and that the
ones with no detected magnetic clouds may be observed when crossed
sufficiently away from the flux rope core.
Title: Generic profile evolution of Interplanetary Coronal Mass
Ejections and flux ropes in the inner heliosphere.
Authors: Janvier, Miho
Bibcode: 2021cosp...43E1743J
Altcode:
Coronal Mass Ejections are large disturbances emanating from
the Sun. They transport solar plasma and magnetic field in the
interplanetary medium and can interact with the space environments of
planets. Known as one of the most important drivers of space weather,
improving our understanding of how interplanetary CMEs (ICMEs) and
the flux ropes within them evolve, as well as their generic features,
is critical to develop prediction tools for space weather. On the other
hand, it has been suspected that flaring stars may also be the source
of exo-CME activity, although direct evidences of their existence remain
to be found. Then, studies of CME evolution in the heliosphere may shed
some light on what to be expected for their exo-CME counterpart in
other astrospheres. ICMEs in the Solar System are routinely measured
in situ by spacecraft dedicated to the monitoring of the solar wind
(such as ACE at the Lagrangian point 1), or as a by-product of planetary
missions (e.g. Messenger, Venus Express). ICMEs can then be monitored at
different heliospheric distances, allowing a survey of their evolution
with distance from the Sun. In particular, statistical analyses such
as superposed epoch studies can reveal generic features in the time
series of in situ parameters. By combining different catalogues of
ICMEs detected at different spacecraft, we investigate the features of
the superposed epochs for the profiles of these events and how these
features evolve with heliospheric distances, solar activity, and with
the presence or not of flux ropes. In particular, we find different
profiles whether ICMEs are propagating fast or slow with respect to the
solar wind, and with different effects on cosmic rays. We interpret the
differences in the profiles of slow and fast ICMEs as the result of
the conditions of ICME ejections as well as propagation processes in
the solar wind. Such a study is important in providing a picture for
how ICMEs propagate in the interplanetary medium and what to expect
in other star systems.
Title: Magnetic Imaging of the Outer Solar Atmosphere (MImOSA):
Unlocking the driver of the dynamics in the upper solar atmosphere
Authors: Peter, H.; Alsina Ballester, E.; Andretta, V.; Auchere, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; del Pino Aleman, T.; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Stepan, J.; Teriaca, L.; Trujillo Bueno, J.
Bibcode: 2021arXiv210101566P
Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability
of planets orbiting these host stars. The lack of information on the
magnetic field in the higher atmospheric layers hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution and high
sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to
measure the large-scale magnetic field in the corona with an aperture
of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30
cm telescope that combines high throughput in the extreme UV with
polarimetry to connect the magnetic measurements of the other two
instruments. This mission to measure the magnetic field will unlock
the driver of the dynamics in the outer solar atmosphere and thereby
greatly advance our understanding of the Sun and the heliosphere.
Title: Signature of the expansion of eruptive flux ropes measured
by electric currents
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Janvier, Miho;
Masson, Sophie; Barczynski, Krzysztof
Bibcode: 2021cosp...43E1758S
Altcode:
MHD models demonstrate that hooks of flare ribbons are the footprints
of eruptive flux ropes and that a decrease of the electric currents
could be the signature of the evolution of the coronal magnetic
field, e.g. the expansion of a line-tied flux rope with constant
end-to-end external twist during the eruption. However in circuit
models the surface electric current has a subsurface fixed source
and therefore the currents should be constant . We analyze 19 X-class
flares observed by Solar Dynamics Observatory (SDO) from 2011 to 2016,
where flare ribbons with hooks are identifiable. For the first time
fine measurements of time-evolution of electric currents inside the
hooks in the observations as well as in the OHM 3D MHD simulation are
performed. Our analysis shows a decrease of the electric current in the
area surrounded by the ribbon hooks during and after the eruption. In
the simulation the rate of current deceasing is similar to that of the
field line elongation. So we interpret the decrease of the electric
currents as due to the expansion of the flux rope in the corona during
the eruption. Our analysis brings a new stone to the standard flare
model in 3D.
Title: Magnetic field fluctuation properties in CME-driven sheath
regions
Authors: Kilpua, K. E. J.; Good, S.; Ala-Lahti, M. M.; Osmane, A.;
Fontaine, D.; Hadid, L.; Yordanova, E.; Janvier, M.
Bibcode: 2020AGUFMSH0440012K
Altcode:
Coronal mass ejection driven sheath regions are important drivers
of space weather. Their structure and formation is however not yet
well understood. In this presentation we discuss general sheath
characteristics and in particular their magnetic field fluctuations
properties (spectral indices, compressibility and intermittency) in
differents parts of the sheath. The results highlight that turbulent
properties can vary considerably within the sheath and support the
view of the complex formation of the sheath and different physical
mechanisms playing a role in generating fluctuations.
Title: Relative coronal abundance diagnostics with Solar Orbiter/SPICE
Authors: Zambrana Prado, N.; Buchlin, E.; Peter, H.; Young, P. R.;
Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Aznar Cuadrado,
R.; Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra,
L.; Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller,
D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Sidher, S.; Teriaca,
L.; Thompson, W. T.; Williams, D.
Bibcode: 2020AGUFMSH038..09Z
Altcode:
Linking solar activity on the surface and in the corona to the inner
heliosphere is one of Solar Orbiter's main goals. Its UV spectrometer
SPICE (SPectral Imaging of the Coronal Environment) will provide
relative abundance measurements which will be key in this quest
as different structures on the Sun have different abundances as a
consequence of the FIP (First Ionization Potential) effect. Solar
Orbiter's unique combination of remote sensing and in-situ instruments
coupled with observation from other missions such as Parker Solar
Probe will allow us to compare in-situ and remote sensing composition
data. With the addition of modeling, these new results will allow us
to trace back the source of heliospheric plasma. As high telemetry
will not always be available with SPICE, we have developed a method
for measuring relative abundances that is both telemetry efficient
and reliable. Unlike methods based on Differential Emission Measure
(DEM) inversion, the Linear Combination Ratio (LCR) method does not
require a large number of spectral lines. This new method is based
on linear combinations of UV spectral lines. The coefficients of
the combinations are optimized such that the ratio of two linear
combinations of radiances would yield the relative abundance of two
elements. We present some abundance diagnostics tested on different
combinations of spectral lines observable by SPICE.
Title: Dynamics and thermal structure in the quiet Sun seen by SPICE
Authors: Peter, H.; Aznar Cuadrado, R.; Schühle, U.; Teriaca, L.;
Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Buchlin, E.;
Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.;
Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.;
Parenti, S.; Schmutz, W. K.; Sidher, S.; Thompson, W. T.; Williams,
D.; Young, P. R.
Bibcode: 2020AGUFMSH038..03P
Altcode:
We will present some of the early data of the Spectral Imaging of the
Coronal Environment (SPICE) instrument on Solar Orbiter. One of the
unique features of SPICE is its capability to record a wide range of
wavelengths in the extreme UV with the possibility to record spectral
lines giving access to a continuous plasma temperature range from 10.000
K to well above 1 MK. The data taken so far were for commissioning
purposes and they can be used for a preliminary evaluation of the
science performance of the instrument. Here we will concentrate on
sample spectra covering the whole wavelength region and on the early
raster maps acquired in bright lines in the quiet Sun close to disk
center. Looking at different quiet Sun features we investigate the
thermal structure of the atmosphere and flow structures. For this
we apply fits to the spectral profiles and check the performance in
terms of Doppler shifts and line widths to retrieve the structure of
the network in terms of dynamics. While the amount of data available
so far is limited, we will have a first look on how quiet Sun plasma
responds to heating events. For this, we will compare spectral lines
forming at different temperatures recorded at strictly the same time.
Title: First Results From SPICE EUV Spectrometer on Solar Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A. S.; Grundy, T.; Guest,
S.; Sidher, S.; Auchere, F.; Carlsson, M.; Hassler, D.; Peter, H.;
Aznar Cuadrado, R.; Buchlin, E.; Caminade, S.; DeForest, C.; Fredvik,
T.; Harra, L. K.; Janvier, M.; Kucera, T. A.; Leeks, S.; Mueller,
D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Teriaca, L.; Thompson,
W. T.; Tustain, S.; Williams, D.; Young, P. R.
Bibcode: 2020AGUFMSH038..02F
Altcode:
SPICE (Spectral Imaging of Coronal Environment) is one of the remote
sensing instruments onboard Solar Orbiter. It is an EUV imaging
spectrometer observing the Sun in two wavelength bands: 69.6-79.4 nm
and 96.6-105.1 nm. SPICE is capable of recording full spectra in these
bands with exposures as short as 1s. SPICE is the only Solar Orbiter
instrument that can measure EUV spectra from the disk and low corona
of the Sun and record all spectral lines simultaneously. SPICE uses
one of three narrow slits, 2"x11', 4''x11', 6''x11', or a wide slit
30''x14'. The primary mirror can be scanned in a direction perpendicular
to the slit, allowing raster images of up to 16' in size. We
present an overview of the first SPICE data taken on several days
during the instrument commissioning carried out by the RAL Space team
between 2020 April 21 and 2020 June 14. We also include results from
SPICE observations at the first Solar Orbiter perihelion at 0.52AU,
taken between June 16-21st. We give examples of full spectra
from the quiet Sun near disk centre and provide a list of key spectral
lines emitted in a range of temperatures between 10,000 K and over 1
million K, from neutral hydrogen and ions of carbon, oxygen, nitrogen,
neon, sulphur and magnesium. We show examples of first raster images
in several strong lines, obtained with different slits and a range
of exposure times between 5s and 180s. We describe the temperature
coverage and density diagnostics, determination of plasma flows, and
discuss possible applications to studies of the elemental abundances
in the corona. We also show the first off-limb measurements with SPICE,
as obtained when the spacecraft pointed at the limb.
Title: Metis - Solar Orbiter Topical Team on "Modelling of CME
propagation/evolution in corona and solar wind in connection with
Space Weather"
Authors: Bemporad, A.; Banerjee, D.; Berlicki, A.; Biondo, R.; Boe,
B.; Calchetti, D.; Capuano, G.; De Leo, Y.; Del Moro, D.; Feng, L.;
Foldes, R.; Frassati, F.; Frazin, R. A.; Giovannelli, L.; Giunta,
A. S.; Heinzel, P.; Ippolito, A.; Janvier, M.; Jerse, G.; Kilpua,
K. E. J.; Laurenza, M.; Lloveras, D.; Magdalenic, J.; Mancuso, S.;
Messerotti, M.; Mierla, M.; Nandy, D.; Napoletano, G.; Nuevo, F.;
Pagano, P.; Pinto, R.; Plainaki, C.; Reale, F.; Romoli, M.; Rodriguez,
L.; Slemer, A.; Spadaro, D.; Susino, R.; Stangalini, M.; Vainio,
R. O.; Valori, G.; Vásquez, A. M.; West, M. J.
Bibcode: 2020AGUFMSH0360027B
Altcode:
Despite the current availability of multi-spacecraft observations of
Coronal Mass Ejections (CMEs) and their interplanetary counterpart
(ICMEs), at present we still don't understand which physical phenomena
are driving their expansion and propagation phases. This also limits
our understanding on how CMEs (observed with remote sensing data)
become ICMEs (observed in situ), how they interact with the background
solar wind, and how their final geo-effectiveness can be modified
during their interplanetary evolution. Such problems match some of
the scientific objectives of the Solar Orbiter Science Activity Plan
and of the Metis coronagraph. Thanks to its multi-channel capability,
Metis (acquiring images in the visible light and at the same time in
the UV HI Lyman-alpha emission) will really provide an unprecedented
view of CMEs and in particular of their thermodynamic evolution. At
closest approaches to the Sun (in the nominal mission), Metis will
acquire high spatial resolution and/or temporal cadence multi-channel
images of CMEs. Farther from the Sun, Metis will shed light on the
early Interplanetary propagation of CMEs. Later on (in the extended
mission) Metis will observe for the first time the CME/ICME propagation
out-of-ecliptic. These novelties will be combined with the unique
vantage point that will be offered by the Solar Orbiter spacecraft,
and supported with valuable data acquired by other on-board remote
sensing (e.g. SPICE, EUI, SoloHI) and in situ (e.g. EPD, MAG,
SWA, RPW) instruments. In this contribution we present the ongoing
activities of the Metis Topical Team on "CME/ICME propagation", (http://metis.oato.inaf.it/topical_teams.html),
an international working group recently established and gathering
scientists from different countries, experts of both in-situ and remote
sensing observations, as well as numerical simulations, and we summarize
the main science objectives discussed during the last months.
Title: Calibrating optical distortions in the Solar Orbiter SPICE
spectrograph
Authors: Thompson, W. T.; Schühle, U.; Young, P. R.; Auchere, F.;
Carlsson, M.; Fludra, A.; Hassler, D.; Peter, H.; Aznar Cuadrado, R.;
Buchlin, E.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.;
Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.;
Parenti, S.; Caminade, S.; Schmutz, W. K.; Teriaca, L.; Williams,
D.; Sidher, S.
Bibcode: 2020AGUFMSH0360029T
Altcode:
The Spectral Imaging of the Coronal Environment (SPICE) instrument on
Solar Orbiter is a high-resolution imaging spectrometer operating
at extreme ultraviolet (EUV) wavelengths from 70.4-79.0 nm and
97.3-104.9 nm. A single-mirror off-axis paraboloid focuses the solar
image onto the entrance slit of the spectrometer section. A Toroidal
Variable Line Space (TVLS) grating images the entrance slit onto a
pair of MCP-intensified APS detectors. Ray-tracing analysis prior
to launch showed that the instrument was subject to a number of
small image distortions which need to be corrected in the final data
product. We compare the ray tracing results with measurements made in
flight. Co-alignment with other telescopes on Solar Orbiter will also
be examined.
Title: First results from the EUI and SPICE observations of Alpha
Leo near Solar Orbiter first perihelion
Authors: Buchlin, E.; Teriaca, L.; Giunta, A. S.; Grundy, T.; Andretta,
V.; Auchere, F.; Peter, H.; Berghmans, D.; Carlsson, M.; Fludra, A.;
Harra, L.; Hassler, D.; Long, D.; Rochus, P. L.; Schühle, U.; Aznar
Cuadrado, R.; Caldwell, M.; Caminade, S.; DeForest, C.; Fredvik, T.;
Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp, E.; Kucera, T. A.;
Müller, D.; Parenti, S.; Schmutz, W. K.; Sidher, S.; Smith, P.;
Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
Bibcode: 2020AGUFMSH0360024B
Altcode:
On June 16th 2020 Solar Orbiter made a dedicated observing campaign
where the spacecraft pointed to the solar limb to allow some of the
high resolution instruments to observe the ingress (at the east limb)
and later the egress (west limb) of the occultation of the star Alpha
Leonis by the solar disk. The star was chosen because its luminosity and
early spectral type ensure high and stable flux at wavelengths between
100 and 122 nanometers, a range observed by the High Resolution EUI
Lyman alpha telescope (HRI-LYA) and by the long wavelength channel
of the SPICE spectrograph. Star observations, when feasible, allow
to gather a great deal of information on the instrument performances,
such as the radiometric performance and the instrument optical point
spread function (PSF). We report here the first results from the
above campaign for the two instruments.
Title: First results from combined EUI and SPICE observations of
Lyman lines of Hydrogen and He II
Authors: Teriaca, L.; Aznar Cuadrado, R.; Giunta, A. S.; Grundy, T.;
Parenti, S.; Auchere, F.; Vial, J. C.; Fludra, A.; Berghmans, D.;
Carlsson, M.; Harra, L.; Hassler, D.; Long, D.; Peter, H.; Rochus,
P. L.; Schühle, U.; Buchlin, E.; Caldwell, M.; Caminade, S.; DeForest,
C.; Fredvik, T.; Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp,
E.; Kucera, T. A.; Mueller, D.; Schmutz, W. K.; Sidher, S.; Smith, P.;
Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
Bibcode: 2020AGUFMSH0360003T
Altcode:
The Solar Orbiter spacecraft carries a powerful set of remote
sensing instruments that allow studying the solar atmosphere with
unprecedented diagnostic capabilities. Many such diagnostics require
the simultaneous usage of more than one instrument. One example of that
is the capability, for the first time, to obtain (near) simultaneous
spatially resolved observations of the emission from the first three
lines of the Lyman series of hydrogen and of He II Lyman alpha. In fact,
the SPectral Imaging of the Coronal Environment (SPICE) spectrometer
can observe the Lyman beta and gamma lines in its long wavelength
(SPICE-LW) channel, the High Resolution Lyman Alpha (HRI-LYA) telescope
of the Extreme Ultraviolet Imager (EUI) acquires narrow band images in
the Lyman alpha line while the Full Disk Imager (FSI) of EUI can take
images dominated by the Lyman alpha line of ionized Helium at 30.4 nm
(FSI-304). Being hydrogen and helium the main components of our star,
these very bright transitions play an important role in the energy
budget of the outer atmosphere via radiative losses and the measurement
of their profiles and radiance ratios is a fundamental constraint to
any comprehensive modelization effort of the upper solar chromosphere
and transition region. Additionally, monitoring their average ratios
can serve as a check out for the relative radiometric performance of
the two instruments throughout the mission. Although the engineering
data acquired so far are far from ideal in terms of time simultaneity
(often only within about 1 h) and line coverage (often only Lyman beta
was acquired by SPICE and not always near simultaneous images from all
three telescopes are available) the analysis we present here still
offers a great opportunity to have a first look at the potential of
this diagnostic from the two instruments. In fact, we have identified
a series of datasets obtained at disk center and at various positions
at the solar limb that allow studying the Lyman alpha to beta radiance
ratio and their relation to He II 30.4 as a function of the position
on the Sun (disk center versus limb and quiet Sun versus coronal holes).
Title: 20 Years of ACE Data: How Superposed Epoch Analyses Reveal
Generic Features in Interplanetary CME Profiles
Authors: Regnault, F.; Janvier, M.; Démoulin, P.; Auchère, F.;
Strugarek, A.; Dasso, S.; Noûs, C.
Bibcode: 2020JGRA..12528150R
Altcode: 2020arXiv201105050R
Interplanetary coronal mass ejections (ICMEs) are magnetic structures
propagating from the Sun's corona to the interplanetary medium. With
over 20 years of observations at the L1 libration point, ACE offers
hundreds of ICMEs detected at different times during several solar
cycles and with different features such as the propagation speed. We
investigate a revisited catalog of more than 400 ICMEs using the
superposed epoch method on the mean, median, and the most probable
values of the distribution of magnetic and plasma parameters. We also
investigate the effects of the speed of ICMEs relative to the solar
wind, the solar cycle, and the existence of a magnetic cloud on the
generic ICME profile. We find that fast-propagating ICMEs (relatively
to the solar wind in front) still show signs of compression at 1 au, as
seen by the compressed sheath and the asymmetric profile of the magnetic
field. While the solar cycle evolution does not impact the generic
features of ICMEs, there are more extreme events during the active part
of the cycle, widening the distributions of all parameters. Finally, we
find that ICMEs with or without a detected magnetic cloud show similar
profiles, which confirms the hypothesis that ICMEs with no detected
magnetic clouds are crossed further away from the flux rope core. Such
a study provides a generic understanding of processes that shape the
overall features of ICMEs in the solar wind and can be extended with
future missions at different locations in the solar system.
Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
Bibcode: 2020A&A...642A...2R
Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk.
Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies.
Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter.
Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission.
Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
Bibcode: 2020A&A...642A...3Z
Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
Title: The Solar Orbiter SPICE instrument. An extreme UV imaging
spectrometer
Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.;
Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini,
K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.;
Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.;
Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau,
J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.;
Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest,
S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler,
D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller,
S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall,
G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris,
N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.;
Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.;
Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy,
B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.;
Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial,
J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward,
S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D.
Bibcode: 2020A&A...642A..14S
Altcode: 2019arXiv190901183A; 2019arXiv190901183S
Aims: The Spectral Imaging of the Coronal Environment (SPICE)
instrument is a high-resolution imaging spectrometer operating at
extreme ultraviolet wavelengths. In this paper, we present the concept,
design, and pre-launch performance of this facility instrument on the
ESA/NASA Solar Orbiter mission.
Methods: The goal of this paper
is to give prospective users a better understanding of the possible
types of observations, the data acquisition, and the sources that
contribute to the instrument's signal.
Results: The paper
discusses the science objectives, with a focus on the SPICE-specific
aspects, before presenting the instrument's design, including optical,
mechanical, thermal, and electronics aspects. This is followed by a
characterisation and calibration of the instrument's performance. The
paper concludes with descriptions of the operations concept and data
processing.
Conclusions: The performance measurements of the
various instrument parameters meet the requirements derived from the
mission's science objectives. The SPICE instrument is ready to perform
measurements that will provide vital contributions to the scientific
success of the Solar Orbiter mission.
Title: Magnetic field fluctuation properties of coronal mass
ejection-driven sheath regions in the near-Earth solar wind
Authors: Kilpua, Emilia K. J.; Fontaine, Dominique; Good, Simon W.;
Ala-Lahti, Matti; Osmane, Adnane; Palmerio, Erika; Yordanova, Emiliya;
Moissard, Clement; Hadid, Lina Z.; Janvier, Miho
Bibcode: 2020AnGeo..38..999K
Altcode:
In this work, we investigate magnetic field fluctuations in
three coronal mass ejection (CME)-driven sheath regions at 1 AU,
with their speeds ranging from slow to fast. The data set we use
consists primarily of high-resolution (0.092 s) magnetic field
measurements from the Wind spacecraft. We analyse magnetic field
fluctuation amplitudes, compressibility, and spectral properties of
fluctuations. We also analyse intermittency using various approaches;
we apply the partial variance of increments (PVIs) method, investigate
probability distribution functions of fluctuations, including their
skewness and kurtosis, and perform a structure function analysis. Our
analysis is conducted separately for three different subregions
within the sheath and one in the solar wind ahead of it, each 1 h
in duration. We find that, for all cases, the transition from the
solar wind ahead to the sheath generates new fluctuations, and the
intermittency and compressibility increase, while the region closest to
the ejecta leading edge resembled the solar wind ahead. The spectral
indices exhibit large variability in different parts of the sheath
but are typically steeper than Kolmogorov's in the inertial range. The
structure function analysis produced generally the best fit with the
extended p model, suggesting that turbulence is not fully developed
in CME sheaths near Earth's orbit. Both Kraichnan-Iroshinikov and
Kolmogorov's forms yielded high intermittency but different spectral
slopes, thus questioning how well these models can describe turbulence
in sheaths. At the smallest timescales investigated, the spectral
indices indicate shallower than expected slopes in the dissipation
range (between -2 and -2.5), suggesting that, in CME-driven sheaths
at 1 AU, the energy cascade from larger to smaller scales could still
be ongoing through the ion scale. Many turbulent properties of sheaths
(e.g. spectral indices and compressibility) resemble those of the slow
wind rather than the fast. They are also partly similar to properties
reported in the terrestrial magnetosheath, in particular regarding
their intermittency, compressibility, and absence of Kolmogorov's type
turbulence. Our study also reveals that turbulent properties can vary
considerably within the sheath. This was particularly the case for the
fast sheath behind the strong and quasi-parallel shock, including a
small, coherent structure embedded close to its midpoint. Our results
support the view of the complex formation of the sheath and different
physical mechanisms playing a role in generating fluctuations in them.
Title: Contribution of the ageing effect to the observed asymmetry
of interplanetary magnetic clouds
Authors: Démoulin, P.; Dasso, S.; Lanabere, V.; Janvier, M.
Bibcode: 2020A&A...639A...6D
Altcode: 2020arXiv200505049D
Context. Large magnetic structures are launched away from the
Sun during solar eruptions. They are observed as (interplanetary)
coronal mass ejections (ICMEs or CMEs) with coronal and heliospheric
imagers. A fraction of them are observed in situ as magnetic clouds
(MCs). Fitting these structures properly with a model requires a better
understanding of their evolution.
Aims: In situ measurements
are made locally when the spacecraft trajectory crosses the magnetic
configuration. These observations are taken for different elements
of plasma and at different times, and are therefore biased by the
expansion of the magnetic configuration. This ageing effect means that
stronger magnetic fields are measured at the front than at the rear of
MCs. This asymmetry is often present in MC data. However, the question
is whether the observed asymmetry can be explained quantitatively from
the expansion alone.
Methods: Based on self-similar expansion,
we derived a method for estimating the expansion rate from the observed
plasma velocity. We next corrected the observed magnetic field and
the spatial coordinate along the spacecraft trajectory for the ageing
effect. This provided corrected data as in the case when the MC internal
structure were observed at the same time.
Results: We apply the
method to 90 best-observed MCs near Earth (1995-2012). The ageing effect
is the main source of the observed magnetic asymmetry for only 28%
of the MCs. After correcting for the ageing effect, the asymmetry is
almost symmetrically distributed between MCs with a stronger magnetic
field at the front and those at the rear of MCs.
Conclusions:
The proposed method can efficiently remove the ageing bias within
in situ data of MCs, and more generally, of ICMEs. This allows us
to analyse the data with a spatial coordinate, such as in models or
remote-sensing observations.
Title: Using Forbush decreases at Earth and Mars to measure the
radial evolution of ICMEs
Authors: von Forstner, Johan; Guo, Jingnan; Wimmer-Schweingruber,
Robert F.; Dumbović, Mateja; Janvier, Miho; Démoulin, Pascal;
Veronig, Astrid; Temmer, Manuela; Papaioannou, Athanasios; Dasso,
Sergio; Hassler, Donald M.; Zeitlin, Cary J.
Bibcode: 2020EGUGA..22.7838V
Altcode:
Interplanetary coronal mass ejections (ICMEs), large clouds of plasma
and magnetic field regularly expelled from the Sun, are one of the
main drivers of space weather effects in the solar system. While
the prediction of their arrival time at Earth and other locations
in the heliosphere is still a complex task, it is also necessary to
further understand the time evolution of their geometric and magnetic
structure, which is even more challenging considering the limited number
of available observation points.Forbush decreases (FDs), short-term
drops in the flux of galactic cosmic rays (GCR), can be caused by the
shielding from strong and/or turbulent magnetic structures in the solar
wind, such as ICMEs and their associated shock/sheath regions. In the
past, FD observations have often been used to determine the arrival
times of ICMEs at different locations in the solar system, especially
where sufficient solar wind plasma and magnetic field measurements are
not (or not always) available. One of these locations is Mars, where the
Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory
(MSL) mission's Curiosity rover has been continuously measuring GCRs and
FDs on the surface for more than 7 years.In this work, we investigate
whether FD data can be used to derive additional information about the
ICME properties than just the arrival time by performing a statistical
study based on catalogs of FDs observed at Earth or Mars. In particular,
we find that the linear correlation between the FD amplitude and the
maximum steepness, which was already seen at Earth by previous authors
(Belov et al., 2008, Abunin et al., 2012), is likewise present at Mars,
but with a different proprtionality factor.By consulting physics-based
analytical models of FDs, we find that this quantity is not expected to
be influenced by the different energy ranges of GCR particles observed
by the instruments at Earth and Mars. Instead, we suggest that the
difference in FD characteristics at the two planets is caused by the
radial enlargement of the ICMEs, and particularly their sheath regions,
as they propagate from Earth (1 AU) to Mars (~ 1.5 AU). This broadening
factor derived from our analysis extends observations for the evolution
closer to the Sun by Janvier et al. (2019, JGR Space Physics) to larger
heliocentric distances and is consistent with these results.
Title: BepiColombo and Solar Orbiter coordinated observations:
scientific cases and measurements opportunities
Authors: Hadid, Lina; Dosa, Melinda; Akos, Madar; Alberti, Tommaso;
Benkhoff, Johannes; Bebesi, Zsofia; Griton, Lea; Ho, George C.; Iwai,
Kazumasa; Janvier, Miho; Milillo, Anna; Miyoshi, Yoshizumi; Mueller,
Daniel; Murukami, Go; Raines, Jim M.; Shiota, Daikou; Walsh, Andrew;
Zender, Joe; Zouganelis, Yannis
Bibcode: 2020EGUGA..2217957H
Altcode:
BepiColombo and Solar Orbiter are two spacecraft that will be
both travelling in the inner heliosphere for 5 years, between the
launch of Solar Orbiter (planned in February 2020) and the end of
the cruise phase of BepiColombo (2018 - 2025). Both BepiColombo
(ESA/JAXA) and Solar Orbiter (ESA/NASA) are carrying exceptional and
complementary plasma instrumental payloads and magnetometers. Besides,
the remote-sensing instruments on board of Solar Orbiter will provide
invaluable information on the state of the Sun, and therefore some
contextual information for BepiColombo observations. During the
five years to come, BepiColombo will evolve between the Earth and
the orbit of Mercury, while Solar Orbiter's highly elliptical orbit
will cover distances from 1.02 AU to 0.28 AU. We present here the
scientific cases, modelling tools, measurement opportunities and
related instruments operations that have been identified in the frame
of potential coordinated observations campaign between the spacecraft.
Title: Electric Current Evolution at the Footpoints of Solar Eruptions
Authors: Barczynski, Krzysztof; Aulanier, Guillaume; Janvier, Miho;
Schmieder, Brigitte; Masson, Sophie
Bibcode: 2020ApJ...895...18B
Altcode: 2020arXiv200407990B
Electric currents play a critical role in the triggering of solar
flares and their evolution. The aim of the present paper is to test
whether the surface electric current has a surface or subsurface
fixed source as predicted by the circuit approach of flare physics,
or is the response of the surface magnetic field to the evolution of
the coronal magnetic field as the MHD approach proposes? Out of all 19
X-class flares observed by SDO from 2011 to 2016 near the disk center,
we analyzed the only nine eruptive flares for which clear ribbon hooks
were identifiable. Flare ribbons with hooks are considered to be the
footprints of eruptive flux ropes in MHD flare models. For the first
time, fine measurements of the time evolution of electric currents
inside the hooks in the observations as well as in the OHM 3D MHD
simulation are performed. Our analysis shows a decrease of the electric
current in the area surrounded by the ribbon hooks during and after the
eruption. We interpret the decrease of the electric currents as due to
the expansion of the flux rope in the corona during the eruption. Our
analysis brings a new contribution to the standard flare model in 3D.
Title: Magnetic twist profile inside magnetic clouds derived with
a superposed epoch analysis
Authors: Lanabere, V.; Dasso, S.; Démoulin, P.; Janvier, M.;
Rodriguez, L.; Masías-Meza, J. J.
Bibcode: 2020A&A...635A..85L
Altcode: 2020arXiv200210606L
Context. Magnetic clouds (MCs) are large-scale interplanetary
transient structures in the heliosphere that travel from the Sun
into the interplanetary medium. The internal magnetic field lines
inside the MCs are twisted, forming a flux rope (FR). This magnetic
field structuring is determined by its initial solar configuration,
by the processes involved during its eruption from the Sun, and
by the dynamical evolution during its interaction with the ambient
solar wind.
Aims: One of the most important properties of the
magnetic structure inside MCs is the twist of the field lines forming
the FR (the number of turns per unit length). The detailed internal
distribution of twist is under debate mainly because the magnetic
field (B) in MCs is observed only along the spacecraft trajectory,
and thus it is necessary to complete observations with theoretical
assumptions. Estimating the twist from the study of a single event
is difficult because the field fluctuations significantly increase
the noise of the observed B time series and thus the bias of the
deduced twist.
Methods: The superposed epoch applied to MCs
has proven to be a powerful technique, permitting the extraction of
their common features, and removing the peculiarity of individual
cases. We apply a superposed epoch technique to analyse the magnetic
components in the local FR frame of a significant sample of moderately
asymmetric MCs observed at 1 au.
Results: From the superposed
profile of B components in the FR frame, we determine the typical
twist distribution in MCs. The twist is nearly uniform in the FR core
(central half part), and it increases moderately, up to a factor two,
towards the MC boundaries. This profile is close to the Lundquist field
model limited to the FR core where the axial field component is above
about one-third of its central value.
Title: Comparing the Properties of ICME-Induced Forbush Decreases
at Earth and Mars
Authors: Freiherr von Forstner, Johan L.; Guo, Jingnan;
Wimmer-Schweingruber, Robert F.; Dumbović, Mateja; Janvier, Miho;
Démoulin, Pascal; Veronig, Astrid; Temmer, Manuela; Papaioannou,
Athanasios; Dasso, Sergio; Hassler, Donald M.; Zeitlin, Cary J.
Bibcode: 2020JGRA..12527662F
Altcode: 2020arXiv200303157V
Forbush decreases (FDs), which are short-term drops in the flux
of galactic cosmic rays, are caused by the shielding from strong
and/or turbulent magnetic structures in the solar wind, especially
interplanetary coronal mass ejections (ICMEs) and their associated
shocks, as well as corotating interaction regions. Such events can be
observed at Earth, for example, using neutron monitors, and also at
many other locations in the solar system, such as on the surface of
Mars with the Radiation Assessment Detector instrument onboard Mars
Science Laboratory. They are often used as a proxy for detecting the
arrival of ICMEs or corotating interaction regions, especially when
sufficient in situ solar wind measurements are not available. We
compare the properties of FDs observed at Earth and Mars, focusing
on events produced by ICMEs. We find that FDs at both locations show
a correlation between their total amplitude and the maximum hourly
decrease, but with different proportionality factors. We explain this
difference using theoretical modeling approaches and suggest that it is
related to the size increase of ICMEs, and in particular their sheath
regions, en route from Earth to Mars. From the FD data, we can derive
the sheath broadening factor to be between about 1.5 and 1.9, agreeing
with our theoretical considerations. This factor is also in line with
previous measurements of the sheath evolution closer to the Sun.
Title: Comparing the Properties of ICME-Induced Forbush Decreases
at Earth and Mars
Authors: Freiherr von Forstner, J. L.; Guo, J.; Wimmer-Schweingruber,
R. F.; Dumbovic, M.; Janvier, M.; Demoulin, P.; Veronig, A.; Temmer,
M.; Hassler, D.; Zeitlin, C.
Bibcode: 2019AGUFMSH41D3339F
Altcode:
Forbush decreases (FDs), short-term drops in the flux of galactic
cosmic rays (GCR), can be caused by the shielding from strong and/or
turbulent magnetic structures in the solar wind, i.e. interplanetary
coronal mass ejections (ICMEs) and their associated shocks as well
as corotating interaction regions (CIRs). FDs are often used as a
proxy for detecting the arrival of ICMEs or CIRs at locations where
sufficient in situ solar wind measurements are not or not always
available, such as at Mars. The Radiation Assessment Detector (RAD)
onboard the Mars Science Laboratory (MSL) mission's Curiosity rover
has been continuously measuring the GCR environment on the surface
of Mars for more than 7 years since its landing in August 2012 and is
thus an excellent source for measurements of FDs at Mars (see e.g. Guo et al. 2018,
A&A). Based on the large catalog of FDs at Mars compiled
by Papaioannou et
al. (2019, Solar Physics) as well as results from our previous
work (Freiherr von
Forstner et al., 2019, Space Weather), we study the parameters
of FDs at Mars and their relations, focusing on events produced by
ICMEs. We then compare these data with catalogs of terrestrial FDs,
investigating whether and to what extent the differences of certain FD
characteristics between the two planets, at two different heliospheric
distances, are related to the evolution of ICMEs between Earth and
Mars. Our results show that there is a linear correlation between
the FD amplitude (drop percentage) and the maximum hourly GCR decrease
during the FD, which was already found at Earth by previous authors (Belov et al., 2008,
Abunin et al.,
2012). However, this correlation has a different proprtionality
factor at Mars than at Earth, especially for ICME-induced events. As
we do not find a clear dependence of this relationship on the observed
GCR energy range, we suggest that this difference is probably caused by
the expansion of the ICME sheath region as it propagates outward from
1 AU to ∼1.5 AU. The expansion factor derived from our analysis is in
line with expansion factors of ICME sheaths within the inner heliosphere
observed by <a href="https://doi.org/10.1029/2018JA025949>Janvier
et al. (2019, JGR Space Physics).
Title: Re-analysis of Lepping's Fitting Method for Magnetic Clouds:
Lundquist Fit Reloaded
Authors: Démoulin, Pascal; Dasso, Sergio; Janvier, Miho; Lanabere,
Vanina
Bibcode: 2019SoPh..294..172D
Altcode: 2019arXiv191209829D
Magnetic clouds (MCs) are a subset of ejecta, launched from the Sun as
coronal mass ejections. The coherent rotation of the magnetic field
vector observed in MCs leads to envision MCs as formed by flux ropes
(FRs). Among all the methods used to analyze MCs, Lepping's method
(Lepping, Burlaga, and Jones in J. Geophys. Res.95, 11957, 1990) is the
broadest used. While this fitting method does not require the axial
field component to vanish at the MC boundaries, this idea is largely
spread in publications. We revisit Lepping's method to emphasize its
hypothesis and the meaning of its output parameters. As originally
defined, these parameters imply a fitted FR which could be smaller
or larger than the studied MC. We rather provide a re-interpretation
of Lepping's results with a fitted model limited to the observed
MC interval. We find that typically the crossed FRs are asymmetric
with a larger side both in size and magnetic flux before or after
the FR axis. At the boundary of the largest side we find an axial
magnetic field component distributed around zero which we justify by
the physics of solar eruptions. In contrast, at the boundary of the
smaller side the axial field distribution is shifted to positive values,
as expected with erosion acting during the interplanetary travel. This
new analysis of Lepping's results has several implications. First,
global quantities, such as magnetic fluxes and helicity, need to be
revised depending on the aim (estimating global properties of FRs just
after the solar launch or at 1 au). Second, the deduced twist profiles
in MCs range quasi-continuously from nearly uniform, to increasing
away from the FR axis, up to a reversal near the MC boundaries. There
is no trace of outsider cases, but a continuum of cases. Finally, the
impact parameter of the remaining FR crossed at 1 au is revised. Its
distribution is compatible with weakly flattened FR cross-sections.
Title: Using U-Nets to Create High-Fidelity Virtual Observations of
the Solar Corona
Authors: Salvatelli, Valentina; Bose, Souvik; Neuberg, Brad; dos
Santos, Luiz F. G.; Cheung, Mark; Janvier, Miho; Gunes Baydin, Atilim;
Gal, Yarin; Jin, Meng
Bibcode: 2019arXiv191104006S
Altcode:
Understanding and monitoring the complex and dynamic processes of
the Sun is important for a number of human activities on Earth and
in space. For this reason, NASA's Solar Dynamics Observatory (SDO)
has been continuously monitoring the multi-layered Sun's atmosphere
in high-resolution since its launch in 2010, generating terabytes of
observational data every day. The synergy between machine learning
and this enormous amount of data has the potential, still largely
unexploited, to advance our understanding of the Sun and extend the
capabilities of heliophysics missions. In the present work, we show that
deep learning applied to SDO data can be successfully used to create a
high-fidelity virtual telescope that generates synthetic observations of
the solar corona by image translation. Towards this end we developed
a deep neural network, structured as an encoder-decoder with skip
connections (U-Net), that reconstructs the Sun's image of one instrument
channel given temporally aligned images in three other channels. The
approach we present has the potential to reduce the telemetry needs
of SDO, enhance the capabilities of missions that have less observing
channels, and transform the concept development of future missions.
Title: Auto-Calibration of Remote Sensing Solar Telescopes with
Deep Learning
Authors: Neuberg, Brad; Bose, Souvik; Salvatelli, Valentina; dos
Santos, Luiz F. G.; Cheung, Mark; Janvier, Miho; Gunes Baydin, Atilim;
Gal, Yarin; Jin, Meng
Bibcode: 2019arXiv191104008N
Altcode:
As a part of NASA's Heliophysics System Observatory (HSO) fleet of
satellites,the Solar Dynamics Observatory (SDO) has continuously
monitored the Sun since2010. Ultraviolet (UV) and Extreme UV (EUV)
instruments in orbit, such asSDO's Atmospheric Imaging Assembly
(AIA) instrument, suffer time-dependent degradation which reduces
instrument sensitivity. Accurate calibration for (E)UV instruments
currently depends on periodic sounding rockets, which are infrequent
and not practical for heliophysics missions in deep space. In the
present work, we develop a Convolutional Neural Network (CNN) that
auto-calibrates SDO/AIA channels and corrects sensitivity degradation
by exploiting spatial patterns in multi-wavelength observations to
arrive at a self-calibration of (E)UV imaging instruments. Our results
remove a major impediment to developing future HSOmissions of the
same scientific caliber as SDO but in deep space, able to observe the
Sun from more vantage points than just SDO's current geosynchronous
orbit.This approach can be adopted to perform autocalibration of other
imaging systems exhibiting similar forms of degradation
Title: The in situ Solar Wind and Galactic Cosmic Ray correlation
at Mars and its comparison with Earth observations
Authors: Guo, Jingnan; Temmer, Manuela; Veronig, Astrid; Janvier,
Miho; Hofmeister, Stefan; Wimmer-Schweingruber, Robert; Halekas, Jasper
Bibcode: 2019EGUGA..21.9366G
Altcode:
The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have
been observing the in situ solar wind properties since its arrival to
Mars at the end of 2014. Together with the Galactic Cosmic Ray (GCR)
observation continuously monitored by the Radiation Assessment Detector
(RAD) on the Martian ground, we are able to analyze the correlation of
the solar wind evolution and the modulated GCR variations at Mars. The
transient variations (mostly observed as short-term decreases) in
these in situ observations are usually related to either the impact
of Coronal Mass Ejections (CMEs) erupted from Solar active regions or
the pass-by of High Speed Streams (HSS) in the solar wind arising from
Coronal Holes (CHs) on the Sun. During the opposition phase in 2016
when Earth and Mars were radially aligned on the same side of the Sun,
we observe the stable evolution of a few CHs on the solar surface over
several solar rotations and analyze the re-current in situ solar wind
and GCR signatures at both Earth and Mars.
Title: Solar data, dataproducts, and tools at MEDOC
Authors: Buchlin, Eric; Caminade, Stéphane; Dufourg, Nicolas;
Auchère, Frédéric; Baudin, Frédéric; Bocchialini, Karine;
Boumier, Patrick; Janvier, Miho; Parenti, Susanna; Alingery, Pablo;
Ballans, Hervé; Chane-Yook, Martine; Dexet, Marc; Mercier, Claude;
Poulleau, Gilles
Bibcode: 2019EGUGA..2117362B
Altcode:
MEDOC (Multi-Experiment Data and Operation Centre), initially created
as a European data and operation centre for the SOHO mission, has
grown with data from other solar physics space missions, from STEREO
to SDO. Derived data products such as DEM maps from SDO/AIA, synoptic
EUV intensity maps from SOHO/EIT, and catalogues of solar structures
are also automatically produced and redistributed. Both the data and
the derived data products are publicly available from web interfaces
and from programmatic interfaces (with clients for IDL and Python),
allowing classical data analysis as well as automatic queries, data
download, and processing to be made on large datasets.
Title: Generalization of the Magnetic Field Configuration of Typical
and Atypical Confined Flares
Authors: Joshi, Navin Chandra; Zhu, Xiaoshuai; Schmieder, Brigitte;
Aulanier, Guillaume; Janvier, Miho; Joshi, Bhuwan; Magara, Tetsuya;
Chandra, Ramesh; Inoue, Satoshi
Bibcode: 2019ApJ...871..165J
Altcode: 2018arXiv181101228J
Atypical flares cannot be naturally explained with standard models. To
predict such flares, we need to define their physical characteristics,
in particular, their magnetic environment, and identify pairs of
reconnected loops. Here, we present in detail a case study of a confined
flare preceded by flux cancellation that leads to the formation of a
filament. The slow rise of the noneruptive filament favors the growth
and reconnection of overlying loops. The flare is only of C5.0 class
but it is a long duration event. The reason is that it is comprised
of three successive stages of reconnection. A nonlinear force-free
field extrapolation and a magnetic topology analysis allow us to
identify the loops involved in the reconnection process and build a
reliable scenario for this atypical confined flare. The main result
is that a curved magnetic polarity inversion line in active regions
is a key ingredient for producing such atypical flares. A comparison
with previous extrapolations for typical and atypical confined flares
leads us to propose a cartoon for generalizing the concept.
Title: Generic Magnetic Field Intensity Profiles of Interplanetary
Coronal Mass Ejections at Mercury, Venus, and Earth From Superposed
Epoch Analyses
Authors: Janvier, Miho; Winslow, Reka M.; Good, Simon; Bonhomme,
Elise; Démoulin, Pascal; Dasso, Sergio; Möstl, Christian; Lugaz,
Noé; Amerstorfer, Tanja; Soubrié, Elie; Boakes, Peter D.
Bibcode: 2019JGRA..124..812J
Altcode: 2019arXiv190109921J
We study interplanetary coronal mass ejections (ICMEs) measured by
probes at different heliocentric distances (0.3-1 AU) to investigate
the propagation of ICMEs in the inner heliosphere and determine how
the generic features of ICMEs change with heliospheric distance. Using
data from the MErcury Surface, Space ENvironment, GEochemistry, and
Ranging (MESSENGER), Venus Express and ACE spacecraft, we analyze with
the superposed epoch technique the profiles of ICME substructures,
namely, the sheath and the magnetic ejecta. We determine that the
median magnetic field magnitude in the sheath correlates well with
ICME speeds at 1 AU, and we use this proxy to order the ICMEs at all
spacecraft. We then investigate the typical ICME profiles for three
categories equivalent to slow, intermediate, and fast ICMEs. Contrary
to fast ICMEs, slow ICMEs have a weaker solar wind field at the front
and a more symmetric magnetic field profile. We find the asymmetry to
be less pronounced at Earth than at Mercury, indicating a relaxation
taking place as ICMEs propagate. We also find that the magnetic
field intensities in the wake region of the ICMEs do not go back
to the pre-ICME solar wind intensities, suggesting that the effects
of ICMEs on the ambient solar wind last longer than the duration of
the transient event. Such results provide an indication of physical
processes that need to be reproduced by numerical simulations of ICME
propagation. The samples studied here will be greatly improved by
future missions dedicated to the exploration of the inner heliosphere,
such as Parker Solar Probe and Solar Orbiter.
Title: Exploring the biases of a new method based on minimum variance
for interplanetary magnetic clouds
Authors: Démoulin, P.; Dasso, S.; Janvier, M.
Bibcode: 2018A&A...619A.139D
Altcode: 2018arXiv180900522D
Context. Magnetic clouds (MCs) are twisted magnetic structures ejected
from the Sun and probed by in situ instruments. They are typically
modeled as flux ropes (FRs).
Aims: Magnetic field measurements
are only available along the 1D spacecraft trajectory. The determination
of the FR global characteristics requires the estimation of the FR axis
orientation. Among the developed methods, the minimum variance (MV)
is the most flexible, and features only a few assumptions. However,
as other methods, MV has biases. We aim to investigate the limits
of the method and extend it to a less biased method.
Methods: We first identified the origin of the biases by testing
the MV method on cylindrical and elliptical models with a temporal
expansion comparable to the one observed in MCs. Then, we developed
an improved MV method to reduce these biases.
Results: In
contrast with many previous publications we find that the ratio of
the MV eigenvalues is not a reliable indicator of the precision of
the derived FR axis direction. Next, we emphasize the importance of
the FR boundaries selected since they strongly affect the deduced
axis orientation. We have improved the MV method by imposing that the
same amount of azimuthal flux should be present before and after the
time of closest approach to the FR axis. We emphasize the importance
of finding simultaneously the FR axis direction and the location of
the boundaries corresponding to a balanced magnetic flux, so as to
minimize the bias on the deduced FR axis orientation. This method
can also define an inner flux-balanced sub-FR. We show that the MV
results are much less biased when a compromize in size of this sub-FR
is achieved.
Conclusions: For weakly asymmetric field temporal
profiles, the improved MV provides a very good determination of the FR
axis orientation. The main remaining bias is moderate (lower than 6°)
and is present mostly on the angle between the flux rope axis and the
plane perpendicular to the Sun-Earth direction.
Title: On the Spatial Coherence of Magnetic Ejecta: Measurements
of Coronal Mass Ejections by Multiple Spacecraft Longitudinally
Separated by 0.01 au
Authors: Lugaz, Noé; Farrugia, Charles J.; Winslow, Reka M.;
Al-Haddad, Nada; Galvin, Antoinette B.; Nieves-Chinchilla, Teresa;
Lee, Christina O.; Janvier, Miho
Bibcode: 2018ApJ...864L...7L
Altcode: 2018arXiv181200911L
Measurements of coronal mass ejections (CMEs) by multiple spacecraft
at small radial separations but larger longitudinal separations is
one of the ways to learn about the three-dimensional structure of
CMEs. Here, we take advantage of the orbit of the Wind spacecraft that
ventured to distances of up to 0.012 au from the Sun-Earth line during
2000-2002. Combined with measurements from the Advanced Composition
Experiment, which is in a tight halo orbit around L1, the multipoint
measurements allow us to investigate how the magnetic field inside
magnetic ejecta (MEs) changes on scales of 0.005-0.012 au. We identify
21 CMEs measured by these two spacecraft for longitudinal separations of
0.007 au or more. We find that the time-shifted correlation between
30 minute averages of the non-radial magnetic field components
measured at the two spacecraft is systematically above 0.97 when the
separation is 0.008 au or less, but is on average 0.89 for greater
separations. Overall, these newly analyzed measurements, combined
with 14 additional ones when the spacecraft separation is smaller,
point toward a scale length of longitudinal magnetic coherence inside
MEs of 0.25-0.35 au for the magnitude of the magnetic field, but
0.06-0.12 au for the magnetic field components. This finding raises
questions about the very nature of MEs. It also highlights the need
for additional “mesoscale” multipoint measurements of CMEs with
longitudinal separations of 0.01-0.2 au.
Title: Manifestation of Coronal Mass Ejections near Earth: A review
Authors: Dasso, Sergio; Rodriguez, . Luciano, , dr.; Demoulin, Pascal;
Masias-Meza, Jimmy J.; Janvier, Miho; Lanabere, Vanina
Bibcode: 2018cosp...42E.768D
Altcode:
Coronal Mass Ejections (CMEs) are launched from the Sun, as a result of
magnetic instabilities, carrying away a huge amount of magnetic flux
and helicity. Interplanetary CMEs (ICMEs) are their manifestations
observed further away in the heliosphere. ICMEs contain different
plasma and magnetic field properties, compared with those of the
ambient solar wind. From the large number of observed ICMEs in the
past years, we significantly increased our knowledge on several of
their properties such as: their global 3D shape, the identification
of the composing sub-structures, the amount of magnetohydrodynamical
quantities transported, as well as how the plasma and magnetic field
are typically distributed inside them.In the present talk we will
present a general review of these aspects of ICMEs. In particular we
will focus on the total amount of magnetic flux and helicity ejected
by CMEs from the Sun along a solar cycle, and on plasma and magnetic
properties of their shock/sheath/flux-rope/wake. These results can
help to understand their interaction with the ambient solar wind and
with planetary magnetic environments. They are particularly crucial
for a better understanding of the Sun-Earth coupling.
Title: Signature of flux ropes before and after eruptions: electric
currents in active regions
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Dalmasse, Kévin;
Janvier, Miho; Gilchrist, Stuart; Zhao, Jie; Dudik, Jaroslav
Bibcode: 2018cosp...42E3026S
Altcode:
Solar observations, nonlinear force-free field extrapolations relying
on these observations, and three-dimensional magnetohydrodynamic (MHD)
models indicate the presence of electric currents in the pre-eruption
state and in the course of eruptions of solar magnetic structures which
are interpreted as flux ropes (sigmoids, filaments, cavities).The MHD
models are able to explain the net currents in active regions by the
existence of strong magnetic shear along the polarity inversion lines,
thus confirming previous observations. The models have also captured
the essence of the behavior of electric currents in active regions
during solar eruptions, predicting current-density increases and
decreases inside flare ribbons and in the interior of expanding flux
ropes, respectively.The observed photospheric current-density maps,
inferred from vector magnetic field observations, exhibit whirling
ribbon patterns similar to the MHD model results, which are interpreted
as the signatures of flux ropes and of quasi-separatrix layers (QSLs)
between the magnetic systems in active regions. We will show how
observations can confirm enhancement of the total current in these
QSLs during the eruptions, and how these observations can be used
to investigate whether current density decrease can be seen at the
footpoints of erupting flux ropes
Title: Constructing a Generic Icme from the Sun to Earth from
Statistical Studies of in Situ Data
Authors: Janvier, Miho; Dasso, Sergio; Demoulin, Pascal
Bibcode: 2018cosp...42E1600J
Altcode:
Interplanetary Coronal Mass Ejections (ICMEs) are detected in situ by
instruments measuring the magnetic field and plasma properties of the
ambient solar wind. In particular, a subset of ICMEs, referred to as
Magnetic Clouds (MCs), is well defined by the presence of a rotating
magnetic field, indicative of a twisted magnetic structure. Shocks,
on the other hand, are also well defined in the interplanetary medium
as sharp discontinuities in the plasma and magnetic properties. Both
structures then allow defining the presence of a sheath region between
the shock and the MC. Over the past years, we have proposed and refined
new statistical methods aiming at analyzing ICME properties, so as
to assess the existence of a generic shape and a generic internal
profile of ICMEs at different distances from the Sun. These methods
rely on the computation from the data of the distribution of the
shock normal and the flux-rope axis directions. From these analysis,
we were able to constrain an analytical shape that describes best these
observed distributions. Another method is a superposed epoch analysis
so as to obtain typical profiles of ICME substructures at different
distances from the Sun. Next, we compare such generic features of
ICMEs to numerical simulations and heliospheric images of CMEs. We
will discuss the commonalities, then the discrepancies that need to
be further understood between the models and the constraints given
by the in situ data. This is important in completing the scenario of
the evolution of solar eruptive flares, from their start in the Sun's
atmosphere to their evolution in the solar wind.
Title: French SKA White Book - The French Community towards the
Square Kilometre Array
Authors: Acero, F.; Acquaviva, J. -T.; Adam, R.; Aghanim, N.; Allen,
M.; Alves, M.; Ammanouil, R.; Ansari, R.; Araudo, A.; Armengaud, E.;
Ascaso, B.; Athanassoula, E.; Aubert, D.; Babak, S.; Bacmann, A.;
Banday, A.; Barriere, K.; Bellossi, F.; Bernard, J. -P.; Bernardini,
M. G.; Béthermin, M.; Blanc, E.; Blanchet, L.; Bobin, J.; Boissier,
S.; Boisson, C.; Boselli, A.; Bosma, A.; Bosse, S.; Bottinelli,
S.; Boulanger, F.; Boyer, R.; Bracco, A.; Briand, C.; Bucher, M.;
Buat, V.; Cambresy, L.; Caillat, M.; Casandjian, J. -M.; Caux,
E.; Célestin, S.; Cerruti, M.; Charlot, P.; Chassande-Mottin, E.;
Chaty, S.; Christensen, N.; Ciesla, L.; Clerc, N.; Cohen-Tanugi, J.;
Cognard, I.; Combes, F.; Comis, B.; Corbel, S.; Cordier, B.; Coriat,
M.; Courtin, R.; Courtois, H.; Da Silva, B.; Daddi, E.; Dallier, R.;
Dartois, E.; Demyk, K.; Denis, J. -M.; Denis, L.; Djannati-Ataï, A.;
Donati, J. -F.; Douspis, M.; van Driel, W.; El Korso, M. N.; Falgarone,
E.; Fantina, A.; Farges, T.; Ferrari, A.; Ferrari, C.; Ferrière, K.;
Flamary, R.; Gac, N.; Gauffre, S.; Genova, F.; Girard, J.; Grenier,
I.; Griessmeier, J. -M.; Guillard, P.; Guillemot, L.; Gulminelli,
F.; Gusdorf, A.; Habart, E.; Hammer, F.; Hennebelle, P.; Herpin, F.;
Hervet, O.; Hughes, A.; Ilbert, O.; Janvier, M.; Josselin, E.; Julier,
A.; Lachaud, C.; Lagache, G.; Lallement, R.; Lambert, S.; Lamy, L.;
Langer, M.; Larzabal, P.; Lavaux, G.; Le Bertre, T.; Le Fèvre, O.;
Le Tiec, A.; Lefloch, B.; Lehnert, M.; Lemoine-Goumard, M.; Levrier,
F.; Limousin, M.; Lis, D.; López-Sepulcre, A.; Macias-Perez, J.;
Magneville, C.; Marcowith, A.; Margueron, J.; Marquette, G.; Marshall,
D.; Martin, L.; Mary, D.; Masson, S.; Maurogordato, S.; Mazauric,
C.; Mellier, Y.; Miville-Deschênes, M. -A.; Montier, L.; Mottez, F.;
Mourard, D.; Nesvadba, N.; Nezan, J. -F.; Noterdaeme, P.; Novak, J.;
Ocvirk, P.; Oertel, M.; Olive, X.; Ollier, V.; Palanque-Delabrouille,
N.; Pandey-Pommier, M.; Pennec, Y.; Pérault, M.; Peroux, C.; Petit,
P.; Pétri, J.; Petiteau, A.; Pety, J.; Pratt, G. W.; Puech, M.;
Quertier, B.; Raffin, E.; Rakotozafy Harison, S.; Rawson, S.; Renaud,
M.; Revenu, B.; Richard, C.; Richard, J.; Rincon, F.; Ristorcelli,
I.; Rodriguez, J.; Schultheis, M.; Schimd, C.; Semelin, B.; Sol, H.;
Starck, J. -L.; Tagger, M.; Tasse, C.; Theureau, G.; Torchinsky, S.;
Vastel, C.; Vergani, S. D.; Verstraete, L.; Vigouroux, X.; Vilmer,
N.; Vilotte, J. -P.; Webb, N.; Ysard, N.; Zarka, P.
Bibcode: 2017arXiv171206950A
Altcode:
The "Square Kilometre Array" (SKA) is a large international radio
telescope project characterised, as suggested by its name, by a total
collecting area of approximately one square kilometre, and consisting
of several interferometric arrays to observe at metric and centimetric
wavelengths. The deployment of the SKA will take place in two sites,
in South Africa and Australia, and in two successive phases. From its
Phase 1, the SKA will be one of the most formidable scientific machines
ever deployed by mankind, and by far the most impressive in terms of
data throughput and required computing power. With the participation
of almost 200 authors from forty research institutes and six private
companies, the publication of this French SKA white paper illustrates
the strong involvement in the SKA project of the French astronomical
community and of a rapidly growing number of major scientific and
technological players in the fields of Big Data, high performance
computing, energy production and storage, as well as system integration.
Title: Analysis and modelling of recurrent solar flares observed
with Hinode/EIS on March 9, 2012
Authors: Polito, V.; Del Zanna, G.; Valori, G.; Pariat, E.; Mason,
H. E.; Dudík, J.; Janvier, M.
Bibcode: 2017A&A...601A..39P
Altcode: 2016arXiv161203504P
Three homologous C-class flares and one last M-class flare were observed
by both the Solar Dynamics Observatory (SDO) and the Hinode EUV Imaging
Spectrometer (EIS) in the AR 11429 on March 9, 2012. All the recurrent
flares occurred within a short interval of time (less than 4 h),
showed very similar plasma morphology and were all confined, until the
last one when a large-scale eruption occurred. The C-class flares are
characterized by the appearance, at approximatively the same locations,
of two bright and compact footpoint sources of ≈3-10 MK evaporating
plasma, and a semi-circular ribbon. During all the flares, the
continuous brightening of a spine-like hot plasma (≈10 MK) structure
is also observed. Spectroscopic observations with Hinode/EIS are used to
measure and compare the blueshift velocities in the Fe xxiii emission
line and the electron number density at the flare footpoints for each
flare. Similar velocities, of the order of 150-200 km s-1,
are observed during the C2.0 and C4.7 confined flares, in agreement
with the values reported by other authors in the study of the last M1.8
class flare. On the other hand, lower electron number densities and
temperatures tend to be observed in flares with lower peak soft X-ray
flux. In order to investigate the homologous nature of the flares, we
performed a non-linear force-free field (NLFFF) extrapolation of the 3D
magnetic field configuration in the corona. The NLFFF extrapolation and
the Quasi-Separatrix Layers (QSLs) provide the magnetic field context
which explains the location of the kernels, spine-like hot plasma and
semi-circular brightenings observed in the (non-eruptive) flares. Given
the absence of a coronal null point, we argue that the homologous
flares were all generated by the continuous recurrence of bald patch
reconnection. The movie associated to Fig. 2 is available at http://www.aanda.org
Title: Apparent and Intrinsic Evolution of Active Region Upflows
Authors: Baker, Deborah; Janvier, Miho; Démoulin, Pascal; Mandrini,
Cristina H.
Bibcode: 2017SoPh..292...46B
Altcode: 2017arXiv170206022B
We analyze the evolution of Fe XII coronal plasma upflows from
the edges of ten active regions (ARs) as they cross the solar disk
using the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) to do
this. Confirming the results of Démoulin et al. (Sol. Phys.283, 341,
2013), we find that for each AR there is an observed long-term evolution
of the upflows. This evolution is largely due to the solar rotation
that progressively changes the viewpoint of dominantly stationary
upflows. From this projection effect, we estimate the unprojected
upflow velocity and its inclination to the local vertical. AR upflows
typically fan away from the AR core by 40° to nearly vertical
for the following polarity. The span of inclination angles is more
spread out for the leading polarity, with flows angled from −29°
(inclined toward the AR center) to 28° (directed away from the
AR). In addition to the limb-to-limb apparent evolution, we identify
an intrinsic evolution of the upflows that is due to coronal activity,
which is AR dependent. Furthermore, line widths are correlated with
Doppler velocities only for the few ARs with the highest velocities. We
conclude that for the line widths to be affected by the solar rotation,
the spatial gradient of the upflow velocities must be large enough
such that the line broadening exceeds the thermal line width of Fe
XII. Finally, we find that upflows occurring in pairs or multiple
pairs are a common feature of ARs observed by Hinode/EIS, with up to
four pairs present in AR 11575. This is important for constraining the
upflow-driving mechanism as it implies that the mechanism is not local
and does not occur over a single polarity. AR upflows originating from
reconnection along quasi-separatrix layers between overpressure AR
loops and neighboring underpressure loops is consistent with upflows
occurring in pairs, unlike other proposed mechanisms that act locally
in one polarity.
Title: Observable Signatures of Energy Release in Braided Coronal
Loops
Authors: Pontin, D. I.; Janvier, M.; Tiwari, S. K.; Galsgaard, K.;
Winebarger, A. R.; Cirtain, J. W.
Bibcode: 2017ApJ...837..108P
Altcode:
We examine the turbulent relaxation of solar coronal loops containing
non-trivial field line braiding. Such field line tangling in the
corona has long been postulated in the context of coronal heating
models. We focus on the observational signatures of energy release
in such braided magnetic structures using MHD simulations and forward
modeling tools. The aim is to answer the following question: if energy
release occurs in a coronal loop containing braided magnetic flux,
should we expect a clearly observable signature in emissions? We
demonstrate that the presence of braided magnetic field lines does not
guarantee a braided appearance to the observed intensities. Observed
intensities may—but need not necessarily—reveal the underlying
braided nature of the magnetic field, depending on the degree and
pattern of the field line tangling within the loop. However, in all
cases considered, the evolution of the braided loop is accompanied
by localized heating regions as the loop relaxes. Factors that
may influence the observational signatures are discussed. Recent
high-resolution observations from Hi-C have claimed the first direct
evidence of braided magnetic fields in the corona. Here we show that
both the Hi-C data and some of our simulations give the appearance of
braiding at a range of scales.
Title: Three-dimensional magnetic reconnection and its application
to solar flares
Authors: Janvier, Miho
Bibcode: 2017JPlPh..83a5301J
Altcode: 2016arXiv161206513J
Solar flares are powerful radiations occurring in the Sun's
atmosphere. They are powered by magnetic reconnection, a phenomenon
that can convert magnetic energy into other forms of energy such as
heat and kinetic energy, and which is believed to be ubiquitous in the
universe. With the ever increasing spatial and temporal resolutions of
solar observations, as well as numerical simulations benefiting from
increasing computer power, we can now probe into the nature and the
characteristics of magnetic reconnection in three dimensions to better
understand the phenomenon's consequences during eruptive flares in
our star's atmosphere. We review in the following the efforts made on
different fronts to approach the problem of magnetic reconnection. In
particular, we will see how understanding the magnetic topology
in three dimensions helps in locating the most probable regions
for reconnection to occur, how the current layer evolves in three
dimensions and how reconnection leads to the formation of flux ropes,
plasmoids and flaring loops.
Title: Evolution of the magnetic field distribution of active regions
Authors: Dacie, S.; Démoulin, P.; van Driel-Gesztelyi, L.; Long,
D. M.; Baker, D.; Janvier, M.; Yardley, S. L.; Pérez-Suárez, D.
Bibcode: 2016A&A...596A..69D
Altcode: 2016arXiv160903723D
Aims: Although the temporal evolution of active regions (ARs)
is relatively well understood, the processes involved continue to be
the subject of investigation. We study how the magnetic field of a
series of ARs evolves with time to better characterise how ARs emerge
and disperse.
Methods: We examined the temporal variation in
the magnetic field distribution of 37 emerging ARs. A kernel density
estimation plot of the field distribution was created on a log-log
scale for each AR at each time step. We found that the central portion
of the distribution is typically linear, and its slope was used to
characterise the evolution of the magnetic field.
Results:
The slopes were seen to evolve with time, becoming less steep as the
fragmented emerging flux coalesces. The slopes reached a maximum value
of -1.5 just before the time of maximum flux before becoming steeper
during the decay phase towards the quiet-Sun value of -3. This behaviour
differs significantly from a classical diffusion model, which produces
a slope of -1. These results suggest that simple classical diffusion
is not responsible for the observed changes in field distribution, but
that other processes play a significant role in flux dispersion.
Conclusions: We propose that the steep negative slope seen during the
late-decay phase is due to magnetic flux reprocessing by (super)granular
convective cells.
Title: Tracing the Evolution of ICMEs from Sun to Earth
Authors: Janvier, M.; Demoulin, P.; Dasso, S.; Masias, J.
Bibcode: 2016AGUFMSH53A..03J
Altcode:
Coronal Mass Ejections (CMEs) are the result of magnetic instabilities
in the Sun's atmosphere, which are consequently launched into the
heliosphere. As their interplanetary counterparts (ICMEs) propagate
in the interplanetary medium, they can interact with the magnetized
environment of planets and other objects in the solar system. They
are believed to be the main drivers of space weather. Over the past
decades, the multiplication of space missions has led to a gold mine in
ICME data, allowing us to deepen our knowledge on their properties and
evolution from the Sun to the Earth. In particular, the identification
of substructures such as shocks and magnetic clouds and their typical
profiles, as well as their properties, can be traced at different
locations away from the Sun. Here, we will review different aspects
of ICMEs, such as their 3D generic shape, the transported physical
quantities as well as their evolution (such as the expansion) in the
inner heliosphere. These aspects can be quantified by in situ data, and
consequently they can provide useful information to constrain analytical
and numerical models as well as remote-sensing data interpretation. They
also provide key questions to be addressed by the future Solar Orbiter
and Solar Probe Plus missions.
Title: Quantitative model for the generic 3D shape of ICMEs at 1 AU
Authors: Démoulin, P.; Janvier, M.; Masías-Meza, J. J.; Dasso, S.
Bibcode: 2016A&A...595A..19D
Altcode: 2016arXiv160808550D
Context. Interplanetary imagers provide 2D projected views of the
densest plasma parts of interplanetary coronal mass ejections (ICMEs),
while in situ measurements provide magnetic field and plasma parameter
measurements along the spacecraft trajectory, that is, along a 1D
cut. The data therefore only give a partial view of the 3D structures
of ICMEs.
Aims: By studying a large number of ICMEs, crossed at
different distances from their apex, we develop statistical methods
to obtain a quantitative generic 3D shape of ICMEs.
Methods:
In a first approach we theoretically obtained the expected statistical
distribution of the shock-normal orientation from assuming simple
models of 3D shock shapes, including distorted profiles, and compared
their compatibility with observed distributions. In a second approach
we used the shock normal and the flux rope axis orientations together
with the impact parameter to provide statistical information across the
spacecraft trajectory.
Results: The study of different 3D shock
models shows that the observations are compatible with a shock that is
symmetric around the Sun-apex line as well as with an asymmetry up to
an aspect ratio of around 3. Moreover, flat or dipped shock surfaces
near their apex can only be rare cases. Next, the sheath thickness and
the ICME velocity have no global trend along the ICME front. Finally,
regrouping all these new results and those of our previous articles,
we provide a quantitative ICME generic 3D shape, including the global
shape of the shock, the sheath, and the flux rope.
Conclusions:
The obtained quantitative generic ICME shape will have implications for
several aims. For example, it constrains the output of typical ICME
numerical simulations. It is also a base for studying the transport
of high-energy solar and cosmic particles during an ICME propagation
as well as for modeling and forecasting space weather conditions
near Earth.
Title: The Characteristics of Solar X-Class Flares and CMEs: A
Paradigm for Stellar Superflares and Eruptions?
Authors: Harra, Louise K.; Schrijver, Carolus J.; Janvier, Miho;
Toriumi, Shin; Hudson, Hugh; Matthews, Sarah; Woods, Magnus M.; Hara,
Hirohisa; Guedel, Manuel; Kowalski, Adam; Osten, Rachel; Kusano,
Kanya; Lueftinger, Theresa
Bibcode: 2016SoPh..291.1761H
Altcode: 2016SoPh..tmp..111H
This paper explores the characteristics of 42 solar X-class flares that
were observed between February 2011 and November 2014, with data from
the Solar Dynamics Observatory (SDO) and other sources. This flare
list includes nine X-class flares that had no associated CMEs. In
particular our aim was to determine whether a clear signature could
be identified to differentiate powerful flares that have coronal
mass ejections (CMEs) from those that do not. Part of the motivation
for this study is the characterization of the solar paradigm for
flare/CME occurrence as a possible guide to the stellar observations;
hence we emphasize spectroscopic signatures. To do this we ask the
following questions: Do all eruptive flares have long durations? Do
CME-related flares stand out in terms of active-region size vs. flare
duration? Do flare magnitudes correlate with sunspot areas, and, if so,
are eruptive events distinguished? Is the occurrence of CMEs related to
the fraction of the active-region area involved? Do X-class flares with
no eruptions have weaker non-thermal signatures? Is the temperature
dependence of evaporation different in eruptive and non-eruptive
flares? Is EUV dimming only seen in eruptive flares? We find only one
feature consistently associated with CME-related flares specifically:
coronal dimming in lines characteristic of the quiet-Sun corona,
i.e. 1 - 2 MK. We do not find a correlation between flare magnitude
and sunspot areas. Although challenging, it will be of importance to
model dimming for stellar cases and make suitable future plans for
observations in the appropriate wavelength range in order to identify
stellar CMEs consistently.
Title: A small mission concept to the Sun-Earth Lagrangian L5 point
for innovative solar, heliospheric and space weather science
Authors: Lavraud, B.; Liu, Y.; Segura, K.; He, J.; Qin, G.; Temmer,
M.; Vial, J. -C.; Xiong, M.; Davies, J. A.; Rouillard, A. P.; Pinto,
R.; Auchère, F.; Harrison, R. A.; Eyles, C.; Gan, W.; Lamy, P.;
Xia, L.; Eastwood, J. P.; Kong, L.; Wang, J.; Wimmer-Schweingruber,
R. F.; Zhang, S.; Zong, Q.; Soucek, J.; An, J.; Prech, L.; Zhang,
A.; Rochus, P.; Bothmer, V.; Janvier, M.; Maksimovic, M.; Escoubet,
C. P.; Kilpua, E. K. J.; Tappin, J.; Vainio, R.; Poedts, S.; Dunlop,
M. W.; Savani, N.; Gopalswamy, N.; Bale, S. D.; Li, G.; Howard, T.;
DeForest, C.; Webb, D.; Lugaz, N.; Fuselier, S. A.; Dalmasse, K.;
Tallineau, J.; Vranken, D.; Fernández, J. G.
Bibcode: 2016JASTP.146..171L
Altcode:
We present a concept for a small mission to the Sun-Earth Lagrangian L5
point for innovative solar, heliospheric and space weather science. The
proposed INvestigation of Solar-Terrestrial Activity aNd Transients
(INSTANT) mission is designed to identify how solar coronal magnetic
fields drive eruptions, mass transport and particle acceleration that
impact the Earth and the heliosphere. INSTANT is the first mission
designed to (1) obtain measurements of coronal magnetic fields from
space and (2) determine coronal mass ejection (CME) kinematics with
unparalleled accuracy. Thanks to innovative instrumentation at a vantage
point that provides the most suitable perspective view of the Sun-Earth
system, INSTANT would uniquely track the whole chain of fundamental
processes driving space weather at Earth. We present the science
requirements, payload and mission profile that fulfill ambitious science
objectives within small mission programmatic boundary conditions.
Title: Evolution of Magnetic Helicity During Eruptive Flares and
Coronal Mass Ejections
Authors: Priest, E. R.; Longcope, D. W.; Janvier, M.
Bibcode: 2016SoPh..291.2017P
Altcode: 2016arXiv160703874P; 2016SoPh..tmp..130P
During eruptive solar flares and coronal mass ejections, a non-potential
magnetic arcade with much excess magnetic energy goes unstable and
reconnects. It produces a twisted erupting flux rope and leaves behind
a sheared arcade of hot coronal loops. We suggest that the twist of the
erupting flux rope can be determined from conservation of magnetic flux
and magnetic helicity and equipartition of magnetic helicity. It depends
on the geometry of the initial pre-eruptive structure. Two cases are
considered, in the first of which a flux rope is not present initially
but is created during the eruption by the reconnection. In the second
case, a flux rope is present under the arcade in the pre-eruptive
state, and the effect of the eruption and reconnection is to add an
amount of magnetic helicity that depends on the fluxes of the rope
and arcade and the geometry.
Title: Superposed epoch study of ICME sub-structures near Earth and
their effects on Galactic cosmic rays
Authors: Masías-Meza, J. J.; Dasso, S.; Démoulin, P.; Rodriguez,
L.; Janvier, M.
Bibcode: 2016A&A...592A.118M
Altcode: 2016arXiv160508130M
Context. Interplanetary coronal mass ejections (ICMEs) are the
interplanetary manifestations of solar eruptions. The overtaken
solar wind forms a sheath of compressed plasma at the front of
ICMEs. Magnetic clouds (MCs) are a subset of ICMEs with specific
properties (e.g. the presence of a flux rope). When ICMEs pass near
Earth, ground observations indicate that the flux of Galactic cosmic
rays (GCRs) decreases.
Aims: The main aims of this paper
are to find common plasma and magnetic properties of different ICME
sub-structures and which ICME properties affect the flux of GCRs near
Earth.
Methods: We used a superposed epoch method applied to
a large set of ICMEs observed in situ by the spacecraft ACE, between
1998 and 2006. We also applied a superposed epoch analysis on GCRs time
series observed with the McMurdo neutron monitors.
Results: We
find that slow MCs at 1 AU have on average more massive sheaths. We
conclude that this is because they are more effectively slowed down
by drag during their travel from the Sun. Slow MCs also have a more
symmetric magnetic field and sheaths expanding similarly as their
following MC, while in contrast, fast MCs have an asymmetric magnetic
profile and a sheath in compression. In all types of MCs, we find that
the proton density and the temperature and the magnetic fluctuations
can diffuse within the front of the MC due to 3D reconnection. Finally,
we derive a quantitative model that describes the decrease in cosmic
rays as a function of the amount of magnetic fluctuations and field
strength.
Conclusions: The obtained typical profiles of sheath,
MC and GCR properties corresponding to slow, middle, and fast ICMEs,
can be used for forecasting or modelling these events, and to better
understand the transport of energetic particles in ICMEs. They are
also useful for improving future operative space weather activities.
Title: Typical Profiles and Distributions of Plasma and Magnetic
Field Parameters in Magnetic Clouds at 1 AU
Authors: Rodriguez, L.; Masías-Meza, J. J.; Dasso, S.; Démoulin,
P.; Zhukov, A. N.; Gulisano, A. M.; Mierla, M.; Kilpua, E.; West,
M.; Lacatus, D.; Paraschiv, A.; Janvier, M.
Bibcode: 2016SoPh..291.2145R
Altcode: 2016SoPh..tmp..113R
Magnetic clouds (MCs) are a subset of interplanetary coronal mass
ejections (ICMEs). They are important because of their simple internal
magnetic field configuration, which resembles a magnetic flux rope,
and because they represent one of the most geoeffective types of solar
transients. In this study, we analyze their internal structure using
a superposed epoch method on 63 events observed at L1 by the Advance
Composition Explorer (ACE), between 1998 and 2006. In this way, we
obtain an average profile for each plasma and magnetic field parameter
at each point of the cloud. Furthermore, we take a fixed time-window
upstream and downstream from the MC to also sample the regions preceding
the cloud and the wake trailing it. We then perform a detailed analysis
of the internal characteristics of the clouds and their surrounding
solar wind environments. We find that the parameters studied are
compatible with log-normal distribution functions. The plasma β and
the level of fluctuations in the magnetic field vector are the best
parameters to define the boundaries of MCs. We find that one third
of the events shows a peak in plasma density close to the trailing
edge of the flux ropes. We provide several possible explanations for
this result and investigate if the density peak is of a solar origin
(e.g. erupting prominence material) or formed during the magnetic cloud
travel from the Sun to 1 AU. The most plausible explanation is the
compression due to a fast overtaking flow, coming from a coronal hole
located to the east of the solar source region of the magnetic cloud.
Title: The SPICE Spectral Imager on Solar Orbiter: Linking the Sun
to the Heliosphere
Authors: Fludra, Andrzej; Haberreiter, Margit; Peter, Hardi; Vial,
Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson,
William; Gabriel, Alan; Morris, Nigel; Caldwell, Martin; Auchere,
Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.; DeForest,
Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne; Janvier, Miho;
Wimmer-Schweingruber, Robert; Griffin, Douglas; Davila, Joseph; Giunta,
Alessandra; Waltham, Nick; Eccleston, Paul; Gottwald, Alexander;
Klein, Roman; Hanley, John; Walls, Buddy; Howe, Chris; Schuehle, Udo
Bibcode: 2016cosp...41E.607F
Altcode:
The SPICE (Spectral Imaging of the Coronal Environment) instrument is
one of the key remote sensing instruments onboard the upcoming Solar
Orbiter Mission. SPICE has been designed to contribute to the science
goals of the mission by investigating the source regions of outflows
and ejection processes which link the solar surface and corona to the
heliosphere. In particular, SPICE will provide quantitative information
on the physical state and composition of the solar atmosphere
plasma. For example, SPICE will access relative abundances of ions to
study the origin and the spatial/temporal variations of the 'First
Ionization Potential effect', which are key signatures to trace the
solar wind and plasma ejections paths within the heliosphere. Here we
will present the instrument and its performance capability to attain the
scientific requirements. We will also discuss how different observation
modes can be chosen to obtain the best science results during the
different orbits of the mission. To maximize the scientific return of
the instrument, the SPICE team is working to optimize the instrument
operations, and to facilitate the data access and their exploitation.
Title: Solar abundances with the SPICE spectral imager on Solar
Orbiter
Authors: Giunta, Alessandra; Haberreiter, Margit; Peter, Hardi;
Vial, Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson, William;
Bocchialini, Karine; Gabriel, Alan; Morris, Nigel; Caldwell, Martin;
Auchere, Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.;
DeForest, Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne;
Janvier, Miho; Wimmer-Schweingruber, Robert; Griffin, Douglas; Baudin,
Frederic; Davila, Joseph; Fludra, Andrzej; Waltham, Nick; Eccleston,
Paul; Gottwald, Alexander; Klein, Roman; Hanley, John; Walls, Buddy;
Howe, Chris; Schuehle, Udo; Gyo, Manfred; Pfiffner, Dany
Bibcode: 2016cosp...41E.681G
Altcode:
Elemental composition of the solar atmosphere and in particular
abundance bias of low and high First Ionization Potential (FIP)
elements are a key tracer of the source regions of the solar wind. These
abundances and their spatio-temporal variations, as well as the other
plasma parameters , will be derived by the SPICE (Spectral Imaging
of the Coronal Environment) EUV spectral imager on the upcoming
Solar Orbiter mission. SPICE is designed to provide spectroheliograms
(spectral images) using a core set of emission lines arising from ions
of both low-FIP and high-FIP elements. These lines are formed over
a wide range of temperatures, enabling the analysis of the different
layers of the solar atmosphere. SPICE will use these spectroheliograms
to produce dynamic composition maps of the solar atmosphere to be
compared to in-situ measurements of the solar wind composition of
the same elements (i.e. O, Ne, Mg, Fe). This will provide a tool to
study the connectivity between the spacecraft (the Heliosphere) and
the Sun. We will discuss the SPICE capabilities for such composition
measurements.
Title: Evolution of flare ribbons, electric currents, and
quasi-separatrix layers during an X-class flare
Authors: Janvier, M.; Savcheva, A.; Pariat, E.; Tassev, S.;
Millholland, S.; Bommier, V.; McCauley, P.; McKillop, S.; Dougan, F.
Bibcode: 2016A&A...591A.141J
Altcode: 2016arXiv160407241J
Context. The standard model for eruptive flares has been extended
to three dimensions (3D) in the past few years. This model predicts
typical J-shaped photospheric footprints of the coronal current
layer, forming at similar locations as the quasi-separatrix layers
(QSLs). Such a morphology is also found for flare ribbons observed in
the extreme ultraviolet (EUV) band, and in nonlinear force-free field
(NLFFF) magnetic field extrapolations and models.
Aims: We
study the evolution of the photospheric traces of the current density
and flare ribbons, both obtained with the Solar Dynamics Observatory
instruments. We aim to compare their morphology and their time
evolution, before and during the flare, with the topological features
found in a NLFFF model.
Methods: We investigated the photospheric
current evolution during the 06 September 2011 X-class flare
(SOL2011-09-06T22:20) occurring in NOAA AR 11283 from observational data
of the magnetic field obtained with the Helioseismic and Magnetic Imager
aboard the Solar Dynamics Observatory. We compared this evolution with
that of the flare ribbons observed in the EUV filters of the Atmospheric
Imager Assembly. We also compared the observed electric current density
and the flare ribbon morphology with that of the QSLs computed from
the flux rope insertion method-NLFFF model.
Results: The NLFFF
model shows the presence of a fan-spine configuration of overlying
field lines, due to the presence of a parasitic polarity, embedding
an elongated flux rope that appears in the observations as two parts
of a filament. The QSL signatures of the fan configuration appear as
a circular flare ribbon that encircles the J-shaped ribbons related
to the filament ejection. The QSLs, evolved via a magnetofrictional
method, also show similar morphology and evolution as both the current
ribbons and the EUV flare ribbons obtained several times during the
flare.
Conclusions: For the first time, we propose a combined
analysis of the photospheric traces of an eruptive flare, in a complex
topology, with direct measurements of electric currents and QSLs
from observational data and a magnetic field model. The results,
obtained by two different and independent approaches 1) confirm
previous results of current increase during the impulsive phase of the
flare and 2) show how NLFFF models can capture the essential physical
signatures of flares even in a complex magnetic field topology. A movie associated to Fig. 1 is available in electronic form at http://www.aanda.org
Title: Evidence of flux rope and sigmoid in Active Regions prior
eruptions
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Janvier, Miho;
Bommier, Veronique; Dudik, Jaroslav; Gilchrist, Stuart; Zhao, Jie
Bibcode: 2016cosp...41E1750S
Altcode:
In the solar corona, the magnetic field is dominant, and the current
density vector is nearly aligned with the magnetic field lines
for strong and stressed field regions. Stressed and highly twisted
flux ropes are at the origin of eruptive events such as flares and
coronal mass ejections, which inject material into the interplanetary
medium. The standard three dimensional (3D) flare model predicts
the complex evolution of flare loops and the flux rope before
the eruption. Flux ropes are not directly observed in the corona,
however it has started to be possible to detect their footprints
in the photosphere. Recent high spatial and temporal resolution
spectro-polarimeters have allowed us to compute the photospheric
electric currents and follow their evolution. Characteristics pattern
like J-shaped ribbons indicate the presence of a flux rope before
the flare. The results confirm the predictions of the 3D MHD standard
model of eruptive flares. It is interesting to compare the magnetic
helicity of the ejected flux rope with the in situ measurements of the
corresponding ICME at L1. We will show some examples (February 15 2011,
July 12 2012, Sept 10 2014).
Title: Evolution of the Topology, Electric Currents, and Ribbons
during an X-class Flare
Authors: Savcheva, Antonia; Janvier, M.; Pariat, E.; Tassev, S.
Bibcode: 2016shin.confE.126S
Altcode:
The standard model for eruptive flares has in the past few years been
extended to 3D. It predicts typical J-shaped photospheric footprints
of the coronal current layer, forming at similar locations as the
Quasi-Separatrix Layers (QSLs). Such a morphology is also found for
flare ribbons observed in EUV, as well as in non-linear force-free
field (NLFFF) magnetic field extrapolations and models. We study the
evolution of the photospheric traces of the current density and the
flare ribbons, both obtained with SDO instruments. We aim at comparing
their morphology and their time evolution, before and during the flare,
with the topological features found in a NLFFF and an unstable magnetic
field model. For this purpose we investigate the photospheric current
evolution during the 06 September 2011 X-class flare occurring in NOAA
AR11283 from observational data of the magnetic field obtained with
HMI. This evolution is compared with that of the flare ribbons observed
with AIA. We also compare the observed electric current density and the
flare ribbon morphology with that of the QSLs computed from magnetic
field models obtained from the the flux rope insertion method. Both
the NLFFF and the unstable (eruptive) model show the presence of a
fan-spine configuration of overlying field lines, due to the presence
of a parasitic polarity, embedding an elongated flux rope that appears
in the observations as two parts of a filament. The magnetofrictional
evolution of the unstable model tell a consistent story of the filament
eruption in which topology plays an important role. The photospheric
QSL traces of the fan configuration appear as an elongated flare
ribbon that encircles the J-shaped ribbons related to the filament
ejection. The QSLs, evolved via a magnetofrictional method, also show
similar morphology and evolution as both the current ribbons and the
EUV flare ribbons obtained at several times during the flare. For the
first time, we propose a combined analysis of the photospheric traces
of an eruptive flare, in a complex topology, with direct measurements
of electric currents and QSLs from observational data and a magnetic
field model. The results, obtained by two different and independent
approaches, 1) confirm previous results of current increase during
the impulsive phase of the flare, 2) show how NLFFF extrapolations can
capture the essential physical signatures of flares even in a complex
magnetic field topology.
Title: Magnetic energy release and topology in the solar atmosphere
Authors: Mandrini, Cristina H.; Janvier, Miho
Bibcode: 2016cosp...41E1241M
Altcode:
The energy released in a wide range of atmospheric events in the Sun
is contained in current-carrying magnetic fields that have emerged
after traversing the convection zone. Once the magnetic flux reaches
the solar atmosphere, it may be further stressed via motions at the
photosphere. Magnetic field reconnection is thought to be the mechanism
through which the stored magnetic energy is transformed into kinetic
energy of accelerated particles, mass flows, and radiative energy
along the whole electromagnetic spectrum. Though this mechanism is
efficient only at very small spatial scales, it implies a large-scale
restructuring of the magnetic field inferred from the analysis of
observations, models of the coronal magnetic field and numerical
simulations, combined with the computation of the magnetic field
topology. The consequences of energy release include phenomena that
range from nano-flares and the slow solar wind to powerful flares that
may be accompanied by the ejection of large amounts of plasma into
the interplanetary medium. We will discuss how the computation and
analysis of the magnetic field topology, applied to a wide variety of
observed and modeled magnetic configurations, can be used to identify
the energy release locations and their physical characteristics.
Title: Manifestation of Coronal Mass Ejections near Earth: A review
Authors: Dasso, Sergio; Rodriguez, Luciano; Demoulin, Pascal;
Masías-Meza, Jimmy J.; Janvier, Miho
Bibcode: 2016cosp...41E.405D
Altcode:
Coronal Mass Ejections (CMEs) are launched from the Sun, as a result of
magnetic instabilities, carrying away a huge amount of magnetic flux and
helicity. Interplanetary CMEs (ICMEs) are their manifestation observed
further away in the heliosphere. ICMEs produce important changes of
plasma and magnetic field properties in the interplanetary medium, with
respect to the ones of the ambient solar wind. From the large number
of observed ICMEs, in the past years we significantly increased our
kwnoledge on several of their properties, such as: the identification
of the composing sub-structures and their local properties, their global
3D shape, the amount of magnetohydrodynamical quantities transported in
the heliosphere by the associated flux ropes, as well as how the plasma
and magnetic field are distributed inside them. In the present talk we
will present a general review of these aspects of ICMEs. In particular
we will focuss on the total amount of magnetic flux and helicity ejected
by CMEs from the Sun along a solar cycle, and on plasma and magnetic
properties of their shock-sheath-flux_rope-wake. These results can
help to understand their interaction with the ambient solar wind and
with planetary magnetic environments. They are particularly crucial
for a better understanding of the Sun-Earth coupling.
Title: Slipping Magnetic Reconnection, Chromospheric Evaporation,
Implosion, and Precursors in the 2014 September 10 X1.6-Class
Solar Flare
Authors: Dudík, Jaroslav; Polito, Vanessa; Janvier, Miho; Mulay,
Sargam M.; Karlický, Marian; Aulanier, Guillaume; Del Zanna, Giulio;
Dzifčáková, Elena; Mason, Helen E.; Schmieder, Brigitte
Bibcode: 2016ApJ...823...41D
Altcode: 2016arXiv160306092D
We investigate the occurrence of slipping magnetic reconnection,
chromospheric evaporation, and coronal loop dynamics in the 2014
September 10 X-class flare. Slipping reconnection is found to be present
throughout the flare from its early phase. Flare loops are seen to slip
in opposite directions toward both ends of the ribbons. Velocities
of 20-40 km s-1 are found within time windows where the
slipping is well resolved. The warm coronal loops exhibit expanding and
contracting motions that are interpreted as displacements due to the
growing flux rope that subsequently erupts. This flux rope existed and
erupted before the onset of apparent coronal implosion. This indicates
that the energy release proceeds by slipping reconnection and not via
coronal implosion. The slipping reconnection leads to changes in the
geometry of the observed structures at the Interface Region Imaging
Spectrograph slit position, from flare loop top to the footpoints in
the ribbons. This results in variations of the observed velocities of
chromospheric evaporation in the early flare phase. Finally, it is found
that the precursor signatures, including localized EUV brightenings as
well as nonthermal X-ray emission, are signatures of the flare itself,
progressing from the early phase toward the impulsive phase, with
the tether-cutting being provided by the slipping reconnection. The
dynamics of both the flare and outlying coronal loops is found to be
consistent with the predictions of the standard solar flare model in
three dimensions.
Title: Evolution of the Topology, Electric Currents, and Ribbons
during an X-class Flare
Authors: Savcheva, Antonia; Janvier, Miho; Pariat, Etienne
Bibcode: 2016SPD....4740101S
Altcode:
The standard model for eruptive flares has in the past few years
been extended to 3D. It predicts typical J-shaped photospheric
footprints of the coronal current layer, forming at similar locations
as the Quasi-Separatrix Layers (QSLs). We study the evolution of
the photospheric traces of the current density and the flare ribbons
observed with SDO. We aim at comparing their morphology and their time
evolution, before and during the flare, with the topological features
found in a magnetic field model. For this purpose we investigate the
photospheric current evolution during the 6 Sep 2011 X-class flare
occurring in AR11283 from observational data of the magnetic field
obtained with HMI. This evolution is compared with that of the flare
ribbons observed with AIA. We also compare the observed electric current
density and the flare ribbon morphology with that of the QSLs computed
from magnetic field models obtained from the the flux rope insertion
method. Both the NLFFF and the unstable (eruptive) model show the
presence of a fan-spine configuration of overlying field lines, due
to the presence of a parasitic polarity, embedding in elongated flux
rope that appears in the observations as two parts of a filament. The
magnetofrictional evolution of the unstable model tells a consistent
story of the filament eruption in which topology plays an important
role. The photospheric QSL traces of the fan configuration appear as
an elongated flare ribbon that encircles the J-shaped ribbons related
to the filament ejection. The QSLs, evolved via a magnetofrictional
method, also show similar morphology and evolution as both the current
ribbons and the EUV flare ribbons obtained at several times during
the flare. For the first time, we propose a combined analysis of the
photospheric traces of an eruptive flare, in a complex topology, with
direct measurements of electric currents and QSLs from observational
data and a magnetic field model. The results obtained by two independent
approaches confirm previous results and show how NLFFF models can
capture the essential physical signatures of flares even in a complex
magnetic field topology.
Title: Magnetic Flux and Helicity of Magnetic Clouds
Authors: Démoulin, P.; Janvier, M.; Dasso, S.
Bibcode: 2016SoPh..291..531D
Altcode: 2015SoPh..tmp..183D; 2015arXiv150901068D
Magnetic clouds (MCs) are formed by flux ropes (FRs) launched from
the Sun as part of coronal mass ejections (CMEs). They carry away
a large amount of magnetic flux and helicity. The main aim of this
study is to quantify these amounts from in situ measurements of MCs
at 1 AU. The fit of these data by a local FR model provides the axial
magnetic field strength, the radius, the magnetic flux, and the helicity
per unit length along the FR axis. We show that these quantities are
statistically independent of the position along the FR axis. We then
derive the generic shape and length of the FR axis from two sets of
MCs. These results improve the estimation of magnetic helicity. Next,
we evaluate the total magnetic flux and helicity that cross the
sphere of radius of 1 AU, centred at the Sun, per year and during a
solar cycle. We also include in the study two sets of small FRs that
do not have all the typical characteristics of MCs. While small FRs
are at least ten times more numerous than MCs, the magnetic flux and
helicity are dominated by the contribution from the larger MCs. In
one year they carry away the magnetic flux of about 25 large active
regions and the magnetic helicity of 200 of them. MCs carry away an
amount of unsigned magnetic helicity similar to the amount estimated
for the solar dynamo and that measured in emerging active regions.
Title: From Coronal Observations to MHD Simulations, the Building
Blocks for 3D Models of Solar Flares (Invited Review)
Authors: Janvier, M.; Aulanier, G.; Démoulin, P.
Bibcode: 2015SoPh..290.3425J
Altcode: 2015SoPh..tmp...63J; 2015arXiv150505299J
Solar flares are energetic events taking place in the Sun's atmosphere,
and their effects can greatly impact the environment of the surrounding
planets. In particular, eruptive flares, as opposed to confined flares,
launch coronal mass ejections into the interplanetary medium, and
as such, are one of the main drivers of space weather. After briefly
reviewing the main characteristics of solar flares, we summarise the
processes that can account for the build-up and release of energy
during their evolution. In particular, we focus on the development
of recent 3D numerical simulations that explain many of the observed
flare features. These simulations can also provide predictions of the
dynamical evolution of coronal and photospheric magnetic field. Here
we present a few observational examples that, together with numerical
modelling, point to the underlying physical mechanisms of the eruptions.
Title: Slipping reconnection and chromospheric evaporation in the
10 September 2014 flare
Authors: Dudík, Jaroslav; Janvier, Miho; Polito, Vanessa; Mulay,
Sargam; Del Zanna, Giulio; Mason, Helen; Aulanier, Guillaume
Bibcode: 2015IAUGA..2252237D
Altcode:
We study the occurrence of slipping reconnection in the long-duration
X-class flare of 2014 September 10. From the start, the flare shows
apparent slippage of hot Fe XXI flare loops observed in the 131A
channel of SDO/AIA. Using the time-distance plots, we show that the
slipping motion of the flare loops proceeds in counter directions in
both flare ribbons. Simultaneous IRIS Fe XXI observations show the
occurrence of chromospheric evaporation at brightening kernels that are
involved in the slipping reconnection of AIA loops. This happens also
during a flux-rope breakout accompanied by a faint 'magnetic implosion'
of a coronal loop. Based on the 3D MHD flare model, we argue that the
'implosion' is caused by the erupting flux rope pushing the neighbouring
loops aside, with the low-lying loops being squeezed.
Title: Strong coronal channelling and interplanetary evolution of
a solar storm up to Earth and Mars
Authors: Möstl, Christian; Rollett, Tanja; Frahm, Rudy A.; Liu,
Ying D.; Long, David M.; Colaninno, Robin C.; Reiss, Martin A.;
Temmer, Manuela; Farrugia, Charles J.; Posner, Arik; Dumbović,
Mateja; Janvier, Miho; Démoulin, Pascal; Boakes, Peter; Devos, Andy;
Kraaikamp, Emil; Mays, Mona L.; Vršnak, Bojan
Bibcode: 2015NatCo...6.7135M
Altcode: 2015arXiv150602842M; 2015NatCo...6E7135M
The severe geomagnetic effects of solar storms or coronal mass
ejections (CMEs) are to a large degree determined by their propagation
direction with respect to Earth. There is a lack of understanding of
the processes that determine their non-radial propagation. Here we
present a synthesis of data from seven different space missions of a
fast CME, which originated in an active region near the disk centre
and, hence, a significant geomagnetic impact was forecasted. However,
the CME is demonstrated to be channelled during eruption into a
direction +37+/-10° (longitude) away from its source region, leading
only to minimal geomagnetic effects. In situ observations near Earth
and Mars confirm the channelled CME motion, and are consistent with
an ellipse shape of the CME-driven shock provided by the new Ellipse
Evolution model, presented here. The results enhance our understanding
of CME propagation and shape, which can help to improve space weather
forecasts.
Title: Comparing generic models for interplanetary shocks and magnetic
clouds axis configurations at 1 AU
Authors: Janvier, M.; Dasso, S.; Démoulin, P.; Masías-Meza, J. J.;
Lugaz, N.
Bibcode: 2015JGRA..120.3328J
Altcode: 2015arXiv150306128J
Interplanetary coronal mass ejections (ICMEs) are the manifestation
of solar transient eruptions, which can significantly modify the
plasma and magnetic conditions in the heliosphere. They are often
preceded by a shock, and a magnetic flux rope is detected in situ
in a third to half of them. The main aim of this study is to obtain
the best quantitative shape for the flux rope axis and for the shock
surface from in situ data obtained during spacecraft crossings of
these structures. We first compare the orientation of the flux rope
axes and shock normals obtained from independent data analyses of
the same events, observed in situ at 1 AU from the Sun. Then we
carry out an original statistical analysis of axes/shock normals
by deriving the statistical distributions of their orientations. We
fit the observed distributions using the distributions derived from
several synthetic models describing these shapes. We show that the
distributions of axis/shock orientations are very sensitive to their
respective shape. One classical model, used to analyze interplanetary
imager data, is incompatible with the in situ data. Two other models
are introduced, for which the results for axis and shock normals lead
to very similar shapes; the fact that the data for MCs and shocks
are independent strengthens this result. The model which best fits
all the data sets has an ellipsoidal shape with similar aspect ratio
values for all the data sets. These derived shapes for the flux rope
axis and shock surface have several potential applications. First,
these shapes can be used to construct a consistent ICME model. Second,
these generic shapes can be used to develop a quantitative model to
analyze imager data, as well as constraining the output of numerical
simulations of ICMEs. Finally, they will have implications for space
weather forecasting, in particular, for forecasting the time arrival
of ICMEs at the Earth.
Title: Strong coronal deflection of a CME and its interplanetary
evolution to Earth and Mars
Authors: Möstl, Christian; Rollett, Tanja; Frahm, Rudy A.; Liu, Ying
D.; Long, David M.; Colaninno, Robin C.; Reiss, Martin A.; Temmer,
Manuela; Farrugia, Charles J.; Posner, Arik; Dumbovic, Mateja; Janvier,
Miho; Demoulin, Pascal; Boakes, Peter; Devos, Andy; Kraaikamp, Emil;
Mays, Mona L.; Vrsnak, Bojan
Bibcode: 2015EGUGA..17.1366M
Altcode:
We discuss multipoint imaging and in situ observations of the coronal
mass ejection (CME) on January 7 2014 which resulted in a major false
alarm. While the source region was almost at disk center facing Earth,
the eruption was strongly deflected in the corona, and in conjunction
with its particular orientation this CME missed Earth almost entirely,
leading to no significant geomagnetic effects. We demonstrate this
by a synthesis of data from 7 different heliospheric and planetary
space missions (STEREO-A/B, SOHO, SDO, Wind, Mars Express, Mars
Science Laboratory). The CMEs ecliptic part was deflected by 37
± 10° in heliospheric longitude, a value larger than previously
thought. Multipoint in situ observations at Earth and Mars confirm
the deflection, and are consistent with an elliptical interplanetary
shock shape of aspect ratio 1.4 ± 0.4. We also discuss our new method,
the Ellipse Evolution (ElEvo) model, which allows us to optimize the
global shape of the CME shock with multipoint in situ observations of
the interplanetary CME arrival. ElEvo, which is an extension to the
Drag-Based-Model by Vrsnak et al., may also be used for real time space
weather forecasting. The presented results enhance our understanding
of CME deflection and shape, which are fundamental ingredients for
improving space weather forecasts.
Title: Particle Acceleration in Plasmoid Ejections Derived from
Radio Drifting Pulsating Structures
Authors: Nishizuka, N.; Karlický, M.; Janvier, M.; Bárta, M.
Bibcode: 2015ApJ...799..126N
Altcode: 2014arXiv1412.7904N
We report observations of slowly drifting pulsating structures
(DPSs) in the 0.8-4.5 GHz frequency range of the RT4 and RT5 radio
spectrographs at Ondřejov Observatory, between 2002 and 2012. We
found 106 events of DPSs, which we classified into four cases:
(I) single events with a constant frequency drift (12 events), (II)
multiple events occurring in the same flare with constant frequency
drifts (11 events), (III) single or multiple events with increasing
or decreasing frequency drift rates (52 events), and (IV) complex
events containing multiple events occurring at the same time in a
different frequency range (31 events). Many DPSs are associated with
hard X-ray (HXR) bursts (15-25 keV) and soft X-ray (SXR) gradient
peaks, as they typically occurred at the beginning of HXR peaks. This
indicates that DPS events are related to the processes of fast energy
release and particle acceleration. Furthermore, interpreting DPSs
as signatures of plasmoids, we measured their ejection velocity,
their width, and their height from the DPS spectra, from which we
also estimated the reconnection rate and the plasma beta. In this
interpretation, constant frequency drift indicates a constant velocity
of a plasmoid, and an increasing/decreasing frequency drift indicates a
deceleration/acceleration of a plasmoid ejection. The reconnection rate
shows a good positive correlation with the plasmoid velocity. Finally
we confirmed that some DPS events show plasmoid counterparts in Solar
Dynamics Observatory/Atmospheric Imaging Assembly images.
Title: In situ properties of small and large flux ropes in the
solar wind
Authors: Janvier, M.; Démoulin, P.; Dasso, S.
Bibcode: 2014JGRA..119.7088J
Altcode: 2014arXiv1408.5520J
Two populations of twisted magnetic field tubes, or flux ropes
(hereafter, FRs), are detected by in situ measurements in the solar
wind. While small FRs are crossed by the observing spacecraft within
few hours, with a radius typically less than 0.1 AU, larger FRs,
or magnetic clouds (hereafter, MCs), have durations of about half a
day. The main aim of this study is to compare the properties of both
populations of FRs observed by the Wind spacecraft at 1 AU. To do so,
we use standard correlation techniques for the FR parameters, as well
as histograms and more refined statistical methods. Although several
properties seem at first different for small FRs and MCs, we show
that they are actually governed by the same propagation physics. For
example, we observe no in situ signatures of expansion for small FRs,
contrary to MCs. We demonstrate that this result is in fact expected:
small FRs expand similar to MCs, as a consequence of a total pressure
balance with the surrounding medium, but the expansion signature is
well hidden by velocity fluctuations. Next, we find that the FR radius,
velocity, and magnetic field strength are all positively correlated,
with correlation factors than can reach a value >0.5. This
result indicates a remnant trace of the FR ejection process from the
corona. We also find a larger FR radius at the apex than at the legs
(up to 3 times larger at the apex), for FR observed at 1 AU. Finally,
assuming that the detected FRs have a large-scale configuration in
the heliosphere, we derived the mean axis shape from the probability
distribution of the axis orientation. We therefore interpret the small
FR and MC properties in a common framework of FRs interacting with
the solar wind, and we disentangle the physics present behind their
common and different features.
Title: Are There Different Populations of Flux Ropes in the Solar
Wind?
Authors: Janvier, M.; Démoulin, P.; Dasso, S.
Bibcode: 2014SoPh..289.2633J
Altcode: 2014SoPh..tmp...26J; 2014arXiv1401.6812J
Flux ropes are twisted magnetic structures that can be detected by
in-situ measurements in the solar wind. However, different properties of
detected flux ropes suggest different types of flux-rope populations. As
such, are there different populations of flux ropes? The answer is
positive and is the result of the analysis of four lists of flux ropes,
including magnetic clouds (MCs), observed at 1 AU. The in-situ data for
the four lists were fitted with the same cylindrical force-free field
model, which provides an estimate of the local flux-rope parameters
such as its radius and orientation. Since the flux-rope distributions
have a broad dynamic range, we went beyond a simple histogram analysis
by developing a partition technique that uniformly distributes the
statistical fluctuations across the radius range. By doing so, we found
that small flux ropes with radius R<0.1 AU have a steep power-law
distribution in contrast to the larger flux ropes (identified as MCs),
which have a Gaussian-like distribution. Next, from four CME catalogs,
we estimated the expected flux-rope frequency per year at 1 AU. We
found that the predicted numbers are similar to the frequencies of MCs
observed in-situ. However, we also found that small flux ropes are at
least ten times too abundant to correspond to CMEs, even to narrow
ones. Investigating the different possible scenarios for the origin
of these small flux ropes, we conclude that these twisted structures
can be formed by blowout jets in the low corona or in coronal streamers.
Title: Electric Currents in Flare Ribbons: Observations and
Three-dimensional Standard Model
Authors: Janvier, M.; Aulanier, G.; Bommier, V.; Schmieder, B.;
Démoulin, P.; Pariat, E.
Bibcode: 2014ApJ...788...60J
Altcode: 2014arXiv1402.2010J
We present for the first time the evolution of the photospheric electric
currents during an eruptive X-class flare, accurately predicted by the
standard three-dimensional (3D) flare model. We analyze this evolution
for the 2011 February 15 flare using Helioseismic and Magnetic
Imager/Solar Dynamics Observatory magnetic observations and find
that localized currents in J-shaped ribbons increase to double their
pre-flare intensity. Our 3D flare model, developed with the OHM code,
suggests that these current ribbons, which develop at the location of
extreme ultraviolet brightenings seen with Atmospheric Imaging Assembly
imagery, are driven by the collapse of the flare's coronal current
layer. These findings of increased currents restricted in localized
ribbons are consistent with the overall free energy decrease during a
flare, and the shapes of these ribbons also give an indication of how
twisted the erupting flux rope is. Finally, this study further enhances
the close correspondence obtained between the theoretical predictions
of the standard 3D model and flare observations, indicating that the
main key physical elements are incorporated in the model.
Title: Mean shape of interplanetary shocks deduced from in situ
observations and its relation with interplanetary CMEs
Authors: Janvier, M.; Démoulin, P.; Dasso, S.
Bibcode: 2014A&A...565A..99J
Altcode:
Context. Shocks are frequently detected by spacecraft in the
interplanetary space. However, the in situ data of a shock do
not provide direct information on its overall properties even
when a following interplanetary coronal mass ejection (ICME) is
detected.
Aims: The main aim of this study is to constrain
the general shape of ICME shocks with a statistical study of shock
orientations.
Methods: We first associated a set of shocks
detected near Earth over 10 years with a sample of ICMEs over the
same period. We then analyzed the correlations between shock and
ICME parameters and studied the statistical distributions of the
local shock normal orientation. Supposing that shocks are uniformly
detected all over their surface projected on the 1 AU sphere, we
compared the shock normal distribution with synthetic distributions
derived from an analytical shock shape model. Inversely, we derived
a direct method to compute the typical general shape of ICME shocks
by integrating observed distributions of the shock normal.
Results: We found very similar properties between shocks with and
without an in situ detected ICME, so that most of the shocks detected
at 1 AU are ICME-driven even when no ICME is detected. The statistical
orientation of shock normals is compatible with a mean shape having a
rotation symmetry around the Sun-apex line. The analytically modeled
shape captures the main characteristics of the observed shock normal
distribution. Next, by directly integrating the observed distribution,
we derived the mean shock shape, which is found to be comparable for
shocks with and without a detected ICME and weakly affected by the
limited statistics of the observed distribution. We finally found a
close correspondence between this statistical result and the leading
edge of the ICME sheath that is observed with STEREO imagers.
Conclusions: We have derived a mean shock shape that only depends on
one free parameter. This mean shape can be used in various contexts,
such as studies for high-energy particles or space weather forecasts.
Title: Slipping Magnetic Reconnection during an X-class Solar Flare
Observed by SDO/AIA
Authors: Dudík, J.; Janvier, M.; Aulanier, G.; Del Zanna, G.;
Karlický, M.; Mason, H. E.; Schmieder, B.
Bibcode: 2014ApJ...784..144D
Altcode: 2014arXiv1401.7529D
We present SDO/AIA observations of an eruptive X-class flare of
2012 July 12, and compare its evolution with the predictions of a
three-dimensional (3D) numerical simulation. We focus on the dynamics of
flare loops that are seen to undergo slipping reconnection during the
flare. In the Atmospheric Imaging Assembly (AIA) 131 Å observations,
lower parts of 10 MK flare loops exhibit an apparent motion with
velocities of several tens of km s-1 along the developing
flare ribbons. In the early stages of the flare, flare ribbons consist
of compact, localized bright transition-region emission from the
footpoints of the flare loops. A differential emission measure analysis
shows that the flare loops have temperatures up to the formation of
Fe XXIV. A series of very long, S-shaped loops erupt, leading to a
coronal mass ejection observed by STEREO. The observed dynamics are
compared with the evolution of magnetic structures in the "standard
solar flare model in 3D." This model matches the observations well,
reproducing the apparently slipping flare loops, S-shaped erupting
loops, and the evolution of flare ribbons. All of these processes are
explained via 3D reconnection mechanisms resulting from the expansion
of a torus-unstable flux rope. The AIA observations and the numerical
model are complemented by radio observations showing a noise storm
in the metric range. Dm-drifting pulsation structures occurring
during the eruption indicate plasmoid ejection and enhancement of the
reconnection rate. The bursty nature of radio emission shows that the
slipping reconnection is still intermittent, although it is observed
to persist for more than an hour.
Title: Highlights of Interplanetary Coronal Mass Ejections and its
impact on the terrestrial environment
Authors: Dasso, Sergio; Janvier, Miho; Demoulin, Pascal; Masías
Meza, Jimmy
Bibcode: 2014cosp...40E.637D
Altcode:
Interplanetary Coronal Mass Ejections (ICMEs) are meso-scale transient
objects in the heliosphere, ejected by the Sun from the destabilisation
of a portion of coronal magnetic field. They imply large modifications
of the heliospheric plasma and magnetic field properties. Then, an
ICME passing nearby Earth generates strong variations of the input of
energy, momentum and particles, from the interplanetary medium to the
terrestrial environment. The study of ICMEs has greatly advanced in the
last few years, thanks to multi-spacecraft observations of the solar
corona and the solar wind, combined with high performance numerical
modelling. The comparisons between models and recent observations
now answer several open questions, such as the typical configuration
(internal and global) of ICMEs, as well as how they are affected
due to their interaction with the ambient solar wind during their
propagation in the interplanetary medium. This talk will provide a
summary of recent advances in the field of ICMEs, and will present
several aspects of the interaction with the ambient solar wind that
have serious consequences on the level of Sun-Earth coupling.
Title: Structure of ICMEs and their driven shocks at 1 AU, and
consequences on Forbush decreases
Authors: Dasso, Sergio; Janvier, Miho; Demoulin, Pascal; Masias-Meza,
Jimmy J.
Bibcode: 2014cosp...40E.636D
Altcode:
Solar wind structures, such as interplanetary (IP) shocks, can affect
the transport of energetic particles in the heliosphere. In particular,
the presence of IP shocks driven by interplanetary coronal mass
ejections (ICMEs) is typically associated with a transient variation
of the energetic particles flux (e.g., Forbush decreases, FDs). A FD
can present two steps: one of them produced by a diffusive barrier
associated with the turbulent region behind the shock, and the another
one produced by the ICME itself. However, not every IP shock driven
by an ICME is followed by a two-step FD, and it is under debate what
are the properties of the solar wind for determining the presence of a
two-step Forbush decrease, the presence of a single-step FD, or even
the absence of a FD after the passage of the ICME. Magnetic clouds
(MCs) are a subset of ICMEs, which present clear evidence in favor
of the presence of an interplanetary flux rope in the solar wind. We
recently found constraints to the geometrical shape of ICME shocks from
a statistical study of shock orientations, and found constraints to the
global shape of MCs from a statistical study of main axis orientation
of a large sample of magnetic clouds, both at one astronomical unit
from the Sun. The main aim of this study is to establish the link
between Forbush decreases and the MC/shock properties, taking into
account these geometrical shapes of MC axis and shocks surfaces. We
present here a combined analysis of events MC-shock-FD, in order to
better understand the effects of interplanetary structures on the
propagation of energetic particles in the heliosphere.
Title: Flux rope axis geometry of magnetic clouds deduced from in
situ data
Authors: Janvier, Miho; Démoulin, Pascal; Dasso, Sergio
Bibcode: 2014IAUS..300..265J
Altcode:
Magnetic clouds (MCs) consist of flux ropes that are ejected from the
low solar corona during eruptive flares. Following their ejection, they
propagate in the interplanetary medium where they can be detected by in
situ instruments and heliospheric imagers onboard spacecraft. Although
in situ measurements give a wide range of data, these only depict the
nature of the MC along the unidirectional trajectory crossing of a
spacecraft. As such, direct 3D measurements of MC characteristics are
impossible. From a statistical analysis of a wide range of MCs detected
at 1 AU by the Wind spacecraft, we propose different methods to deduce
the most probable magnetic cloud axis shape. These methods include
the comparison of synthetic distributions with observed distributions
of the axis orientation, as well as the direct integration of observed
probability distribution to deduce the global MC axis shape. The overall
shape given by those two methods is then compared with 2D heliospheric
images of a propagating MC and we find similar geometrical features.
Title: Global axis shape of magnetic clouds deduced from the
distribution of their local axis orientation
Authors: Janvier, M.; Démoulin, P.; Dasso, S.
Bibcode: 2013A&A...556A..50J
Altcode: 2013arXiv1305.4039J
Context. Coronal mass ejections (CMEs) are routinely tracked with
imagers in the interplanetary space, while magnetic clouds (MCs)
properties are measured locally by spacecraft. However, both imager
and in situ data do not provide any direct estimation of the general
flux rope properties.
Aims: The main aim of this study
is to constrain the global shape of the flux rope axis from local
measurements and to compare the results from in-situ data with imager
observations.
Methods: We performed a statistical analysis of the
set of MCs observed by WIND spacecraft over 15 years in the vicinity
of Earth. We analyzed the correlation between different MC parameters
and studied the statistical distributions of the angles defining the
local axis orientation. With the hypothesis of having a sample of MCs
with a uniform distribution of spacecraft crossing along their axis,
we show that a mean axis shape can be derived from the distribution
of the axis orientation. As a complement, while heliospheric imagers
do not typically observe MCs but only their sheath region, we analyze
one event where the flux rope axis can be estimated from the STEREO
imagers.
Results: From the analysis of a set of theoretical
models, we show that the distribution of the local axis orientation
is strongly affected by the overall axis shape. Next, we derive the
mean axis shape from the integration of the observed orientation
distribution. This shape is robust because it is mostly determined
from the overall shape of the distribution. Moreover, we find no
dependence on the flux rope inclination on the ecliptic. Finally, the
derived shape is fully consistent with the one derived from heliospheric
imager observations of the June 2008 event.
Conclusions: We have
derived a mean shape of MC axis that only depends on one free parameter,
the angular separation of the legs (as viewed from the Sun). This mean
shape can be used in various contexts, such as studies of high-energy
particles or space weather forecasts.
Title: The standard flare model in three dimensions. III. Slip-running
reconnection properties
Authors: Janvier, M.; Aulanier, G.; Pariat, E.; Démoulin, P.
Bibcode: 2013A&A...555A..77J
Altcode: 2013arXiv1305.4053J
Context. A standard model for eruptive flares aims at describing
observational 3D features of the reconnecting coronal magnetic
field. Extensions to the 2D model require the physical understanding of
3D reconnection processes at the origin of the magnetic configuration
evolution. However, the properties of 3D reconnection without null point
and separatrices still need to be analyzed.
Aims: We focus on
magnetic reconnection associated with the growth and evolution of a
flux rope and associated flare loops during an eruptive flare. We aim
at understanding the intrinsic characteristics of 3D reconnection in
the presence of quasi-separatrix layers (QSLs), how QSL properties are
related to the slip-running reconnection mode in general, and how this
applies to eruptive flares in particular.
Methods: We studied
the slip-running reconnection of field lines in a magnetohydrodynamic
simulation of an eruptive flare associated with a torus-unstable flux
rope. The squashing degree and the mapping norm are two parameters
related to the QSLs. We computed them to investigate their relation
with the slip-running reconnection speed of selected field lines.
Results: Field lines associated with the flux rope and the flare loops
undergo a continuous series of magnetic reconnection, which results
in their super-Alfvénic slipping motion. The time profile of their
slippage speed and the space distribution of the mapping norm are shown
to be strongly correlated. We find that the motion speed is proportional
to the mapping norm. Moreover, this slip-running motion becomes faster
as the flux rope expands, since the 3D current layer evolves toward a
current sheet, and QSLs to separatrices.
Conclusions: The present
analysis extends our understanding of the 3D slip-running reconnection
regime. We identified a controlling parameter of the apparent velocity
of field lines while they slip-reconnect, enabling the interpretation
of the evolution of post flare loops. This work completes the standard
model for flares and eruptions by giving its 3D properties.
Title: Does spacecraft trajectory strongly affect detection of
magnetic clouds?
Authors: Démoulin, P.; Dasso, S.; Janvier, M.
Bibcode: 2013A&A...550A...3D
Altcode: 2012arXiv1211.5343D
Context. Magnetic clouds (MCs) are a subset of interplanetary coronal
mass ejections (ICMEs). One property of MCs is the presence of a
magnetic flux rope. Is the difference between ICMEs with and without
MCs intrinsic or rather due to an observational bias?
Aims:
As the spacecraft has no relationship with the MC trajectory, the
frequency distribution of MCs versus the spacecraft distance to the
MCs' axis is expected to be approximately flat. However, Lepping &
Wu (2010, Ann. Geophys., 28, 1539) confirmed that it is a strongly
decreasing function of the estimated impact parameter. Is a flux rope
more frequently undetected for larger impact parameter?
Methods:
In order to answer the questions above, we explore the parameter space
of flux rope models, especially the aspect ratio, boundary shape,
and current distribution. The proposed models are analyzed as MCs
by fitting a circular linear force-free field to the magnetic field
computed along simulated crossings.
Results: We find that the
distribution of the twist within the flux rope and the non-detection
due to too low field rotation angle or magnitude only weakly affect the
expected frequency distribution of MCs versus impact parameter. However,
the estimated impact parameter is increasingly biased to lower values
as the flux rope cross section is more elongated orthogonally to the
crossing trajectory. The observed distribution of MCs is a natural
consequence of a flux rope cross section flattened on average by a
factor 2 to 3 depending on the magnetic twist profile. However, the
faster MCs at 1 AU, with V > 550 km s-1, present an almost
uniform distribution of MCs vs. impact parameter, which is consistent
with round-shaped flux ropes, in contrast with the slower ones.
Conclusions: We conclude that the sampling of MCs at various distances
from the axis does not significantly affect their detection. The large
part of ICMEs without MCs could be due to a too strict criteria for
MCs or to the fact that these ICMEs are encountered outside their flux
rope or near the leg region, or they do not contain a flux rope.
Title: The standard flare model in three dimensions. II. Upper limit
on solar flare energy
Authors: Aulanier, G.; Démoulin, P.; Schrijver, C. J.; Janvier, M.;
Pariat, E.; Schmieder, B.
Bibcode: 2013A&A...549A..66A
Altcode: 2012arXiv1212.2086A
Context. Solar flares strongly affect the Sun's atmosphere as well as
the Earth's environment. Quantifying the maximum possible energy of
solar flares of the present-day Sun, if any, is thus a key question in
heliophysics.
Aims: The largest solar flares observed over the
past few decades have reached energies of a few times 1032
erg, possibly up to 1033 erg. Flares in active Sun-like
stars reach up to about 1036 erg. In the absence of direct
observations of solar flares within this range, complementary methods
of investigation are needed to assess the probability of solar flares
beyond those in the observational record.
Methods: Using
historical reports for sunspot and solar active region properties
in the photosphere, we scaled to observed solar values a realistic
dimensionless 3D MHD simulation for eruptive flares, which originate
from a highly sheared bipole. This enabled us to calculate the magnetic
fluxes and flare energies in the model in a wide paramater space.
Results: Firstly, commonly observed solar conditions lead to modeled
magnetic fluxes and flare energies that are comparable to those
estimated from observations. Secondly, we evaluate from observations
that 30% of the area of sunspot groups are typically involved in
flares. This is related to the strong fragmentation of these groups,
which naturally results from sub-photospheric convection. When the
model is scaled to 30% of the area of the largest sunspot group ever
reported, with its peak magnetic field being set to the strongest value
ever measured in a sunspot, it produces a flare with a maximum energy of
~6 × 1033 erg.
Conclusions: The results of the model
suggest that the Sun is able to produce flares up to about six times as
energetic in total solar irradiance fluence as the strongest directly
observed flare of Nov. 4, 2003. Sunspot groups larger than historically
reported would yield superflares for spot pairs that would exceed tens
of degrees in extent. We thus conjecture that superflare-productive
Sun-like stars should have a much stronger dynamo than in the Sun.
Title: The standard flare model in three dimensions. I. Strong-to-weak
shear transition in post-flare loops
Authors: Aulanier, G.; Janvier, M.; Schmieder, B.
Bibcode: 2012A&A...543A.110A
Altcode:
Context. The standard CSHKP model for eruptive flares is
two-dimensional. Yet observational interpretations of photospheric
currents in pre-eruptive sigmoids, shear in post-flare loops, and
relative positioning and shapes of flare ribbons, all together require
three-dimensional extensions to the model.
Aims: We focus on
the strong-to-weak shear transition in post-flare loops, and on the
time-evolution of the geometry of photospheric electric currents, which
occur during the development of eruptive flares. The objective is to
understand the three-dimensional physical processes, which cause them,
and to know how much the post-flare and the pre-eruptive distributions
of shear depend on each other.
Methods: The strong-to-weak shear
transition in post-flare loops is identified and quantified in a flare
observed by STEREO, as well as in a magnetohydrodynamic simulation
of CME initiation performed with the OHM code. In both approaches,
the magnetic shear is evaluated with field line footpoints. In the
simulation, the shear is also estimated from ratios between magnetic
field components.
Results: The modeled strong-to-weak shear
transition in post-flare loops comes from two effects. Firstly,
a reconnection-driven transfer of the differential magnetic shear,
from the pre- to the post-eruptive configuration. Secondly, a vertical
straightening of the inner legs of the CME, which induces an outer shear
weakening. The model also predicts the occurrence of narrow electric
current layers inside J-shaped flare ribbons, which are dominated
by direct currents. Finally, the simulation naturally accounts for
energetics and time-scales for weak and strong flares, when typical
scalings for young and decaying solar active regions are applied.
Conclusions: The results provide three-dimensional extensions to
the standard flare model. These extensions involve MHD processes that
should be tested with observations.
Title: Slip-running reconnection and evolution of shear in post-flare
loops
Authors: Janvier, Miho; Schmieder, Brigitte; Pariat, Etienne;
Aulanier, Guillaume
Bibcode: 2012cosp...39..816J
Altcode: 2012cosp.meet..816J
We analyze the physical mechanisms of an eruptive flare via 3D
magnetohydrodynamic simulations of a flux rope. We focus on the
relaxation process associated with the reconnection of magnetic field
lines driven by the free expansion of the magnetic field. First, the
origin of the shearing of post-flare magnetic loops is investigated
in relation to the pre-flare geometry of the magnetic field. Indeed,
space-borne satellites can observe the temporal changes of post-flare
structures that are important observational manifestations of the
solar flare phenomenon. As such, understanding the evolution of
post-flare loops can reveal the characteristics of the pre-flare
magnetic field. Here, we introduce different proxies to quantify
the shear angle. We show that strong geometrical similarities exist
between the initial magnetic field and the post-flare loops. Analysis
of the eruption dynamics shows that magnetic reconnection at the origin
of the post-flare field lines forms less and less sheared magnetic
loops on top of one another. We confirm this tendency by direct
measurements of the shear angle seen in flare events such as that
of May 9, 2011 recorded by STEREO-B/EUVI. Our results also highlight
that vertical stretching of the magnetic field lines may play a role
in the shear angle evolution of post-flare loops. The analysis of
the eruptive flare evolution is followed by a detailed investigation
of the flux rope growth and of the post-flare loops formation due to
coronal slip-running reconnection. For that, we study the dynamics of
different regions around two ribbons of opposite current. We find that
these ribbons correspond to quasi-separatrix layers (QSLs), associated
with J-shaped pre-flare magnetic field lines, reconnected S-shaped
flux rope lines and post-flare loops. Simulations with very small time
steps are required so as to show the detailed time evolution of those
QSLs as well as the time variations of the slip-running velocities. Our
results provide a fully 3D extension of the standard 2D flare model.
Title: Structure-Driven Nonlinear Instability as the Origin of the
Explosive Reconnection Dynamics in Resistive Double Tearing Modes
Authors: Janvier, M.; Kishimoto, Y.; Li, J. Q.
Bibcode: 2011PhRvL.107s5001J
Altcode:
The onset of abrupt magnetic reconnection events, observed in the
nonlinear evolution of double tearing modes (DTM), is investigated via
reduced resistive magnetohydrodynamic simulations. We have identified
the critical threshold for the parameters characterizing the linear
DTM stability leading to the bifurcation to the explosive dynamics. A
new type of secondary instability is discovered that is excited
once the magnetic islands on each rational surface reach a critical
structure characterized here by the width and the angle rating their
triangularization. This new instability is an island structure-driven
nonlinear instability, identified as the trigger of the subsequent
nonlinear dynamics which couples flow and flux perturbations. This
instability only weakly depends on resistivity.
Title: Venus Express science planning
Authors: Titov, D. V.; Svedhem, H.; Koschny, D.; Hoofs, R.; Barabash,
S.; Bertaux, J. -L.; Drossart, P.; Formisano, V.; Häusler, B.;
Korablev, O.; Markiewicz, W. J.; Nevejans, D.; Pätzold, M.; Piccioni,
G.; Zhang, T. L.; Merritt, D.; Witasse, O.; Zender, J.; Accomazzo,
A.; Sweeney, M.; Trillard, D.; Janvier, M.; Clochet, A.
Bibcode: 2006P&SS...54.1279T
Altcode:
Venus Express is the first European mission to the planet Venus. Its
payload consists of seven instruments and will investigate the
atmosphere, the plasma environment, and the surface of Venus from
orbit. Science planning is a complex process that takes into account
requests from all experiments and the operational constraints. The
planning of the science operations is based on synergetic approach to
provide good coverage of science themes derived from the main mission
goals. Typical observations in a single orbit - so-called "science
cases" are used to build the mission science activity plan. The nominal
science mission (from June 4, 2006 till October 2, 2007) is divided
in nine phases depending on observational conditions, occurrences of
the solar and Earth occultation, and particular science goals. The
observation timelines for each phase were developed in a coordinated
way to optimize the payload activity, maximize the overall mission
science return, and to fit into the available mission budgets.
Title: SOHO Microvibrations: Analyses, Tests and Flight Results
Authors: Laurens, Ph.; Decoux, E.; Janvier, M.
Bibcode: 1997ESASP.381..489L
Altcode: 1997sgnc.conf..489L
No abstract at ADS
Title: Atelier scientifique: une autre façon d'enseigner les sciences
au collège.
Authors: Janvier, M.
Bibcode: 1996LAstr.110...44J
Altcode:
No abstract at ADS
Title: Hermes rendezvous and navigation system
Authors: Frezet, M.; Riant, P.; Janvier, M.; Caldichoury, M.
Bibcode: 1989ESASP.297..207F
Altcode: 1989ioot.conf..207F
No abstract at ADS