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Author name code: jurcak
ADS astronomy entries on 2022-09-14
author:"Jurcak, Jan"
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Title: The European Solar Telescope
Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.;
Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein,
C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz
Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados,
M.; the EST team
2022arXiv220710905Q Altcode:
The European Solar Telescope (EST) is a project aimed at studying
the magnetic connectivity of the solar atmosphere, from the deep
photosphere to the upper chromosphere. Its design combines the knowledge
and expertise gathered by the European solar physics community during
the construction and operation of state-of-the-art solar telescopes
operating in visible and near-infrared wavelengths: the Swedish 1m Solar
Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR,
the French Télescope Héliographique pour l'Étude du Magnétisme
et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope
(DOT). With its 4.2 m primary mirror and an open configuration, EST will
become the most powerful European ground-based facility to study the Sun
in the coming decades in the visible and near-infrared bands. EST uses
the most innovative technological advances: the first adaptive secondary
mirror ever used in a solar telescope, a complex multi-conjugate
adaptive optics with deformable mirrors that form part of the optical
design in a natural way, a polarimetrically compensated telescope design
that eliminates the complex temporal variation and wavelength dependence
of the telescope Mueller matrix, and an instrument suite containing
several (etalon-based) tunable imaging spectropolarimeters and several
integral field unit spectropolarimeters. This publication summarises
some fundamental science questions that can be addressed with the
telescope, together with a complete description of its major subsystems.
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Title: Characterization of magneto-convection in sunspots. The
Gough-Tayler stability criterion in MURaM sunspot simulations
Authors: Schmassmann, M.; Rempel, M.; Bello González, N.;
Schlichenmaier, R.; Jurčák, J.
2021A&A...656A..92S Altcode:
Context. Observations have shown that in stable sunspots, the umbral
boundary is outlined by a critical value of the vertical magnetic
field component. However, the nature of the distinct magnetoconvection
regimes in the umbra and penumbra is still unclear. <BR /> Aims: We
analyse a sunspot simulation in an effort to understand the origin
of the convective instabilities giving rise to the penumbral and
umbral distinct regimes. <BR /> Methods: We applied the criterion
from Gough & Tayler (1966, MNRAS, 133, 85), accounting for the
stabilising effect of the vertical magnetic field, to investigate
the convective instabilities in a MURaM sunspot simulation. <BR />
Results: We find: (1) a highly unstable shallow layer right beneath the
surface extending all over the simulation box in which convection is
triggered by radiative cooling in the photosphere; (2) a deep umbral
core (beneath −5 Mm) stabilised against overturning convection
that underlies a region with stable background values permeated
by slender instabilities coupled to umbral dots; (3) filamentary
instabilities below the penumbra nearly parallel to the surface and
undulating instabilities coupled to the penumbra which originate
in the deep layers. These deep-rooted instabilities result in the
vigorous magneto-convection regime characteristic of the penumbra; (4)
convective downdrafts in the granulation, penumbra, and umbra develop
at about 2 km s<SUP>−1</SUP>, 1 km s<SUP>−1</SUP>, and 0.1 km
s<SUP>−1</SUP>, respectively, indicating that the granular regime of
convection is more vigorous than the penumbra convection regime, which,
in turn, is more vigorous than the close-to-steady umbra; (5) the GT
criterion outlines both the sunspot magnetopause and peripatopause,
highlighting the tripartite nature of the sub-photospheric layers
of magnetohydrodynamic (MHD) sunspot models; and, finally, (6)
the Jurčák criterion is the photospheric counterpart of the GT
criterion in deep layers. <BR /> Conclusions: The GT criterion as a
diagnostic tool reveals the tripartite nature of sunspot structure
with distinct regimes of magneto-convection in the umbra, penumbra,
and granulation operating in realistic MHD simulations. <P
/>Movies associated with Figs. 2 and 3 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141607/olm">https://www.aanda.org</A>
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Title: Properties of the inner penumbra boundary and temporal
evolution of a decaying sunspot (Corrigendum)
Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry,
P.; Kuckein, C.; Jurčák, J.
2021A&A...652C...7B Altcode:
No abstract at ADS
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Title: Magnetic properties on the boundary of an evolving pore
Authors: García-Rivas, M.; Jurčák, J.; Bello González, N.
2021A&A...649A.129G Altcode: 2021arXiv210208459G
Context. Analyses of the magnetic properties on umbrae boundaries
have led to the Jurčák criterion, which states that umbra-penumbra
boundaries in stable sunspots are equally defined by a constant value
of the vertical magnetic field, B<SUB>ver</SUB><SUP>crit</SUP>, and by
a 50% continuum intensity of the quiet Sun, I<SUB>QS</SUB>. Umbrae with
vertical magnetic fields stronger than B<SUB>ver</SUB><SUP>crit</SUP>
are stable, whereas umbrae with vertical magnetic fields weaker than
B<SUB>ver</SUB><SUP>crit</SUP> are unstable and prone to vanishing. <BR
/> Aims: We aim to investigate the existence of a critical value of
the vertical magnetic field on a pore boundary and its role in the
evolution of the magnetic structure. <BR /> Methods: We analysed
SDO/HMI vector field maps corrected for scattered light and with a
temporal cadence of 12 min during a 26.5-hour period. A continuum
intensity threshold (I<SUB>c</SUB> = 0.55 I<SUB>QS</SUB>) is used to
define the pore boundary and we study the temporal evolution of the
magnetic properties there. <BR /> Results: We observe well-defined
stages in the pore evolution: (1) during the initial formation
phase, total magnetic field strength (B) and vertical magnetic field
(B<SUB>ver</SUB>) increase to their maximum values of ∼1920 G and
∼1730 G, respectively; (2) then the pore reaches a stable phase;
(3) in a second formation phase, the pore undergoes a rapid growth
in terms of size, along with a decrease in B and B<SUB>ver</SUB> on
its boundary. In the newly formed area of the pore, B<SUB>ver</SUB>
remains mostly below 1731 G and B remains everywhere below 1921 G;
(4) ultimately, pore decay starts. We find overall that pore areas with
B<SUB>ver</SUB> < 1731 G, or equivalently B < 1921 G, disintegrate
faster than regions that fulfil this criteria. <BR /> Conclusions:
We find that the most stable regions of the pore, similarly to the
case of umbral boundaries, are defined by a critical value of the
vertical component of the magnetic field that is comparable to that
found in stable sunspots. In addition, in this case study, the same
pore areas can be similarly well-defined by a critical value of the
total magnetic field strength.
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Title: Evaluating the Reliability of a Simple Method to Map the
Magnetic Field Azimuth in the Solar Chromosphere
Authors: Jurčák, Jan; Štěpán, Jiří; Trujillo Bueno, Javier
2021ApJ...911...23J Altcode: 2021arXiv210202880J
The Zeeman effect is of limited utility for probing the magnetism
of the quiet solar chromosphere. The Hanle effect in some spectral
lines is sensitive to such magnetism, but the interpretation of the
scattering polarization signals requires taking into account that the
chromospheric plasma is highly inhomogeneous and dynamic (i.e., that
the magnetic field is not the only cause of symmetry breaking). Here
we investigate the reliability of a well-known formula for mapping the
azimuth of chromospheric magnetic fields directly from the scattering
polarization observed in the Ca II 8542 Å line, which is typically
in the saturation regime of the Hanle effect. To this end, we use
the Stokes profiles of the Ca II 8542 Å line computed with the PORTA
radiative transfer code in a three-dimensional (3D) model of the solar
chromosphere, degrading them to mimic spectropolarimetric observations
for a range of telescope apertures and noise levels. The simulated
observations are used to obtain the magnetic field azimuth at each
point of the field of view, which we compare with the actual values
within the 3D model. We show that, apart from intrinsic ambiguities,
the method provides solid results. Their accuracy depends more on
the noise level than on the telescope diameter. Large-aperture solar
telescopes, like DKIST and EST, are needed to achieve the required
polarimetric sensitivity using reasonable exposure times.
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Title: Solar pores - A magnetic evolution laboratory
Authors: García-Rivas, M.; Jurčák, J.; Bello González, N.
2020sea..confE.198G Altcode:
Analyses of the vector magnetic field on solar magnetic structures led
to the Jurčák criterion, an empirical law that connects a critical
value of the vertical component of the magnetic field to the umbral
magnetoconvective mode in stable sunspots. We study the evolution of the
vertical component of the magnetic field (B<SUB>ver</SUB>) on evolving
pores and the existence of an equivalent critical vertical magnetic
value to provide steadiness. Indeed, we find that areas with weak
B<SUB>ver</SUB> are unstable and granulation takes over them. However,
areas with strong B<SUB>ver</SUB> show longer lifetimes.
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Title: A distinct magnetic property of the inner penumbral
boundary. III. Analysis of simulated sunspots
Authors: Jurčák, Jan; Schmassmann, Markus; Rempel, Matthias; Bello
González, Nazaret; Schlichenmaier, Rolf
2020A&A...638A..28J Altcode: 2020arXiv200403940J
Context. Analyses of sunspot observations revealed a fundamental
magnetic property of the umbral boundary: the invariance of the
vertical component of the magnetic field. <BR /> Aims: We analyse
the magnetic properties of the umbra-penumbra boundary in simulated
sunspots and thus assess their similarity to observed sunspots. We
also aim to investigate the role of the plasma β and the ratio of
kinetic to magnetic energy in simulated sunspots in the convective
motions because these quantities cannot be reliably determined from
observations. <BR /> Methods: We used a set of non-gray simulation
runs of sunspots with the MURaM code. The setups differed in terms
of subsurface magnetic field structure and magnetic field boundary
imposed at the top of the simulation domain. These data were used to
synthesize the Stokes profiles, which were then degraded to the Hinode
spectropolarimeter-like observations. Then, the data were treated
like real Hinode observations of a sunspot, and magnetic properties
at the umbral boundaries were determined. <BR /> Results: Simulations
with potential field extrapolation produce a realistic magnetic field
configuration on the umbral boundaries of the sunspots. Two simulations
with a potential field upper boundary, but different subsurface
magnetic field structures, differ significantly in the extent of their
penumbrae. Increasing the penumbra width by forcing more horizontal
magnetic fields at the upper boundary results in magnetic properties
that are not consistent with observations. This implies that the size of
the penumbra is given by the subsurface structure of the magnetic field,
that is, by the depth and inclination of the magnetopause, which is
shaped by the expansion of the sunspot flux rope with height. None of
the sunspot simulations is consistent with the observed properties of
the magnetic field and the direction of the Evershed flow at the same
time. Strong outward-directed Evershed flows are only found in setups
with an artificially enhanced horizontal component of the magnetic
field at the top boundary that are not consistent with the observed
magnetic field properties at the umbra-penumbra boundary. We stress
that the photospheric boundary of simulated sunspots is defined by a
magnetic field strength of equipartition field value.
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Title: Exploiting Solar Visible-Range Observations by Inversion
Techniques: From Flows in the Solar Subsurface to a Flaring Atmosphere
Authors: Švanda, Michal; Jurčák, Jan; Korda, David; Kašparová,
Jana
2020rfma.book..349S Altcode:
Observations of the Sun in the visible spectral range belong to standard
measurements obtained by instruments both on the ground and in the
space. Nowadays, both nearly continuous full-disc observations with
medium resolution and dedicated campaigns of high spatial, spectral
and/or temporal resolution constitute a holy grail for studies that
can capture (both) the long- and short-term changes in the dynamics
and energetics of the solar atmosphere. Observations of photospheric
spectral lines allow us to estimate not only the intensity at small
regions, but also various derived data products, such as the Doppler
velocity and/or the components of the magnetic field vector. We show
that these measurements contain not only direct information about the
dynamics of solar plasmas at the surface of the Sun but also imprints
of regions below and above it. Here, we discuss two examples: First,
the local time-distance helioseismology as a tool for plasma dynamic
diagnostics in the near subsurface and second, the determination of
the solar atmosphere structure during flares. The methodology in both
cases involves the technique of inverse modelling.
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Title: Chromospheric Heating by Acoustic Waves Compared to Radiative
Cooling. II. Revised Grid of Models
Authors: Abbasvand, Vahid; Sobotka, Michal; Heinzel, Petr; Švanda,
Michal; Jurčák, Jan; del Moro, Dario; Berrilli, Francesco
2020ApJ...890...22A Altcode: 2020arXiv200103413A
Acoustic and magnetoacoustic waves are considered to be possible
agents of chromospheric heating. We present a comparison of deposited
acoustic energy flux with total integrated radiative losses in the
middle chromosphere of the quiet Sun and a weak plage. The comparison
is based on a consistent set of high-resolution observations acquired
by the Interferometric Bidimensional Spectrometer instrument in the
Ca II 854.2 nm line. The deposited acoustic-flux energy is derived
from Doppler velocities observed in the line core and a set of 1737
non-local thermodynamic equilibrium 1D hydrostatic semi-empirical
models, which also provide the radiative losses. The models are obtained
by scaling the temperature and column mass of five initial models by
Vernazza et al. (1981; VAL) B-F to get the best fit of synthetic to
observed profiles. We find that the deposited acoustic-flux energy in
the quiet-Sun chromosphere balances 30%-50% of the energy released by
radiation. In the plage, it contributes by 50%-60% in locations with
vertical magnetic field and 70%-90% in regions where the magnetic
field is inclined more than 50° to the solar surface normal.
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Title: Exploiting solar visible-range observations by inversion
techniques: from flows in the solar subsurface to a flaring atmosphere
Authors: Švanda, Michal; Jurčák, Jan; Korda, David; Kašparová,
Jana
2020arXiv200103874S Altcode:
Observations of the Sun in the visible spectral range belong to standard
measurements obtained by instruments both on the ground and in the
space. Nowadays, both nearly continuous full-disc observations with
medium resolution and dedicated campaigns of high spatial, spectral
and/or temporal resolution constitute a holy grail for studies that
can capture (both) the long- and short-term changes in the dynamics
and energetics of the solar atmosphere. Observations of photospheric
spectral lines allow us to estimate not only the intensity at small
regions, but also various derived data products, such as the Doppler
velocity and/or the components of the magnetic field vector. We show
that these measurements contain not only direct information about the
dynamics of solar plasmas at the surface of the Sun but also imprints
of regions below and above it. Here, we discuss two examples: First,
the local time-distance helioseismology as a tool for plasma dynamic
diagnostics in the near subsurface and second, the determination of
the solar atmosphere structure during flares. The methodology in both
cases involves the technique of inverse modelling.
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Title: Science Requirement Document (SRD) for the European Solar
Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
J.; Utz, D.; Zuccarello, F.
2019arXiv191208650S Altcode:
The European Solar Telescope (EST) is a research infrastructure
for solar physics. It is planned to be an on-axis solar telescope
with an aperture of 4 m and equipped with an innovative suite of
spectro-polarimetric and imaging post-focus instrumentation. The EST
project was initiated and is driven by EAST, the European Association
for Solar Telescopes. EAST was founded in 2006 as an association
of 14 European countries. Today, as of December 2019, EAST consists
of 26 European research institutes from 18 European countries. The
Preliminary Design Phase of EST was accomplished between 2008 and
2011. During this phase, in 2010, the first version of the EST Science
Requirement Document (SRD) was published. After EST became a project
on the ESFRI roadmap 2016, the preparatory phase started. The goal
of the preparatory phase is to accomplish a final design for the
telescope and the legal governance structure of EST. A major milestone
on this path is to revisit and update the Science Requirement Document
(SRD). The EST Science Advisory Group (SAG) has been constituted by
EAST and the Board of the PRE-EST EU project in November 2017 and has
been charged with the task of providing with a final statement on the
science requirements for EST. Based on the conceptual design, the SRD
update takes into account recent technical and scientific developments,
to ensure that EST provides significant advancement beyond the current
state-of-the-art. The present update of the EST SRD has been developed
and discussed during a series of EST SAG meetings. The SRD develops
the top-level science objectives of EST into individual science
cases. Identifying critical science requirements is one of its main
goals. Those requirements will define the capabilities of EST and the
post-focus instrument suite. The technical requirements for the final
design of EST will be derived from the SRD.
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Title: The influence of Hinode/SOT NFI instrumental effects on the
visibility of simulated prominence fine structures in Hα
Authors: Gunár, S.; Jurčák, J.; Ichimoto, K.
2019A&A...629A.118G Altcode:
Context. Models of entire prominences with their numerous fine
structures distributed within the prominence magnetic field use
approximate radiative transfer techniques to visualize the simulated
prominences. However, to accurately compare synthetic images of
prominences obtained in this way with observations and to precisely
analyze the visibility of even the faintest prominence features,
it is important to take into account the influence of instrumental
properties on the synthetic spectra and images. <BR /> Aims: In the
present work, we investigate how synthetic Hα images of simulated
prominences are impacted by the instrumental effects induced by the
Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT)
onboard the Hinode satellite. <BR /> Methods: To process the synthetic
Hα images provided by 3D Whole-Prominence Fine Structure (WPFS) models
into SOT-like synthetic Hα images, we take into account the effects of
the integration over the theoretical narrow-band transmission profile
of NFI Lyot filter, the influence of the stray-light and point spread
function (PSF) of Hinode/SOT, and the observed noise level. This allows
us to compare the visibility of the prominence fine structures in the
SOT-like synthetic Hα images with the synthetic Hα line-center images
used by the 3D models and with a pair of Hinode/SOT NFI observations
of quiescent prominences. <BR /> Results: The comparison between
the SOT-like synthetic Hα images and the synthetic Hα line-center
images shows that all large and small-scale features are very similar
in both visualizations and that the same very faint prominence fine
structures can be discerned in both. This demonstrates that the
computationally efficient Hα line-center visualization technique
can be reliably used for the purpose of visualization of complex 3D
prominence models. In addition, the qualitative comparison between the
SOT-like synthetic images and prominence observations shows that the
3D WPFS models can reproduce large-scale prominence features rather
well. However, the distribution of the prominence fine structures
is significantly more diffuse in the observations than in the models
and the diffuse intensity areas surrounding the observed prominences
are also not present in the synthetic images. We also found that the
maximum intensities reached in the models are about twice as high as
those present in the observations-an indication that the mass-loading
assumed in the present 3D WPFS models might be too large.
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Title: A Quantitative Comparison of Observed and Theoretical Stokes
Profiles of the Ca II 8542 Å Line in the Quiet Sun
Authors: Jurčák, J.; Stěpán, J.; Bianda, M.; Trujillo Bueno, J.
2019ASPC..526..235J Altcode:
We present an analysis of the Stokes profiles of the Ca II 8542 Å
line produced by the joint action of atomic level polarization and the
Hanle and Zeeman effects. We compare spectropolarimetric observations
of this line in a quiet region at the solar disk centre, taken with
the ZIMPOL instrument at IRSOL, with the theoretical Stokes profiles
computed with the PORTA radiative transfer code using as solar model
atmosphere a 3D snapshot taken from a radiation MHD simulation of
an enhanced-network region. Even though the spatial sampling of the
ZIMPOL observations is only 1.43 arcsec/pixel, we detect Q/I, U/I and
V/I polarization signals of the order of 0.1%. The synthetic line
profiles have been obtained by solving the full 3D NLTE radiative
transfer problem taking into account the symmetry breaking effects
due to the model's horizontal inhomogeneities and macroscopic velocity
gradients. After spatial and spectral degradation, in some locations
we find similar amplitudes between the observed and calculated linear
polarization profiles. However, in general, the observations show
stronger polarization signals than the calculated ones, a discrepancy
that could be used to refine the numerical models of the quiet solar
chromosphere.
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Title: New Insights on Penumbra Magneto-Convection
Authors: Bello González, N.; Jurčák, J.; Schlichenmaier, R.;
Rezaei, R.
2019ASPC..526..261B Altcode:
Fully-fledged penumbrae are a well characterised phenomenon from
an observational point of view. Also, MHD simulations reproduce the
observed characteristics and provide us with insights on the physical
mechanisms possibly running behind the observed processes. Yet, how this
penumbral magneto-convection sets in is still an open question. Due to
the fact that penumbra formation is a relatively fast process (of the
order of hours), it has eluded its observation with sufficient spatial
resolution by both space- and ground-based solar observatories. Only
recently, some researchers have witnessed the onset of both orphan
and sunspot penumbrae in detail. We are one of those. In July 2009, we
observed the early stages of the NOAA 11024 AR leading sunspot while
developing its penumbra. The spectro-polarimetric dataset lead us to
new observational findings. In this contribution, we put into context
our and other authors' results to draw the overall picture of sunspot
formation. Most important, the comparison on the properties of different
types of penumbrae lead us to the conclusion that the formation of
penumbrae is not just one mechanism. While the sole cause necessary
for penumbral magneto-convection is a stably inclined magnetic field,
observations show that inclined fields can be caused by flux emergence,
to form orphan penumbrae, or by field lines transported down from
upper photospheric layers, to form sunspot penumbra. This conclusion,
together with the recent findings by Jur\čák and collaborators on
a canonical value of the vertical component of the magnetic field
blocking the action of penumbral magneto-convection in umbral areas,
is a crucial step forward towards the understanding of the coupling
of solar plasmas and magnetic fields in penumbral atmospheres.
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Title: Recent advancements in the EST project
Authors: Jurčák, Jan; Collados, Manuel; Leenaarts, Jorrit; van Noort,
Michiel; Schlichenmaier, Rolf
2019AdSpR..63.1389J Altcode: 2018arXiv181100851J
The European Solar Telescope (EST) is a project of a new-generation
solar telescope. It has a large aperture of 4 m, which is necessary for
achieving high spatial and temporal resolution. The high polarimetric
sensitivity of the EST will allow to measure the magnetic field in the
solar atmosphere with unprecedented precision. Here, we summarise the
recent advancements in the realisation of the EST project regarding
the hardware development and the refinement of the science requirements.
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Title: Properties of the inner penumbral boundary and temporal
evolution of a decaying sunspot
Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry,
P.; Kuckein, C.; Jurčák, J.
2018A&A...620A.191B Altcode: 2018arXiv181013185B
Context. It has been empirically determined that the umbra-penumbra
boundaries of stable sunspots are characterized by a constant value of
the vertical magnetic field. <BR /> Aims: We analyzed the evolution
of the photospheric magnetic field properties of a decaying sunspot
belonging to NOAA 11277 between August 28-September 3, 2011. The
observations were acquired with the spectropolarimeter on-board of
the Hinode satellite. We aim to prove the validity of the constant
vertical magnetic-field boundary between the umbra and penumbra in
decaying sunspots. <BR /> Methods: A spectral-line inversion technique
was used to infer the magnetic field vector from the full-Stokes
profiles. In total, eight maps were inverted and the variation of
the magnetic properties in time were quantified using linear or
quadratic fits. <BR /> Results: We find a linear decay of the umbral
vertical magnetic field, magnetic flux, and area. The penumbra showed
a linear increase of the vertical magnetic field and a sharp decay
of the magnetic flux. In addition, the penumbral area quadratically
decayed. The vertical component of the magnetic field is weaker on the
umbra-penumbra boundary of the studied decaying sunspot compared to
stable sunspots. Its value seem to be steadily decreasing during the
decay phase. Moreover, at any time of the sunspot decay shown, the inner
penumbra boundary does not match with a constant value of the vertical
magnetic field, contrary to what is seen in stable sunspots. <BR />
Conclusions: During the decaying phase of the studied sunspot, the
umbra does not have a sufficiently strong vertical component of the
magnetic field and is thus unstable and prone to be disintegrated by
convection or magnetic diffusion. No constant value of the vertical
magnetic field is found for the inner penumbral boundary.
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Title: Heating of the solar photosphere during a white-light flare
Authors: Jurčák, Jan; Kašparová, Jana; Švanda, Michal; Kleint,
Lucia
2018A&A...620A.183J Altcode: 2018arXiv181107794J
Context. The Fe I lines observed by the Hinode/SOT spectropolarimeter
were always seen in absorption, apart from the extreme solar limb. Here
we analyse a unique dataset capturing these lines in emission during
a solar white-light flare. <BR /> Aims: We analyse the temperature
stratification in the solar photosphere during a white-light flare and
compare it with the post-white-light flare state. <BR /> Methods: We
used two scans of the Hinode/SOT spectropolarimeter to infer, by means
of the LTE inversion code Stokes Inversion based on Response function
(SIR), the physical properties in the solar photosphere during and
after a white-light flare. The resulting model atmospheres are compared
and the changes are related to the white-light flare. <BR /> Results:
We show that the analysed white-light flare continuum brightening is
probably not caused by the temperature increase at the formation height
of the photospheric continuum. However, the photosphere is heated
by the flare approximately down to log τ = -0.5 and this results
in emission profiles of the observed Fe I lines. From the comparison
with the post-white-light flare state of the atmosphere, we estimate
that the major contribution to the increase in the continuum intensity
originates in the heated chromosphere.
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Title: Comparison of theoretical and observed Ca II 8542 Stokes
profiles in quiet regions at the centre of the solar disc
Authors: Jurčák, J.; Štěpán, J.; Trujillo Bueno, J.; Bianda, M.
2018A&A...619A..60J Altcode: 2018arXiv180809470J
Context. Interpreting the Stokes profiles observed in quiet regions
of the solar chromosphere is a challenging task. The Stokes Q and U
profiles are dominated by the scattering polarisation and the Hanle
effect, and these processes can only be correctly quantified if 3D
radiative transfer effects are taken into account. Forward-modelling
of the intensity and polarisation of spectral lines using a 3D model
atmosphere is a suitable approach in order to statistically compare
the theoretical and observed line profiles. <BR /> Aims: Our aim is to
present novel observations of the Ca II 8542 Å line profiles in a quiet
region at the centre of the solar disc and to quantitatively compare
them with the theoretical Stokes profiles obtained by solving the
problem of the generation and transfer of polarised radiation in a 3D
model atmosphere. We aim at estimating the reliability of the 3D model
atmosphere, excluding its known lack of dynamics and/or insufficient
density, using not only the line intensity but the full vector of
Stokes parameters. <BR /> Methods: We used data obtained with the
ZIMPOL instrument at the Istituto Ricerche Solari Locarno (IRSOL) and
compared the observations with the theoretical profiles computed with
the PORTA radiative transfer code, using as solar model atmosphere a
3D snapshot taken from a radiation-magnetohydrodynamics simulation. The
synthetic profiles were degraded to match the instrument and observing
conditions. <BR /> Results: The degraded theoretical profiles of the
Ca II 8542 line are qualitatively similar to the observed ones. We
confirm that there is a fundamental difference in the widths of all
Stokes profiles: the observed lines are wider than the theoretical
lines. We find that the amplitudes of the observed profiles are larger
than those of the theoretical ones, which suggests that the symmetry
breaking effects in the solar chromosphere are stronger than in the
model atmosphere. This means that the isosurfaces of temperature,
velocity, and magnetic field strength and orientation are more
corrugated in the solar chromosphere than in the currently available
3D radiation-magnetohydrodynamics simulation.
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Title: Understanding the HMI Pseudocontinuum in White-light Solar
Flares
Authors: Švanda, Michal; Jurčák, Jan; Kašparová, Jana; Kleint,
Lucia
2018ApJ...860..144S Altcode: 2018arXiv180503369S
We analyze observations of the X9.3 solar flare (SOL2017-09-06T11:53)
observed by SDO/HMI and Hinode/Solar Optical Telescope. Our aim is to
learn about the nature of the HMI pseudocontinuum I <SUB>c</SUB> used as
a proxy for the white-light continuum. From model atmospheres retrieved
by an inversion code applied to the Stokes profiles observed by the
Hinode satellite, we synthesize profiles of the Fe I 617.3 nm line and
compare them to HMI observations. Based on a pixel-by-pixel comparison,
we show that the value of I <SUB>c</SUB> represents the continuum level
well in quiet-Sun regions only. In magnetized regions, it suffers from
a simplistic algorithm that is applied to a complex line shape. During
this flare, both instruments also registered emission profiles in the
flare ribbons. Such emission profiles are poorly represented by the
six spectral points of HMI and the MDI-like algorithm does not account
for emission profiles in general; thus, the derived pseudocontinuum
intensity does not approximate the continuum value properly.
---------------------------------------------------------
Title: The magnetic nature of umbra-penumbra boundary in sunspots
Authors: Jurčák, J.; Rezaei, R.; González, N. Bello; Schlichenmaier,
R.; Vomlel, J.
2018A&A...611L...4J Altcode: 2018arXiv180108983J
Context. Sunspots are the longest-known manifestation of solar
activity, and their magnetic nature has been known for more than a
century. Despite this, the boundary between umbrae and penumbrae,
the two fundamental sunspot regions, has hitherto been solely
defined by an intensity threshold. Aim. Here, we aim at studying the
magnetic nature of umbra-penumbra boundaries in sunspots of different
sizes, morphologies, evolutionary stages, and phases of the solar
cycle. <BR /> Methods: We used a sample of 88 scans of the Hinode/SOT
spectropolarimeter to infer the magnetic field properties in at the
umbral boundaries. We defined these umbra-penumbra boundaries by
an intensity threshold and performed a statistical analysis of the
magnetic field properties on these boundaries. <BR /> Results: We
statistically prove that the umbra-penumbra boundary in stable sunspots
is characterised by an invariant value of the vertical magnetic field
component: the vertical component of the magnetic field strength
does not depend on the umbra size, its morphology, and phase of the
solar cycle. With the statistical Bayesian inference, we find that the
strength of the vertical magnetic field component is, with a likelihood
of 99%, in the range of 1849-1885 G with the most probable value
of 1867 G. In contrast, the magnetic field strength and inclination
averaged along individual boundaries are found to be dependent on the
umbral size: the larger the umbra, the stronger and more horizontal
the magnetic field at its boundary. <BR /> Conclusions: The umbra and
penumbra of sunspots are separated by a boundary that has hitherto been
defined by an intensity threshold. We now unveil the empirical law of
the magnetic nature of the umbra-penumbra boundary in stable sunspots:
it is an invariant vertical component of the magnetic field.
---------------------------------------------------------
Title: Normal and counter Evershed flows in the photospheric penumbra
of a sunspot. SPINOR 2D inversions of Hinode-SOT/SP observations
Authors: Siu-Tapia, A.; Lagg, A.; Solanki, S. K.; van Noort, M.;
Jurčák, J.
2017A&A...607A..36S Altcode: 2017arXiv170907386S
Context. The Evershed effect, a nearly horizontal outflow of material
seen in the penumbrae of sunspots in the photospheric layers, is a
common characteristic of well-developed penumbrae, but is still not well
understood. Even less is known about photospheric horizontal inflows in
the penumbra, also known as counter Evershed flows. <BR /> Aims: Here we
present a rare feature observed in the penumbra of the main sunspot of
AR NOAA 10930. This spot displays the normal Evershed outflow in most
of the penumbra, but harbors a fast photospheric inflow of material
over a large sector of the disk-center penumbra. We investigate the
driving forces of both, the normal and the counter Evershed flows. <BR
/> Methods: We invert the spectropolarimetric data from Hinode SOT/SP
using the spatially coupled version of the SPINOR inversion code,
which allows us to derive height-dependent maps of the relevant
physical parameters in the sunspot. These maps show considerable fine
structure. Similarities and differences between the normal Evershed
outflow and the counter Evershed flow are investigated. <BR /> Results:
In both the normal and the counter Evershed flows, the material flows
from regions with field strengths of the order of 1.5-2 kG to regions
with stronger fields. The sources and sinks of both penumbral flows
display opposite field polarities, with the sinks (tails of filaments)
harboring local enhancements in temperature, which are nonetheless
colder than their sources (heads of filaments). <BR /> Conclusions:
The anti-correlation of the gradients in the temperature and magnetic
pressure between the endpoints of the filaments from the two distinct
penumbral regions is compatible with both the convective driver and
the siphon flow scenarios. A geometrical scale of the parameters is
necessary to determine which is the dominant force driving the flows.
---------------------------------------------------------
Title: Granular cells in the presence of magnetic field
Authors: Jurčák, J.; Lemmerer, B.; van Noort, M.
2017IAUS..327...34J Altcode:
We present a statistical study of the dependencies of the shapes
and sizes of the photospheric convective cells on the magnetic field
properties. This analysis is based on a 2.5 hour long SST observations
of active region NOAA 11768. We have blue continuum images taken with a
cadence of 5.6 sec that are used for segmentation of individual granules
and 270 maps of spectropolarimetric CRISP data allowing us to determine
the properties of the magnetic field along with the line-of-sight
velocities. The sizes and shapes of the granular cells are dependent
on the the magnetic field strength, where the granules tend to be
smaller in regions with stronger magnetic field. In the presence of
highly inclined magnetic fields, the eccentricity of granules is high
and we do not observe symmetric granules in these regions. The mean
up-flow velocities in granules as well as the granules intensities
decrease with increasing magnetic field strength.
---------------------------------------------------------
Title: A distinct magnetic property of the inner penumbral
boundary. II. Formation of a penumbra at the expense of a pore
Authors: Jurčák, J.; Bello González, N.; Schlichenmaier, R.;
Rezaei, R.
2017A&A...597A..60J Altcode: 2016arXiv161201745J; 2016A&A...597A..60J
Context. We recently presented evidence that stable
umbra-penumbra boundaries are characterised by a distinct
canonical value of the vertical component of the magnetic
field, B<SUP>stable</SUP><SUB>ver</SUB>. In order to trigger
the formation of a penumbra, large inclinations in the magnetic
field are necessary. In sunspots, the penumbra develops and
establishes by colonising both umbral areas and granulation, that
is, penumbral magneto-convection takes over in umbral regions with
B<SUB>ver</SUB><B<SUP>stable</SUP><SUB>ver</SUB>, as well as
in granular convective areas. Eventually, a stable umbra-penumbra
boundary settles at B<SUP>stable</SUP><SUB>ver</SUB>. <BR /> Aims:
Here, we aim to study the development of a penumbra initiated at
the boundary of a pore, where the penumbra colonises the entire pore
ultimately. <BR /> Methods: We have used Hinode/SOT G-band images to
study the evolution of the penumbra. Hinode/SOT spectropolarimetric
data were used to infer the magnetic field properties in the studied
region. <BR /> Results: The penumbra forms at the boundary of a pore
located close to the polarity inversion line of NOAA 10960. As the
penumbral bright grains protrude into the pore, the magnetic flux in
the forming penumbra increases at the expense of the pore magnetic
flux. Consequently, the pore disappears completely giving rise to an
orphan penumbra. At all times, the vertical component of the magnetic
field in the pore is smaller than B<SUP>stable</SUP><SUB>ver</SUB>
≈ 1.8 kG. <BR /> Conclusions: Our findings are in an agreement
with the need of B<SUP>stable</SUP><SUB>ver</SUB> for establishing
a stable umbra-penumbra boundary: while B<SUB>ver</SUB> in
the pore is smaller than B<SUP>stable</SUP><SUB>ver</SUB>, the
protrusion of penumbral grains into the pore area is not blocked,
a stable pore-penumbra boundary does not establish, and the pore
is fully overtaken by the penumbral magneto-convective mode. This
scenario could also be one of the mechanisms giving rise to orphan
penumbrae. <P />The movie associated to Fig. 1 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201628547/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Canonical Bver value on umbra/penumbra boundaries
Authors: Jurcak, Jan; Bello González, Nazaret; Schlichenmaier, Rolf;
Rezaei, Reza
2017psio.confE.112J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Slipping reconnection in a solar flare observed in high
resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
Volkmer, R.; Waldmann, T.
2016A&A...596A...1S Altcode: 2016arXiv160500464S
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
filter. Context observations from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
Telescope (SOT) onboard Hinode, and the Interface Region Imaging
Spectrograph (IRIS) show that this ribbon is part of a larger one
that extends through the neighboring positive polarities and also
participates in several other flares within the active region. We
reconstructed a time series of 140 s of Ca II H images by means of the
multiframe blind deconvolution method, which resulted in spatial and
temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary, but three move along the
ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
which provides evidence of a slipping reconnection at small spatial
scales. <P />Movies associated to Figs. 1 and 2 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Chromospheric Heating by Acoustic Waves Compared to Radiative
Cooling
Authors: Sobotka, M.; Heinzel, P.; Švanda, M.; Jurčák, J.; del Moro,
D.; Berrilli, F.
2016ApJ...826...49S Altcode: 2016arXiv160504794S
Acoustic and magnetoacoustic waves are among the possible candidate
mechanisms that heat the upper layers of the solar atmosphere. A weak
chromospheric plage near the large solar pore NOAA 11005 was observed
on 2008 October 15, in the Fe I 617.3 nm and Ca II 853.2 nm lines of
the Interferometric Bidimemsional Spectrometer attached to the Dunn
Solar Telescope. In analyzing the Ca II observations (with spatial
and temporal resolutions of 0.″4 and 52 s) the energy deposited by
acoustic waves is compared to that released by radiative losses. The
deposited acoustic flux is estimated from the power spectra of Doppler
oscillations measured in the Ca II line core. The radiative losses
are calculated using a grid of seven one-dimensional hydrostatic
semi-empirical model atmospheres. The comparison shows that the
spatial correlation of the maps of radiative losses and acoustic flux
is 72%. In a quiet chromosphere, the contribution of acoustic energy
flux to radiative losses is small, only about 15%. In active areas
with a photospheric magnetic-field strength between 300 and 1300 G
and an inclination of 20°-60°, the contribution increases from 23%
(chromospheric network) to 54% (a plage). However, these values have
to be considered as lower limits and it might be possible that the
acoustic energy flux is the main contributor to the heating of bright
chromospheric network and plages.
---------------------------------------------------------
Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.
2016IAUS..320...68S Altcode:
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5-m GREGOR telescope, using a 0.1 nm Ca II H interference
filter. Context observations from SDO/AIA, Hinode/SOT, and IRIS show
that the ribbon is a part of a larger one that extends through the
neighboring positive polarities and also participates in several
other flares within the active region. A 140 second long time series
of Ca II H images was reconstructed by means of the Multi-Frame
Blind Deconvolution method, giving the respective spatial and
temporal resolutions of 0”.1 and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary but three move along the
ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
providing evidence for the presence of slipping reconnection at small
spatial scales.
---------------------------------------------------------
Title: Parallelization of the SIR code for the investigation of
small-scale features in the solar photosphere
Authors: Thonhofer, Stefan; Bellot Rubio, Luis R.; Utz, Dominik;
Hanslmeier, Arnold; Jurçák, Jan
2015IAUS..305..251T Altcode: 2015arXiv150303710T
Magnetic fields are one of the most important drivers of the highly
dynamic processes that occur in the lower solar atmosphere. They span a
broad range of sizes, from large- and intermediate-scale structures such
as sunspots, pores and magnetic knots, down to the smallest magnetic
elements observable with current telescopes. On small scales, magnetic
flux tubes are often visible as Magnetic Bright Points (MBPs). Apart
from simple V/I magnetograms, the most common method to deduce their
magnetic properties is the inversion of spectropolarimetric data. Here
we employ the SIR code for that purpose. SIR is a well-established
tool that can derive not only the magnetic field vector and other
atmospheric parameters (e.g., temperature, line-of-sight velocity),
but also their stratifications with height, effectively producing
3-dimensional models of the lower solar atmosphere. In order to enhance
the runtime performance and the usability of SIR we parallelized the
existing code and standardized the input and output formats. This and
other improvements make it feasible to invert extensive high-resolution
data sets within a reasonable amount of computing time. An evaluation
of the speedup of the parallel SIR code shows a substantial improvement
in runtime.
---------------------------------------------------------
Title: A distinct magnetic property of the inner penumbral
boundary. Formation of a stable umbra-penumbra boundary in a sunspot
Authors: Jurčák, J.; Bello González, N.; Schlichenmaier, R.;
Rezaei, R.
2015A&A...580L...1J Altcode:
Context. A sunspot emanates from a growing pore or protospot. In order
to trigger the formation of a penumbra, large inclinations at the
outskirts of the protospot are necessary. The penumbra develops and
establishes by colonising both umbral areas and granulation. Evidence
for a unique stable boundary value for the vertical component of the
magnetic field strength, B<SUP>stable</SUP><SUB>ver</SUB>, was found
along the umbra-penumbra boundary of developed sunspots. <BR /> Aims: We
study the changing value of B<SUB>ver</SUB> as the penumbra forms and as
it reaches a stable state. We compare this with the corresponding value
in fully developed penumbrae. <BR /> Methods: We use broadband G-band
images and spectropolarimetric GFPI/VTT data to study the evolution
of and the vertical component of the magnetic field on a forming
umbra-penumbra boundary. For comparison with stable sunspots, we also
analyse the two maps observed by Hinode/SP on the same spot after the
penumbra formed. <BR /> Results: The vertical component of the magnetic
field, B<SUB>ver</SUB>, at the umbra-penumbra boundary increases during
penumbra formation owing to the incursion of the penumbra into umbral
areas. After 2.5 h, the penumbra reaches a stable state as shown
by the GFPI data. At this stable stage, the simultaneous Hinode/SP
observations show a B<SUB>ver</SUB> value comparable to that of
umbra-penumbra boundaries of fully fledged sunspots. <BR /> Conclusions:
We confirm that the umbra-penumbra boundary, traditionally defined by
an intensity threshold, is also characterised by a distinct canonical
magnetic property, namely by B<SUB>ver</SUB><SUP>stable</SUP>. During
the penumbra formation process, the inner penumbra extends
into regions where the umbra previously prevailed. Hence, in
areas where B<SUB>ver</SUB><B<SUP>stable</SUP><SUB>ver</SUB>,
the magneto-convection mode operating in the umbra turns into a
penumbral mode. Eventually, the inner penumbra boundary settles at
B<SUB>ver</SUB><SUP>stable</SUP>, which hints toward the role of
B<SUB>ver</SUB><SUP>stable</SUP> as inhibitor of the penumbral mode
of magneto-convection.
---------------------------------------------------------
Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, Michal; Dudik, Jaroslav; Denker, Carsten; Balthasar,
Horst; Jurcak, Jan; Liu, Wenjuan; GREGOR Team
2015IAUGA..2246841S Altcode:
A small flare ribbon above a sunspot with a light bridge was observed on
7 November 2014 around 12:00 UT in the blue imaging channel of GREGOR,
using a 0.1 nm Ca II H interference filter. Context observations from
SDO/AIA, Hinode/SOT and IRIS show that the ribbon is a part of a larger
ribbon extending through the neighbouring negative polarities that also
participates in several other flares within the active region. A 140
s long time series of Ca II H images was reconstructed by means of the
Multi Frame Blind Deconvolution method, giving the respective spatial
and temporal resolutions of 0.1" and 1 s. Light curves and horizontal
velocities of small-scale brightenings in the flare ribbon located
above an umbral core were measured. Some of them are stationary but
three brightenings move in opposite directions along the ribbon with
speeds of 7 - 11 km/s. Expecting that the brightenings correspond to
footpoints of flare loops, their motions can be interpreted in terms
of the slipping reconnection model.
---------------------------------------------------------
Title: A distinct magnetic property of the inner penumbral boundary
Authors: Jurčák, Jan; Bello Gonzalez, Nazaret; Schlichenmaier,
Rolf; Rezaei, Reza
2015arXiv150608574J Altcode:
A sunspot emanates from a growing pore or protospot. In order to
trigger the formation of a penumbra, large inclinations at the
outskirts of the protospot are necessary. The penumbra develops and
establishes by colonising both umbral areas and granulation. Evidence
for a unique stable boundary value for the vertical component of the
magnetic field strength, $B^{\rm stable}_{\rm ver}$, was found along
the umbra-penumbra boundary of developed sunspots. We use broadband
G-band images and spectropolarimetric GFPI/VTT data to study the
evolution of and the vertical component of the magnetic field on a
forming umbra-penumbra boundary. For comparison with stable sunspots,
we also analyse the two maps observed by Hinode/SP on the same spot
after the penumbra formed. The vertical component of the magnetic
field, $B_{\rm ver}$, at the umbra-penumbra boundary increases
during penumbra formation owing to the incursion of the penumbra into
umbral areas. After 2.5 hours, the penumbra reaches a stable state
as shown by the GFPI data. At this stable stage, the simultaneous
Hinode/SP observations show a $B_{\rm ver}$ value comparable to that of
umbra-penumbra boundaries of fully fledged sunspots. We confirm that
the umbra-penumbra boundary, traditionally defined by an intensity
threshold, is also characterised by a distinct canonical magnetic
property, namely by $B^{\rm stable}_{\rm ver}$. During the penumbra
formation process, the inner penumbra extends into regions where the
umbra previously prevailed. Hence, in areas where $B_{\rm ver} <
B^{\rm stable}_{\rm ver}$, the magneto-convection mode operating in
the umbra turns into a penumbral mode. Eventually, the inner penumbra
boundary settles at $B^{\rm stable}_{\rm ver}$, which hints toward the
role of $B_{\rm ver}^{\rm stable}$ as inhibitor of the penumbral mode
of magneto-convection.
---------------------------------------------------------
Title: Magnetic bright point dynamics and evolutions observed by
Sunrise/IMaX and other instruments
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L.; Thonhofer,
S.; Jurčák, J.
2015hsa8.conf..689U Altcode:
In this proceeding we will have a closer look on recent observations
and results regarding the dynamics and evolution of so-called magnetic
bright points (MBPs). MBPs are manifestations of kG magnetic field
strong flux concentrations seen in the solar photosphere. They belong
to the class of small-scale solar magnetic features with diameters
starting from low values around the current observational resolution
limit - about 100 km - up to a few hundred km. They might play an
important role in several key research questions like the total solar
irradiance variation (TSI variation) as well as the solar atmospheric
heating problem. Especially their dynamic behaviour is of interest
for the heating problem as they might trigger all kinds of MHD waves
which travel up to the higher solar atmospheric layers, where they can
get damped leading to a heating of the plasma. Furthermore they might
engage in magnetic field reconnection processes leading consequently
also to a heating. Due to these reasons, and also for the sake of a
better understanding of the physical processes involved on small-scales,
detailed investigations on the dynamical behaviour and evolution of
such magnetic field proxies like MBPs is in order. In this conference
proceeding we wish to give in a first part an overview about the
obtained knowledge so far. In a second part we highlight recent results
regarding the dynamical evolution of plasma parameters of MBPs such as
magnetic field strength, temperature, and line of sight velocity. This
proceeding is completed by an outlook on what can and should be done
in the near future with available data from recent telescopes.
---------------------------------------------------------
Title: Evolution of magnetic field inclination in a forming penumbra
Authors: Jurčák, Jan; Bello González, Nazaret; Schlichenmaier,
Rolf; Rezaei, Reza
2014PASJ...66S...3J Altcode: 2014PASJ..tmp...93J
As a sunspot penumbra forms, the magnetic field vector at the outer
boundary of the protospot undergoes a transformation. We study the
changes of the magnetic field vector at this boundary as a penumbral
segment forms. We analyze a set of spectropolarimetric maps covering
2 hr during the formation of a sunspot in NOAA 11024. The data were
recorded with the GFPI instrument attached to the German VTT. We
observe a stationary umbra/quiet Sun boundary, where the magnetic
field becomes more horizontal with time. The magnetic field inclination
increases by 5°, reaching a maximum value of about 59°. The maximum
inclination coincides with the onset of filament formation. In time,
the penumbra filaments become longer and the penumbral bright grains
protrude into the umbra, where the magnetic field is stronger and
more vertical. Consequently, we observe a decrease in the magnetic
field inclination at the boundary as the penumbra grows. In summary,
in order to initiate the formation of the penumbra, the magnetic
field at the umbral (protospot) boundary becomes more inclined. As
the penumbra grows, the umbra/penumbra boundary migrates inwards,
and at this boundary the magnetic field turns more vertical again,
while it remains inclined in the outer penumbra.
---------------------------------------------------------
Title: The Formation and Disintegration of Magnetic Bright Points
Observed by Sunrise/IMaX
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.;
Jurčák, J.; Martínez Pillet, V.; Solanki, S. K.; Schmidt, W.
2014ApJ...796...79U Altcode: 2014arXiv1411.3240U
The evolution of the physical parameters of magnetic bright points
(MBPs) located in the quiet Sun (mainly in the interwork) during
their lifetime is studied. First, we concentrate on the detailed
description of the magnetic field evolution of three MBPs. This
reveals that individual features follow different, generally complex,
and rather dynamic scenarios of evolution. Next, we apply statistical
methods on roughly 200 observed MBP evolutionary tracks. MBPs are found
to be formed by the strengthening of an equipartition field patch,
which initially exhibits a moderate downflow. During the evolution,
strong downdrafts with an average velocity of 2.4 km s<SUP>-1</SUP>
set in. These flows, taken together with the concurrent strengthening of
the field, suggest that we are witnessing the occurrence of convective
collapses in these features, although only 30% of them reach kG field
strengths. This fraction might turn out to be larger when the new 4
m class solar telescopes are operational as observations of MBPs with
current state of the art instrumentation could still be suffering from
resolution limitations. Finally, when the bright point disappears
(although the magnetic field often continues to exist) the magnetic
field strength has dropped to the equipartition level and is generally
somewhat weaker than at the beginning of the MBP's evolution. Also,
only relatively weak downflows are found on average at this stage of
the evolution. Only 16% of the features display upflows at the time
that the field weakens, or the MBP disappears. This speaks either for
a very fast evolving dynamic process at the end of the lifetime, which
could not be temporally resolved, or against strong upflows as the cause
of the weakening of the field of these magnetic elements, as has been
proposed based on simulation results. It is noteworthy that in about 10%
of the cases, we observe in the vicinity of the downflows small-scale
strong (exceeding 2 km s<SUP>-1</SUP>) intergranular upflows related
spatially and temporally to these downflows. The paper is complemented
by a detailed discussion of aspects regarding the applied methods,
the complementary literature, and in depth analysis of parameters
like magnetic field strength and velocity distributions. An important
difference to magnetic elements and associated bright structures in
active region plage is that most of the quiet Sun bright points display
significant downflows over a large fraction of their lifetime (i.e.,
in more than 46% of time instances/measurements they show downflows
exceeding 1 km s<SUP>-1</SUP>).
---------------------------------------------------------
Title: Magnetic field and radiative transfer modelling of a quiescent
prominence
Authors: Gunár, S.; Schwartz, P.; Dudík, J.; Schmieder, B.; Heinzel,
P.; Jurčák, J.
2014A&A...567A.123G Altcode:
<BR /> Aims: The aim of this work is to analyse the multi-instrument
observations of the June 22, 2010 prominence to study its structure in
detail, including the prominence-corona transition region and the dark
bubble located below the prominence body. <BR /> Methods: We combined
results of the 3D magnetic field modelling with 2D prominence fine
structure radiative transfer models to fully exploit the available
observations. <BR /> Results: The 3D linear force-free field model
with the unsheared bipole reproduces the morphology of the analysed
prominence reasonably well, thus providing useful information about
its magnetic field configuration and the location of the magnetic
dips. The 2D models of the prominence fine structures provide a good
representation of the local plasma configuration in the region dominated
by the quasi-vertical threads. However, the low observed Lyman-α
central intensities and the morphology of the analysed prominence
suggest that its upper central part is not directly illuminated from the
solar surface. <BR /> Conclusions: This multi-disciplinary prominence
study allows us to argue that a large part of the prominence-corona
transition region plasma can be located inside the magnetic dips in
small-scale features that surround the cool prominence material located
in the dip centre. We also argue that the dark prominence bubbles
can be formed because of perturbations of the prominence magnetic
field by parasitic bipoles, causing them to be devoid of the magnetic
dips. Magnetic dips, however, form thin layers that surround these
bubbles, which might explain the occurrence of the cool prominence
material in the lines of sight intersecting the prominence bubbles. <P
/>Movie and Appendix A are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322777/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Orphan penumbrae: Submerging horizontal fields
Authors: Jurčák, J.; Bellot Rubio, L. R.; Sobotka, M.
2014A&A...564A..91J Altcode: 2014arXiv1402.6558J
<BR /> Aims: We investigate the properties of orphan penumbrae,
which are photospheric filamentary structures observed in active
regions near polarity inversion lines that resemble the penumbra of
regular sunspots but are not connected to any umbra. <BR /> Methods:
We use Hinode data from the Solar Optical Telescope to determine the
properties of orphan penumbrae. Spectropolarimetric data are employed
to obtain the vector magnetic field and line-of-sight velocities in
the photosphere. Magnetograms are used to study the overall evolution
of these structures, and G-band and Ca ii H filtergrams are to
investigate their brightness and apparent horizontal motions. <BR />
Results: Orphan penumbrae form between regions of opposite polarity in
places with horizontal magnetic fields. Their magnetic configuration
is that of Ω-shaped flux ropes. In the two cases studied here,
the opposite-polarity regions approach each other with time and the
whole structure submerges as the penumbral filaments disappear. Orphan
penumbrae are very similar to regular penumbrae, including the existence
of strong gas flows. Therefore, they could have a similar origin. The
main difference between them is the absence of a "background" magnetic
field in orphan penumbrae. This could explain most of the observed
differences. <BR /> Conclusions: The fast flows we detect in orphan
penumbrae may be caused by the siphon flow mechanism. Based on the
similarities between orphan and regular penumbrae, we propose that
the Evershed flow is also a manifestation of siphon flows. <P />A
movie attached to Fig. 11 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322340/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: New insights into the evolution of magnetic bright point
plasma parameters
Authors: Utz, Dominik; Hanslmeier, Arnold; Bellot Rubio, L. R.;
Del Toro Iniesta, Jose Carlos; Jurcak, Jan
2014cosp...40E3448U Altcode:
The dynamics within the solar atmosphere are governed by the Suńs
magnetic fields. In the recent years the resolution limits were steadily
driven up by better and better instruments and telescopes (like Hinode,
Sunrise, NST, Gregor, ..) leading to higher resolved data. Therefore
the interest in ever smaller magnetic field structures within the solar
atmosphere rises. Among the smallest yet identified structures are
so-called magnetic bright points (MBPs). These features are thought to
be made up of single flux tubes and they have been studied exhaustively
in the Fraunhofer G-band since the 70´s of the last century. They are
important features not only due to their small scale (about 200 km in
diameter) and hence used as proxies for the smallest solar magnetic
field physics and processes, but also because they are involved in
topics like the chromospheric/coronal heating problem or the total
solar irradiance variation. In the current contribution we want to
study the evolution of important plasma parameters of MBPs, such
as temperature, magnetic field strength and line of sight velocity,
to get a deeper understanding of the involved physics and occuring
processes. Among the used data will be G-band filtergam data from
Hinode/SOT and spectro-polarimetric data from the IMaX instrument
onboard the Sunrise mission.
---------------------------------------------------------
Title: Dynamics of the solar atmosphere above a pore with a light
bridge
Authors: Sobotka, M.; Švanda, M.; Jurčák, J.; Heinzel, P.; Del Moro,
D.; Berrilli, F.
2013A&A...560A..84S Altcode: 2013arXiv1309.7790S
Context. Solar pores are small sunspots lacking a penumbra that have
a prevailing vertical magnetic-field component. They can include light
bridges at places with locally reduced magnetic field. Like sunspots,
they exhibit a wide range of oscillatory phenomena. <BR /> Aims:
A large isolated pore with a light bridge (NOAA 11005) is studied
to obtain characteristics of a chromospheric filamentary structure
around the pore, to analyse oscillations and waves in and around
the pore, and to understand the structure and brightness of the light
bridge. <BR /> Methods: Spectral imaging observations in the line Ca II
854.2 nm and complementary spectropolarimetry in Fe I lines, obtained
with the DST/IBIS spectrometer and HINODE/SOT spectropolarimeter,
were used to measure photospheric and chromospheric velocity fields,
oscillations, waves, the magnetic field in the photosphere, and
acoustic energy flux and radiative losses in the chromosphere. <BR />
Results: The chromospheric filamentary structure around the pore has
all important characteristics of a superpenumbra: it shows an inverse
Evershed effect and running waves, and has a similar morphology and
oscillation character. The granular structure of the light bridge in
the upper photosphere can be explained by radiative heating. Acoustic
waves leaking up from the photosphere along the inclined magnetic
field in the light bridge transfer enough energy flux to balance
the entire radiative losses of the light-bridge chromosphere. <BR />
Conclusions: A penumbra is not a necessary condition for the formation
of a superpenumbra. The light bridge is heated by radiation in the
photosphere and by acoustic waves in the chromosphere.
---------------------------------------------------------
Title: Atmosphere above a large solar pore
Authors: Sobotka, M.; Švanda, M.; Jurčák, J.; Heinzel, P.; Del
Moro, D.
2013JPhCS.440a2049S Altcode: 2013arXiv1302.4893S
A large solar pore with a granular light bridge was observed on October
15, 2008 with the IBIS spectrometer at the Dunn Solar Telescope and a
69-min long time series of spectral scans in the lines Ca II 854.2 nm
and Fe I 617.3 nm was obtained. The intensity and Doppler signals in the
Ca II line were separated. This line samples the middle chromosphere
in the core and the middle photosphere in the wings. Although no
indication of a penumbra is seen in the photosphere, an extended
filamentary structure, both in intensity and Doppler signals, is
observed in the Ca II line core. An analysis of morphological and
dynamical properties of the structure shows a close similarity to a
superpenumbra of a sunspot with developed penumbra. A special attention
is paid to the light bridge, which is the brightest feature in the
pore seen in the Ca II line centre and shows an enhanced power of
chromospheric oscillations at 3-5 mHz. Although the acoustic power
flux in the light bridge is five times higher than in the "quiet"
chromosphere, it cannot explain the observed brightness.
---------------------------------------------------------
Title: Temporal variations in solar magnetic bright points intensity
and plasma parameters
Authors: Jurčák, J.; Utz, D.; Bellot Rubio, L. R.
2013JPhCS.440a2032J Altcode:
Magnetic bright points are one of the finest magnetic structures
observed in the solar atmosphere. They possibly represent single
flux tubes in quiet Sun regions. Their formation is described by the
convective collapse model, while the decay phase of these structures
is not well characterized yet. We attempt to follow the evolution of a
few selected examples of MBPs and to study their changes in brightness
and also the variations of plasma parameters during their lifetime. We
use data from the Hinode satellite and the Sunrise mission. The G-band
observations taken with a cadence of 30 seconds by the Hinode Solar
Optical Telescope (SOT) show very fast changes of the maximum intensity
of these structures. The complementary spectropolarimetric data, which
are used to estimate the plasma parameters, were taken with a cadence
of approximately two minutes. The variations of plasma parameters
cannot be matched one to one to the changes in intensity due to the
different temporal resolution. However, the slow changes of intensity
with large amplitude are matched with variations of magnetic field
strength and line-of-sight (LOS) velocity. The Sunrise/IMaX data have
a temporal resolution of 32 seconds and show fast variations in the
line wing intensity. These variations are associated with changes in
the magnetic field strength and LOS velocity.
---------------------------------------------------------
Title: Variations of Magnetic Bright Point Properties with Longitude
and Latitude as Observed by Hinode/SOT G-band Data
Authors: Utz, D.; Hanslmeier, A.; Veronig, A.; Kühner, O.; Muller,
R.; Jurčák, J.; Lemmerer, B.
2013SoPh..284..363U Altcode: 2012arXiv1212.1310U
Small-scale magnetic fields can be observed on the Sun in
high-resolution G-band filtergrams as magnetic bright points (MBPs). We
study Hinode/Solar Optical Telescope (SOT) longitude and latitude scans
of the quiet solar surface taken in the G-band in order to characterise
the centre-to-limb dependence of MBP properties (size and intensity). We
find that the MBP's sizes increase and their intensities decrease
from the solar centre towards the limb. The size distribution can be
fitted using a log-normal function. The natural logarithm of the mean
(μ parameter) of this function follows a second-order polynomial
and the generalised standard deviation (σ parameter) follows a
fourth-order polynomial or equally well (within statistical errors)
a sine function. The brightness decrease of the features is smaller
than one would expect from the normal solar centre-to-limb variation;
that is to say, the ratio of a MBP's brightness to the mean intensity
of the image increases towards the limb. The centre-to-limb variations
of the intensities of the MBPs and the quiet-Sun field can be fitted by
a second-order polynomial. The detailed physical process that results
in an increase of a MBP's brightness and size from Sun centre to the
limb is not yet understood and has to be studied in more detail in
the future.
---------------------------------------------------------
Title: Magnetic field strength distribution of magnetic bright points
inferred from filtergrams and spectro-polarimetric data
Authors: Utz, D.; Jurčák, J.; Hanslmeier, A.; Muller, R.; Veronig,
A.; Kühner, O.
2013A&A...554A..65U Altcode: 2013arXiv1304.5508U
Context. Small scale magnetic fields can be observed on the Sun in
G-band filtergrams as magnetic bright points (MBPs) or identified in
spectro-polarimetric measurements due to enhanced signals of Stokes
profiles. These magnetic fields and their dynamics play a crucial role
in understanding the coronal heating problem and also in surface dynamo
models. MBPs can theoretically be described to evolve out of a patch of
a solar photospheric magnetic field with values below the equipartition
field strength by the so-called convective collapse model. After the
collapse, the magnetic field of MBPs reaches a higher stable magnetic
field level. <BR /> Aims: The magnetic field strength distribution of
small scale magnetic fields as seen by MBPs is inferred. Furthermore,
we want to test the model of convective collapse and the theoretically
predicted stable value of about 1300 G. <BR /> Methods: We used four
different data sets of high-resolution Hinode/SOT observations that were
recorded simultaneously with the broadband filter device (G-band, Ca
II-H) and the spectro-polarimeter. To derive the magnetic field strength
distribution of these small scale features, the spectropolarimeter
(SP) data sets were treated by the Merlin inversion code. The four data
sets comprise different solar surface types: active regions (a sunspot
group and a region with pores), as well as quiet Sun. <BR /> Results:
In all four cases the obtained magnetic field strength distribution of
MBPs is similar and shows peaks around 1300 G. This agrees well with the
theoretical prediction of the convective collapse model. The resulting
magnetic field strength distribution can be fitted in each case by a
model consisting of log-normal components. The important parameters,
such as geometrical mean value and multiplicative standard deviation,
are similar in all data sets, so only the relative weighting of the
components is different.
---------------------------------------------------------
Title: Creating 3-dimensional Models of the Photosphere using the
SIR Code
Authors: Thonhofer, S.; Utz, D.; Jurčák, J.; Pauritsch, J.;
Hanslmeier, A.; Lemmerer, B.
2013CEAB...37..471T Altcode:
A high-resolution 3-dimensional model of the photospheric magnetic
field is essential for the investigation of magnetic features such
as sunspots, pores or smaller elements like single flux tubes seen
as magnetic bright points. The SIR code is an advanced inversion code
that retrieves physical quantities, e.g. magnetic field, from Stokes
profiles. Based on this code, we developed a program for automated
inversion of Hinode SOT/SP data and for storing these results in
3-dimensional data cubes in the form of fits files. We obtained models
of the temperature, magnetic field strength, magnetic field angles
and LOS-velocity in a region of the quiet sun. We will give a first
discussion of those parameters in regards of small scale magnetic
fields and what we can obtain and learn in the future.
---------------------------------------------------------
Title: A Magnetic Bright Point Case Study
Authors: Utz, D.; Jurčák, J.; Bellot-Rubio, L.; del Toro Iniesta,
J. C.; Thonhofer, S.; Hanslmeier, A.; Veronig, A.; Muller, R.;
Lemmerer, B.
2013CEAB...37..459U Altcode:
Due to its magnetic fields our host star - the Sun - becomes the
interesting object for research as we know it. The magnetic fields
themselves cover different spatial, lifetime and strength scales and
reach down from enormous flux concentrations like active sunspot
groups to single isolated magnetic flux tubes and even weaker,
predominantly inclined intranetwork structures. Flux tubes can be seen
in filtergram observations as magnetic bright points (MBPs). They are
of interest for research not only due to their sheer existence but
due to their important role in atmospheric heating (wave heating as
well as reconnection processes), to their role in the understanding
of creation and annihilation of magnetic fields as well as to their
influence on the total solar irradiance variation. In this study we
present a close look onto an evolutionary track of an MBP from its
formation to its disintegration. Physical quantities of MBPs like
their magnetic field strength and inclination, their line-of-sight
velocity, and their temperature at different heights are inferred
from the inversion of spectropolarimetric data. Original data are
taken from the Sunrise/IMaX instrument and constitute a time series
of some 60 min. The presented case resembles the convective collapse
model and is in agreement with previous studies.
---------------------------------------------------------
Title: IBIS: High-Resolution Multi-Height Observations and Magnetic
Field Retrieval
Authors: Del Moro, D. .; Berrilli, F.; Stangalini, M.; Giannattasio,
F.; Piazzesi, R.; Giovannelli, L.; Viticchiè, B.; Vantaggiato, M.;
Sobotka, M.; Jurčák, J.; Criscuoli, S.; Giorgi, F.; Zuccarello, F.
2012ASPC..463...33D Altcode:
IBIS (Interferometric BIdimensional Spectrometer) allows us to measure
the four Stokes parameters in several spectroscopic lines with high
spatial and spectral resolutions. With this information, we can
retrieve both the dynamics and the magnetic field at different layers
of the Photosphere and Chromosphere. The high spectral, spatial and
temporal resolutions and the polarimetric sensitivity of IBIS allows
us to study different phenomena taking place in the solar atmosphere
with new tools. As an example, we highlight some applications of
IBIS observations and analysis: <BR /> · Radiative and dynamical
properties of Photospheric Bright Points versus their magnetic field
concentration. <BR /> · Close up analysis of magnetic, velocity and
temperature field in a solar pore. <BR /> · MHD wave propagation from
the photosphere to the chromosphere in complex magnetic configuration.
---------------------------------------------------------
Title: Magnetic and velocity fields of a solar pore
Authors: Sobotka, M.; Del Moro, D.; Jurčák, J.; Berrilli, F.
2012A&A...537A..85S Altcode:
Context. Solar pores are intermediate-size magnetic flux features
that emerge at the surface of the Sun. The absence of a filamentary
penumbra indicates that there is a relatively simple magnetic structure
with a prevailing vertical magnetic field. <BR /> Aims: Relations
between the magnetic field components, line-of-sight velocities,
and horizontal motions in and around a large pore (D<SUB>eff</SUB> =
8”.5) are analysed to provide observational constraints on theoretical
models and numerical simulations. <BR /> Methods: Spectropolarimetric
observations in Fe I 617.3 nm of the pore NOAA 11005 with the IBIS
spectrometer attached to the Dunn Solar Telescope are inverted into
series of maps of thermal, magnetic, and velocity parameters using the
SIR code. Horizontal velocities are obtained from series of white-light
images by means of local correlation tracking. <BR /> Results: The
magnetic field B extends from the visible pore border of more than 3”.5
and has a radial structure in a form of spines that are co-spatial with
dark intergranular lanes. The horizontal component B<SUB>hor</SUB> is
more extended than the vertical component B<SUB>z</SUB>. The temperature
linearly decreases with increasing B<SUB>z</SUB>, by about - 300 K
kG<SUP>-1</SUP> in the photosphere and - 800 K kG<SUP>-1</SUP> in the
umbra. The temperature contrast of granulation increases with increasing
magnetic field strength and is then suppressed for B<SUB>z</SUB> >
1200 G. Granular upflows dominate in regions with B<SUB>z</SUB> <
600-700 G. Line-of-sight velocities are lower in stronger fields,
except for fast isolated downflows at the pore's border. The velocity
signature of granulation is suppressed completely for B<SUB>hor</SUB>
> 1000 G. Horizontal motions of granules start to be damped for
B<SUB>z</SUB> > 500 G and recurrently exploding granules appear
only in magnetic fields comparable to or weaker than the equipartition
field strength 400 G.
---------------------------------------------------------
Title: Azimuthal variations of magnetic field strength and inclination
on penumbral boundaries
Authors: Jurčák, J.
2011A&A...531A.118J Altcode:
<BR /> Aims: I try to determine the properties of the magnetic field
on the inner and outer penumbral boundaries and find out if either
magnetic field strength or inclination are constant there and if
these plasma parameters depend on the sunspot area. <BR /> Methods:
The spectropolarimetric data obtained with the Hinode satellite were
analysed. Active regions located mostly around the disc centre were
selected to compare sunspots of different sizes. The magnetic field
strength and inclination were estimated using the inversions of observed
Stokes profiles. <BR /> Results: Both the magnetic field strength and
inclination do not vary along individual outer penumbral boundaries,
and the magnetic field probably becomes weaker and more vertical with
decreasing sunspot area. The magnetic field strength and inclination
are changing along the inner penumbral boundaries and also depend on
the umbral area. Weaker magnetic fields are more vertical on the inner
penumbral boundaries, which leads to a constant vertical component
of the magnetic field on these boundaries. The vertical component of
the magnetic field is possibly independent of the umbral area. <BR />
Conclusions: The inner penumbral boundaries are defined by the critical
value of the vertical component of the magnetic field. This implies
that the penumbral filaments have a convective origin.
---------------------------------------------------------
Title: Temporal downflows in a penumbra
Authors: Jurčák, J.; Katsukawa, Y.
2010A&A...524A..21J Altcode:
<BR /> Aims: We analyze temporal downflow patches that are located
in a penumbra and have the same polarity of the magnetic field as
a sunspot umbra. <BR /> Methods: The repetitive 2” wide raster
scans of penumbral regions that are taken with one minute cadence by
the Hinode spectropolarimeter are used to detect the line-of-sight
velocities in the penumbra from enhanced signals in the wings of
Stokes V profiles. The lifetimes and positions within penumbra of the
identified downflow patches are investigated. The plasma properties
of the downflow patches are determined using the inversions of the
observed Stokes profiles. <BR /> Results: The temporal downflows
have lifetimes of up to fourteen minutes. Some of them are related
to the disappearance or weakening of nearby upflow regions or to the
chromospheric brightenings. The downflows take place in regions with
stronger and more vertical magnetic fields than the upflow regions.
---------------------------------------------------------
Title: A new type of small-scale downflow patches in sunspot penumbrae
Authors: Katsukawa, Y.; Jurčák, J.
2010A&A...524A..20K Altcode: 2010arXiv1007.1702K
Context. Magnetic and flow structures in a sunspot penumbra are created
by strong interplay between inclined magnetic fields and photospheric
convection. They exhibit a complex nature that cannot always be
explained by the well-known Evershed flow. <BR /> Aims: A sunspot
penumbra is observationally examined to reveal properties of small-scale
flow structures and their relationship to the filamentary magnetic
structures and the Evershed flow. We also study how the photospheric
dynamics are related to chromospheric activities. <BR /> Methods: This
study is based on data analysis of spectro-polarimetric observations of
photospheric Fe I lines with the Solar Optical Telescope aboard Hinode
in a sunspot penumbra at different heliocentric angles. Vector magnetic
fields and velocities are derived using the spectro-polarimetric
data and a Stokes inversion technique. An observation with a Ca II H
filtergram co-spatial and co-temporal with the spectro-polarimetric
one is also used to study possible chromospheric responses. <BR />
Results: We find small patches with downflows in the photospheric
layers. The downflow patches have a size of 0.5” or smaller and
a different geometrical configuration from the Evershed flow. The
downflow velocity is about 1 km s<SUP>-1</SUP> in the lower photspheric
layers and is almost zero in the upper layers. Some of the downflow
patches are associated with brightenings seen in Ca II H images. <BR
/> Conclusions: The downflows are possible observational signatures
of downward flows driven by magnetic reconnection in the interlaced
magnetic field configuration, where upward flows make brightenings in
the chromosphere. Another possibility is that they are concentrated
downward flows of overturning magnetoconvection.
---------------------------------------------------------
Title: Three-Dimensional View of Transient Horizontal Magnetic Fields
in the Photosphere
Authors: Ishikawa, Ryohko; Tsuneta, Saku; Jurčák, Jan
2010ApJ...713.1310I Altcode: 2010arXiv1003.1376I
We infer the three-dimensional magnetic structure of a transient
horizontal magnetic field (THMF) during its evolution through
the photosphere using SIRGAUS inversion code. The SIRGAUS code
is a modified version of SIR (Stokes Inversion based on Response
function), and allows for retrieval of information on the magnetic and
thermodynamic parameters of the flux tube embedded in the atmosphere
from the observed Stokes profiles. Spectropolarimetric observations of
the quiet Sun at the disk center were performed with the Solar Optical
Telescope on board Hinode with Fe I 630.2 nm lines. Using repetitive
scans with a cadence of 130 s, we first detect the horizontal field
that appears inside a granule, near its edge. On the second scan,
vertical fields with positive and negative polarities appear at both
ends of the horizontal field. Then, the horizontal field disappears
leaving the bipolar vertical magnetic fields. The results from the
inversion of the Stokes spectra clearly point to the existence of
a flux tube with magnetic field strength of ~400 G rising through
the line-forming layer of the Fe I 630.2 nm lines. The flux tube is
located at around log τ<SUB>500</SUB> ~ 0 at Δt = 0 s and around log
τ<SUB>500</SUB> ~ -1.7 at Δt = 130 s. At Δt = 260 s, the horizontal
part is already above the line-forming region of the analyzed lines. The
observed Doppler velocity is maximally 3 km s<SUP>-1</SUP>, consistent
with the upward motion of the structure as retrieved from the SIRGAUS
code. The vertical size of the tube is smaller than the thickness of
the line-forming layer. The THMF has a clear Ω-shaped loop structure
with the apex located near the edge of a granular cell. The magnetic
flux carried by this THMF is estimated to be 3.1 × 10<SUP>17</SUP> Mx.
---------------------------------------------------------
Title: Scattering Polarization in the Fe I 630 nm Emission Lines at
the Extreme Limb of the Sun
Authors: Lites, B. W.; Casini, R.; Manso Sainz, R.; Jurčák, J.;
Ichimoto, K.; Ishikawa, R.; Okamoto, T. J.; Tsuneta, S.; Bellot
Rubio, L.
2010ApJ...713..450L Altcode:
Spectro-polarimetric observations with the Solar Optical Telescope
onboard Hinode reveal the emission spectrum of the Fe I 630 nm lines
at the solar limb. The emission shell extends for less than 1” thereby
making it extremely difficult to detect from ground-based observatories
viewing the limb through the Earth's atmosphere. The linear polarization
signal is clearly due to scattering and it is predominantly oriented
in the radial direction. Using a comprehensive atomic model of
iron, we are able to interpret qualitatively the observed signals,
including the radial orientation of the linear polarization. The Hanle
effect causes the linear polarization of the Fe I 630 nm lines to be
sensitive to magnetic fields between ~0.1 G and ~40 G, and also to
be sensitive to the field's topology for stronger fields. The overall
degree of observed polarization can be reproduced by randomly oriented
horizontal magnetic fields of strength ≈2 G. The discovery of their
scattering polarization signals thus opens a new diagnostic opportunity
for these lines.
---------------------------------------------------------
Title: Evolution of Umbral Dots and Penumbral Grains
Authors: Sobotka, M.; Jurčák, J.
2010ASSP...19..507S Altcode: 2010mcia.conf..507S
On 27 February 2007, Hinode SOT/SP acquired a time series of full-Stokes
spectra of a regular, medium-sized sunspot NOAA 10944 located near
the center of the solar disk. The inversion code SIR (Ruiz Cobo and
del Toro Iniesta 1992, ApJ 398, 375) was applied to these data and a
3-h long time series of 34 spatial 3D maps of plasma parameters in the
umbra and penumbra were computed. The temporal and spatial resolutions
are 5.5 min and 0 :0032, respectively. A simultaneous series of SOT/BFI
G-band images was utilized for complementary measurements of horizontal
motions and sizes of small-scale features.
---------------------------------------------------------
Title: Downflow Patches in a Penumbra Observed with the Hinode
Spectro-Polarimeter
Authors: Katsukawa, Y.; Jurčák, J.
2009ASPC..415..117K Altcode:
We here present a new observational signature of dynamics in a sunspot
penumbra. The dynamics are observed as a small patch of downflows
distributed sparsely in a center-side penumbra, and not observed in
a limb-side penumbra. The distribution suggests that the downflow is
aligned to magnetic field lines relatively vertical to the surface. The
flow might be related to dissipation of magnetic energies in a penumbra.
---------------------------------------------------------
Title: Evolution of Physical Characteristics of Umbral Dots and
Penumbral Grains
Authors: Sobotka, M.; Jurčák, J.
2009ApJ...694.1080S Altcode:
A time series of full-Stokes spectropolarimetric observations of
the sunspot NOAA 10944, acquired with HINODE/SOT in 2007 February, is
analyzed. The data were inverted using the code SIR into a series of 34
maps covering 3 hr of umbra and penumbra evolution. The retrieved maps
of plasma parameters show the spatial distribution of temperature,
line-of-sight velocity, magnetic field strength, and inclination
in two different ranges of optical depths corresponding to the low
and high photosphere. In these maps, the evolution of central and
peripheral umbral dots (CUDs and PUDs) and penumbral grains (PGs) was
traced. While CUDs do not show any excess of line-of-sight velocity
and magnetic field inclination with respect to the surrounding umbra,
upflows of 400 m s<SUP>-1</SUP> and a more horizontal magnetic field
are detected in the low photospheric layers of PUDs. PGs have even
stronger upflows and magnetic field inclination in the low photosphere
than PUDs. The absolute values of these parameters decrease when PGs
evolve into PUDs. It seems that PGs and PUDs are of a similar physical
nature. Both classes of features appear in regions with a weaker and
more horizontal magnetic field and their formation height reaches
the low photosphere. On the other hand, CUDs appear in regions with
a stronger and more vertical magnetic field and they are formed too
deep to detect upflows and changes in magnetic field inclination.
---------------------------------------------------------
Title: The Properties of Penumbral Microjets - Inclinations and
Possible Potospheric Response
Authors: Jurcak, J.; Katsukawa, Y.
2008ESPM...12.2.25J Altcode:
The dependence of penumbral microjets inclination on the position
within penumbra is investigated using the Ca II images taken with Hinode
SOT. The penumbral microjet inclination is increasing towards the outer
edge of the penumbra; from 35 deg at the umbra-penumbra boundary up
to 70 deg at the penumbra/quiet sun boundary. The comparison with the
inclination of photospheric magnetic field suggest that the penumbral
microjet follows the opening magnetic field lines of a vertical flux
tube that creates the sunspot. Another data set of Ca II images with
simultaneous SP measurements is used to study the possible relation
between the penumbral microjets and the downflows observed in middle
of the centre-side penumbra. Some of these downflow patches can be
associated with the Ca II brightenings and might correspond to the
reconnection outflow. As is retrieved from the Stokes inversion, the
downflow preferentially take place in the lower photosphere and this
may provide a constraint on a reconnection site.
---------------------------------------------------------
Title: The properties of penumbral microjets inclination
Authors: Jurčák, J.; Katsukawa, Y.
2008A&A...488L..33J Altcode: 2008arXiv0808.0757J
Aims: We investigate the dependence of penumbral microjets inclination
on the position within penumbra. <BR />Methods: The high cadence
observations taken on 10 November 2006 with the Hinode satellite
through the Ca II H and G-band filters were analysed to determine the
inclination of penumbral microjets. The results were then compared with
the inclination of the magnetic field determined through the inversion
of the spectropolarimetric observations of the same region. <BR
/>Results: The penumbral microjet inclination is increasing towards
the outer edge of the penumbra. The results suggest that the penumbral
microjet follows the opening magnetic field lines of a vertical flux
tube that creates the sunspot.
---------------------------------------------------------
Title: Differences between Central and Peripheral Umbral Dots
Authors: Sobotka, M.; Jurcak, J.
2008ESPM...12.2.23S Altcode:
A time series of full-Stokes spectropolarimetric observations of the
sunspot NOAA 10944, acquired with Hinode SOT/SP in February 2007,
is analysed. The data were inverted using the code SIR into a series
of 33 maps covering 3 hours of the umbra and penumbra evolution. Each
map describes the spatial distribution of temperature, line-of-sight
velocity, and magnetic field vector in two different ranges of optical
depths corresponding to lower and upper photosphere. In these maps,
several long-lived central (CUDs) and moving peripheral (PUDs)
umbral dots were selected and their evolution was traced. While CUDs
show only a very weak signature of LOS velocity and magnetic field
inclination, in the low layers of PUDs were detected upflows of 500
m/s and an enhanced field inclination with respect to the surrounding
umbra. These parameters decrease gradually during the evolution of
PUDs. Hence, concerning the physical characteristics, PUDs resemble
rather penumbral grains (from which they often originate) than CUDs.
---------------------------------------------------------
Title: Erratum: The Analysis of Penumbral Fine Structure Using an
Advanced Inversion Technique
Authors: Jurcák, Jan; Bellot Rubio, Luis; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi;
Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.; Tsuneta,
Saku
2008PASJ...60..933J Altcode:
In the article [PASJ 59, S601-S606 (2007)], the word ”CSIC” was
omitted from the affiliation of Dr. Luis Bellot Rubio. The correct
affiliation is : <SUP>2</SUP>Instituto de Astrofísica de Andalucía
(CSIC), Apdo. de Correos 3004, 18080 Granada, Spain
---------------------------------------------------------
Title: Photospheric Signature of Penumbral Microjets
Authors: Katsukawa, Y.; Jurcak, J.; Ichimoto, K.; Suemtasu, Y.;
Tsuneta, S.; Shimizu, T.; Berger, T. E.; Shine, R. A.; Tarbell, T. D.;
Lites, B. W.
2008AGUSMSP53A..03K Altcode:
HINODE Solar Optical Telescope (SOT) discovered ubiquitous occurrence
of fine-scale jetlike activities in penumbral chromospheres, which
are referred to as penumbral microjets. The microjets' small width
of 400 km and short duration of less than 1 min make them difficult
to identify in existing ground-based observations. The apparent
rise velocity is faster than 50km/s and is roughly comparable to
the Alfven speed in the sunspot chromosphere. These properties of
penumbral microjets suggest that magnetic reconnection in uncombed
magnetic field configuration is the most possible cause of penumbral
microjets. In order to understand magnetic configuration associated with
penumbral microjets and prove the chromospheric magnetic reconnection
hypothesis, we investigated relationship between penumbral microjets
seen in CaIIH images and photospheric magnetic fields measured by
the HINODE spectro-polarimeter. We found the inclination angles of
penumbral microjets measured in CaII H images are roughly consistent
with inclination angles of relatively vertical magnetic field
component in uncombed magnetic field configuration. In addition,
strong and transient downflows are observed in the photosphere near
the boundary of a horizontal flux tube associated with a penumbral
microjet. The size of the downflow region is about 300km, which is
close to the width of penumbral microjets seen in CaII H images. The
downflow velocity of several km/s might be a result of an outflow of
chromospheric magnetic reconnection and suffer deceleration due to
the higher density in the photosphere.
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Title: Penumbral models in the light of Hinode spectropolarimetric
observations
Authors: Jurčák, J.; Bellot Rubio, L. R.
2008A&A...481L..17J Altcode: 2007arXiv0711.1692J
Aims:The realism of current models of the penumbra is assessed
by comparing their predictions with the plasma properties
of penumbral filaments as retrieved from spectropolarimetric
observations. <BR />Methods: The spectropolarimeter onboard Hinode
allows us, for the first time, to distinguish the fine structure
of the penumbra. Therefore, we can use one-component inversions to
obtain the stratifications of plasma parameters in each pixel. The
correlations between the plasma parameters and the continuum intensity
are studied. <BR />Results: We find that, in the outer penumbra,
the stronger flows and higher values of magnetic field inclination
tend to be located in dark filaments. This finding does not seem to
be compatible with the scenario of a field-free gappy penumbra.
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Title: The Analysis of Penumbral Fine Structure Using an Advanced
Inversion Technique
Authors: Jurcák, Jan; Bellot Rubio, Luis; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi;
Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.; Tsuneta,
Saku
2007PASJ...59S.601J Altcode: 2007arXiv0707.1560J
We present a method to study the penumbral fine structure using data
obtained by the spectropolarimeter on board Hinode. For the first
time, the penumbral filaments can be considered as being resolved in
spectropolarimetric measurements. This enables us to use inversion
codes with only one-component model atmospheres, and thus to assign
the obtained stratifications of the plasma parameters directly to the
penumbral fine structure. This approach was applied to the limb-side
part of the penumbra in the active region NOAA10923. Preliminary results
show a clear dependence of the plasma parameters on the continuum
intensity in the inner penumbra, i.e., a weaker and horizontal magnetic
field along with an increased line-of-sight velocity are found in the
low layers of the bright filaments. The results in the mid penumbra
are ambiguous, and future analyses are necessary to unveil the magnetic
field structure and other plasma parameters there.
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Title: The Use of Spectro-Polarimetric Measurements to determine
the Plasma Heating
Authors: Jurčák, J.; Martinez Pillet, V.; Sobotka, M.
2007ASPC..369..171J Altcode:
We present the possible use of spectro-polarimetric measurements on
a set of data recorded with La Palma Stokes Polarimeter attached to
the Swedish Vacuum Solar Telescope. The stratification over the solar
atmosphere of different physical parameters is retrieved from these data
using the Stokes Inversion based on Response functions (SIR). We derive
the vertical component of electric current density coming out from the
stratification of the magnetic field strength and orientation of the
magnetic field vector. We also found spatial and height correlation
between the temperature enhancement and increase of electric current
density, this could be caused by the energy dissipation stored in the
magnetic field configuration.
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Title: Observational Evidence for Rising Penumbral Flux Tubes?
Authors: Jurčák, J.; Sobotka, M.
2007SoPh..241..223J Altcode:
On 13 May 2000 parts of a penumbra were observed in an active region
NOAA 8990 with the La Palma Stokes Polarimeter attached to the Swedish
Vacuum Solar Telescope. The stratification over the solar atmosphere of
different physical parameters is retrieved from these data by using the
Stokes inversion based on response functions. The results confirm the
previous findings of the penumbral structure. In general, the magnetic
field becomes weaker and more horizontal with increasing distance from
the umbra and the line-of-sight velocities are increasing towards the
outer boundary of the penumbra. The results also suggest the existence
of the unresolved fine structure of the penumbra. The stratifications
of the temperature and of the magnetic field strength indicate the
presence of rising flux tubes, which were predicted theoretically by
Schlichenmaier, Jahn and Schmidt (1998, Astron. Astrophys.337, 897).
---------------------------------------------------------
Title: The observational counterpart of the rising flux tube model?
Authors: Jurčák, J.; Sobotka, M.
2007msfa.conf..225J Altcode:
An analysis of Stokes observations of a penumbra in active region NOAA
8990 is presented. The observations were recorded with the La Palma
Stokes Polarimeter attached to the 1-m Swedish Solar Telescope. The
stratification in the solar atmosphere of different physical parameters
is retrieved from these data using the Stokes Inversion based on
Response functions (SIR). Our results confirm previous findings,
that with increasing distance from the umbra the magnetic field
becomes weaker and more horizontal and the line-of-sight velocities
increase. The results suggest the existence of unresolved filamentary
structure in the spatial distributions of temperature, magnetic field
strength and inclination. The maps of temperature and magnetic field
strength along the vertical cuts through the penumbra indicate the
presence of rising flux tubes, predicted theoretically by Schlichenmaier
et al. (1998).
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Title: The magnetic canopy above light bridges
Authors: Jurčák, J.; Martínez Pillet, V.; Sobotka, M.
2006A&A...453.1079J Altcode:
An analysis of high-resolution Stokes observations of two light
bridges in active region NOAA 8990 is presented. The observations were
recorded with the La Palma Stokes Polarimeter attached to the Swedish
Vacuum Solar Telescope. The stratification over the solar atmosphere
of different physical parameters is retrieved from these data using
the Stokes inversion based on response functions (SIR). Our results
confirm previous observations of features such as the decrease in
magnetic field strength and the increase in inclination in the light
bridges. We also confirm a temperature increase in these structures
with respect to the surrounding umbrae. The maps of the magnetic field
strength and of the orientation of the magnetic field vector indicate
the presence of a canopy structure above the light bridges. We derive
the vertical component of electric current density (J_z) from the
configuration of the magnetic field. The increased temperature found
in the upper layers is studied in the context of the proposed canopy
topology and could also explain the recently observed chromospheric
heating processes found above light bridges.
---------------------------------------------------------
Title: The Canopy Structure above Light Bridges
Authors: Jurčák, J.; Sobotka, M.; Martínez Pillet, V.
2006CEAB...30...55J Altcode:
An analysis of high-resolution Stokes observations of two light bridges
in the active region NOAA 8990 is presented. The observations were
recorded with the La Palma Stokes Polarimeter attached to the Swedish
Vacuum Solar Telescope. The stratification of different physical
parameters is retrieved using the Stokes Inversion based on Response
functions (SIR). Our results confirm the decrease of magnetic field
strength and the increase of inclination in light bridges. We find a
complex temperature stratification in these structures Coming out from
the stratification of the magnetic field strength and the orientation
of the magnetic field vector, we suggest a canopy structure above the
light bridge. We derive the vertical component of electric current
density (J<SUB>z</SUB>). The increase of J<SUB>z</SUB> corresponds to
temperature enhancements that might be caused by the energy dissipation
stored in the magnetic field.
---------------------------------------------------------
Title: The Magnetic Configuration in Light Bridges
Authors: Jurčák, J.; Sobotka, M.; Martínez Pillet, V.
2005ESASP.600E...8J Altcode: 2005dysu.confE...8J; 2005ESPM...11....8J
No abstract at ADS
---------------------------------------------------------
Title: The structure of a penumbral connection between solar pores
Authors: Hirzberger, J.; Stangl, S.; Gersin, K.; Jurčák, J.;
Puschmann, K. G.; Sobotka, M.
2005A&A...442.1079H Altcode:
High resolution 2D-spectro-polarimetric observations have been used
to analyse the magnetic field and flow topologies of a penumbral
connection between two opposite polarity solar pores. A filamentary
structured Evershed-like material flow from one pore to the other
along the magnetic field lines has been detected. The flow channels
are co-spatial with bright penumbral filaments close to the pore which
feeds the flow and the clear brightness-velocity relation vanishes close
to the pore which represents the sink of the flow. The boundary between
umbra and penumbra of the two pores show significant differences: bright
comet-like penumbral grains represent endings of penumbral filaments
at the flow sources whereas no such grains were found at the sinks of
the flow. Furthermore, a systematic variation of the asymmetries of
measured Stokes V profiles across the penumbral connection have been
found. The obtained results are in accordance with the widely-accepted
uncombed penumbra hypothesis and the moving flux tube model.
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Title: Velocity Fields in an Irregular Sunspot
Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V.
2005ASSL..320..227J Altcode: 2005smp..conf..227J
No abstract at ADS
---------------------------------------------------------
Title: Velocity fields in an irregular sunspot
Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V.
2003ESASP.535..109J Altcode: 2003iscs.symp..109J
Line-of-sight velocity fields in an irregular sunspot (NOAA 8990)
have been determined from Stokes-I spectra of the line Fe I 630.15
nm, obtained with the La Palma Stokes Polarimeter at the Swedish
Vacuum Solar Telescope on May 13, 2000. We show and discuss the
resulting velocity maps, the dependence of velocities on the
continuum intensities, and the correlation between velocities and
line asymmetries.
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Title: Burst phenomena in solar flares
Authors: Kotrč, P.; Kupryakov, Yu. A.; Jurčák, J.
2002ESASP.477..139K Altcode: 2002scsw.conf..139K
Solar flares are rapid dissipative processes in which the energy
accumulated in the magnetic field is released in the forms of plasma
heating, explosive plasma flows with flare shock generations, particle
accelerations, and emissions in a very broad range of frequencies
ranging from radio waves up to gamma-rays. As solar flares and related
phenomena influence not only the processes in the solar atmosphere, but
also in the heliosphere, they belong to important components of space
weather. While some of the flares pass quietly, another ones express
as very active. Courses of some flares are rather monotone while the
others are accompanied by bursts during which sudden and usually short
increase of the radiation outputs can be detected. Analyzing data from
catalogues and various observations we studied rapid changes occurring
in solar flare X-ray, radio and optical radiation, especially flare
optical spectra including their possible polarization as well as other
indirect evidence of accelerated particle beams occurrence.