Author name code: jurcak ADS astronomy entries on 2022-09-14 author:"Jurcak, Jan" ------------------------------------------------------------------------ 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 Bibcode: 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. 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. Bibcode: 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.
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.
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.
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−1, 1 km s−1, and 0.1 km s−1, 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.
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.

Movies associated with Figs. 2 and 3 are available at https://www.aanda.org 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. Bibcode: 2021A&A...652C...7B Altcode: No abstract at ADS Title: Magnetic properties on the boundary of an evolving pore Authors: García-Rivas, M.; Jurčák, J.; Bello González, N. Bibcode: 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, Bvercrit, and by a 50% continuum intensity of the quiet Sun, IQS. Umbrae with vertical magnetic fields stronger than Bvercrit are stable, whereas umbrae with vertical magnetic fields weaker than Bvercrit are unstable and prone to vanishing.
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.
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 (Ic = 0.55 IQS) is used to define the pore boundary and we study the temporal evolution of the magnetic properties there.
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 (Bver) 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 Bver on its boundary. In the newly formed area of the pore, Bver remains mostly below 1731 G and B remains everywhere below 1921 G; (4) ultimately, pore decay starts. We find overall that pore areas with Bver < 1731 G, or equivalently B < 1921 G, disintegrate faster than regions that fulfil this criteria.
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. 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 Bibcode: 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. Title: Solar pores - A magnetic evolution laboratory Authors: García-Rivas, M.; Jurčák, J.; Bello González, N. Bibcode: 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 (Bver) on evolving pores and the existence of an equivalent critical vertical magnetic value to provide steadiness. Indeed, we find that areas with weak Bver are unstable and granulation takes over them. However, areas with strong Bver show longer lifetimes. 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 Bibcode: 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.
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.
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.
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. 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 Bibcode: 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. 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 Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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.
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.
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.
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. 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. Bibcode: 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. Title: New Insights on Penumbra Magneto-Convection Authors: Bello González, N.; Jurčák, J.; Schlichenmaier, R.; Rezaei, R. Bibcode: 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. Title: Recent advancements in the EST project Authors: Jurčák, Jan; Collados, Manuel; Leenaarts, Jorrit; van Noort, Michiel; Schlichenmaier, Rolf Bibcode: 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. 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. Bibcode: 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.
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.
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.
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.
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. Title: Heating of the solar photosphere during a white-light flare Authors: Jurčák, Jan; Kašparová, Jana; Švanda, Michal; Kleint, Lucia Bibcode: 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.
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.
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.
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. 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. Bibcode: 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.
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.
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.
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. Title: Understanding the HMI Pseudocontinuum in White-light Solar Flares Authors: Švanda, Michal; Jurčák, Jan; Kašparová, Jana; Kleint, Lucia Bibcode: 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 c 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 c 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. Bibcode: 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.
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.
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.
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. Bibcode: 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.
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.
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.
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).
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. Bibcode: 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. Bibcode: 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, Bstablever. 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 Bver<Bstablever, as well as in granular convective areas. Eventually, a stable umbra-penumbra boundary settles at Bstablever.
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.
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.
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 Bstablever ≈ 1.8 kG.
Conclusions: Our findings are in an agreement with the need of Bstablever for establishing a stable umbra-penumbra boundary: while Bver in the pore is smaller than Bstablever, 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.

The movie associated to Fig. 1 is available at http://www.aanda.org Title: Canonical Bver value on umbra/penumbra boundaries Authors: Jurcak, Jan; Bello González, Nazaret; Schlichenmaier, Rolf; Rezaei, Reza Bibcode: 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. Bibcode: 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-1. 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.

Movies associated to Figs. 1 and 2 are available at http://www.aanda.org Title: Chromospheric Heating by Acoustic Waves Compared to Radiative Cooling Authors: Sobotka, M.; Heinzel, P.; Švanda, M.; Jurčák, J.; del Moro, D.; Berrilli, F. Bibcode: 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. Bibcode: 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-1. 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 Bibcode: 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. Bibcode: 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, Bstablever, was found along the umbra-penumbra boundary of developed sunspots.
Aims: We study the changing value of Bver as the penumbra forms and as it reaches a stable state. We compare this with the corresponding value in fully developed penumbrae.
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.
Results: The vertical component of the magnetic field, Bver, 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 Bver value comparable to that of umbra-penumbra boundaries of fully fledged sunspots.
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 Bverstable. During the penumbra formation process, the inner penumbra extends into regions where the umbra previously prevailed. Hence, in areas where Bver<Bstablever, the magneto-convection mode operating in the umbra turns into a penumbral mode. Eventually, the inner penumbra boundary settles at Bverstable, which hints toward the role of Bverstable 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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-1 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-1) 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-1). Title: Magnetic field and radiative transfer modelling of a quiescent prominence Authors: Gunár, S.; Schwartz, P.; Dudík, J.; Schmieder, B.; Heinzel, P.; Jurčák, J. Bibcode: 2014A&A...567A.123G Altcode:
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.
Methods: We combined results of the 3D magnetic field modelling with 2D prominence fine structure radiative transfer models to fully exploit the available observations.
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.
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.

Movie and Appendix A are available in electronic form at http://www.aanda.org Title: Orphan penumbrae: Submerging horizontal fields Authors: Jurčák, J.; Bellot Rubio, L. R.; Sobotka, M. Bibcode: 2014A&A...564A..91J Altcode: 2014arXiv1402.6558J
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.
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.
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.
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.

A movie attached to Fig. 11 is available in electronic form at http://www.aanda.org 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 Bibcode: 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. Bibcode: 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.
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.
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.
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.
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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.
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.
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.
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. Bibcode: 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. Bibcode: 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. Bibcode: 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:
· Radiative and dynamical properties of Photospheric Bright Points versus their magnetic field concentration.
· Close up analysis of magnetic, velocity and temperature field in a solar pore.
· 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. Bibcode: 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.
Aims: Relations between the magnetic field components, line-of-sight velocities, and horizontal motions in and around a large pore (Deff = 8''.5) are analysed to provide observational constraints on theoretical models and numerical simulations.
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.
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 Bhor is more extended than the vertical component Bz. The temperature linearly decreases with increasing Bz, by about - 300 K kG-1 in the photosphere and - 800 K kG-1 in the umbra. The temperature contrast of granulation increases with increasing magnetic field strength and is then suppressed for Bz > 1200 G. Granular upflows dominate in regions with Bz < 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 Bhor > 1000 G. Horizontal motions of granules start to be damped for Bz > 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. Bibcode: 2011A&A...531A.118J Altcode:
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.
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.
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.
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. Bibcode: 2010A&A...524A..21J Altcode:
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.
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.
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. Bibcode: 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.
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.
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.
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-1 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.
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 Bibcode: 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 τ500 ~ 0 at Δt = 0 s and around log τ500 ~ -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-1, 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 × 1017 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1 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. Bibcode: 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. Bibcode: 2008A&A...488L..33J Altcode: 2008arXiv0808.0757J Aims: We investigate the dependence of penumbral microjets inclination on the position within penumbra.
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.
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. Bibcode: 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 Bibcode: 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 : 2Instituto 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. Bibcode: 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. Title: Penumbral models in the light of Hinode spectropolarimetric observations Authors: Jurčák, J.; Bellot Rubio, L. R. Bibcode: 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.
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.
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. 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 Bibcode: 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. Title: The Use of Spectro-Polarimetric Measurements to determine the Plasma Heating Authors: Jurčák, J.; Martinez Pillet, V.; Sobotka, M. Bibcode: 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. Title: Observational Evidence for Rising Penumbral Flux Tubes? Authors: Jurčák, J.; Sobotka, M. Bibcode: 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. Bibcode: 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). Title: The magnetic canopy above light bridges Authors: Jurčák, J.; Martínez Pillet, V.; Sobotka, M. Bibcode: 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. Bibcode: 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 (Jz). The increase of Jz 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. Bibcode: 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. Bibcode: 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. Title: Velocity Fields in an Irregular Sunspot Authors: Jurčák, J.; Sobotka, M.; Martínez-Pillet, V. Bibcode: 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. Bibcode: 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. Title: Burst phenomena in solar flares Authors: Kotrč, P.; Kupryakov, Yu. A.; Jurčák, J. Bibcode: 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.