Author name code: dudik ADS astronomy entries on 2022-09-14 author:"Dudik, Jaroslav" ------------------------------------------------------------------------ Title: Filament Leg--Leg Reconnection as a Source of Prominent Supra-Arcade Downflows Authors: Dudik, Jaroslav; Aulanier, Guillaume; Kasparova, Jana; Karlicky, Marian; Zemanova, Alena; Lorincik, Juraj; Druckmuller, Miloslav Bibcode: 2022arXiv220900306D Altcode: We report on interaction of the legs of the erupting filament of 2012 August 31 and associated prominent supra-arcade downflows (P-SADs) as observed by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. We employ a number of image processing techniques to enhance weak interacting features. As the filament erupts, both legs stretch outwards. The positive-polarity leg also untwists and splits into two parts. The first part runs into the conjugate (negative-polarity) leg, tearing it apart. The second part then converges into the remnant of the conjugate leg, after which both weaken and finally disappear. All these episodes of interaction of oppositely-oriented filament legs are followed by appearance of P-SADs, seen in the on-disk projection to be shaped as loop-tops, along with many weaker SADs. All SADs are preceded by hot supra-arcade downflowing loops. This observed evolution is consistent with the three-dimensional rr-rf (leg-leg) reconnection, where the erupting flux rope reconnects with itself. In our observations, as well as in some models, the reconnection in this geometry is found to be long-lasting. It plays a substantial role in the evolution of the flux rope of the erupting filament and leads to prominent supra-arcade downflows. Title: Diagnostics of non-Maxwellian electron distributions in solar active regions from Fe XII lines observed by Hinode/EIS and IRIS Authors: Del Zanna, G.; Polito, V.; Dudík, J.; Testa, P.; Mason, H. E.; Dzifčáková, E. Bibcode: 2022arXiv220707026D Altcode: We present joint Hinode/EIS and IRIS observations of Fe XII lines in active regions, both on-disk and off-limb. We use an improved calibration for the EIS data, and find that the 192.4 A / 1349 A observed ratio is consistent with the values predicted by CHIANTI and the coronal approximation in quiescent areas, but not in all active region observations, where the ratio is often lower than expected by up to a factor of about two. We investigate a number of physical mechanisms that could affect this ratio, such as opacity and absorption from cooler material. We find significant opacity in the EIS Fe XII 193 and 195 A lines, but not in the 192.4 A line, in agreement with previous findings. As we cannot rule out possible EUV absorption by H, He and He II in the on-disk observations, we focus on an off-limb observation where such absorption is minimal. After considering these, as well as possible non-equilibrium effects, we suggest that the most likely explanation for the observed low Fe XII 192.4 A / 1349 A ratio is the presence of non-Maxwellian electron distributions in the active regions. This is in agreement with previous findings based on EIS and IRIS observations independently. Title: Blueshifted Si IV 1402.77 Å Line Profiles in a Moving Flare Kernel Observed by IRIS Authors: Lörinčík, Juraj; Dudík, Jaroslav; Polito, Vanessa Bibcode: 2022ApJ...934...80L Altcode: We analyze the spectra of a slipping flare kernel observed during the 2015 June 22 M6.5-class flare by the Interface Region Imaging Spectrograph (IRIS). During the impulsive and peak phases of the flare, loops exhibiting an apparent slipping motion along the ribbons were observed in the 131 Å channel of SDO/AIA. The IRIS spectrograph slit observed a portion of the ribbons, including a moving kernel corresponding to a flare loop footpoint in Si IV, C II, and Mg II at a very-high 1 s cadence. The spectra observed in the kernel were mostly redshifted and exhibited pronounced red wings, as typically observed in large flares. However, in a small region in one of the ribbons, the Si IV 1402.77 Å line was partially blueshifted, with the corresponding Doppler velocity ∣v D∣ exceeding 50 km s-1. In the same region, the C II 1334.53, 1335.66, and 1335.71 Å lines were weakly blueshifted (∣v D∣ < 20 km s-1) and showed pronounced blue wings, which were also observed in the Mg II k 2796.35 Å as well as the Mg II triplet 2798.75 and 2798.82 Å lines. Using high-cadence AIA observations we found that the region where the blueshifts occurred corresponds to the accelerating kernel front as it moved through a weak field region. The IRIS observations with high resolution allowed us to capture the acceleration of the kernel under the slit for the first time. The unique observations of blueshifted chromospheric and TR lines provide new constraints for current models of flares. Title: KAPPA package and diagnostics of the kappa-distribution from EUV solar spectra Authors: Dzifcakova, Elena; Dudik, Jaroslav; Zemanova, Alena; Lorincik, Juraj Bibcode: 2022cosp...44.1218D Altcode: Many theoretical calculations and several diagnostics support an idea of the presence of non-Maxwellian electron distributions in the solar corona and transition region. The kappa-distributions as well as other distributions exhibiting high-energy tails change individual ionization, recombination and collisional excitation rates. These changes are reflected in the changes ionization equilibrium, populations of energy levels and therefore in line intensities. This enables diagnostics of non-Maxwellian distributions from observations. Theoretical spectra for different kappa-distributions, temperatures and electron densities can be obtained using the latest version KAPPA package which provides fast calculations of synthetic spectra for kappa-distributions. This allows us to search for diagnostic opportunities and enables us to study how kappa-distributions influence the observed temperature distribution in emitting plasma. We showed that forbidden lines have a great potential for non-thermal diagnostics. The Fe XVII and Fe XVIII lines in soft X-ray spectral range observable by Marshall Grazing-Incidence X-ray Spectrometer (MaGIXS) are also suitable to diagnose kappa-distributions. Finally, the Fe XI - Fe XIII lines observed by the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode spacecraft were used to diagnose kappa in the active region and for the quiet Sun. It was found that the quiet Sun spectra are consistent with a Maxwellian distribution but the spectrum of coronal loops, moss, and for the transient loop observed within active region are strongly non-Maxwellian with kappa as low as 2. Title: Blueshifted Si IV 1402.77Å line profiles in a moving flare kernel observed by IRIS Authors: Lörinčík, Juraj; Dudík, Jaroslav; Polito, Vanessa Bibcode: 2022arXiv220610114L Altcode: We analyze spectra of a slipping flare kernel observed during the 2015 June 22 M6.5-class flare by the Interface Region Imaging Spectrograph (IRIS). During the impulsive and peak phases of the flare, loops exhibiting an apparent slipping motion along the ribbons were observed in the 131Å channel of SDO/AIA. The IRIS spectrograph slit observed a portion of the ribbons, including a moving kernel corresponding to a flare loop footpoint in Si IV, C II, and Mg II at a very-high 1 s cadence. The spectra observed in the kernel were mostly redshifted and exhibited pronounced red wings, as typically observed in large flares. However, in a small region in one of the ribbons, the Si IV 1402.77Å line was partially blueshifted, with the corresponding Doppler velocity |v_{D}| exceeding 50 km s$^{-1}$. In the same region, the C II 1334.53Å, 1335.66Å and 1335.71Å lines were weakly blueshifted (|v_{D}| < 20 km s$^{-1}$) and showed pronounced blue wings, which were observed also in the Mg II k 2796.35Å as well as the Mg II triplet 2798.75Å and 2798.82Å lines. Using high-cadence AIA observations we found that the region where the blueshifts occurred corresponds to the accelerating kernel front as it moved through a weak-field region. The IRIS observations with high resolution allowed us to capture the acceleration of the kernel under the slit for the first time. The unique observations of blueshifted chromospheric and TR lines provide new constrains for current models of flares. Title: Diagnostics of Non-Maxwellian Electron Distributions in Solar Active Regions from Fe XII Lines Observed by the Hinode Extreme Ultraviolet Imaging Spectrometer and Interface Region Imaging Spectrograph Authors: Del Zanna, G.; Polito, V.; Dudík, J.; Testa, P.; Mason, H. E.; Dzifčáková, E. Bibcode: 2022ApJ...930...61D Altcode: We present joint Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) and Interface Region Imaging Spectrograph (IRIS) observations of Fe XII lines in active regions, both on-disk and off-limb. We use an improved calibration for the EIS data, and find that the 192.4 Å/1349 Å observed ratio is consistent with the values predicted by CHIANTI and the coronal approximation in quiescent areas, but not in all active-region observations, where the ratio is often lower than expected by up to a factor of about two. We investigate a number of physical mechanisms that could affect this ratio, such as opacity and absorption from cooler material. We find significant opacity in the EIS Fe XII 193 and 195 Å lines, but not in the 192.4 Å line, in agreement with previous findings. As we cannot rule out possible EUV absorption by H, He, and He II in the on-disk observations, we focus on an off-limb observation where such absorption is minimal. After considering these, as well as possible nonequilibrium effects, we suggest that the most likely explanation for the observed low Fe XII 192.4 Å/1349 Å ratio is the presence of non-Maxwellian electron distributions in the active regions. This is in agreement with previous findings based on EIS and IRIS observations independently. Title: KAPPA: A Package for the Synthesis of Optically Thin Spectra for the Non-Maxwellian κ-distributions. II. Major Update to Compatibility with CHIANTI Version 10 Authors: Dzifčáková, Elena; Dudík, Jaroslav; Zemanová, Alena; Lörinčík, Juraj; Karlický, Marian Bibcode: 2021ApJS..257...62D Altcode: KAPPA is a database and software for the calculation of the optically thin spectra for the non-Maxwellian κ-distributions that were recently diagnosed in the plasma of solar coronal loops, flares, as well as in the transition region. KAPPA is based on the widely used CHIANTI database and reproduces many of its capabilities for κ-distributions. Here we perform a major update of the KAPPA database, including a near-complete recalculation of the ionization, recombination, excitation, and deexcitation rates for all ions in the database, as well as an implementation of the two-ion model for calculations of relative-level populations (and intensities) if these are modified by ionization and recombination from or to excited levels. As an example of KAPPA usage, we explore novel diagnostics of κ, and show that O III lines near 500 and 700 Å provide a strong sensitivity to κ, with some line intensity ratios changing by a factor of up to 2-4 compared to Maxwellian. This is much larger than previously employed diagnostics of κ. Title: Saddle-shaped Solar Flare Arcades Authors: Lörinčík, Juraj; Dudík, Jaroslav; Aulanier, Guillaume Bibcode: 2021ApJ...909L...4L Altcode: 2021arXiv210210858L Arcades of flare loops form as a consequence of magnetic reconnection powering solar flares and eruptions. We analyze the morphology and evolution of flare arcades that formed during five well-known eruptive flares. We show that the arcades have a common saddle-like shape. The saddles occur despite the fact that the flares were of different classes (C to X), occurred in different magnetic environments, and were observed in various projections. The saddles are related to the presence of longer, relatively higher, and inclined flare loops, consistently observed at the ends of the arcades, which we term "cantles." Our observations indicate that cantles typically join straight portions of flare ribbons with hooked extensions of the conjugate ribbons. The origin of the cantles is investigated in stereoscopic observations of the 2011 May 9 eruptive flare carried out by the Atmospheric Imaging Assembly and Extreme Ultraviolet Imager. The mutual separation of the instruments led to ideal observational conditions allowing for simultaneous analysis of the evolving cantle and the underlying ribbon hook. Based on our analysis we suggest that the formation of one of the cantles can be explained by magnetic reconnection between the erupting structure and its overlying arcades. We propose that the morphology of flare arcades can provide information about the reconnection geometries in which the individual flare loops originate. Title: Electron Densities in the Solar Corona Measured Simultaneously in the Extreme Ultraviolet and Infrared Authors: Dudík, Jaroslav; Del Zanna, Giulio; Rybák, Ján; Lörinčík, Juraj; Dzifčáková, Elena; Mason, Helen E.; Tomczyk, Steven; Galloy, Michael Bibcode: 2021ApJ...906..118D Altcode: 2020arXiv201109175D Accurate measurements of electron density are critical for determination of the plasma properties in the solar corona. We compare the electron densities diagnosed from Fe XIII lines observed by the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode mission with the near-infrared (NIR) measurements provided by the ground-based Coronal Multichannel Polarimeter (CoMP). To do that, the emissivity-ratio method based on all available observed lines of Fe XIII is used for both EIS and CoMP. The EIS diagnostics is further supplemented by the results from Fe XII lines. We find excellent agreement, within 10%, between the electron densities measured from both extreme-ultraviolet and NIR lines. In the five regions selected for detailed analysis, we obtain electron densities of log(Ne [cm-3]) = 8.2-8.6. Where available, the background subtraction has a significant impact on the diagnostics, especially on the NIR lines, where the loop contributes less than a quarter of the intensity measured along the line of sight. For the NIR lines, we find that the line center intensities are not affected by stray light within the instrument, and recommend using these for density diagnostics. The measurements of the Fe XIII NIR lines represent a viable method for density diagnostics using ground-based instrumentation. Title: Diagnostics of Kappa Distributions from Optically Thin Solar Spectra Authors: Dudík, Jaroslav; Dzifčáková, Elena Bibcode: 2021ASSL..464...53D Altcode: We review the diagnostics of the non-Maxwellian Kappa distributions from the remote-sensing spectroscopic observations of the optically thin parts of the solar atmosphere. While the electron distributions are typically diagnosed from ratios of emission line intensities alongside other plasma parameters such as electron densities and temperature, the ion distributions affect the shape of the line profiles and are more readily seen. The electron Kappa distributions relies on accurate calculations of synthetic spectra which in turn depend on evaluation of the ionization, recombination, and collisional excitation rates. Even though the observational uncertainties can be significant, recent results point out to a possibly widespread presence of low κ-values, typically κ = 2, in many regions of the solar atmosphere, including the transition region, active region corona, and solar flares, especially the reconnection region. Title: Magnetic support of the solar filaments Authors: Schmieder, Brigitte; Aulanier, Guillaume; Gunár, Stanislav; Dudik, Jaroslav; Heinzel, Petr Bibcode: 2021cosp...43E1766S Altcode: The scale height in prominence is 500 km at maximum. However, non activated prominences can reach an altitude of 50000 km or more. Hanging filaments observed over the limb give the impression of quasi vertical structures. It was already the view in the past but reactivated by the movies of Hinode in Ca II line showing fuzzing vertical structures. In the corona it is not possible to measure the magnetic field supporting prominences. Only extrapolations of the photospheric magnetic field explain how cool plasma embedded in the dips of the magnetic field lines can be supported in the hot corona. I will review a few papers showing the distribution of the cool plasma dips and the observations of filaments on the disk visible in H$\alpha$ and in UV. A recent paper shows how a 3D extrapolation model and a radiative-transfer based H$\alpha$ visualization method leads to H$\alpha$ prominence fine structures. Finally, I will discuss the perspective effects on the perceived morphology of observed and modeled prominences. Title: Imaging Evidence for Solar Wind Outflows Originating from a Coronal Mass Ejection Footpoint Authors: Lörinčík, Juraj; Dudík, Jaroslav; Aulanier, Guillaume; Schmieder, Brigitte; Golub, Leon Bibcode: 2021ApJ...906...62L Altcode: 2020arXiv201004250L We report on Atmospheric Imaging Assembly observations of plasma outflows originating in a coronal dimming during a 2015 April 28 filament eruption. After the filament started to erupt, two flare ribbons formed, one of which had a well-visible hook enclosing a core (twin) dimming region. Along multiple funnels located in this dimming, a motion of plasma directed outward started to be visible in the 171 and 193 Å filter channels of the instrument. In time-distance diagrams, this motion generated a strip-like pattern, which lasted for more than 5 hr and whose characteristics did not change along the funnel. We therefore suggest the motion is a signature of outflows corresponding to velocities ranging between ≍70 and 140 km s-1. Interestingly, the pattern of the outflows and their velocities were found to be similar to those we observed in a neighboring ordinary coronal hole. Therefore, the outflows were most likely a signature of a coronal mass ejection-induced solar wind flowing along the open-field structures rooted in the dimming region. Further, the evolution of the hook encircling the dimming region was examined in the context of the latest predictions imposed for 3D magnetic reconnection. The observations indicate that the filament's footpoints were, during their transformation to the dimming region, reconnecting with surrounding canopies. To our knowledge, our observations present the first imaging evidence for outflows of plasma from a dimming region. Title: Links between prominence/filament magnetic field and plasma: What can 3D WPFS models teach us? Authors: Gunár, Stanislav; Schmieder, Brigitte; Aulanier, Guillaume; Heinzel, Petr; Mackay, Duncan; Dudik, Jaroslav Bibcode: 2021cosp...43E1769G Altcode: The magnetic field constitutes the skeleton and the driving force of prominences/filaments. It supports the dense prominence plasma against gravity and insulates it from the hot, coronal environment. The magnetic field is also responsible for the prominence stability, evolution and eruptions which affect the heliosphere and ultimately the Earth. However, a strong imbalance exists between the numerous efforts in detailed modelling of prominence magnetic field and its understanding from observations. That is due to the complex nature of the direct (and indirect) observations of solar magnetic fields which are challenging at the best of times and even more so in prominences or filaments. The direct observations of the prominence magnetic field require high-precision spectro-polarimetric measurements and realistic assumptions about the plasma structure which allow us to infer the field configuration from its effect on the polarized light emergent from the observed structures. The indirect observations rely on the perceived location, shape and dynamics of the prominence or filament plasma, often using moving small-scale plasma structures as tracers guided by the field lines. Both methods thus rely on the presence of observable plasma in the magnetic field configuration, and on the radiation which carries the information about the in-situ conditions to the observer. No prominence/filament magnetic field measurements are made without these two additional components, which are sometimes an afterthought in the magnetic field models. We have developed 3D Whole-Prominence Fine Structure (WPFS) models to illuminate the links between the prominence magnetic field, its plasma distributed among numerous fine structures and the radiation which carries the information about the prominence physical conditions to the observer. What can we learn from these 3D models? For example, we can see that a small change of the magnetic field configuration can have a large effect on the perceived structure of prominences and filaments visible in the H-alpha line. Consequently, this means that significant changes observed in prominences or filaments do not need to suggest that equally large changes in the underlying magnetic field configuration had to occur. In another example, we see that seemingly incomparable differences in the morphological look of prominences (long horizontal fine structures versus small blobs of plasma arranged into more-less vertical features) may not need to imply the existence of radically different magnetic field configurations. Rather, they might simply be manifestations of projection effects that can differ greatly depending on the viewing angle under which we observe the naturally three-dimensional prominences/filaments. Title: Lyrids 2020 observations by AMOS, spectral, visual and photographic methods Authors: Toth, Juraj; Matlovic, Pavol; Zigo, Pavol; Kornos, Leonard; Simon, Jaroslav; Paulech, Tomas; Balaz, Martin; Polcic, Ludovit; Pisarcikova, Adriana; Zilkova, Danica; Bartkova, Daniela; Dudik, Jaroslav; Licandro, Javier; Masiar, Jan; Kaniansky, Stanislav; Barsa, Robert; Veres, Peter Bibcode: 2020JIMO...48..199T Altcode: We present observations of the 2020 Lyrid meteor shower by different techniques from Slovakia and the Canary Islands. The visual observations have been supported by video observations using the AMOS systems and are in good agreement with IMO visual data. We also present data of a Lyrid fireball observed on 2020 April 21 at 23h53m20s UTC by multiple stations of AMOS, AMOS-Spec and by a digital photographer. The fireball was about -4.5 magnitude and left a dust trail photographically visible for about 22 minutes. Just several minutes before, very long fireball was observed at 23h45m29s UTC by AMOS stations as well as another photographer from Kosice. The images illustrate the beauty of the night sky. Title: Flare Expansion to a Magnetic Rope Accompanied by Rare Radio Bursts Authors: Zemanová, Alena; Karlický, Marian; Kašparová, Jana; Dudík, Jaroslav Bibcode: 2020ApJ...905..111Z Altcode: 2021arXiv210108633Z We present multispectral analysis (radio, Hα, ultraviolet (UV)/extreme ultraviolet (EUV), and hard X-ray) of a confined flare from 2015 March 12. This flare started within the active region NOAA 12 297 and then it expanded into a large preexisting magnetic rope embedded with a cold filament. The expansion started with several brightenings located along the rope. This process was accompanied by a group of slowly positively drifting bursts in the 0.8-2 GHz range. The frequency drift of these bursts was 45-100 MHz s-1. One of the bursts had an S-like form. During the brightening of the rope we observed a unique bright EUV structure transverse to the rope axis. The structure was observed in a broad range of temperatures and it moved along the rope with the velocity of about 240 km s-1. When the structure dissipated, we saw a plasma further following twisted threads in the rope. The observed slowly positively drifting bursts were interpreted considering particle beams and we show that one with the S-like form could be explained by the beam propagating through the helical structure of the magnetic rope. The bright structure transverse to the rope axis was interpreted considering line-of-sight effects and the dissipation-spreading process, which we found to be more likely. Title: Plasma Diagnostics from Active Region and Quiet-Sun Spectra Observed by Hinode/EIS: Quantifying the Departures from a Maxwellian Distribution Authors: Lörinčík, Juraj; Dudík, Jaroslav; del Zanna, Giulio; Dzifčáková, Elena; Mason, Helen E. Bibcode: 2020ApJ...893...34L Altcode: 2020arXiv200307091L We perform plasma diagnostics, including that of the non-Maxwellian κ-distributions, in several structures observed in the solar corona by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on board the Hinode spacecraft. To prevent uncertainties due to the in-flight calibration of EIS, we selected spectral atlases observed shortly after the launch of the mission. One spectral atlas contains an observation of an active region, while the other is an off-limb quiet-Sun region. To minimize the uncertainties of the diagnostics, we rely only on strong lines and average the signal over a spatial area within selected structures. Multiple plasma parameters are diagnosed, such as the electron density, the differential emission measure, and the non-Maxwellian parameter κ. To do that, we use a simple, well-converging iterative scheme based on refining the initial density estimates via the differential emission measure (DEM) and κ. We find that while the quiet-Sun spectra are consistent with a Maxwellian distribution, the coronal loops and moss observed within the active region are strongly non-Maxwellian with κ ⪅ 3. These results were checked by calculating synthetic ratios using DEMs obtained as a function of κ. Ratios predicted using the DEMs assuming κ-distributions converged to the ratios observed in the quiet Sun and coronal loops. To our knowledge, this work presents a strong evidence of the presence of different electron distributions between two physically distinct parts of the solar corona. Title: Diagnostics of non-thermal-distributions from solar flare EUV line spectra Authors: Dzifčáková, Elena; Zemanová, Alena; Dudík, Jaroslav; Lörinčík, Juraj Bibcode: 2020IAUS..354..414D Altcode: Spectral line intensities observed by the Extreme Ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) during 2012 March 9 M6.3 flare were used to diagnose a presence of a non-thermal electron distribution represented by a κ-distribution. The diagnosed electron densities ($≈ 2 × {10^{11}}{{c}}{{{m}}^{ - 3}}$) are affected only a little by the presence of the non-thermal distribution, and are within the uncertainties of observation. On the other hand, the temperature diagnostics based on the line ratios involving different ionization degrees is strongly affected by the type of the electron distribution. The distribution functions diagnosed from relative Fe line intensities demonstrate the presence of strongly non-thermal distributions during the impulsive phase of the flare and later their gradual thermalization. Title: Observation of All Pre- and Post-reconnection Structures Involved in Three-dimensional Reconnection Geometries in Solar Eruptions Authors: Dudík, Jaroslav; Lörinčík, Juraj; Aulanier, Guillaume; Zemanová, Alena; Schmieder, Brigitte Bibcode: 2019ApJ...887...71D Altcode: 2019arXiv191008620D We report on observations of the two newly identified reconnection geometries involving erupting flux ropes. In 3D, a flux rope can reconnect either with a surrounding coronal arcade (recently named “ar-rf” reconnection) or with itself (“rr-rf” reconnection), and both kinds of reconnection create a new flux-rope field line and a flare loop. For the first time, we identify all four constituents of both reconnections in a solar eruptive event, the filament eruption of 2011 June 7 observed by Solar Dynamics Observatory/Atmospheric Imaging Assembly. The ar-rf reconnection manifests itself as shift of one leg of the filament by more than 25″ northward. At its previous location, a flare arcade is formed, while the new location of the filament leg previously corresponded to a footpoint of a coronal loop in 171 Å. In addition, the evolution of the flare ribbon hooks is also consistent with the occurrence of ar-rf reconnection as predicted by MHD simulations. Specifically, the growing hook sweeps footpoints of preeruptive coronal arcades, and these locations become inside the hook. Furthermore, the rr-rf reconnection occurs during the peak phase above the flare arcade, in an apparently X-type geometry involving a pair of converging bright filament strands in the erupting filament. A new flare loop forms near the leg of one of the strands, while a bright blob, representing a remnant of the same strand, is seen ascending into the erupting filament. All together, these observations vindicate recent predictions of the 3D standard solar-flare model. Title: Manifestations of Three-dimensional Magnetic Reconnection in an Eruption of a Quiescent Filament: Filament Strands Turning to Flare Loops Authors: Lörinčík, Juraj; Dudík, Jaroslav; Aulanier, Guillaume Bibcode: 2019ApJ...885...83L Altcode: 2019arXiv190903825L We report on observations of the conversion of bright filament strands into flare loops during the 2012 August 31 filament eruption. Prior to the eruption, individual bright strands composing one of the legs of the filament were observed in the 171 Å filter channel data of the Atmospheric Imaging Assembly. After the onset of the eruption, one of the hooked ribbons started to propagate and contract, sweeping footpoints of the bright filament strands as well as coronal loops located close by. Later on, hot flare loops appeared in regions swept by the hook, where the filament strands were rooted. Timing and localization of these phenomena suggest that they are caused by reconnection of field lines composing the filament at the hook, which, to our knowledge, has not been observed before. This process is not included in the standard flare model (CSHKP), as it does not address footpoints of erupting flux ropes and ribbon hooks. It has, however, been predicted using the recent three-dimensional extensions to the standard flare model. There, the erupting flux rope can reconnect with surrounding coronal arcades as the hooked extensions of current ribbons sweep its footpoints. This process results in formation of flare loops rooted in previous footpoints of the flux rope. Our observations of sweeping of filament footpoints are well described by this scenario. In all observed cases, all of the footpoints of the erupting filament became footpoints of flare loops. This process was observed to last for about 150 minutes, throughout the whole eruption. Title: Observations of a Footpoint Drift of an Erupting Flux Rope Authors: Zemanová, Alena; Dudík, Jaroslav; Aulanier, Guillaume; Thalmann, Julia K.; Gömöry, Peter Bibcode: 2019ApJ...883...96Z Altcode: 2019arXiv190802082Z We analyze the imaging observations of an M-class eruptive flare of 2015 November 4. The pre-eruptive Hα filament was modeled by the nonlinear force-free field model, which showed that it consisted of two helical systems. Tether-cutting reconnection involving these two systems led to the formation of a hot sigmoidal loop structure rooted in a small hook that formed at the end of the flare ribbon. Subsequently, the hot loops started to slip away from the small hook until it disappeared. The loops continued slipping and the ribbon elongated itself by several tens of arcseconds. A new and larger hook then appeared at the end of the elongated ribbon with hot and twisted loops rooted there. After the eruption of these hot loops, the ribbon hook expanded and later contracted. We interpret these observations in the framework of the recent three-dimensional (3D) extensions to the standard solar flare model predicting the drift of the flux rope footpoints. The hot sigmoidal loop is interpreted as the flux rope, whose footpoints drift during the eruption. While the deformation and drift of the new hook can be described by the model, the displacement of the flux rope footpoint from the filament to that of the erupting flux rope indicate that the hook evolution can be more complex than those captured by the model. Title: Velocities of Flare Kernels and the Mapping Norm of Field Line Connectivity Authors: Lörinčík, Juraj; Aulanier, Guillaume; Dudík, Jaroslav; Zemanová, Alena; Dzifčáková, Elena Bibcode: 2019ApJ...881...68L Altcode: 2019arXiv190601880L We report on observations of flare ribbon kernels during the 2012 August 31 filament eruption. In the 1600 and 304 Å channels of the Atmospheric Imaging Assembly, flare kernels were observed to move along flare ribbons at velocities v ∥ of up to 450 km s-1. Kernel velocities were found to be roughly anticorrelated with strength of the magnetic field. An apparent slipping motion of the flare loops was observed in the 131 Å only for the slowest kernels moving through the strong-B region. In order to interpret the observed relation between B LOS and v ∥, we examined the distribution of the norm N, a quantity closely related to the slippage velocity. We calculated the norm N of the quasi-separatrix layers (QSLs) in MHD model of a solar eruption adapted to the magnetic environment that qualitatively agrees to that of the observed event. We found that both the modeled N and velocities of kernels reach their highest values in the same weak-field regions, one located in the curved part of the ribbon hook and the other in the straight part of the conjugate ribbon located close to a parasitic polarity. Contrariwise, lower values of the kernel velocities are seen at the tip of the ribbon hook, where the modeled N is low. Because the modeled distribution of N matches the observed dynamics of kernels, this supports the notion that the kernel motions can be interpreted as a signature of QSL reconnection during the eruption. Title: Signatures of the non-Maxwellian κ-distributions in optically thin line spectra. II. Synthetic Fe XVII-XVIII X-ray coronal spectra and predictions for the Marshall Grazing-Incidence X-ray Spectrometer (MaGIXS) Authors: Dudík, Jaroslav; Dzifčáková, Elena; Del Zanna, Giulio; Mason, Helen E.; Golub, Leon L.; Winebarger, Amy R.; Savage, Sabrina L. Bibcode: 2019A&A...626A..88D Altcode: 2019arXiv190510356D
Aims: We investigated the possibility of diagnosing the degree of departure from the Maxwellian distribution using the Fe XVII-Fe XVIII spectra originating in plasmas in collisional ionization equilibrium, such as in the cores of solar active regions or microflares.
Methods: The original collision strengths for excitation are integrated over the non-Maxwellian electron κ-distributions characterized by a high-energy tail. Synthetic X-ray emission line spectra were calculated for a range of temperatures and κ. We focus on the 6-24 Å spectral range to be observed by the upcoming Marshall Grazing-Incidence X-ray Spectrometer MaGIXS.
Results: We find that many line intensity ratios are sensitive to both T and κ. Best diagnostic options are provided if a ratio involving both Fe XVII and Fe XVIII is combined with another ratio involving lines formed within a single ion. The sensitivity of such diagnostics to κ is typically a few tens of per cent. Much larger sensitivity, of about a factor of two to three, can be obtained if the Fe XVIII 93.93 Å line observed by SDO/AIA is used in conjuction with the X-ray lines.
Conclusions: We conclude that the MaGIXS instrument is well-suited for detection of departures from the Maxwellian distribution, especially in active region cores. Title: Drifting of the line-tied footpoints of CME flux-ropes Authors: Aulanier, Guillaume; Dudík, Jaroslav Bibcode: 2019A&A...621A..72A Altcode: 2018arXiv181104253A Context. Bridging the gap between heliospheric and solar observations of eruptions requires the mapping of interplanetary coronal mass ejection (CME) footpoints down to the Sun's surface. But this not straightforward. Improving the understanding of the spatio-temporal evolutions of eruptive flares requires a comprehensive standard model. But the current model is only two-dimensional and cannot address the question of interplanetary CME footpoints.
Aims: Existing 3D extensions to the standard model show that flux-rope footpoints are surrounded by curved-shaped quasi-separatrix layer (QSL) footprints that can be related with hook-shaped flare-ribbons. We build upon this finding and further address the joint questions of their time-evolution, and of the formation of flare loops at the ends of the flaring polarity inversion line (PIL) of the erupting bipole, which are both relevant for flare understanding in general and for interplanetary CME studies in particular.
Methods: We calculated QSLs and relevant field lines in an MHD simulation of a torus-unstable flux-rope. The evolving QSL footprints are used to define the outer edge of the flux rope at different times, and to identify and characterize new 3D reconnection geometries and sequences that occur above the ends of the flaring PIL. We also analyzed flare-ribbons as observed in the extreme ultraviolet by SDO/AIA and IRIS during two X-class flares.
Results: The flux-rope footpoints are drifting during the eruption, which is unexpected due to line-tying. This drifting is due to a series of coronal reconnections that erode the flux rope on one side and enlarge it on the other side. Other changes in the flux-rope footpoint-area are due to multiple reconnections of individual field lines whose topology can evolve sequentially from arcade to flux rope and finally to flare loop. These are associated with deformations and displacements of QSL footprints, which resemble those of the studied flare ribbons.
Conclusions: Our model predicts continuous deformations and a drifting of interplanetary CME flux-rope footpoints whose areas are surrounded by equally evolving hooked-shaped flare-ribbons, as well as the formation of flare loops at the ends of flaring PILs which originate from the flux-rope itself, both of which being due to purely three-dimensional reconnection geometries. The observed evolution of flare-ribbons in two events supports the model, but more observations are required to test all its predictions. Title: Fast velocities of flare ribbon kernels and ribbon elongation in a quescent filament eruption of 2012 August 31 observed by SDO/AIA Authors: Lörinčík, Juraj; Dudík, Jaroslav; Kašparová, Jana; Aulanier, Guillaume; Zemanová, Alena; Dzifčáková, Elena Bibcode: 2018csc..confE..63L Altcode: We report on SDO observations of an eruption of a quiescent filament from 2012 August 31. In the 1600 Å filter channel of AIA, flare ribbons were observed to elongate at velocities up to 480 km s^{-1} and flare kernels move along a ribbon at velocity of ≈ 260 km s^{-1}. In order to investigate the emission observed in the 1600 Å channel, we used synthetic spectra modeled using CHIANTI and RADYN models of flare atmospheres with beam parameters constrained using fits of RHESSI spectra. We found out that depending on parameters of heating of a flare model, thickness of a region where the emission of the 1600 Å filter channel originates ranges between 10^{-2} and 10^{2} km. Information on dimensions of the formation region were then utilized to estimate densities in flare ribbons using inversions of the emission measure. These were found to range between 10^{10} - 4.10^{12} cm^{-3} for flare atmospheres heated by beams of different parameters. Together with B_{LOS} data from SDO/HMI, diagnosed densities were used to calculate Alfvén velocities in observed ribbons. These can be as small as 17 km s^{-1} for flare ribbons observed in region of weak magnetic field at latter stages of heating. This finding suggests that elongation of ribbons and motion of kernels might not be related to waves. Motions along the PIL are well-described in the 3D model of solar eruptions of Aulanier et al. 2013 (A&A, 543, 110). However, EUV observations of flare loops revealed that velocity of their apparent slipping motion is much lower than velocity of elongation of a ribbon, which is observed in a close vicinity. Therefore, observed phenomena can not be directly related to super-Alvénic regime of magnetic slipping reconnection introduced in the 3D model. Title: The nature of imploding loops during solar eruptions as revealed by MHD simulations and AIA observations Authors: Aulanier, Guillaume; Dudik, Jaroslav; Zucarello, F. P.; Demoulin, Pascal; Schmieder, Brigitte Bibcode: 2018csc..confE..19A Altcode: Over the last years AIA revealed the frequent occurence of contracting loops at the flanks of erupting active regions. Those have often been interpreted as an evidence of the implosion conjecture that relates magnetic energy decreases with volume contractions in the Sun's corona. So as to unveil the physical nature of these features we carried out observational analyses of two solar eruptions observed with AIA with different projection angles, which we coupled with new analyses of a generic zero-beta MHD simulation of an asymmetric eruption driven by the torus instability, that was not designed for this particular study. The simulation does display contracting loops in general. And the synthetic time-slices of the simulation, when rotated to the right projections, do match the observed ones. But in the simulation these inward motions are not due to any volume contraction. Instead they are associated with two large-scale quasi-incompressible coronal-vortices. Those develop at the flanks of the erupting flux ropes, as most of the compressive component of the flow is evacuated away by an Alfven wave in the early stages of the eruption. We argue that this behavior is merely a magnetic version of the usual pressure-driven formation of vortex rings in hydrodyanmics. This result implies that during a solar eruption, the free magnetic-energy from the pre-erupting active-region is converted not only in the flare and the CME, but is also "lost" in the generation of these two large-scale coronal vortices. Title: Importance of the Hα Visibility and Projection Effects for the Interpretation of Prominence Fine-structure Observations Authors: Gunár, Stanislav; Dudík, Jaroslav; Aulanier, Guillaume; Schmieder, Brigitte; Heinzel, Petr Bibcode: 2018ApJ...867..115G Altcode: We construct a new 3D Whole-prominence Fine-structure (WPFS) model based on a prominence magnetic field configuration designed to qualitatively approximate the morphology of a quiescent prominence observed on 2010 June 22. The model represents an entire prominence with its numerous fine structures formed by a prominence plasma located in dips in the prominence magnetic field. We use the constructed 3D model and employ a radiative-transfer-based Hα visualization method to analyze the Hα visibility of prominence fine structures and its effect on the perceived morphology of observed and modeled prominences. We qualitatively compare three techniques used for visualization of modeled prominences—visualizations drawing magnetic dips up to a height of 1 pressure scale height, drawing the full extent of magnetic dips, and the synthetic Hα visualization—and discuss their suitability for direct comparison between models and observations of prominences and filaments. We also discuss the role of visibility of the prominence fine structures in the estimation of the total height of prominences, which may indicate the height of pre-erupting flux ropes. This parameter is critical for the observational determination of the flux-rope stability. In addition, we employ the WPFS model to assess the effects caused by a projection of the naturally three-dimensional and heterogeneous prominences onto a two-dimensional plane of the sky. We discuss here how the morphological structures of prominences differ when observed in projections from different viewing angles. We also discuss the shapes of the dipped magnetic field lines and the perceived projection of motions of prominence fine structures along such field lines. Title: Broad Non-Gaussian Fe XXIV Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3-class Flare Observed by Hinode/EIS Authors: Polito, Vanessa; Dudík, Jaroslav; Kašparová, Jana; Dzifčáková, Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin Bibcode: 2018ApJ...864...63P Altcode: 2018arXiv180709361P We analyze the spectra of high-temperature Fe XXIV lines observed by the Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) during the impulsive phase of the X8.3-class flare on 2017 September 10. The line profiles are broad, show pronounced wings, and clearly depart from a single-Gaussian shape. The lines can be well fitted with κ distributions, with values of κ varying between ≈1.7 and 3. The regions where we observe the non-Gaussian profiles coincide with the location of high-energy (≈100-300 keV) hard X-ray (HXR) sources observed by RHESSI, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of nonthermal microwave sources with the Expanded Owens Valley Solar Array at and above the HXR loop-top source. We also investigate the effect of taking into account κ distributions in the temperature diagnostics based on the ratio of the Fe XXIII λ263.76 and Fe XXIV λ255.1 EIS lines. We found that these lines can be formed at much higher temperatures than expected (up to log(T[K]) ≈ 7.8) if departures from Maxwellian distributions are taken into account. Although larger line widths are expected because of these higher formation temperatures, the observed line widths still imply nonthermal broadening in excess of 200 km s-1. The nonthermal broadening related to HXR emission is better interpreted by turbulence than by chromospheric evaporation. Title: Signature of flux ropes before and after eruptions: electric currents in active regions Authors: Schmieder, Brigitte; Aulanier, Guillaume; Dalmasse, Kévin; Janvier, Miho; Gilchrist, Stuart; Zhao, Jie; Dudik, Jaroslav Bibcode: 2018cosp...42E3026S Altcode: Solar observations, nonlinear force-free field extrapolations relying on these observations, and three-dimensional magnetohydrodynamic (MHD) models indicate the presence of electric currents in the pre-eruption state and in the course of eruptions of solar magnetic structures which are interpreted as flux ropes (sigmoids, filaments, cavities).The MHD models are able to explain the net currents in active regions by the existence of strong magnetic shear along the polarity inversion lines, thus confirming previous observations. The models have also captured the essence of the behavior of electric currents in active regions during solar eruptions, predicting current-density increases and decreases inside flare ribbons and in the interior of expanding flux ropes, respectively.The observed photospheric current-density maps, inferred from vector magnetic field observations, exhibit whirling ribbon patterns similar to the MHD model results, which are interpreted as the signatures of flux ropes and of quasi-separatrix layers (QSLs) between the magnetic systems in active regions. We will show how observations can confirm enhancement of the total current in these QSLs during the eruptions, and how these observations can be used to investigate whether current density decrease can be seen at the footpoints of erupting flux ropes Title: Can 3D whole-prominence fine structure models be used for assessment of the prominence plasma mass and distribution prior to the onset of CMEs? Authors: Gunár, Stanislav; Schmieder, Brigitte; Aulanier, Guillaume; Anzer, Ulrich; Heinzel, Petr; Mackay, Duncan; Dudik, Jaroslav Bibcode: 2018cosp...42E1316G Altcode: Two complex 3D models of entire prominences including their numerous fine structures were recently developed. The first 3D Whole-Prominence Fine Structure (WPFS) model was developed by Gunár and Mackay. The second 3D WPFS model was put forward by Gunár, Aulanier, Dudík, Heinzel, and Schmieder. These 3D prominence models combine simulations of the 3D magnetic field configuration of an entire prominence with a detailed description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along hundreds of fine structures. The assumed prominence plasma has realistic density and temperature distributions including the prominence-corona transition region.These 3D WPFS models allow us to study the distribution and the mass of the prominence plasma contained in prominence magnetic field configurations. These can be crucial during the onset and early evolution of CMEs. Moreover, prominence plasma represents a bulk of the material ejected by CMEs into the interplanetary space. Here, we investigate the potential of using the 3D WPFS models for assessment of the role the prominence plasma plays in the initiation and evolution of CMEs. Title: Broad Non-Gaussian fe XXIV Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3-CLASS Flare Observed by Hinode/eis Authors: Polito, Vanessa; Dudik, Jaroslav; Kasparova, Jana; Dzifcakova, Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin Bibcode: 2018shin.confE.212P Altcode: We analyze the spectra of high temperature Fe XXIV lines observed by Hinode/EIS during the impulsive phase the X8.3-class flare on September 10, 2017. The line profiles are broad, show pronounced wings, and clearly depart from a single Gaussian shape. The lines can be well fitted with the ? distributions, with values of ? varying between ?1.7 to 3. The region where we observe the non-Gaussian profiles coincides with the location of high-energy (?100-300 keV) HXR sources observed by RHESSI, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of a non-thermal microwave sources with EOVSA at and above the HXR looptop source. We also investigate the effect of taking into account ? distributions in the temperature diagnostics based on the ratio of the Fe XXIII 263.76 ?A and Fe XXIV 255.1 ?A EIS lines. We found that these lines can be formed at much higher temperatures than expected (up to log(T [K]) ? 7.8), if departures from Maxwellian distributions are taken into account. Although larger line widths are expected because of these higher formation temperatures, the observed line widths still imply non-thermal broadening in excess of 200kms?1. Title: Non-equilibrium ionization by a periodic electron beam. II. Synthetic Si IV and O IV transition region spectra Authors: Dzifčáková, Elena; Dudík, Jaroslav Bibcode: 2018A&A...610A..67D Altcode: 2017arXiv171106653D Context. Transition region (TR) spectra typically show the Si IV 1402.8 Å line to be enhanced by a factor of 5 or more compared to the neighboring O IV 1401.2 Å, contrary to predictions of ionization equilibrium models and the Maxwellian distribution of particle energies. Non-equilibrium effects in TR spectra are therefore expected.
Aims: To investigate the combination of non-equilibrium ionization and high-energy particles, we apply the model of the periodic electron beam, represented by a κ-distribution that recurs at periods of several seconds, to plasma at chromospheric temperatures of 104 K. This simple model can approximate a burst of energy release involving accelerated particles.
Methods: Instantaneous time-dependent charge states of silicon and oxygen were calculated and used to synthesize the instantaneous and period-averaged spectra of Si IV and O IV.
Results: The electron beam drives the plasma out of equilibrium. At electron densities of Ne = 1010 cm-3, the plasma is out of ionization equilibrium at all times in all cases we considered, while for a higher density of Ne = 1011 cm-3, ionization equilibrium can be reached toward the end of each period, depending on the conditions. In turn, the character of the period-averaged synthetic spectra also depends on the properties of the beam. While the case of κ = 2 results in spectra with strong or even dominant O IV, higher values of κ can approximate a range of observed TR spectra. Spectra similar to typically observed spectra, with the Si IV 1402.8 Å line about a factor 5 higher than O IV 1401.2 Å, are obtained for κ = 3. An even higher value of κ = 5 results in spectra that are exclusively dominated by Si IV, with negligible O IV emission. This is a possible interpretation of the TR spectra of UV (Ellerman) bursts, although an interpretation that requires a density that is 1-3 orders of magnitude lower than for equilibrium estimates.

Movies associated to Fig. A.1 are available at https://www.aanda.org Title: Solar Radio Burst Associated with the Falling Bright EUV Blob Authors: Karlický, Marian; Zemanová, Alena; Dudík, Jaroslav; Radziszewski, Krzysztof Bibcode: 2018ApJ...854L..29K Altcode: 2018arXiv180406206K At the beginning of the 2015 November 4 flare, in the 1300-2000 MHz frequency range, we observed a very rare slow positively drifting burst. We searched for associated phenomena in simultaneous EUV observations made by IRIS, SDO/AIA, and Hinode/XRT, as well as in H α observations. We found that this radio burst was accompanied with the bright blob, visible at transition region, coronal, and flare temperatures, falling down to the chromosphere along the dark loop with a velocity of about 280 km s-1. The dark loop was visible in H α but disappeared afterward. Furthermore, we found that the falling blob interacted with the chromosphere as expressed by a sudden change of the H α spectra at the location of this interaction. Considering different possibilities, we propose that the observed slow positively drifting burst is generated by the thermal conduction front formed in front of the falling hot EUV blob. Title: Spectroscopic Diagnostics of the Non-Maxwellian κ-distributions Using SDO/EVE Observations of the 2012 March 7 X-class Flare Authors: Dzifčáková, Elena; Zemanová, Alena; Dudík, Jaroslav; Mackovjak, Šimon Bibcode: 2018ApJ...853..158D Altcode: 2018arXiv180102936D Spectroscopic observations made by the Extreme Ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) during the 2012 March 7 X5.4-class flare (SOL2012-03-07T00:07) are analyzed for signatures of the non-Maxwellian κ-distributions. Observed spectra were averaged over 1 minute to increase photon statistics in weaker lines and the pre-flare spectrum was subtracted. Synthetic line intensities for the κ-distributions are calculated using the KAPPA database. We find strong departures (κ ≲ 2) during the early and impulsive phases of the flare, with subsequent thermalization of the flare plasma during the gradual phase. If the temperatures are diagnosed from a single line ratio, the results are strongly dependent on the value of κ. For κ = 2, we find temperatures about a factor of two higher than the commonly used Maxwellian ones. The non-Maxwellian effects could also cause the temperatures diagnosed from line ratios and from the ratio of GOES X-ray channels to be different. Multithermal analysis reveals the plasma to be strongly multithermal at all times with flat DEMs. For lower κ, the {{DEM}}κ are shifted toward higher temperatures. The only parameter that is nearly independent of κ is electron density, where we find log({n}{{e}} [{{cm}}-3]) ≈ 11.5 almost independently of time. We conclude that the non-Maxwellian effects are important and should be taken into account when analyzing solar flare observations, including spectroscopic and imaging ones. Title: Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review) Authors: Dudík, Jaroslav; Dzifčáková, Elena; Meyer-Vernet, Nicole; Del Zanna, Giulio; Young, Peter R.; Giunta, Alessandra; Sylwester, Barbara; Sylwester, Janusz; Oka, Mitsuo; Mason, Helen E.; Vocks, Christian; Matteini, Lorenzo; Krucker, Säm; Williams, David R.; Mackovjak, Šimon Bibcode: 2017SoPh..292..100D Altcode: 2017arXiv170603396D We review the presence and signatures of the non-equilibrium processes, both non-Maxwellian distributions and non-equilibrium ionization, in the solar transition region, corona, solar wind, and flares. Basic properties of the non-Maxwellian distributions are described together with their influence on the heat flux as well as on the rates of individual collisional processes and the resulting optically thin synthetic spectra. Constraints on the presence of high-energy electrons from observations are reviewed, including positive detection of non-Maxwellian distributions in the solar corona, transition region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed as well, especially in connection to hydrodynamic and generalized collisional-radiative modeling. Predicted spectroscopic signatures of non-equilibrium ionization depending on the assumed plasma conditions are summarized. Finally, we discuss the future remote-sensing instrumentation that can be used for the detection of these non-equilibrium phenomena in various spectral ranges. Title: Expanding and Contracting Coronal Loops as Evidence of Vortex Flows Induced by Solar Eruptions Authors: Dudík, J.; Zuccarello, F. P.; Aulanier, G.; Schmieder, B.; Démoulin, P. Bibcode: 2017ApJ...844...54D Altcode: 2017arXiv170604783D Eruptive solar flares were predicted to generate large-scale vortex flows at both sides of the erupting magnetic flux rope. This process is analogous to a well-known hydrodynamic process creating vortex rings. The vortices lead to advection of closed coronal loops located at the peripheries of the flaring active region. Outward flows are expected in the upper part and returning flows in the lower part of the vortex. Here, we examine two eruptive solar flares, the X1.1-class flare SOL2012-03-05T03:20 and the C3.5-class SOL2013-06-19T07:29. In both flares, we find that the coronal loops observed by the Atmospheric Imaging Assembly in its 171 Å, 193 Å, or 211 Å passbands show coexistence of expanding and contracting motions, in accordance with the model prediction. In the X-class flare, multiple expanding and contracting loops coexist for more than 35 minutes, while in the C-class flare, an expanding loop in 193 Å appears to be close by and cotemporal with an apparently imploding loop arcade seen in 171 Å. Later, the 193 Å loop also switches to contraction. These observations are naturally explained by vortex flows present in a model of eruptive solar flares. Title: Synthetic IRIS spectra of the solar transition region: Effect of high-energy tails Authors: Dzifčáková, E.; Vocks, C.; Dudík, J. Bibcode: 2017A&A...603A..14D Altcode: 2017arXiv170508728D
Aims: The solar transition region satisfies the conditions for presence of non-Maxwellian electron energy distributions with high-energy tails at energies corresponding to the ionization potentials of many ions emitting in the extreme-ultraviolet and ultraviolet portions of the spectrum.
Methods: We calculate the synthetic Si iv, O iv, and S iv spectra in the far ultraviolet channel of the Interface Region Imaging Spectrograph (IRIS). Ionization, recombination, and excitation rates are obtained by integration of the cross-sections or their approximations over the model electron distributions considering particle propagation from the hotter corona.
Results: The ionization rates are significantly affected by the presence of high-energy tails. This leads to the peaks of the relative abundance of individual ions to be broadened with pronounced low-temperature shoulders. As a result, the contribution functions of individual lines observable by IRIS also exhibit low-temperature shoulders, or their peaks are shifted to temperatures an order of magnitude lower than for the Maxwellian distribution. The integrated emergent spectra can show enhancements of Si iv compared to O iv by more than a factor of two.
Conclusions: The high-energy particles can have significant impact on the emergent spectra and their presence needs to be considered even in situations without strong local acceleration. Title: Non-Maxwellian Analysis of the Transition-region Line Profiles Observed by the Interface Region Imaging Spectrograph Authors: Dudík, Jaroslav; Polito, Vanessa; Dzifčáková, Elena; Del Zanna, Giulio; Testa, Paola Bibcode: 2017ApJ...842...19D Altcode: 2017arXiv170502104D We investigate the nature of the spectral line profiles for transition-region (TR) ions observed with the Interface Region Imaging Spectrograph (IRIS). In this context, we analyzed an active-region observation performed by IRIS in its 1400 Å spectral window. The TR lines are found to exhibit significant wings in their spectral profiles, which can be well fitted with a non-Maxwellian κ distribution. The fit with a κ distribution can perform better than a double-Gaussian fit, especially for the strongest line, Si IV 1402.8 Å. Typical values of κ found are about 2, occurring in a majority of spatial pixels where the TR lines are symmetric, I.e., the fit can be performed. Furthermore, all five spectral lines studied (from Si IV, O IV, and S IV) appear to have the same full-width at half-maximum irrespective of whether the line is an allowed or an intercombination transition. A similar value of κ is obtained for the electron distribution by the fitting of the line intensities relative to Si IV 1402.8 Å, if photospheric abundances are assumed. The κ distributions, however, do not remove the presence of non-thermal broadening. Instead, they actually increase the non-thermal width. This is because, for κ distributions, TR ions are formed at lower temperatures. The large observed non-thermal width lowers the opacity of the Si IV line sufficiently enough for this line to become optically thin. Title: Analysis and modelling of recurrent solar flares observed with Hinode/EIS on March 9, 2012 Authors: Polito, V.; Del Zanna, G.; Valori, G.; Pariat, E.; Mason, H. E.; Dudík, J.; Janvier, M. Bibcode: 2017A&A...601A..39P Altcode: 2016arXiv161203504P Three homologous C-class flares and one last M-class flare were observed by both the Solar Dynamics Observatory (SDO) and the Hinode EUV Imaging Spectrometer (EIS) in the AR 11429 on March 9, 2012. All the recurrent flares occurred within a short interval of time (less than 4 h), showed very similar plasma morphology and were all confined, until the last one when a large-scale eruption occurred. The C-class flares are characterized by the appearance, at approximatively the same locations, of two bright and compact footpoint sources of ≈3-10 MK evaporating plasma, and a semi-circular ribbon. During all the flares, the continuous brightening of a spine-like hot plasma (≈10 MK) structure is also observed. Spectroscopic observations with Hinode/EIS are used to measure and compare the blueshift velocities in the Fe xxiii emission line and the electron number density at the flare footpoints for each flare. Similar velocities, of the order of 150-200 km s-1, are observed during the C2.0 and C4.7 confined flares, in agreement with the values reported by other authors in the study of the last M1.8 class flare. On the other hand, lower electron number densities and temperatures tend to be observed in flares with lower peak soft X-ray flux. In order to investigate the homologous nature of the flares, we performed a non-linear force-free field (NLFFF) extrapolation of the 3D magnetic field configuration in the corona. The NLFFF extrapolation and the Quasi-Separatrix Layers (QSLs) provide the magnetic field context which explains the location of the kernels, spine-like hot plasma and semi-circular brightenings observed in the (non-eruptive) flares. Given the absence of a coronal null point, we argue that the homologous flares were all generated by the continuous recurrence of bald patch reconnection.

The movie associated to Fig. 2 is available at http://www.aanda.org Title: Vortex and Sink Flows in Eruptive Flares as a Model for Coronal Implosions Authors: Zuccarello, F. P.; Aulanier, G.; Dudík, J.; Démoulin, P.; Schmieder, B.; Gilchrist, S. A. Bibcode: 2017ApJ...837..115Z Altcode: 2017arXiv170200199Z Eruptive flares are sudden releases of magnetic energy that involve many phenomena, several of which can be explained by the standard 2D flare model and its realizations in 3D. We analyze a 3D magnetohydrodynamics simulation, in the framework of this model, that naturally explains the contraction of coronal loops in the proximity of the flare sites, as well as the inflow toward the region above the cusp-shaped loops. We find that two vorticity arcs located along the flanks of the erupting magnetic flux rope are generated as soon as the eruption begins. The magnetic arcades above the flux rope legs are then subjected to expansion, rotation, or contraction depending on which part of the vortex flow advects them. In addition to the vortices, an inward-directed magnetic pressure gradient exists in the current sheet below the magnetic flux rope. It results in the formation of a sink that is maintained by reconnection. We conclude that coronal loop apparent implosions observed during eruptive flares are the result of hydromagnetic effects related to the generation of vortex and sink flows when a flux rope moves in a magnetized environment. Title: Can the non-Maxwellian kappa-distributions be diagnosed in the solar corona? Authors: Dudík, J.; Dzifcakova, E.; Del Zanna, G.; Mackovjak, Š.; Mason, H. E. Bibcode: 2016AGUFMSH21D2555D Altcode: We report on the search of signatures of the non-Maxwellian kappa-distributions in the emission line spectra of the solar corona. A survey of coronal lines is performed for single-ion and multi-ion diagnostics using ions spanning the temperature range of 0.5 - 6 MK. State-of-art excitation cross-sections are integrated directly to obtain the corresponding non-Maxwellian excitation and deexcitation rates. Ionization and recombination rates are obtained by approximative methods. We find that there are only a few good diagnostic options. This is due to majority of lines being formed from similar energy levels. The best diagnostic options rely on lines formed at different excitation tresholds, i.e., at different wavelengths. This highlights the importance of absolute intensity calibration of space-borne spectrometers. The applicability of these methods is demonstrated on analysis of a dedicated extreme-ultraviolet observations made in the Fe XI-XIII lines by the Hinode/EIS satellite during HOP 226. The observations are performed in an active region containing a filament and several coronal loops. A transient coronal loop appears at the foot of a filament and is preceded by activity within this filament. EIS spectra are used to diagnose the electron density, but also reveal that the transient loop is highly non-Maxwellian, characterized by a kappa=2 distribution. We discuss the methods for separation the non-Maxwellian effects from the effects of plasma multi-thermality arising due to finite spatial resolution, as well as the effect of kappa-distributions on the degree of multithermality diagnosed in various observed coronal features. 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: Density diagnostics derived from the O iv and S iv intercombination lines observed by IRIS Authors: Polito, V.; Del Zanna, G.; Dudík, J.; Mason, H. E.; Giunta, A.; Reeves, K. K. Bibcode: 2016A&A...594A..64P Altcode: 2016arXiv160705072P The intensity of the O iv 2s2 2p 2P-2s2p24P and S iv 3 s2 3p 2P-3s 3p24 P intercombination lines around 1400 Å observed with the Interface Region Imaging Spectrograph (IRIS) provide a useful tool to diagnose the electron number density (Ne) in the solar transition region plasma. We measure the electron number density in a variety of solar features observed by IRIS, including an active region (AR) loop, plage and brightening, and the ribbon of the 22-June-2015 M 6.5 class flare. By using the emissivity ratios of O iv and S iv lines, we find that our observations are consistent with the emitting plasma being near isothermal (logT[K] ≈ 5) and iso-density (Ne ≈ 1010.6 cm-3) in the AR loop. Moreover, high electron number densities (Ne ≈ 1013 cm-3) are obtained during the impulsive phase of the flare by using the S iv line ratio. We note that the S iv lines provide a higher range of density sensitivity than the O iv lines. Finally, we investigate the effects of high densities (Ne ≳ 1011 cm-3) on the ionization balance. In particular, the fractional ion abundances are found to be shifted towards lower temperatures for high densities compared to the low density case. We also explored the effects of a non-Maxwellian electron distribution on our diagnostic method.

The movie associated to Fig. 3 is available at http://www.aanda.org Title: Evidence of flux rope and sigmoid in Active Regions prior eruptions Authors: Schmieder, Brigitte; Aulanier, Guillaume; Janvier, Miho; Bommier, Veronique; Dudik, Jaroslav; Gilchrist, Stuart; Zhao, Jie Bibcode: 2016cosp...41E1750S Altcode: In the solar corona, the magnetic field is dominant, and the current density vector is nearly aligned with the magnetic field lines for strong and stressed field regions. Stressed and highly twisted flux ropes are at the origin of eruptive events such as flares and coronal mass ejections, which inject material into the interplanetary medium. The standard three dimensional (3D) flare model predicts the complex evolution of flare loops and the flux rope before the eruption. Flux ropes are not directly observed in the corona, however it has started to be possible to detect their footprints in the photosphere. Recent high spatial and temporal resolution spectro-polarimeters have allowed us to compute the photospheric electric currents and follow their evolution. Characteristics pattern like J-shaped ribbons indicate the presence of a flux rope before the flare. The results confirm the predictions of the 3D MHD standard model of eruptive flares. It is interesting to compare the magnetic helicity of the ejected flux rope with the in situ measurements of the corresponding ICME at L1. We will show some examples (February 15 2011, July 12 2012, Sept 10 2014). Title: Slipping Magnetic Reconnection, Chromospheric Evaporation, Implosion, and Precursors in the 2014 September 10 X1.6-Class Solar Flare Authors: Dudík, Jaroslav; Polito, Vanessa; Janvier, Miho; Mulay, Sargam M.; Karlický, Marian; Aulanier, Guillaume; Del Zanna, Giulio; Dzifčáková, Elena; Mason, Helen E.; Schmieder, Brigitte Bibcode: 2016ApJ...823...41D Altcode: 2016arXiv160306092D We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. Slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions toward both ends of the ribbons. Velocities of 20-40 km s-1 are found within time windows where the slipping is well resolved. The warm coronal loops exhibit expanding and contracting motions that are interpreted as displacements due to the growing flux rope that subsequently erupts. This flux rope existed and erupted before the onset of apparent coronal implosion. This indicates that the energy release proceeds by slipping reconnection and not via coronal implosion. The slipping reconnection leads to changes in the geometry of the observed structures at the Interface Region Imaging Spectrograph slit position, from flare loop top to the footpoints in the ribbons. This results in variations of the observed velocities of chromospheric evaporation in the early flare phase. Finally, it is found that the precursor signatures, including localized EUV brightenings as well as nonthermal X-ray emission, are signatures of the flare itself, progressing from the early phase toward the impulsive phase, with the tether-cutting being provided by the slipping reconnection. The dynamics of both the flare and outlying coronal loops is found to be consistent with the predictions of the standard solar flare model in three dimensions. Title: Non-equilibrium ionization by a periodic electron beam. I. Synthetic coronal spectra and implications for interpretation of observations Authors: Dzifčáková, E.; Dudík, J.; Mackovjak, Š. Bibcode: 2016A&A...589A..68D Altcode: 2016arXiv160304256D Context. Coronal heating is currently thought to proceed via the mechanism of nanoflares, small-scale and possibly recurring heating events that release magnetic energy.
Aims: We investigate the effects of a periodic high-energy electron beam on the synthetic spectra of coronal Fe ions.
Methods: Initially, the coronal plasma is assumed to be Maxwellian with a temperature of 1 MK. The high-energy beam, described by a κ-distribution, is then switched on every period P for the duration of P/ 2. The periods are on the order of several tens of seconds, similar to exposure times or cadences of space-borne spectrometers. Ionization, recombination, and excitation rates for the respective distributions are used to calculate the resulting non-equilibrium ionization state of Fe and the instantaneous and period-averaged synthetic spectra.
Results: Under the presence of the periodic electron beam, the plasma is out of ionization equilibrium at all times. The resulting spectra averaged over one period are almost always multithermal if interpreted in terms of ionization equilibrium for either a Maxwellian or a κ-distribution. Exceptions occur, however; the EM-loci curves appear to have a nearly isothermal crossing-point for some values of κs. The instantaneous spectra show fast changes in intensities of some lines, especially those formed outside of the peak of the respective EM(T) distributions if the ionization equilibrium is assumed.

Movies 1-5 are available in electronic form at http://www.aanda.org Title: Erratum: Erratum to: Ionisation Equilibrium for the Non-Maxwellian Electron n-Distributions in Solar Flares: Updated Calculations Authors: Dzifčáková, Elena; Dudík, Jaroslav Bibcode: 2016SoPh..291..729D Altcode: 2016SoPh..tmp...11D No abstract at ADS 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: Updated calculations of the ionization equilibrium for the non-Maxwellian electron n-distributions in solar flares Authors: Dzifčáková, Elena; Dudík, Jaroslav Bibcode: 2016IAUS..320..243D Altcode: The assumption of an equilibrium (Maxwellian) distribution of electron energies cannot explain observed high intensities of the Si XIId satellite lines relative to the Si XIII allowed lines during the flares. However, the presence of n-distribution with a higher and narrower shape than the Maxwellian one is able to explain this behavior. We calculated the ionization equilibrium for the non-thermal n-distributions using the latest atomic data for each element up to the proton number of 30. Significant changes in the shape and maxima of the ion abundance peak occur and can strongly influence the temperature diagnostics. Title: Simultaneous IRIS and Hinode/EIS Observations and Modelling of the 2014 October 27 X2.0 Class Flare Authors: Polito, V.; Reep, J. W.; Reeves, K. K.; Simões, P. J. A.; Dudík, J.; Del Zanna, G.; Mason, H. E.; Golub, L. Bibcode: 2016ApJ...816...89P Altcode: 2015arXiv151206378P We present a study of the X2-class flare which occurred on 2014 October 27 and was observed with the Interface Region Imaging Spectrograph (IRIS) and the EUV Imaging Spectrometer (EIS) on board the Hinode satellite. Thanks to the high cadence and spatial resolution of the IRIS and EIS instruments, we are able to compare simultaneous observations of the Fe xxi 1354.08 Å and Fe xxiii 263.77 Å high-temperature emission (≳10 MK) in the flare ribbon during the chromospheric evaporation phase. We find that IRIS observes completely blueshifted Fe xxi line profiles, up to 200 km s-1 during the rise phase of the flare, indicating that the site of the plasma upflows is resolved by IRIS. In contrast, the Fe xxiii line is often asymmetric, which we interpret as being due to the lower spatial resolution of EIS. Temperature estimates from SDO/AIA and Hinode/XRT show that hot emission (log(T[K]) > 7.2) is first concentrated at the footpoints before filling the loops. Density-sensitive lines from IRIS and EIS give estimates of electron number density of ≳1012 cm-3 in the transition region lines and 1010 cm-3 in the coronal lines during the impulsive phase. In order to compare the observational results against theoretical predictions, we have run a simulation of a flare loop undergoing heating using the HYDRAD 1D hydro code. We find that the simulated plasma parameters are close to the observed values that are obtained with IRIS, Hinode, and AIA. These results support an electron beam heating model rather than a purely thermal conduction model as the driving mechanism for this flare. Title: Ionisation Equilibrium for the Non-Maxwellian Electron n -Distributions in Solar Flares: Updated Calculations Authors: Dzifčáková, Elena; Dudík, Jaroslav Bibcode: 2015SoPh..290.3545D Altcode: 2015SoPh..tmp..104D We use the latest available atomic data to calculate the ionisation and recombination rates for the non-Maxwellian n -distributions, which were shown previously to provide a good fit to the enhanced intensities of dielectronic satellite lines during solar flares. The ionisation and recombination coefficients are subsequently used to derive the ionisation equilibrium. To do so, we consider odd values of n ranging from 1 to 19, i.e., from Maxwellian to strongly non-Maxwellian cases. These calculations involve all elements with proton number up to 30, i.e., H to Zn. The n -distributions modify both the ionisation and the recombination rates. The ionisation rates decrease more steeply at lower pseudo-temperatures, while the radiative recombination rate is reduced due to a lower number of low-energy electrons. The peaks of the dielectronic recombination rates become narrower. These changes are reflected in the ionisation equilibrium. Ion abundance peaks become narrower and can also be shifted, mostly towards higher temperatures. The He-like ions are an important exception, as they are formed in a larger temperature range than that for the Maxwellian distribution. The ions Si XIII - XIV used previously for the diagnostics of the n -distributions are affected only weakly, confirming the determination of n . The ionisation equilibria are available as the electronic supplementary material in a format compatible with the CHIANTI database. Title: On the possibility to diagnose a kappa-distribution from EVE flare spectra Authors: Dzifcakova, Elena; Dudík, Jaroslav Bibcode: 2015IAUGA..2254765D Altcode: X-ray flare emission is strongly affected by the non-thermal part of the electron distribution. RHESSI observations and also recent theoretical derivations showed that the electron distribution function in coronal X-ray sources could be a kappa-distribution. An effect of kappa-distribution on the relative intensities of spectral lines of Fe XVIII - Fe XXIV observed in SDO/EVE flare spectra was calculated using KAPPA package based on the CHIANTI. Together with CHIANTI, this allows us to estimate the influence of the kappa-distributions on the diagnostics of electron density and temperature from the flare spectra. The possibility to diagnose parameters of the kappa-distribution from EVE flare spectra is discussed. The synthetic spectra for the kappa-distribution are compared with the observed flare spectra. Title: Updated calculations of the ionization equilibrium for the non-Maxwellian electron n-distributions in solar flares Authors: Dzifcakova, Elena; Dudík, Jaroslav Bibcode: 2015IAUGA..2254777D Altcode: Observed flare high intensities of the Si XIId satellite lines in comparison with the Si XIII allowed lines cannot be interpreted under the assumption of a Maxwellian distribution. This behavior of the relative line intensities can be explained by the presence of n-distribution with a higher and narrower shape than the Maxwellian one. This distribution can be formed in flaring plasma in the electric double layers and its presence is associated with type III radio bursts.The latest atomic data to calculate the ionization equilibrium for the non-thermal n-distributions with n ranging from 1 to 19 were used. These calculations involve each of elements with atomic number up to 30. The n-distributions influence both the ionization and recombination rates and make the ion abundance peaks narrower. They can also shift the maxima of the ion abundance peaks in comparison with the Maxwellian distribution and can influence the temperature diagnostics. Title: Slipping reconnection and chromospheric evaporation in the 10 September 2014 flare Authors: Dudík, Jaroslav; Janvier, Miho; Polito, Vanessa; Mulay, Sargam; Del Zanna, Giulio; Mason, Helen; Aulanier, Guillaume Bibcode: 2015IAUGA..2252237D Altcode: We study the occurrence of slipping reconnection in the long-duration X-class flare of 2014 September 10. From the start, the flare shows apparent slippage of hot Fe XXI flare loops observed in the 131A channel of SDO/AIA. Using the time-distance plots, we show that the slipping motion of the flare loops proceeds in counter directions in both flare ribbons. Simultaneous IRIS Fe XXI observations show the occurrence of chromospheric evaporation at brightening kernels that are involved in the slipping reconnection of AIA loops. This happens also during a flux-rope breakout accompanied by a faint 'magnetic implosion' of a coronal loop. Based on the 3D MHD flare model, we argue that the 'implosion' is caused by the erupting flux rope pushing the neighbouring loops aside, with the low-lying loops being squeezed. Title: 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: Imaging and Spectroscopic Observations of a Transient Coronal Loop: Evidence for the Non-Maxwellian K Distributions Authors: Dudík, Jaroslav; Mackovjak, Šimon; Dzifčáková, Elena; Del Zanna, Giulio; Williams, David R.; Karlický, Marian; Mason, Helen E.; Lörinčík, Juraj; Kotrč, Pavel; Fárník, František; Zemanová, Alena Bibcode: 2015ApJ...807..123D Altcode: 2015arXiv150504333D We report on the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) and Hinode/EUV Imaging Spectrograph (EIS) observations of a transient coronal loop. The loop brightens up in the same location after the disappearance of an arcade formed during a B8.9-class microflare 3 hr earlier. EIS captures this loop during its brightening phase, as observed in most of the AIA filters. We use the AIA data to study the evolution of the loop, as well as to perform the differential emission measure (DEM) diagnostics as a function of κ. The Fe xi-Fe xiii lines observed by EIS are used to perform the diagnostics of electron density and subsequently the diagnostics of κ. Using ratios involving the Fe xi 257.772 Å self-blend, we diagnose κ ≲ 2, i.e., an extremely non-Maxwellian distribution. Using the predicted Fe line intensities derived from the DEMs as a function of κ, we show that, with decreasing κ, all combinations of ratios of line intensities converge to the observed values, confirming the diagnosed κ ≲ 2. These results represent the first positive diagnostics of κ-distributions in the solar corona despite the limitations imposed by calibration uncertainties. Title: Sunspot waves and flare energy release Authors: Sych, R.; Karlický, M.; Altyntsev, A.; Dudík, J.; Kashapova, L. Bibcode: 2015A&A...577A..43S Altcode: 2014arXiv1409.2947S Context. We study the possibility of flare process triggering by waves propagating from the sunspot along a magnetic loop (channel) to a nearby flare site.
Aims: We present a relationship between the dynamics of ~3-min slow magnetoacoustic waves in the sunspot and flare emergence process. Waves propagating in the magnetic channel whose one foot is anchored in the umbra represent the disturbing agent responsible for triggering the flare energy release.
Methods: We applied time-distance plots and pixel wavelet filtration methods to obtain spatio-temporal distribution of wave power variations in radio and SDO/AIA data. To find the magnetic channel, we used potential magnetic field extrapolation of SDO/HMI magnetograms. The propagation velocity of wave fronts was measured from wave locations at specific times.
Results: In the correlation curves of the 17 GHz (NoRH) radio emission, we found a monotonous energy amplification of the 3-min waves in the sunspot umbra before the 2012 June 7 flare. This amplification was associated with an increase in the length of the oscillatory wakes in coronal loops (SDO/AIA, 171 Å) prior to the flare onset. A peculiarity of the flare is the constant level of the flare emission in soft X-rays (RHESSI, 3-25 keV) for ~10 min after the short impulsive phase, which indicates continuing energy release. Throughout this time, we found transverse oscillations of the flare loop with a 30 s period in the radio-frequency range (NoRH, 17 GHz). This period appears to be related to the 3-min waves from the sunspot. The magnetic field extrapolation based on SDO/HMI magnetograms shows the existence of the magnetic channel (waveguide) connecting the sunspot with the energy release region.
Conclusions: We analysed the sunspot 3-min wave dynamics and found a correlation between the oscillation power amplification and flare triggering in the region connected to the sunspot through the magnetic channel. We propose that this amplified wave flux triggered the flare. The flare occurred because of this amplified flux, however, and because a sufficient amount of free magnetic energy was accumulated in close vicinity to the magnetic channel prior to the flare. Furthermore, because of loop heating, the wave velocity (sound velocity) increased with the penetration of waves into the energy release site. The heating is shown to be able to proceed after the flare main peak owing to a further energy pumping in the form of waves from the sunspot and additional reconnection episodes in the flare region. Title: KAPPA: A Package for Synthesis of Optically Thin Spectra for the Non-Maxwellian κ-distributions Based on the Chianti Database Authors: Dzifčáková, Elena; Dudík, Jaroslav; Kotrč, Pavel; Fárník, František; Zemanová, Alena Bibcode: 2015ApJS..217...14D Altcode: 2015arXiv150200853D Non-Maxwellian κ-distributions have been detected in the solar transition region and in flares. These distributions are characterized by a high-energy tail and a near-Maxwellian core and are known to have a significant impact on the resulting optically thin spectra arising from collisionally dominated astrophysical plasmas. We developed the KAPPA package for the synthesis of such line and continuum spectra. The package is based on the freely available CHIANTI database and software, and can be used in a similar manner. Ionization and recombination rates together with the ionization equilibria are provided for a range of κ values. Distribution-averaged collision strengths for excitation are obtained using an approximate method for all transitions in all ions available within CHIANTI. The validity of this approximate method is tested through a comparison with direct calculations. Typical precisions of better than 5% are found with all cases being within 10%. Tools for the calculation of synthetic line and continuum intensities are provided and described. Examples of the synthetic spectra and SDO/AIA responses to emission for the κ-distributions are given. Title: KAPPA: Optically thin spectra synthesis for non-Maxwellian kappa-distributions Authors: Dzifcáková, Elena; Dudík, Jaroslav; Kotrc, Pavel; Fárník, Frantisek; Zemanová, Alena Bibcode: 2015ascl.soft02008D Altcode: Based on the freely available CHIANTI (ascl:9911.004) database and software, KAPPA synthesizes line and continuum spectra from the optically thin spectra that arise from collisionally dominated astrophysical plasmas that are the result of non-Maxwellian κ-distributions detected in the solar transition region and flares. Ionization and recombination rates together with the ionization equilibria are provided for a range of κ values. Distribution-averaged collision strengths for excitation are obtained by an approximate method for all transitions in all ions available within CHIANTI; KAPPA also offers tools for calculating synthetic line and continuum intensities. Title: On the Area Expansion of Magnetic Flux Tubes in Solar Active Regions Authors: Dudík, Jaroslav; Dzifčáková, Elena; Cirtain, Jonathan W. Bibcode: 2014ApJ...796...20D Altcode: 2014arXiv1409.6947D We calculated the three-dimensional (3D) distribution of the area expansion factors in a potential magnetic field, extrapolated from the high-resolution Hinode/SOT magnetogram of the quiescent active region NOAA 11482. Retaining only closed loops within the computational box, we show that the distribution of area expansion factors show significant structure. Loop-like structures characterized by locally lower values of the expansion factor are embedded in a smooth background. These loop-like flux tubes have squashed cross-sections and expand with height. The distribution of the expansion factors show an overall increase with height, allowing an active region core characterized by low values of the expansion factor to be distinguished. The area expansion factors obtained from extrapolation of the Solar Optical Telescope magnetogram are compared to those obtained from an approximation of the observed magnetogram by a series of 134 submerged charges. This approximation retains the general flux distribution in the observed magnetogram, but removes the small-scale structure in both the approximated magnetogram and the 3D distribution of the area expansion factors. We argue that the structuring of the expansion factor can be a significant ingredient in producing the observed structuring of the solar corona. However, due to the potential approximation used, these results may not be applicable to loops exhibiting twist or to active regions producing significant flares. Title: Signatures of the non-Maxwellian κ-distributions in optically thin line spectra. I. Theory and synthetic Fe IX-XIII spectra Authors: Dudík, J.; Del Zanna, G.; Mason, H. E.; Dzifčáková, E. Bibcode: 2014A&A...570A.124D Altcode: 2014arXiv1408.0950D
Aims: We investigate the possibility of diagnosing the degree of departure from the Maxwellian distribution using single-ion spectra originating in astrophysical plasmas in collisional ionization equilibrium.
Methods: New atomic data for excitation of Fe ix - Fe xiii are integrated under the assumption of a κ-distribution of electron energies. Diagnostic methods using lines of a single ion formed at any wavelength are explored. Such methods minimize uncertainties from the ionization and recombination rates, as well as the possible presence of non-equilibrium ionization. Approximations to the collision strengths are also investigated.
Results: The calculated intensities of most of the Fe ix - Fe xiii EUV lines show consistent behaviour with κ at constant temperature. Intensities of these lines decrease with κ, with the vast majority of ratios of strong lines showing little or no sensitivity to κ. Several of the line ratios, especially involving temperature-sensitive lines, show a sensitivity to κ that is of the order of several tens of per cent, or, in the case of Fe ix, up to a factor of two. Forbidden lines in the near-ultraviolet, visible, or infrared parts of the spectrum are an exception, with smaller intensity changes or even a reverse behaviour with κ. The most conspicuous example is the Fe x 6378.26 Å red line, whose intensity incerases with κ. This line is a potentially strong indicator of departures from the Maxwellian distribution. We find that it is possible to perform density diagnostics independently of κ, with many Fe xi, Fe xii, and Fe xiii line ratios showing strong density-sensitivity and negligible sensitivity to κ and temperature. We also tested different averaging of the collision strengths. It is found that averaging over 0.01 interval in log(E [ Ryd ]) is sufficient to produce accurate distribution-averaged collision strengths Υ(T,κ) at temperatures of the ion formation in ionization equilibrium.

Appendices are available in electronic form at http://www.aanda.org 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: Slipping Magnetic Reconnection during an X-class Solar Flare Observed by SDO/AIA Authors: Dudík, J.; Janvier, M.; Aulanier, G.; Del Zanna, G.; Karlický, M.; Mason, H. E.; Schmieder, B. Bibcode: 2014ApJ...784..144D Altcode: 2014arXiv1401.7529D We present SDO/AIA observations of an eruptive X-class flare of 2012 July 12, and compare its evolution with the predictions of a three-dimensional (3D) numerical simulation. We focus on the dynamics of flare loops that are seen to undergo slipping reconnection during the flare. In the Atmospheric Imaging Assembly (AIA) 131 Å observations, lower parts of 10 MK flare loops exhibit an apparent motion with velocities of several tens of km s-1 along the developing flare ribbons. In the early stages of the flare, flare ribbons consist of compact, localized bright transition-region emission from the footpoints of the flare loops. A differential emission measure analysis shows that the flare loops have temperatures up to the formation of Fe XXIV. A series of very long, S-shaped loops erupt, leading to a coronal mass ejection observed by STEREO. The observed dynamics are compared with the evolution of magnetic structures in the "standard solar flare model in 3D." This model matches the observations well, reproducing the apparently slipping flare loops, S-shaped erupting loops, and the evolution of flare ribbons. All of these processes are explained via 3D reconnection mechanisms resulting from the expansion of a torus-unstable flux rope. The AIA observations and the numerical model are complemented by radio observations showing a noise storm in the metric range. Dm-drifting pulsation structures occurring during the eruption indicate plasmoid ejection and enhancement of the reconnection rate. The bursty nature of radio emission shows that the slipping reconnection is still intermittent, although it is observed to persist for more than an hour. Title: Differential emission measure analysis of active region cores and quiet Sun for the non-Maxwellian κ-distributions Authors: Mackovjak, Š.; Dzifčáková, E.; Dudík, J. Bibcode: 2014A&A...564A.130M Altcode: Context. The non-Maxwellian κ-distributions have been detected in the solar wind and can explain intensities of some transition region lines. Presence of such distributions in the outer layers of the solar atmosphere influences the ionization and excitation equilibrium and widens the line contribution functions. This behavior may be reflected on the reconstructed differential emission measure (DEM).
Aims: We aim to investigate the influence of κ-distributions on the reconstructed DEMs.
Methods: We perform DEM reconstruction for three active region cores and a quiet Sun region using the Withbroe-Sylwester method and the regularization method.
Results: We find that the reconstructed DEMs depend on the value of κ. The DEMs of the active region cores show similar behavior with decreasing κ, or an increasing departure from the Maxwellian distribution. For lower κ, the peaks of the DEMs are typically shifted to higher temperatures and the DEMs themselves become more concave. This is caused by the less steep high-temperature slopes for lower κ. However, the low-temperature slopes do not change significantly even for extremely low κ. The behavior of the quiet-Sun DEM distribution is different. It becomes progressively less multithermal for lower κ with the EM-loci plots that indicate near-isothermal plasma for κ = 2.
Conclusions: The κ-distributions can influence the reconstructed DEMs. The slopes of the DEM, however, do not change with κ significantly enough to produce different constraints on the heating mechanism in terms of frequency of coronal heating events. Title: Diagnostics for the O IV and Si IV lines observed by IRIS Authors: Dudik, Jaroslav; Mason, Helen; Del Zanna, Giulio; Golub, Leon; Dzifcakova, Elena Bibcode: 2014cosp...40E.754D Altcode: We investigate the formation of the IRIS O IV and Si IV lines under non-Maxwellian conditions characterized by kappa-distributions. It is found that the Si IV lines are always formed at lower temperatures than the O IV lines. However, as the departure from the Maxwellian increases, the peak formation temperatures are shifted progressively to lower and lower temperatures. Coupled with the slope of the differential emission measure (DEM), it is possible for the Si IV lines to be formed very close to the solar chromosphere, with the majority of the O IV intensities coming from a different, higher part of the transition region. The predicted spectra for kappa-distributions exhibit very low O IV intensities compared to Si IV, analogously to what is observed by the IRIS spacecraft. Potential density diagnostics are discussed, as well as the contribution of photoexcitation to the formation of these lines. Title: Chromospheric evaporation in recurrent flares Authors: Polito, V.; Mason, Helen; Del Zanna, Giulio; Dudik, Jaroslav Bibcode: 2014cosp...40E2581P Altcode: We present high-cadence (3 minutes) Hinode/EIS observations of small recurrent flares and provide densities and velocities of the upflowing plasma in the locations of the chromospheric evaporation. Lines formed in the 2-10 MK range have significant blueshifts, of the order of 50 km/s or more. This upflowing plasma is the source of the 10 MK plasma that emits strongly in EUV and X-ray lines after the impulsive phases. We use the high-cadence and high-resolution SDO/AIA images to describe the locations of the upflows, and magnetograms to locate the ribbons. One interesting feature is that the recurrent flares are confined, until the last one when a large-scale eruption occurs. Title: New calculations of the ionization equilibrium for the non-Maxwellian electron distribution in solar flares Authors: Dzifcakova, Elena; Dudik, Jaroslav Bibcode: 2014cosp...40E.772D Altcode: It has been shown that observed flare high intensities of the Si XII satellite lines in comparison with the Si XIII allowed lines cannot be explained under the assumption of a Maxwellian distribution. The real electron distribution function in the region of a formation of these lines should decrease much faster than for the Maxwellian one. The so-called n-distribution has been proposed for the explanation of the observed line intensities. This distribution can be formed in the electric double layers in flaring plasma and its presence is associated with type III radio bursts. We used new atomic data to calculate the ionization and recombination rates for the non-thermal n-distributions with a higher and narrower shape than the Maxwellian one. These calculations involve each of elements with atomic number up to 30. The n-distributions influence both the ionization and recombination rates and make the ion abundance peaks narrower. They can also shift the maxima of the ion abundance peaks in comparison with Maxwellian distribution and can influence the temperature diagnostics. Synthetic spectra for n-distributions are compared with the observed flare spectra. Title: Solar Transition Region Lines Observed by the Interface Region Imaging Spectrograph: Diagnostics for the O IV and Si IV Lines Authors: Dudík, J.; Del Zanna, G.; Dzifčáková, E.; Mason, H. E.; Golub, L. Bibcode: 2014ApJ...780L..12D Altcode: 2013arXiv1311.6978D The formation of the transition region O IV and Si IV lines observable by the Interface Region Imaging Spectrograph (IRIS) is investigated for both Maxwellian and non-Maxwellian conditions characterized by a κ-distribution exhibiting a high-energy tail. The Si IV lines are formed at lower temperatures than the O IV lines for all κ. In non-Maxwellian situations with lower κ, the contribution functions are shifted to lower temperatures. Combined with the slope of the differential emission measure, it is possible for the Si IV lines to be formed at very different regions of the solar transition region than the O IV lines; possibly close to the solar chromosphere. Such situations might be discernible by IRIS. It is found that photoexcitation can be important for the Si IV lines, but is negligible for the O IV lines. The usefulness of the O IV ratios for density diagnostics independently of κ is investigated and it is found that the O IV 1404.78 Å/1399.77 Å ratio provides a good density diagnostics except for very low T combined with extreme non-Maxwellian situations. Title: H to Zn Ionization Equilibrium for the Non-Maxwellian Electron κ-distributions: Updated Calculations Authors: Dzifčáková, E.; Dudík, J. Bibcode: 2013ApJS..206....6D Altcode: 2013arXiv1304.4064D New data for the calculation of ionization and recombination rates have been published in the past few years, most of which are included in the CHIANTI database. We used these data to calculate collisional ionization and recombination rates for the non-Maxwellian κ-distributions with an enhanced number of particles in the high-energy tail, which have been detected in the solar transition region and the solar wind. Ionization equilibria for elements H to Zn are derived. The κ-distributions significantly influence both the ionization and recombination rates and widen the ion abundance peaks. In comparison with the Maxwellian distribution, the ion abundance peaks can also be shifted to lower or higher temperatures. The updated ionization equilibrium calculations result in large changes for several ions, notably Fe VIII-Fe XIV. The results are supplied in electronic form compatible with the CHIANTI database. Title: Fast Magnetoacoustic Waves in a Fan Structure Above a Coronal Magnetic Null Point Authors: Mészárosová, H.; Dudík, J.; Karlický, M.; Madsen, F. R. H.; Sawant, H. S. Bibcode: 2013SoPh..283..473M Altcode: 2013arXiv1301.2485M We analyze the 26 November 2005 solar radio event observed interferometrically at frequencies of 244 and 611 MHz by the Giant Metrewave Radio Telescope (GMRT) in Pune, India. These observations are used to make interferometric maps of the event at both frequencies with the time cadence of 1 s from 06:50 to 07:12 UT. These maps reveal several radio sources. The light curves of these sources show that only two sources at 244 MHz and 611 MHz are well correlated in time. The EUV flare is more localized with flare loops located rather away from the radio sources. Using SoHO/MDI observations and potential magnetic field extrapolation we demonstrate that both the correlated sources are located in the fan structure of magnetic field lines starting from a coronal magnetic null point. Wavelet analysis of the light curves of the radio sources detects tadpoles with periods in the range P=10 - 83 s. These wavelet tadpoles indicate the presence of fast magnetoacoustic waves that propagate in the fan structure of the coronal magnetic null point. We estimate the plasma parameters in the studied radio sources and find them consistent with the presented scenario involving the coronal magnetic null point. Title: SDO/AIA Prominence physical conditions Authors: Schmieder, B.; Parenti, S.; Dudik, J.; Aulanier, G.; Heinzel, P.; Zapior, M.; Golub, L. Bibcode: 2013enss.confE..27S Altcode: SDO/AIA has carried out continuous observations of prominences in multiple wavelengths, with high spatial and temporal resolution. These data provide us an opportunity to understand the physical conditions and dynamics of prominences. The surprising brightness of prominences in some coronal lines has been well explained by the presence of transition region lines in the bandpass of the filters (171 A, 131 A), a result that leads us to revise our model of the transition region of prominences and to consider a relatively dense transition region in some prominence evolutionary phases or in some viewing orientation. An additional aspect of prominence dynamics will be presented with a new quasi-static MHD model proposed for bubbles and plumes. We propose an alternative to the interpretation that thermal instabilities are responsible for the formation of bubbles. The bubbles are found to correspond to magnetic separatrices formed by emerging magnetic field close to prominence footpoints. Title: Dielectronic satellite lines and double layers in solar flares Authors: Dzifčáková, E.; Karlický, M.; Dudík, J. Bibcode: 2013A&A...550A..60D Altcode: Context. Particle acceleration during solar flares results in departures of the distribution of particle energies from the Maxwellian distribution. Apart from the high-energy tail, the bulk of the distribution was recently also found to be significantly affected, due, e.g., to the presence of double layers.
Aims: We investigate the influence of several proposed non-Maxwellian distribution functions on the X-ray flare line spectra. The distribution functions considered are sharply peaked and include the n-distribution, the moving Maxwellian distribution, and the distribution formed in strong double layers in the flaring plasma.
Methods: Synthetic Si xiid-Si xiv spectra involving allowed and dielectronic transitions at 5 - 6 Å are calculated numerically. The parameters chosen for the calculations correspond to the impulsive phase of solar flares, as inferred by previous authors.
Results: The Si xiid λ5.56/Si xiii λ5.68 and Si xiid λ5.82/Si xiii λ5.68 ratios depend on the relative number of electrons at energies corresponding to the formation of the Si xiid lines. Therefore, these ratios increase with the increasing narrowness of the peak of the electron distribution function. The highest ratios are achieved for the distribution formed in double layers, while the moving Maxwellian distribution is less likely to reproduce the observed enhancement of Si xiid intensities. However, the ratio of the allowed Si xiv λ5.22/Si xiii λ5.68 transitions depends on the ionization equilibrium. This ratio is very small for the double-layer distribution. Combination of the double-layer distribution with a Maxwellian distribution with the same mean energy significantly enhances this ratio, while keeping the Si xiid intensities sufficiently increased to explain the characteristics of the observed spectra.
Conclusions: These results support the presence of double layers in the plasma during impulsive phase of solar flares. Title: On the Possibility to Diagnose the Non-Maxwellian κ-Distributions from the Hinode/EIS EUV Spectra Authors: Mackovjak, Š.; Dzifčáková, E.; Dudík, J. Bibcode: 2013SoPh..282..263M Altcode: 2012SoPh..tmp..273M We investigate the possibility to diagnose the κ-distributions from the EUV spectra observed by the Hinode/EIS spectrometer. Observable lines of the most abundant elements except Fe are considered. Synthetic spectra for the κ-distributions with κ=2 - 10 and the Maxwellian distribution were calculated for a range of temperatures and electron densities. We find that only a small number of O, S, Ca, and Ni line ratios are sensitive to κ. A list of the best diagnostic options using transition region and coronal lines is provided. Usually, the line ratios sensitive to κ are also sensitive to electron density. Weak O IV lines are a notable exception. These lines offer greatest sensitivity to κ from all the lines observed by Hinode/EIS. Density diagnostics using lines of the non-Fe elements is discussed and the influence of κ on the diagnostics of electron density is presented. The density diagnostics using these non-Fe EIS lines are strongly affected by both known and unknown blends. Therefore, we performed the density diagnostics using the Fe XII - XIV lines. Subsequently, these proposed diagnostic methods for κ-distributions are tested using the spectral atlas obtained by Brown et al. (Astrophys. J. Suppl.176, 511, 2008). These data do not provide conclusive evidence for the presence of κ-distributions due to possible plasma multitermality, a low observed signal-to-noise ratio, and unremovable or unknown blends. Title: Magnetic Topology of Bubbles in Quiescent Prominences Authors: Dudík, J.; Aulanier, G.; Schmieder, B.; Zapiór, M.; Heinzel, P. Bibcode: 2012ApJ...761....9D Altcode: We study a polar-crown prominence with a bubble and its plume observed in several coronal filters by the SDO/AIA and in Hα by the MSDP spectrograph in Białków (Poland) to address the following questions: what is the brightness of prominence bubbles in EUV with respect to the corona outside of the prominence and the prominence coronal cavity? What is the geometry and topology of the magnetic field in the bubble? What is the nature of the vertical threads seen within prominences? We find that the brightness of the bubble and plume is lower than the brightness of the corona outside of the prominence, and is similar to that of the coronal cavity. We constructed linear force-free models of prominences with bubbles, where the flux rope is perturbed by inclusion of parasitic bipoles. The arcade field lines of the bipole create the bubble, which is thus devoid of magnetic dips. Shearing the bipole or adding a second one can lead to cusp-shaped prominences with bubbles similar to the observed ones. The bubbles have complex magnetic topology, with a pair of coronal magnetic null points linked by a separator outlining the boundary between the bubble and the prominence body. We conjecture that plume formation involves magnetic reconnection at the separator. Depending on the viewing angle, the prominence can appear either anvil-shaped with predominantly horizontal structures, or cusp-shaped with predominantly vertical structuring. The latter is an artifact of the alignment of magnetic dips with respect to the prominence axis and the line of sight. Title: Can bubbles in quiescent prominences be purely magnetic phenomena? Authors: Dudik, Jaroslav; Schmieder, Brigitte; Aulanier, Guillaume; Zapior, Maciej; Heinzel, Petr Bibcode: 2012cosp...39..486D Altcode: 2012cosp.meet..486D We present a model of the magnetic field constituting quiescent prominences. The model assumes a linear force-free field with a weakly twisted flux-tube in an OX/OF topology perturbed by presence of parasitic polarities within the filament channel. The parasitic polarities locally create the cusp-shaped prominences with bubbles exactly as those observed by the SDO/AIA and Bialkow Observatory. We find that the observations are best reproduced if the parasitic bipoles are sheared with respect to the main inversion line. We show that the bubbles are in fact constituted by the arcade-like field lines, as opposed to that of the prominence, which is created by magnetic dips. A pair of null points is always associated with the parasitic bipole. These null points are connected by a separator passing through the prominence bubble. We show how the presence of an additional parasitic bipole moves the separator to the boundary between the bubble and the rest of the prominence, producing a topology favorable for reconnection and possibly for the formation of plumes. Title: X-ray and EUV Filter Responses for Nonthermal κ-Distributions Authors: Dzifčáková, E.; Dudík, J.; Karlický, M. Bibcode: 2012ASPC..456..135D Altcode: We calculate the XRT and AIA filter responses to emission for nonthermal electron kappa-distributions. The filter responses are in general wider and shifted to higher temperatures. This can affect temperature diagnostic during flares. We analyze the effect of nonthermal kappa-distributions on the resulting forward models of AR emission and show that their influence is small except for the extreme nonthermal cases. Title: Temperature Diagnostic of a Brightening Observed by Hinode/XRT Authors: Dudík, J.; Reeves, K. K.; Schmieder, B.; Dzifčáková, E.; Golub, L. Bibcode: 2012ASPC..456..137D Altcode: We analyze the temperature distribution of the active region brightening observed by HINODE/XRT. The temperature structure is derived using various filter-ratio techniques and DEM analysis. The results are compared and it is found that the filter-ratio techniques are accurate only for relatively narrow DEMs. Title: The non-Maxwellian continuum in the X-ray, UV, and radio range Authors: Dudík, J.; Kašparová, J.; Dzifčáková, E.; Karlický, M.; Mackovjak, Š. Bibcode: 2012A&A...539A.107D Altcode:
Aims: We investigate the X-ray, UV, and also the radio continuum arising from plasmas with a non-Maxwellian distribution of electron energies. The two investigated types of distributions are the κ- and n-distributions.
Methods: We derived analytical expressions for the non-Maxwellian bremsstrahlung and free-bound continuum spectra. The spectra were calculated using available cross-sections. Then we compared the bremsstrahlung spectra arising from the different bremsstrahlung cross-sections that are routinely used in solar physics.
Results: The behavior of the bremsstrahlung spectra for the non-Maxwellian distributions is highly dependent on the assumed type of the distribution. At flare temperatures and hard X-ray energies, the bremsstrahlung is greatly increased for κ-distributions and exhibits a strong high-energy tail. With decreasing κ, the maximum of the bremsstrahlung spectrum decreases and moves to higher wavelengths. In contrast, the maximum of the spectra for n-distributions increases with increasing n, and the spectrum then falls off very steeply with decreasing wavelength. In the millimeter radio range, the non-Maxwellian bremsstrahlung spectra are almost parallel to the thermal bremsstrahlung. Therefore, the non-Maxwellian distributions cannot be detected by off-limb observations made by the ALMA instrument. The free-bound continua are also highly dependent on the assumed type of the distribution. For n-distributions, the ionization edges disappear and a smooth continuum spectrum is formed for n ≧ 5. Opposite behavior occurs for κ-distributions where the ionization edges are in general significantly enhanced, with details depending on κ and T through the ionization equilibrium. We investigated how the non-Maxwellian κ-distributions can be determined from the observations of the continuum and conclude that one can sample the low-energy part of the distribution from the continuum.

Appendix A is available in electronic form at http://www.aanda.org Title: On the physical meaning of n-distributions in solar flares Authors: Karlický, M.; Dzifčáková, E.; Dudík, J. Bibcode: 2012A&A...537A..36K Altcode:
Aims: We investigate the physical meaning of the n-distributions detected in solar flares.
Methods: We consider a Maxwellian velocity distribution with a velocity drift. This distribution is analytically integrated to obtain the energy distribution, and its stability is investigated numerically using a fully electromagnetic particle-in-cell code.
Results: It is shown that the derived moving Maxwellian energy distribution is very similar to the n-distribution, especially in their high-energy parts. Both these distributions are mutually fitted and a relation between their parameters found. Contrary to the n-distribution, the moving Maxwellian distribution has a simple physical meaning, e.g., the electron component of the return current in the beam-plasma system. However, for high drift velocities of such a component, the moving Maxwellian distribution is unstable. Therefore to keep the form of this distribution similar to the n-distribution, some stabilization processes are necessary. If so, then the high intensities of the Si xiid 5.56 Å and 5.82 Å satellite lines and their evolution in solar flares can be explained by moving Maxwellian distributions instead of the n-distributions. Thus, our previous results connected with the n-distributions can be understood in a new, physically profound way. Title: Is it possible to model observed active region coronal emission simultaneously in EUV and X-ray filters? Authors: Dudík, J.; Dzifčáková, E.; Karlický, M.; Kulinová, A. Bibcode: 2011A&A...531A.115D Altcode:
Aims: We investigate the possibility of modeling the active region coronal emission in the EUV and X-ray filters using one, universal, steady heating function, tied to the properties of the magnetic field.
Methods: We employ a simple, static model to compute the temperature and density distributions in the active region corona. The model allows us to explore a wide range of parameters of the heating function. The predicted EUV and X-ray emission in the filters of EIT/SOHO and XRT/Hinode are calculated and compared with observations. Using the combined improved filter-ratio (CIFR) method, a temperature diagnostic is employed to compare the modeled temperature structure of the active region with the temperature structure derived from the observations.
Results: The global properties of the observations are most closely matched for heating functions scaling as B_00.7-0.8/L_0^{0.5} that depend on the spatially variable heating scale-length. The modeled X-ray emission originates from locations where large heating scale-lengths are found. However, the majority of the loops observed in the 171 and 195 filters can be modeled only by loops with very short heating scale-lengths. These loops are known to be thermally unstable. We are unable to find a model that both matches the observations in all EUV and X-ray filters, and contains only stable loops. As a result, although our model with a steady heating function can explain some of the emission properties of the 171 and 195 loops, it cannot explain their observed lifetimes. Thus, the model does not lead to a self-consistent solution. The performance of the CIFR method is evaluated and we find that the diagnosed temperature can be approximated with a geometric mean of the emission-measure weighted and maximum temperature along the line of sight.
Conclusions: We conclude that if one universal heating function exists, it should be at least partially time-dependent. Title: The ionization equilibrium and flare line spectra for the electron distribution with a power-law tail Authors: Dzifčáková, E.; Homola, M.; Dudík, J. Bibcode: 2011A&A...531A.111D Altcode: Context. Electron energy spectra exhibiting a high-energy tail are commonly observed during solar flares.
Aims: We investigate the influence of the high-energy tail and thermal or nonthermal plasma bulk on the ionization equilibrium of Si and Si flare line spectra.
Methods: We construct a realistically composed distribution that reflects the fits to RHESSI observations. We describe the high-energy tail by a power-law distribution and the bulk of the electron distribution by either the Maxwellian or n-distribution. The shape of this composed distribution is described by three parameters: the ratio of the plasma bulk density to the density of the high-energy tail, the power-law index of the high-energy tail, and the parameter n, which describes the bulk of the distribution.
Results: Both the plasma bulk and the high-energy tail change the ionization equilibrium. The relative ion abundances are sensitive to the shape of the plasma bulk, but are much less sensitive to the high-energy tail. The high-energy tail increases the ratio of temperature-sensitive lines Si XIV λ5.22/Si XIII λ5.68. Because this ratio can be fitted with a thermal distribution with higher temperature, the high-energy tail influences the temperature diagnostics from flare lines. The high-energy tail has only a small effect on the ratio of the satellite-to-allowed Si XIId/Si XIII lines, which are dominantly sensitive on the shape of the plasma bulk. This enables us to perform an accurate diagnostic of the parameter n describing the plasma bulk.
Conclusions: The realistically composed distribution is able to explain the observed features of the RESIK X-ray flare line spectra. Title: The bound-bound and free-free radiative losses for the nonthermal distributions in solar and stellar coronae Authors: Dudík, J.; Dzifčáková, E.; Karlický, M.; Kulinová, A. Bibcode: 2011A&A...529A.103D Altcode: Context. The radiative-loss function is an important ingredient in the physics of the solar corona, transition region, and flares.
Aims: We investigate the radiative losses due to the bound-bound transitions and bremsstrahlung for nonthermal κ- and n-distributions.
Methods: The bound-bound radiative losses are computed by integrating synthetic spectra. An analytical expression is derived for nonthermal bremsstrahlung. The bremsstrahlung is computed numerically using accurate values of the free-free Gaunt factor.
Results: We find that the changes in radiative-loss functions due to nonthermal distributions are several times greater than the errors due to the missing contribution of the free-bound continuum or errors in atomic data. For κ-distributions, the radiative-loss functions are in general weaker than for Maxwellian distribution, with a few exceptions caused by the behavior of Fe. The peaks of the radiative-loss functions are in general flatter. The situation is opposite for n-distributions, for which the radiative-loss functions have higher and narrower peaks. Local minima and maxima of the radiative-loss functions may also be shifted. The contribution from bremsstrahlung only changes by a few percent except in the extreme nonthermal case of κ = 2. Stability analysis reveals that the X-ray loops are stable against the radiatively-driven thermal instability.

The calculated radiative losses for nonthermal distributions are available as two electronic tables at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A103 Title: VizieR Online Data Catalog: Radiative losses in solar and stellar coronae (Dudik+, 2011) Authors: Dudik, J.; Dzifcakova, E.; Karlicky, M.; Kulinova, A. Bibcode: 2011yCat..35290103D Altcode: 2011yCat..35299103D The radiative losses due to bound-bound and free-free transitions calculated for plasma with nonthermal {kappa}- and n-distributions of electron energies are presented. The radiative losses are calculated for the values of {kappa}=2, 3, 5, and 10 (rloss_k.dat) and n=1 (Maxwellian), 3, 5, and 11 (rloss_n.dat) as function of temperature (T) or pseudo-temperature (tau) for the assumed value of electron density ne=1016m-3. The ne*nH factor is not included in the calculations.

(2 data files). Title: Emisia C IV a magnetická topológia Title: Emisia C IV a magnetická topológia Title: C IV emission and magnetic topology. Authors: Mackovjak, Š.; Dudík, J.; Dzifčáková, E. Bibcode: 2010nspm.conf...78M Altcode: The contribution discusses a study of emissions of carbon ion C IV during solar flares. Data on the emission of the "clean" C IV and "clean" UV continuum were obtained from the emission observed in three TRACE UV filters 1550, 1600 and 1700. Their correlation was examined. We also studied the spatial correlation of flare nuclei with images in the calcium ion Ca II line and mainly its relation to quasiseparatrix positions calculated by extrapolation of the photospheric magnetogram assuming linear force-free approximation of the magnetic field. Perticular results were summarized and applied to a selected flare. Title: Kappa-distribúcie a ohrev koróny Title: Kappa-distribúcie a ohrev koróny Title: Kappa-distributions and coronal heating. Authors: Dudík, J.; Dzifčáková, E.; Kulinová, A.; Karlický, M. Bibcode: 2010nspm.conf..161D Altcode: Particle energy kappa-distributions (distributions with non-thermal tails) have been diagnosed in plasma of the transition region and also in solar flares. Theoretical models suggest a link between kappa-distributions and dynamic heating of the corona. Since the presence of non-thermal distributions leads to changes in intensities of emission lines, we have examined their effect on the total radiation losses of the corona as well as responses of the EUV and X-ray filters. Temperature responses of the filters are wider for kappa-distributions than in the case of the Maxwell distribution, and their respective maxima are shifted towards higher temperatures. On the other hand, the total radiation losses of the corona are lower compared to the Maxwell distribution except for the extreme non-thermal case. This means that lower heating energy is needed to reach the same corona temperature in case of kappa-distributions. In this work we discuss the effect of element abundances and specific ions on the total radiation losses of the corona. Title: EUV filter responses to plasma emission for the nonthermal κ-distributions Authors: Dudík, J.; Kulinová, A.; Dzifčáková, E.; Karlický, M. Bibcode: 2009A&A...505.1255D Altcode: The responses to plasma emission of the TRACE EUV filters are computed by integrating their spectral responses over the synthetic spectra obtained from the CHIANTI database. The filter responses to emission are functions of temperature, electron density, and the assumed electron distribution function. It is shown here that, for the nonthermal κ-distributions, the resulting responses to emission are more broadly dependent on T, and their maxima are flatter than for the Maxwellian electron distribution. The positions of the maxima can also be shifted. Filter reponses to T are density-dependent as well. The influence of the nonthermal κ-distributions on the diagnostics of T from the observations in all three EUV filters is discussed. Title: Analytical model of static coronal loops Authors: Dudík, J.; Dzifčáková, E.; Karlický, M.; Kulinová, A. Bibcode: 2009A&A...502..957D Altcode: By solving the energy-equilibrium equation in the stationary case, we derive analytical formulae in the form of scaling laws for non-uniformly heated and gravitationally stratified coronal loops. The heating is assumed to be localized in the chromosphere and to exponentially decrease with increasing distance along the loop strand. This exponential behavior of the heating and pressure profiles implies that we need to use the mean-value theorem, and in turn fit the mean-value parameters of the scaling laws to the results of the numerical simulations. The radiative-loss function is approximated by a power-law function of the temperature, and its effect on the resulting scaling laws for coronal loops is studied. We find that this effect is more important than the effect of varying loop geometry. We also find that the difference in lengths of the different loop strands in a loop with expanding cross-section does not produce differences in the EUV emission of these strands significant enough to explain the observed narrowness of the coronal loops. Title: Hydrostatic Modelling of Active Region EUV and X-ray Emission Authors: Dudik, J.; Dzifcakova, E.; Kulinova, A.; Karlicky, M. Bibcode: 2008ESPM...12.3.65D Altcode: The hydrostatic modeling of active region NOAA 10963 coronal EUV and X-ray emission is presented. The model considers three-dimensional magnetic field structure obtained by the extraplation of the longitudinal magnetogram in potential or linear force-free approximation. We derived new scaling laws for loop apex temperature and footpoint pressure as functions of loop length, volumetric heating rate and heating scale height. These scaling laws assume a power-law dependency of radiative loss function on the temperature, a power-law dependency of the heating function on the loop length and field strength at the loop base. The scaling laws are applied to the results of the field extrapolations in AR NOAA 10963 in order to calculate the temperature and density distributions in the active region corona. The functions of filter response to emissivity has been calculated by using the CHIANTI atomic database. Unlike previous authors, we are able to get emitting loop structures in EUV. The results show that the heating scale height plays important role in modeling of the active region emission. The computed emission is compared with observations and the implications on the heating function are discussed. Title: Topological Departures from Translational Invariance along a Filament Observed by THEMIS Authors: Dudík, J.; Aulanier, G.; Schmieder, B.; Bommier, V.; Roudier, T. Bibcode: 2008SoPh..248...29D Altcode: 2008SoPh..tmp...53D We study the topology of the 3D magnetic field in a filament channel to address the following questions: Is a filament always formed in a single flux tube? How does the photospheric magnetic field lead to filament interruptions and to feet formation? What is the relation between feet-related field lines and the parasitic polarities? What can topological analyses teach us about EUV filament channels? To do so, we consider a filament observed on 6 October 2004 with THEMIS/MTR, in Hα with the full line profile simultaneously and cospatially with its photospheric vector magnetic field. The coronal magnetic field was calculated from a "linear magnetohydrostatic" extrapolation of a composite THEMIS-MDI magnetogram. Its free parameters were adjusted to get the best match possible between the distribution of modeled plasma-supporting dips and the Hα filament morphology. The model results in moderate plasma β≤1 at low altitudes in the filament, in conjunction with non-negligible departures from force-freeness measured by various metrics. The filament here is formed by a split flux tube. One part of the flux tube is rooted in the photosphere aside an observed interruption in the filament. This splitted topology is due to strong network polarities on the edge of the filament channel, not to flux concentrations closer to the filament. We focus our study to the northwest portion of the filament. The related flux tube is highly fragmented at low altitudes. This fragmentation is due to small flux concentrations of two types. First, some locally distort the tube, leading to noticeable thickness variations along the filament body. Second, parasitic polarities, associated with filament feet, result in secondary dips above the related local inversion line. These dips belong to long field lines that pass below the flux tube. Many of these field lines are not rooted near the related foot. Finally, the present model shows that the coronal void interpretation cannot be ruled out to interpret the wideness of EUV filament channels. Title: Simulation of Active Region Coronal Loops EUV Emission Authors: Dudík, J.; Dzifčáková, E.; Karlický, M.; Wu, S. T.; Wang, A. H. Bibcode: 2006ESASP.617E..57D Altcode: 2006soho...17E..71D No abstract at ADS Title: C IV Enhanced Emission and the Non-Thermal Electron Distribution Authors: Dzifčáková, E.; Kulinová, A.; Tóthová, D.; Dudík, J. Bibcode: 2005ESASP.600E.120D Altcode: 2005ESPM...11..120D; 2005dysu.confE.120D No abstract at ADS Title: Changes in Filament Connectivity and its Structure during the C-Class Flare Authors: Kulinová, A.; Dzifčáková, E.; Dudík, J. Bibcode: 2005ESASP.600E.129K Altcode: 2005ESPM...11..129K; 2005dysu.confE.129K No abstract at ADS