Author name code: karlicky ADS astronomy entries on 2022-09-14 author:"Karlicky, Marian" ------------------------------------------------------------------------ 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: Zebra Stripes with High Gyro-Harmonic Numbers Authors: Benáček, Jan; Karlický, Marian Bibcode: 2022SoPh..297..103B Altcode: 2022arXiv220810131B Solar radio zebras are used in the determination of the plasma density and magnetic field in solar flare plasmas. Analyzing observed zebra stripes and assuming their generation by the double-plasma resonance (DPR) instability, high values of the gyro-harmonic number are found. In some cases they exceed one hundred, in disagreement with the DPR growth rates computed up to now, which decrease with increasing gyro-harmonic number. We address the question of how zebras with high values of the gyro-harmonic numbers s are generated. For this purpose, we compute the growth rates of the DPR instability in a very broad range of s , considering a loss-cone κ -distribution of superthermal electrons and varying the loss-cone angle, electron energies, and background plasma temperature. We have numerically calculated the dispersion relations and the growth rates of the upper-hybrid waves and found that the growth rates increase with increasing gyro-harmonic numbers if the loss-cone angles are ∼80∘. The highest growth rates for these loss-cone angles are obtained for velocity vκ=0.15 c . The growth rates as a function of the gyro-harmonic number still show well distinct peaks, which correspond to zebra-stripe frequencies. The contrast between peak growth rates and surrounding growth rate levels increases as the κ index increases and the background temperature decreases. Zebras with high values of s can be generated in regions where loss-cone distributions of superthermal electrons with large loss-cone angles (∼80∘) are present. Furthermore, owing to the high values of s , the magnetic field is relatively weak and has a small spatial gradient in such regions. Title: Simulations of solar radio zebras Authors: Karlický, M. Bibcode: 2022A&A...661A..56K Altcode: Context. Solar radio zebras are used in diagnostics of solar flare plasmas and it is of great importance to construct accurate models to correctly characterize them.
Aims: We simulated two zebras to verify their double-plasma resonance (DPR) model.
Methods: In our zebra simulations, we used the DPR model in an expanding and compressing part of the loop as well as with the wave propagating along the loop.
Results: Using the DPR model in such a loop, we successfully simulated zebras from the 1 August 2010 and 21 June 2011 flares. We found that increasing the density or decreasing the magnetic field in the part of the loop, where zebra-stripe sources are located, the zebra stripes are shifted to higher frequencies and vice versa. In the case of the 21 June 2011 flare, we confirm that small deviations of zebra-stripe frequencies from their mean values can be explained by waves propagating along the loop. We also confirm high values for the gyro-harmonic number of zebra stripes. We explain an inconsistency in the wave velocities derived from the plasma parameters and from the frequency drift in combination with the density model of the solar atmosphere. Finally, we discuss the high values of the gyro-harmonic number found in the studied zebras. Title: Narrowband Spikes Observed During the 13 June 2012 Flare in the 800 - 2000 MHz Range Authors: Karlický, Marian; Rybák, Ján; Benáček, Jan; Kašparová, Jana Bibcode: 2022SoPh..297...54K Altcode: 2022arXiv220409327K Narrowband (∼5 MHz) and short-lived (∼0.01 s) spikes with three different distributions in the 800 - 2000 MHz radio spectrum of the 13 June 2012 flare are detected and analyzed. We designate them as SB (spikes distributed in a broad band or bands), SZ (spikes distributed in zebra-like bands) and SBN (spikes distributed in broad and narrow bands). On analyzing AIA/SDO images of the active region NOAA 11504, a rough correspondence between groups of the spikes observed at 1000 MHz and peaks in the time profiles of AIA channels taken from the flare subarea close to the leading sunspot is found. Among the types of spikes the SZ type is the most interesting because it resembles zebras. Therefore, using autocorrelation and crosscorrelation methods we compare SZ and SBN spikes with the typical zebra observed in the same frequency range. While the ratio of SZ band frequencies with their frequency separation (220 MHz) is about 4, 5, and 6, in the zebra the frequency stripe separation is about 24 MHz and the ratio is around 50. Moreover, the bandwidth of SZ bands, which consists of clouds of narrowband spikes, is much broader than that of zebra stripes. This comparison indicates that SZ spikes are generated in a different way from the zebra, but in a similar way to SBN spikes. We successfully fit the SZ band frequencies by the Bernstein modes. Based on this fitting we interpret SZ and SBN spikes as those generated in the model of Bernstein modes. Thus, the magnetic field and plasma density in the SZ spike source are estimated to be about 79 G and 8.4 × 109 cm−3, respectively. Title: Dynamics and Characteristics of Waves in the Zebra Radio Source Authors: Yasnov, L. V.; Karlický, M. Bibcode: 2022SoPh..297...35Y Altcode: We analyzed the 17 August 1998 zebra event and showed that some quasi-periodic oscillations modulate the zebra-stripe frequencies. We determined the period of these oscillations as Pn=2.01 ±0.03 (in numbers of zebra stripes) and as Pf=11.8 ±0.17 MHz. In the first part of the analyzed zebra, we found a stable density wave that slowly propagated with the frequency drift less than 0.4 MHz s−1. Then, a stationary density wave appeared followed by a transformation of the waves to ones with longer periods. These long-period waves were recorded before and after the time interval when no zebra stripes were observed. We interpreted these density waves as magnetosonic waves. We calculated their wavelength and propagating velocity, considering two types of density models of the solar atmosphere. We also estimated the characteristic density and magnetic-field strength as N ≈9.2 ×108 cm−1 and B ≈0.73 G, respectively. We found similar velocities derived from drifts of the density wave and velocities calculated from the density and magnetic-field strength considering gyro-harmonic numbers of zebra stripes. Title: Flare energy release and avalanche ionization of plasma by runaway electrons in lower solar atmosphere Authors: Tsap, Yuriy; Kopylova, Yulia; Karlický, Marian Bibcode: 2022OAst...30..216T Altcode: The analysis of the electron acceleration by the quasi-stationary sub-Dreiser electric fields in the lower solar atmosphere has been done. It has been shown that the Dreiser electric field turned out to be several orders of magnitude larger than coronal values due to the inelastic collisions between electrons and hydrogen atoms. The ionization of hydrogen atoms gives rise to the resulting secondary electrons, which become runaway under the action of sub-Dreiser electric fields. This causes an further avalanche-like ionization of the plasma and leads to the acceleration of the large number of fast electrons up to relativistic energies at small (≲ 100 km) distances. 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: Shock-wave Radio Probing of Solar Wind Sources in Coronal Magnetic Fields Authors: Koval, Artem; Karlický, Marian; Stanislavsky, Aleksander; Wang, Bing; Bárta, Miroslav; Gorgutsa, Roman Bibcode: 2021ApJ...923..255K Altcode: 2021arXiv211015863K The space weather effects in the near-Earth environment as well as in atmospheres of other terrestrial planets arise by corpuscular radiation from the Sun, known as the solar wind. The solar magnetic fields govern the solar corona structure. Magnetic-field strength values in the solar wind sources-key information for modeling and forecasting the space weather climate-are derived from various solar space- and ground-based observations, but so far not accounting for specific types of radio bursts. These are "fractured" type II radio bursts attributed to collisions of shock waves with coronal structures emitting the solar wind. Here, we report on radio observations of two "fractured" type II bursts to demonstrate a novel tool for probing of magnetic-field variations in the solar wind sources. These results have a direct impact on interpretations of this class of bursts and contribute to the current studies of the solar wind emitters. Title: Narrowband Spikes Observed during the 2013 November 7 Flare Authors: Karlický, Marian; Benáček, Jan; Rybák, Ján Bibcode: 2021ApJ...910..108K Altcode: 2021arXiv210401345K Narrowband spikes have been observed in solar flares for several decades. However, their exact origin is still discussed. To contribute to understanding of these spikes, we analyze the narrowband spikes observed in the 800-2000 MHz range during the impulsive phase of the 2013 November 7 flare. In the radio spectrum, the spikes started with typical broadband clouds of spikes, and then their distribution in frequencies changed into unique, very narrow bands having noninteger frequency ratios. We successfully fitted frequencies of these narrow spike bands by those, calculating dispersion branches and growth rates of the Bernstein modes. For comparison, we also analyzed the model where the narrow bands of spikes are generated at the upper-hybrid frequencies. Using both models, we estimated the plasma density and magnetic field in spike sources. Then, the models are discussed, and arguments in favor of the model with the Bernstein modes are presented. Analyzing frequency profiles of this spike event by the Fourier method, we found the power-law spectra with the power-law indices varying in the -0.8 to -2.75 interval. Because at some times this power-law index was close to the Kolmogorov spectral index (-5/3), we propose that the spikes are generated through the Bernstein modes in turbulent plasma reconnection outflows or directly in the turbulent magnetic reconnection of solar flares. Title: Spatial quasi-periodic variations of the plasma density and magnetic field in zebra radio sources Authors: Karlický, M.; Yasnov, L. V. Bibcode: 2021A&A...646A.179K Altcode: Context. Radio bursts and their fine structures are an integral part of solar flares. Fine structures in particular are used for diagnostics of solar flare processes. The so-called zebras belong to the most important of such fine structures.
Aims: We analyze seven zebra events in order to search for spatial variations in the plasma density and magnetic field in zebra-stripe sources.
Methods: We used an improved method for estimating the gyroharmonic numbers of zebra-stripe frequencies. We compared observed zebra-stripe frequencies with those calculated in the zebra model. The differences in these frequencies vary and thus show spatial variations in the plasma density and magnetic field.
Results: In six out of seven analyzed zebras, we found a rather high correlation coefficient (about 0.7 and higher) between spatial variations in the density and magnetic field and a strictly periodic function. These density and magnetic field variations are explained by the torsional or sausage magnetoacoustic waves in the loop in which zebra-stripe sources are located. We present the wavelengths of these waves in dependence on the zebra frequency and estimate their periods. 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: The 2017 September 6 Flare: Radio Bursts and Pulsations in the 22-5000 MHz Range and Associated Phenomena Authors: Karlický, Marian; Rybák, Ján Bibcode: 2020ApJS..250...31K Altcode: 2020arXiv200905756K For the 2017 September 6 flare (SOL2017-Sep-06T11:53) we present not only unusual radio bursts but also their interesting time association with the other flare phenomena observed in extreme ultraviolet (EUV), white-light, X-ray, and γ-ray emissions. Using our new method based on wavelets we found quasi-periodic pulsations (QPPs) in several locations of the whole time-frequency domain of the analyzed radio spectrum (11:55-12:07 UT and 22-5000 MHz). Among them the drifting QPPs are new and the most interesting, especially a bidirectional QPP at the time of the hard X-ray and γ-ray peaks and a sunquake start. In the pre-impulsive phase we show an unusual drifting pulsation structure (DPS) in association with the EUV brightenings caused by the interaction of magnetic ropes. In the flare impulsive phase we found an exceptional radio burst drifting from 5000 to 800 MHz. In connection with this drifting burst, we show a U burst at about the onset time of an EUV writhed structure and a drifting radio burst as a signature of a shock wave at high frequencies (1050-1350 MHz). In the peak flare phase we found an indication of an additional energy-release process located at higher altitudes in the solar atmosphere. These phenomena are interpreted considering a rising magnetic rope, magnetosonic waves, and particle beams. Using a density model we estimated the density, wave velocities, and source heights for the bidirectionally drifting QPPs, the density for the pre-impulsive DPS and U burst, and the density and magnetic field strength for the drifting radio burst. Title: Magnetic Field, Electron Density and Their Spatial Scales in Zebra Pattern Radio Sources Authors: Yasnov, L. V.; Karlický, M. Bibcode: 2020SoPh..295...96Y Altcode: Zebra patterns (zebras) play an important role in the plasma diagnostics during solar flares. Considering their double plasma resonance (DPR) model, we present an improved method for the determination of the gyro-harmonic numbers of the zebra stripes that are essential in determining the electron density and magnetic field strength in zebra sources. Furthermore, we present the magnetic field and density spatial scales in zebra sources. Compared to the previous method, we change the basic assumption of the method. Namely, the assumption that the ratio R =Lbh/Lnh (Lbh and Lnh are the magnetic field and density scales) is constant in the whole zebra source is changed to its more generalized form, where the ratio R is a linear function. Using this improved method, first, we determine the gyro-harmonic numbers of several observed zebras and variations of the spatial scales. Then, knowing the gyro-harmonic numbers of zebra stripes, we compute the electron plasma density and magnetic field strength in zebra sources. It is shown that in all cases the gyro-harmonic numbers of zebra stripes are quite high (> ≈50). This significantly reduces the magnetic field strength and thus increases the plasma beta parameter in zebra sources. The change in the ratio of the magnetic field and density scales along the axis of the radiating tube for the studied zebras is within ± 5 percent. For zebras at high frequencies, this ratio increases with the height, and for zebras at lower frequencies it decreases. The ratio of the magnetic field and density scales across the radiating tube is close to 1 and varies in the range 0.87-1.20. Title: Estimating density and magnetic field turbulence in solar flares using radio zebra observations Authors: Karlický, M.; Yasnov, L. Bibcode: 2020A&A...638A..22K Altcode: Context. In solar flares the presence of magnetohydrodynamic turbulence is highly probable. However, information about this turbulence, especially the magnetic field turbulence, is still very limited.
Aims: In this paper we present a new method for estimating levels of the density and magnetic field turbulence in time and space during solar flares at positions of radio zebra sources.
Methods: First, considering the double-plasma resonance model of zebras, we describe a new method for determining the gyro-harmonic numbers of zebra stripes based on the assumption that the ratio R = Lb/Ln (Ln and Lb are the density and magnetic field scales) is constant in the whole zebra source.
Results: Applying both the method proposed in this work and one from a previous paper for comparison, in the 14 February 1999 zebra event we determined the gyro-harmonic numbers of zebra stripes. Then, using the zebra-stripe frequencies with these gyro-harmonic numbers, we estimated the density and magnetic field in the zebra-stripe sources as n = (2.95-4.35) × 1010 cm-3 and B = 17.2-31.9 G, respectively. Subsequently, assuming that the time variation of the zebra-stripe frequencies is caused by the plasma turbulence, we determined the level of the time varying density and magnetic field turbulence in zebra-stripe sources as |Δn/n|t = 0.0112-0.0149 and |ΔB/B|t = 0.0056-0.0074, respectively. The new method also shows deviations in the observed zebra-stripe frequencies from those in the model. We interpret these deviations as being caused by the spatially varying turbulence among zebra-stripe sources; i.e., they depend on their gyro-harmonic numbers. Comparing the observed and model zebra-stripe frequencies at a given time, we estimated the level of this turbulence in the density and magnetic field as |Δn/n|s = 0.0047 and |ΔB/B|s = 0.0024. We found that the turbulence levels depending on time and space in the 14 February 1999 zebra event are different. This indicates some anisotropy of the turbulence, probably caused by the magnetic field structure in the zebra source. Title: Expansion of Hot Plasma with Kappa Distribution into Cold Plasma Authors: Benáček, Jan; Karlický, Marian Bibcode: 2020ApJ...896....9B Altcode: 2020arXiv200604479B The X-ray emission of coronal flare sources can be explained by considering the kappa electron distribution. Motivated by this fact, we study the problem of how hot plasma with the kappa distribution of electrons is confined in these sources. For comparison, we analyze the same problem, but with the Maxwellian distribution. We use a 3D particle-in-cell code, which is large in one direction and thus effectively only one-dimensional, but describe all electromagnetic effects. In the case with the Maxwellian distribution, and in agreement with the previous studies, we show a formation of the double layer at the hot-cold transition region that suppresses the flux of hot electrons from hot plasma into the cold one. In the case with the kappa distribution, contrary to the Maxwellian case, we found that there are several fronts with the double layers in the hot-cold transition region. It is caused by a more extended tail in the kappa case than in the Maxwellian one. The electrons from the extended tail freely escape from the hot plasma into a cold one. They form a beam that generates the return current and also Langmuir turbulence, where Langmuir waves accumulated at some locations. At these locations, owing to the ponderomotive force, Langmuir waves generate density depressions, where the double layers with the thermal fronts that suppress the hot electron flux, are formed. We also show how protons accelerate in these processes. Finally, we compare the Kappa and Maxwellian cases and discuss how these processes could be observed. Title: Transverse oscillations of a double-structured solar filament Authors: Jelínek, P.; Karlický, M.; Smirnova, V. V.; Solov'ev, A. A. Bibcode: 2020A&A...637A..42J Altcode:
Aims: We study the transverse oscillations of a double-structured solar filament.
Methods: We modelled the filament numerically via a 2D magnetohydrodynamic (MHD) model, in which we solved a full set of time-dependent MHD equations by means of the FLASH code, using the adaptive mesh refinement method. We used the wavelet analysis method as a diagnostic tool for analysing periods in simulated oscillations.
Results: We present a model of a solar filament combined with semi-empirical C7 model of the quiet solar atmosphere. This model is an alternative model of a filament based on the magnetostatic solution of MHD equations. We find that this double-structured filament oscillates with two different eigen frequencies. The ratio is approximately 1.75 (∼7.4 min/∼4.2 min), which is characteristic for this type of filament model. To show the details of these oscillations we present a time evolution of the plasma density, temperature, plasma beta parameter, and the ratio of gravity to magnetic pressure taken along the vertical axis of the filament at x = 0. The periods found by numerical simulations are then discussed in comparison with those observed.

The movie associated to Fig. 3 is available at https://www.aanda.org Title: Drifting Pulsation Structure at the Very Beginning of the 2017 September 10 Limb Flare Authors: Karlický, Marian; Chen, Bin; Gary, Dale E.; Kašparová, Jana; Rybák, Jan Bibcode: 2020ApJ...889...72K Altcode: 2019arXiv191212518K Drifting pulsation structures (DPSs) are important radio fine structures usually observed at the beginning of eruptive solar flares. It has been suggested that DPSs carry important information on the energy release processes in solar flares. We study DPS observed in an X8.2-class flare on 2017 September 10 in the context of spatial and spectral diagnostics provided by microwave, EUV, and X-ray observations. We describe DPS and its substructures that were observed for the first time. We use a new wavelet technique to reveal characteristic periods in DPS and their frequency bands. Comparing the periods of pulsations found in this DPS with those in previous DPSs, we found new very short periods in the 0.09-0.15 s range. We present Expanded Owens Valley Solar Array images and spectra of microwave sources observed during the DPS. This DPS at its very beginning has pulsations in two frequency bands (1000-1300 MHz and 1600-1800 MHz), which are interconnected by fast drifting bursts. We show that these double-band pulsations started just at the moment when the ejected filament splits apart in a tearing motion at the location where a signature of the flare current sheet later appeared. Using the standard flare model and previous observations of DPSs, we interpret these double-band pulsations as a radio signature of superthermal electrons trapped in the rising magnetic rope and flare arcade at the moment when the flare magnetic reconnection starts. The results are discussed in a scenario with the plasmoid in the rising magnetic rope. Title: Radio, EUV, and X-Ray Observations during a Filament Rise in the 2011 June 7 Solar Flare Authors: Karlický, Marian; Kašparová, Jana; Sych, Robert Bibcode: 2020ApJ...888...18K Altcode: 2020arXiv200400122K The most energetic flares start with a filament rise followed by magnetic reconnection below this filament. The start of the reconnection corresponds to the beginning of the flare impulsive phase. In this paper we study processes before this phase. During the filament rise we recognize an unusual radio continuum with a starting boundary drifting toward lower frequencies. The estimated velocity of the agent generating this continuum boundary is about 400 km s-1, similar to that of the rising filament. In association with this filament rise, transient X-ray sources and extreme ultraviolet (EUV) brightenings are found near the filament footpoint and outside the locations where later two parallel flare ribbons appear. Moreover, oscillations with a ∼30 s period are found simultaneously in radio, EUV, and X-ray observations. Around the end of these oscillations the flare impulsive phase starts as seen in observations of the drifting pulsation structure and X-ray source located at the upper part of the rising filament. We interpret the unusual radio continuum and transient X-ray sources, which are located outside the two parallel flare ribbons, as those generated during an interaction of the rising filament with the above-lying magnetic loops. The EUV brightening at the filament footpoint could be a signature of the magnetic reconnection inside the magnetic rope carrying the filament. Possible scenarios of the ∼30 s period oscillations in radio, X-ray, and EUV are discussed. Title: Growth Rates of the Electrostatic Waves in Radio Zebra Models Authors: Benáček, Jan; Karlický, Marian Bibcode: 2019ApJ...881...21B Altcode: 2019arXiv190412601B Zebras were observed not only in the solar radio emission but also in radio emissions of Jupiter and the Crab Nebula pulsar. In their models, growth rates of the electrostatic waves play an important role. Considering the plasma composed from the thermal background plasma and hot and rare component with the Dory-Guest-Harris distribution, we compute the growth rates γ and dispersion branches of the electrostatic waves in the ω - k ⊥ domain. We show complexity of the electrostatic wave branches in the upper-hybrid band. In order to compare the results, which we obtained using the kinetic theory and particle-in-cell (PIC) simulations, we define and compute the integrated growth rate Γ, where the “characteristic width” of dispersion branches was considered. We found a very good agreement between the integrated growth rates and those from PIC simulations. For maximal and minimal Γ we showed locations of dispersion branches in the ω - k ⊥ domain. We found that Γ has a maximum when the dispersion branches not only cross the region with high growth rates γ, but when the dispersion branches in this region are sufficiently long and wide. We also mentioned the effects of changes in the background plasma and hot component temperatures. Title: Pulse-beam heating of deep atmospheric layers, their oscillations and shocks modulating the flare reconnection Authors: Jelínek, P.; Karlický, M. Bibcode: 2019A&A...625A...3J Altcode:
Aims: We study the processes occurring after a sudden heating of deep atmospheric layers at the flare arcade footpoints, which is assumed to be caused by particle beams.
Methods: For the numerical simulations we adopt a 2D magnetohydrodynamic (MHD) model, in which we solve a full set of the time-dependent MHD equations by means of the FLASH code, using the adaptive mesh refinement (AMR) method.
Results: In the initial state we consider a model of the solar atmosphere with densities according to the VAL-C model and the magnetic field arcade having the X-point structure above, where the magnetic reconnection is assumed. We found that the sudden pulse-beam heating of deep atmospheric layers at the flare arcade footpoints generates two magnetohydrodynamic shocks, one propagating upwards and the second propagating downwards in the solar atmosphere. The downward-moving shock is reflected at deep and dense atmospheric layers and triggers oscillations of these layers. The period of these oscillations in our case is about 174 s. These oscillations generate the upward-moving magnetohydrodynamic waves that can influence the flare magnetic reconnection in a quasi-periodic way. These processes require a sudden heating in very localized regions in dense atmospheric layers; therefore, they can be also associated with seismic waves. Title: Zebra-stripe sources in the double-plasma resonance model of solar radio zebras Authors: Karlický, M.; Yasnov, L. Bibcode: 2019A&A...624A.119K Altcode: Context. Radio bursts with fine structures are used in diagnostics of solar flare plasmas, of which zebra structures are the most important. However, there is still a debate about their origin.
Aims: The most probable model of zebras is that based on double-plasma resonance (DPR) instability. The paper wants to contribute to a verification of this model.
Methods: We used analytical methods.
Results: We studied the DPR model in two scenarios: a model with the zebra-stripe sources in a single loop and a model with the zebra-stripe sources moving through a fan of magnetic field lines. In the first case, we found several new relations among the parameters of zebra stripes and their sources, which can be used to analyze observed zebras and thus to verify if the zebra is generated according to the DPR model. These relations were derived for the zebra-stripe sources distributed along the loop and also for those having some extent in the loop radius. In the scenario with the moving zebra-stripe sources, we determined the parameters of the 14 December 2006 zebra and estimated a change of the ratio of magnetic field and density scales causing the change of zebra-stripe frequencies. In this case we found that this zebra can be also explained in the model with the zebra-stripe sources in a single loop. Both the interpretations are discussed. Title: Topological Structures of Velocity and Electric Field in the Vicinity of a Cusp-type Magnetic Null Point Authors: Nickeler, Dieter H.; Karlický, Marian; Kraus, Michaela Bibcode: 2019ApJ...873...41N Altcode: 2019arXiv190109913N Topological characteristics reveal important physical properties of plasma structures and astrophysical processes. Physical parameters and constraints are linked with topological invariants, which are important for describing magnetic reconnection scenarios. We analyze stationary nonideal Ohm’s law concerning the Poincaré classes of all involved physical fields in two dimensions by calculating the corresponding topological invariants of their Jacobian (here: particularly the eigenvalues) or Hessian matrices. The magnetic field is assumed to have a cusp structure, and the stagnation point of the plasma flow coincides with the cusp. We find that the stagnation point must be hyperbolic. Furthermore, the functions describing both the resistivity and the ohmic heating have a saddle-point structure, being displaced with respect to the cusp point. These results imply that there is no monotonous relation between current density and anomalous resistivity in the case of a two-dimensional standard magnetic cusp. Title: Growth Rates of the Upper-Hybrid Waves for Power-Law and Kappa Distributions with a Loss-Cone Anisotropy Authors: Yasnov, L. V.; Benáček, J.; Karlický, M. Bibcode: 2019SoPh..294...29Y Altcode: 2019arXiv190405110Y Fine structures of radio bursts play an important role in the diagnostics of the solar flare plasma. Among them the zebras, which are prevalently assumed to be generated by the double-plasma resonance instability, belong to the most important ones. In this paper we compute the growth rate of this instability for two types of the electron distribution: a) for the power-law distribution and b) for the kappa distribution, in both cases with the loss-cone type anisotropy. We find that the growth rate of the upper-hybrid waves for the power-law momentum distribution strongly depends on the pitch-angle boundary. The maximum growth rate is found for the pitch angle θc≈50∘. For small angles the growth rate profile is very flat and for high pitch angles the wave absorption occurs. Furthermore, analyzing the growth rate of the upper-hybrid waves for the kappa momentum distribution we find that a decrease of the characteristic momentum pκ shifts the maximum of the growth rate to lower values of the ratio of the electron-plasma and electron-cyclotron frequencies, and the frequency widths of the growth rate peaks are very broad. But if we consider the kappa distribution which is isotropic up to some large momentum pm and anisotropic with loss-cone above this momentum then distinct peaks of the growth rate appear and thus distinct zebra stripes can be generated. It means that the restriction of small momenta for the anisotropic part of distributions is of principal importance for the zebra stripe generation. Finally, for the zebra stripes observed on 1 August 2010, the growth rates in dependence on the radio frequency are computed. It is shown that in this case the growth rate peaks are more distinct than in usually presented dependencies of growth rates on the ratio of the plasma and cyclotron frequencies. Title: Pulse-beam heating of deep atmospheric layers triggering their oscillations and upwards moving shocks that can modulate the reconnection in solar flares Authors: Jelínek, P.; Karlický, M. Bibcode: 2019arXiv190200292J Altcode: We study processes occurring after a sudden heating of the chromosphere at the flare arcade footpoints which is assumed to be caused by particle beams. For the numerical simulations we adopt a 2-D magnetohydrodynamic (MHD) model, in which we solve a full set of the time-dependent MHD equations by means of the FLASH code, using the Adaptive Mesh Refinement (AMR) method. In the initial state we consider a model of the solar atmosphere with densities according to the VAL-C model and the magnetic field arcade having the X-point structure above, where the magnetic reconnection is assumed. We found that the sudden pulse-beam heating of the chromosphere at the flare arcade footpoints generates magnetohydrodynamic shocks, one propagating upwards and the second one propagating downwards in the solar atmosphere. The downward moving shock is reflected at deep and dense atmospheric layers and triggers oscillations of these layers. These oscillations generate the upwards moving magnetohydrodynamic waves that can influence the above located magnetic reconnection in a quasi-periodic way. Because these processes require a sudden heating in very localized regions in the chromosphere therefore they can be also associated with seismic waves. Title: Determination of Plasma Parameters in Radio Sources of Solar Zebra-patterns Based on Relations between the Zebra-stripe Frequencies and Gyro-harmonic Numbers Authors: Karlický, Marian; Yasnov, Leonid V. Bibcode: 2018ApJ...867...28K Altcode: Solar radio zebras belong to the most important radio fine structures used in diagnostics of solar flare plasmas. In the present paper, assuming the double plasma-resonance model of zebras, we study the relation between zebra-stripe frequencies and gyro-harmonic numbers. We artificially generated two possible types of zebras: the zebra with Sequence A and Sequence B, where an increase of the zebra-stripe frequency corresponds to decrease or increase of the gyro-harmonic number. Analyzing these ideal zebras, we found that the frequency ratios of the neighboring zebra stripes increase in zebras with Sequence A and decrease in zebras with Sequence B. This criterion and corresponding diagrams were applied for nine observed zebras. All these zebras were found to be with Sequence A. Then we checked and confirmed these results by using the new numerical method, where the gyro-harmonic numbers of the zebra stripes with the lowest frequency s 1 were also determined. We found that in all these zebras, the spatial scale of the magnetic field in the zebra-stripe sources was always shorter than that of the plasma density. Knowing the gyro-harmonic numbers and corresponding zebra-stripe frequencies, we determined the magnetic field and plasma density in zebra sources to be 0.84-37.31 G and 0.026 × 1010-16.03 × 1010 cm-3, respectively. Finally, we found that with increasing the gyro-harmonic number s 1, the ratio of perpendicular and parallel scales of the magnetic field and plasma density in the zebra-stripe sources also increases. Title: Fourier Power Spectra of Solar Noise Storms Authors: Karlický, Marian; Rybák, Ján; Monstein, Christian Bibcode: 2018SoPh..293..143K Altcode: We analyzed three noise storms recorded on 200 - 400 MHz Trieste Callisto radio spectra on 2 July 2012, 8 July 2012, and 16 July 2012 by the Fourier method. We divided intervals of the noise storms into five-minute intervals, and in these intervals we computed the mean Fourier spectra as a function of the wave numbers in the frequency and height-scale spaces. We found that these Fourier spectra, where the spectrum from the quiet-activity interval was subtracted, are power-law spectra. The mean power-law index of these spectra in the range ln(kz)=[1.8 ,2.9 ] (where kz is the wave number in the height-scale space) is −1.7 ±0.14 , −1.6 ±0.14 , and −1.5 ±0.12 for the 2 July 2012, the 8 July 2012, and the 16 July 2012 noise storms, respectively. It appears that as the number of Type-I bursts in the studied interval increases, the power-law index becomes closer to −5 /3 ; this is known as the Kolmogorov spectral index. The power-law index of the noise storms is very similar to that of the narrowband dm-spikes found in our previous studies. Furthermore, we found a break in the power spectra at ln(kz)≈2.9 , and the mean power-law index values above this break are −2.9 ±0.46 , −3.1 ±0.65 , and −3.4 ±0.98 , respectively. Title: Double plasma-resonance surfaces in flare loops and radio zebra emission Authors: Karlický, M.; Yasnov, L. Bibcode: 2018A&A...618A..60K Altcode:
Aims: The zebra structures observed in radio waves during solar flares are some of the most important structures used as diagnostics of solar flare plasmas. We here not only analyze the so-called double plasma-resonance (DPR) surfaces, but also estimate the effects of their form on the size of the zebra sources and brightness temperature.
Methods: To compute the DPR surfaces, we used numerical and analytical methods.
Results: We found that except for the case of a constant magnetic field across the loop, the DPR surfaces deviate from the constant plasma density surfaces. We found that the regime with a finite height scale has three forms of resonance surfaces depending on the magnetic field variation across the loop. This magnetic field variation also determines if in the generated zebra structure, an increase in gyro-harmonic number leads to an increase or decrease of the zebra stripe frequency. In the case with an infinite height scale, the resonance surfaces are parallel to the loop axis. Furthermore, we found that for highly polarized zebra structures that are generated at DPR surfaces close to the plasma frequency, the zebra emission is limited to the narrow escaping cone and the emitting source area increases with increasing viewing angle compared to the loop axis. Moreover, with increasing deviation of the DPR surfaces from those of constant density surfaces, the frequency bandwidth of the DPR emission increases and can cause the zebra stripes to overlap, which limits the zebra generation. For the zebra structures observed on 14 February 1999, 6 June 2000, and 1 August 2010 and the observed view perpendicular to the loop axis, we estimated that the brightness temperature is 3.67 × 1014 K, 6.58 × 1013 K, and 7.35 × 1015 K, respectively. These brightness temperatures are much lower than those derived for the view along the loop axis (up to 1017 K), and thus are more realistic. The area of the emitting source for coronal loops in the view perpendicular to the loop axis can be larger by several orders of magnitude than that in the view along the loop axis. Title: Effects of electron distribution anisotropy in spectroscopic diagnostics of solar flares Authors: Dzifčáková, E.; Karlický, M. Bibcode: 2018A&A...618A.176D Altcode:
Aims: We analyzed effects of the bi-Maxwellian electron distribution representing electron temperature anisotropy along and across the magnetic field on the ionization and excitation equilibrium with consequences on the temperature diagnostics of the flare plasma.
Methods: The bi-Maxwellian energy distributions were calculated numerically. Synthetic X-ray line spectra of the bi-Maxwellian distributions were calculated using non-Maxwellian ionization, recombination, excitation and de-excitation rates.
Results: We found that the anisotropic bi-Maxwellian velocity distributions transform to the nonthermal energy distributions with a high-energy tail. Their maximum is shifted to lower energies and contains a higher number of the low-energy particles in comparison with the Maxwellian one. Increasing the deviation of the parameter p = T∥/T⊥ from 1, changes the shape of bi-Maxwellian distributions and ionization equilibrium, and relative line intensities also increase. The effects are more significant for the bi-Maxwellian distribution with T∥ > T⊥. Moreover, considering different acceleration mechanisms and collisional isotropization it is possible that the bi-Maxwellian distributions with high deviations from the Maxwellian distribution are more probable for those with p > 1 than for those with p < 1. Therefore, distributions with p > 1 can be much more easily diagnosed than those with p < 1. Furthermore, we compared the effects of the bi-Maxwellian distributions on the ionization equilibrium and temperature diagnostics with those for the κ-distributions obtained previously. We found that they are similar and at the present state it is difficult to distinguish between the bi-Maxwellian and κ-distributions from the line ratios. Title: Oscillations and Waves in Radio Source of Drifting Pulsation Structures Authors: Karlický, Marian; Rybák, Ján; Bárta, Miroslav Bibcode: 2018SoPh..293...62K Altcode: 2018arXiv180306148K Drifting pulsation structures (DPSs) are considered to be radio signatures of the plasmoids formed during magnetic reconnection in the impulsive phase of solar flares. In the present paper we analyze oscillations and waves in seven examples of drifting pulsation structures, observed by the 800 - 2000 MHz Ondřejov Radiospectrograph. For their analysis we use a new type of oscillation maps, which give us much more information as regards processes in DPSs than that in previous analyses. Based on these oscillation maps, made from radio spectra by the wavelet technique, we recognized quasi-periodic oscillations with periods ranging from about 1 to 108 s in all studied DPSs. This strongly supports the idea that DPSs are generated during a fragmented magnetic reconnection. Phases of most the oscillations in DPSs, especially for the period around 1 s, are synchronized ("infinite" frequency drift) in the whole frequency range of DPSs. For longer periods in some DPSs we found that the phases of the oscillations drift with the frequency drift in the interval from −17 to +287 MHzs−1. We propose that these drifting phases can be caused (a) by the fast or slow magnetosonic waves generated during the magnetic reconnection and propagating through the plasmoid, (b) by a quasi-periodic structure in the plasma inflowing to the reconnection forming a plasmoid, and (c) by a quasi-periodically varying reconnection rate in the X-point of the reconnection close to the plasmoid. Title: Double plasma resonance instability as a source of solar zebra emission Authors: Benáček, J.; Karlický, M. Bibcode: 2018A&A...611A..60B Altcode: 2017arXiv171104281B Context. The double plasma resonance (DPR) instability plays a basic role in the generation of solar radio zebras. In the plasma, consisting of the loss-cone type distribution of hot electrons and much denser and colder background plasma, this instability generates the upper-hybrid waves, which are then transformed into the electromagnetic waves and observed as radio zebras.
Aims: In the present paper we numerically study the double plasma resonance instability from the point of view of the zebra interpretation.
Methods: We use a 3-dimensional electromagnetic particle-in-cell (3D PIC) relativistic model. We use this model in two versions: (a) a spatially extended "multi-mode" model and (b) a spatially limited "specific-mode" model. While the multi-mode model is used for detailed computations and verifications of the results obtained by the "specific-mode" model, the specific-mode model is used for computations in a broad range of model parameters, which considerably save computational time. For an analysis of the computational results, we developed software tools in Python.
Results: First using the multi-mode model, we study details of the double plasma resonance instability. We show how the distribution function of hot electrons changes during this instability. Then we show that there is a very good agreement between results obtained by the multi-mode and specific-mode models, which is caused by a dominance of the wave with the maximal growth rate. Therefore, for computations in a broad range of model parameters, we use the specific-mode model. We compute the maximal growth rates of the double plasma resonance instability with a dependence on the ratio between the upper-hybrid ωUH and electron-cyclotron ωce frequency. We vary temperatures of both the hot and background plasma components and study their effects on the resulting growth rates. The results are compared with the analytical ones. We find a very good agreement between numerical and analytical growth rates. We also compute saturation energies of the upper-hybrid waves in a very broad range of parameters. We find that the saturation energies of the upper-hybrid waves show maxima and minima at almost the same values of ωUH/ωce as the growth rates, but with a higher contrast between them than the growth rate maxima and minima. The contrast between saturation energy maxima and minima increases when the temperature of hot electrons increases. Furthermore, we find that the saturation energy of the upper-hybrid waves is proportional to the density of hot electrons. The maximum saturated energy can be up to one percent of the kinetic energy of hot electrons. Finally we find that the saturation energy maxima in the interval of ωUH/ωce = 3-18 decrease according to the exponential function. All these findings can be used in the interpretation of solar radio zebras. 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: Very rare bursts observed in the 0.8-2.0 GHz solar radio spectra Authors: Jiřička, K.; Karlický, M. Bibcode: 2018CEAB...42....5J Altcode: Besides typical and known radio bursts there are very rare bursts that are not up to now commonly known and explained. In more than twenty years of observations in the 0.8-2.0 GHz frequency range by the Ondřejov radiospectrograph we found several such very rare bursts. In this paper six examples of them are presented and described. Title: Brightness Temperature of Radio Zebras and Wave Energy Densities in Their Sources Authors: Yasnov, L. V.; Benáček, J.; Karlický, M. Bibcode: 2017SoPh..292..163Y Altcode: 2017arXiv170201278Y We estimated the brightness temperature of radio zebras (zebra pattern - ZP), considering that ZPs are generated in loops having an exponential density profile in their cross section. We took into account that when in a plasma there is a source emitting in all directions, then in the escape process from the plasma the emission has a directional character nearly perpendicular to the constant-density profile. Owing to the high directivity of the plasma emission (for emission at frequencies close to the plasma frequency), the region from which the emission escapes can be very small. We estimated the brightness temperature of three observed ZPs for two values of the density scale height (1 and 0.21 Mm) and two values of the loop width (1 and 2 arcsec). In all cases, high brightness temperatures were obtained. For the higher value of the density scale height, the brightness temperature was estimated to be 1.1 ×1015 - 1.3 ×1017K, and for the lower value, it was 4.7 ×1013 - 5.6 ×1015K. These temperatures show that the observational probability of a burst with a ZP, which is generated in the transition region with a steep gradient of the plasma density, is significantly higher than for a burst generated in a region with smoother changes of the plasma density. We also computed the saturation energy density of the upper-hybrid waves (according to the double plasma resonance model, they are generated in the zebra source) using a 3D particle-in-cell model with a loss-cone type of distribution of hot electrons. We found that this saturated energy is proportional to the ratio of hot electron and background plasma densities. Thus, comparing the growth rate and collisional damping of the upper-hybrid waves, we estimated minimum densities of hot electrons as well as the minimum value of the saturation energy density of the upper-hybrid waves. Finally, we compared the computed energy density of the upper-hybrid waves with the energy density of the electromagnetic waves in the zebra source and thus estimated the efficiency of the wave transformation. Title: Oscillations Excited by Plasmoids Formed During Magnetic Reconnection in a Vertical Gravitationally Stratified Current Sheet Authors: Jelínek, P.; Karlický, M.; Van Doorsselaere, T.; Bárta, M. Bibcode: 2017ApJ...847...98J Altcode: 2017arXiv170306674J Using the FLASH code, which solves the full set of the 2D non-ideal (resistive) time-dependent magnetohydrodynamic (MHD) equations, we study processes during the magnetic reconnection in a vertical gravitationally stratified current sheet. We show that during these processes, which correspond to processes in solar flares, plasmoids are formed due to the tearing mode instability of the current sheet. These plasmoids move upward or downward along the vertical current sheet and some of them merge into larger plasmoids. We study the density and temperature structure of these plasmoids and their time evolution in detail. We found that during the merging of two plasmoids, the resulting larger plasmoid starts to oscillate with a period largely determined by L/{c}{{A}}, where L is the size of the plasmoid and c A is the Alfvén speed in the lateral parts of the plasmoid. In our model, L/{c}{{A}} evaluates to ∼ 25 {{s}}. Furthermore, the plasmoid moving downward merges with the underlying flare arcade, which causes oscillations of the arcade. In our model, the period of this arcade oscillation is ∼ 35 {{s}}, which also corresponds to L/{c}{{A}}, but here L means the length of the loop and c A is the average Alfvén speed in the loop. We also show that the merging process of the plasmoid with the flare arcade is a complex process as presented by complex density and temperature structures of the oscillating arcade. Moreover, all these processes are associated with magnetoacoustic waves produced by the motion and merging of plasmoids. Title: Hot-cold plasma transition region: collisionless case Authors: Karlicky, Marian; Karlicky, Frantisek Bibcode: 2017arXiv170907622K Altcode: We study processes at the transition region between hot (rare) and cold (dense) plasma in the collisionless regime. We use a 3-dimensional electromagnetic particle-in-cell (3-D PIC) relativistic code. Motivated by the transition region in the solar atmosphere the temperature and density ratio of the plasmas is chosen as 100 and 0.01, respectively. For better understanding of studied processes we make two types of computations: a) without any interactions among plasma particles (free expansion) and b) with the full electromagnetic interactions. In both the cases we found that the flux of cold plasma electrons and protons from colder plasma to hotter one dominates over the flux of hot plasma electrons and protons in the opposite direction. Thus, the plasma in the hotter part of the system becomes colder and denser during time evolution. In the case without any interactions among particles the cold plasma electrons and protons freely penetrate into the hot plasma. But, the cold plasma electrons are faster than cold plasma protons and therefore they penetrate deeper into the hotter part of the system than the protons. Thus, the cooling of the electron and proton components of the plasma in the hotter part of the system is different. On the other hand, in the case with the electromagnetic interactions, owing to the plasma property, which tries to keep the total electric current constant everywhere (close to zero in our case), the cold plasma electrons penetrate into the hotter part of the system together with the cold plasma protons. The plasma waves generated at the transition region during these processes reduce the number of electrons escaping from the hot plasma into the colder one. Therefore these waves support a temperature jump between hot and cold plasma. Title: Fast-mode Coronal EUV Wave Trains Associated with Solar Flares and CMEs Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Karlicky, Marian; Chen, Bin Bibcode: 2017SPD....48.0401L Altcode: As a new observational phenomenon, Quasi-periodic, Fast Propagating EUV wave trains (QFPs) are fast-mode magnetosonic waves closely related to quasi-periodic pulsations commonly detected in solar flares (traditionally with non-imaging observations). They can provide critical clues to flare energy release and serve as new tools for coronal seismology. We report recent advances in observing and modeling QFPs, including evidence of heating and cooling cycles revealed with differential emission measure (DEM) analysis that are consistent with alternating compression and rarefaction expected for magnetosonic waves. Through a statistical survey, we found a preferential association of QFPs with eruptive flares (with CMEs) rather than confined flares (without CMEs). We also identified some correlation with quasi-periodic radio bursts observed at JVLA and Ondrejov observatories. We will discuss the implications of these results and the potential roles of QFPs in coronal heating and energy transport. Title: Oscillations in the 45 - 5000 MHz Radio Spectrum of the 18 April 2014 Flare Authors: Karlický, Marian; Rybák, Ján; Monstein, Christian Bibcode: 2017SoPh..292...94K Altcode: 2017arXiv170602836K Using a new type of oscillation map, made from the radio spectra by the wavelet technique, we study the 18 April 2014 M7.3 flare (SOL2014-04-18T13:03:00L245C017). We find a quasi-periodic character of this flare with periods in the range 65 - 115 seconds. At the very beginning of this flare, in connection with the drifting pulsation structure (plasmoid ejection), we find that the 65 - 115 s oscillation phase slowly drifts towards lower frequencies, which indicates an upward propagating wave initiated at the start of the magnetic reconnection. Many periods (1 - 200 seconds) are found in the drifting pulsation structure, which documents multi-scale and multi-periodic processes. On this drifting structure, fiber bursts with a characteristic period of about one second are superimposed, whose frequency drift is similar to that of the drifting 65 - 115 s oscillation phase. We also checked periods found in this flare by the EUV Imaging Spectrometer (EIS)/Hinode and Interface Region Imaging Spectrograph (IRIS) observations. We recognize the type III bursts (electron beams) as proposed, but their time coincidence with the EIS and IRIS peaks is not very good. The reason probably is that the radio spectrum is a whole-disk record consisting of all bursts from any location, while the EIS and IRIS peaks are emitted only from locations of slits in the EIS and IRIS observations. Title: Shock-reflected electrons and X-ray line spectra Authors: Dzifčáková, E.; Vandas, M.; Karlický, M. Bibcode: 2017A&A...603A..17D Altcode: 2017arXiv170511007D
Aims: The aim of this paper is to try to explain the physical origin of the non-thermal electron distribution that is able to form the enhanced intensities of satellite lines in the X-ray line spectra observed during the impulsive phases of some solar flares.
Methods: Synthetic X-ray line spectra of the distributions composed of the distribution of shock reflected electrons and the background Maxwellian distribution are calculated in the approximation of non-Maxwellian ionization, recombination, excitation and de-excitation rates. The distribution of shock reflected electrons is determined analytically.
Results: We found that the distribution of electrons reflected at the nearly-perpendicular shock resembles, at its high-energy part, the so called n-distribution. Therefore it could be able to explain the enhanced intensities of Si xiid satellite lines. However, in the region immediately in front of the shock its effect is small because electrons in background Maxwellian plasma are much more numerous there. Therefore, we propose a model in which the shock reflected electrons propagate to regions with smaller densities and different temperatures. Combining the distribution of the shock-reflected electrons with the Maxwellian distribution having different densities and temperatures we found that spectra with enhanced intensities of the satellite lines are formed at low densities and temperatures of the background plasma when the combined distribution is very similar to the n-distribution also in its low-energy part. In these cases, the distribution of the shock-reflected electrons controls the intensity ratio of the allowed Si xiii and Si xiv lines to the Si xiid satellite lines. The high electron densities of the background plasma reduce the effect of shock-reflected electrons on the composed electron distribution function, which leads to the Maxwellian spectra. Title: Chains of type-I radio bursts and drifting pulsation structures Authors: Karlický, M. Bibcode: 2017A&A...602A.122K Altcode:
Aims: Owing to similarities of chains of type-I radio bursts and drifting pulsation structures the question arises as to whether both these radio bursts are generated by similar processes.
Methods: Characteristics and parameters of both these radio bursts are compared.
Results: We present examples of both types of bursts and show their similarities and differences. Then, for chains of type-I bursts, a similar model as for drifting pulsation structures (DPSs) is proposed. We show that, similar to the DPS model, the chains of type-I bursts can be generated by the fragmented magnetic reconnection associated with plasmoid interactions. To support this new model of chains of type-I bursts, we present an effect of merging two plasmoids to form one larger plasmoid on the radio spectrum of DPS. This process can also explain the `wavy' appearance of some chains of type-I bursts. Further, we show that the chains of type-I bursts with the wavy appearance can be used for estimation of the magnetic field strength in their sources. We think that differences of chains of type-I bursts and DPSs are mainly owing to different regimes of the magnetic field reconnection. While in the case of chains of type-I bursts, the magnetic reconnection and plasmoid interactions are in the quasi-separatrix layer of the active region in more or less quasi-saturated regime, in the case of DPSs, observed in the impulsive phase of eruptive flares, the magnetic reconnection and plasmoid interactions are in the current sheet formed under the flare magnetic rope, which moves upwards and forces this magnetic reconnection. Title: Are chains of type I radio bursts generated by similar processes as drifting pulsation structures observed during solar flares? Authors: Karlicky, Marian Bibcode: 2017arXiv170408532K Altcode: We present examples of the both types of bursts and show their similarities and differences. Then for chains of type I bursts a similar model as for drifting pulsation structures (DPSs) is proposed. We show that similarly as in the DPS, the chains of type I bursts can be generated by the fragmented magnetic reconnection associated with plasmoids interactions. To support this new model of chains of type I bursts, we present an effect of merging of two plasmoids to one larger plasmoid on the radio spectrum of DPS. This process can also explain the "wavy" appearance of some chains of type I bursts. Then we show that the chains of type I bursts with the "wavy" appearance can be used for estimation of the magnetic field strength in their sources. We think that differences of chains of type I bursts and DPSs are mainly owing to different regimes of the magnetic field reconnection. While in the case of chains of type I bursts the magnetic reconnection and plasmoid interactions are in the quasi-separatrix layer of the active region in more or less quasi-saturated regime, in the case of DPSs, observed in the impulsive phase of eruptive flares, the magnetic reconnection and plasmoids interactions are in the current sheet formed under the flare magnetic rope, which moves upwards and forces this magnetic reconnection. Title: Investigating the Origins of Two Extreme Solar Particle Events: Proton Source Profile and Associated Electromagnetic Emissions Authors: Kocharov, Leon; Pohjolainen, Silja; Mishev, Alexander; Reiner, Mike J.; Lee, Jeongwoo; Laitinen, Timo; Didkovsky, Leonid V.; Pizzo, Victor J.; Kim, Roksoon; Klassen, Andreas; Karlicky, Marian; Cho, Kyung-Suk; Gary, Dale E.; Usoskin, Ilya; Valtonen, Eino; Vainio, Rami Bibcode: 2017ApJ...839...79K Altcode: We analyze the high-energy particle emission from the Sun in two extreme solar particle events in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth’s magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 1998 May 2 event is associated with a flare and a coronal mass ejection (CME), which were well observed by the Nançay Radioheliograph, thus the images of the radio sources are available. For the 2003 November 2 event, the low corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory are available. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images, and other data available for both events. We find a common scenario for both eruptions, including the flare’s dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME. Title: Electric Current Filamentation Induced by 3D Plasma Flows in the Solar Corona Authors: Nickeler, Dieter H.; Wiegelmann, Thomas; Karlický, Marian; Kraus, Michaela Bibcode: 2017ApJ...837..104N Altcode: 2017arXiv170203986N Many magnetic structures in the solar atmosphere evolve rather slowly, so they can be assumed as (quasi-)static or (quasi-)stationary and represented via magnetohydrostatic (MHS) or stationary magnetohydrodynamic (MHD) equilibria, respectively. While exact 3D solutions would be desired, they are extremely difficult to find in stationary MHD. We construct solutions with magnetic and flow vector fields that have three components depending on all three coordinates. We show that the noncanonical transformation method produces quasi-3D solutions of stationary MHD by mapping 2D or 2.5D MHS equilibria to corresponding stationary MHD states, that is, states that display the same field-line structure as the original MHS equilibria. These stationary MHD states exist on magnetic flux surfaces of the original 2D MHS states. Although the flux surfaces and therefore also the equilibria have a 2D character, these stationary MHD states depend on all three coordinates and display highly complex currents. The existence of geometrically complex 3D currents within symmetric field-line structures provides the basis for efficient dissipation of the magnetic energy in the solar corona by ohmic heating. We also discuss the possibility of maintaining an important subset of nonlinear MHS states, namely force-free fields, by stationary flows. We find that force-free fields with nonlinear flows only arise under severe restrictions of the field-line geometry and of the magnetic flux density distribution. Title: Temperature dependent growth rates of the upper-hybrid waves and solar radio zebra patterns Authors: Benáček, J.; Karlický, M.; Yasnov, L. V. Bibcode: 2017A&A...598A.106B Altcode: 2017arXiv170106520B Context. The zebra patterns observed in solar radio emission are very important for flare plasma diagnostics. The most promising model of these patterns is based on double plasma resonance instability, which generates upper-hybrid waves, which can be then transformed into the zebra emission.
Aims: We aim to study in detail the double plasma resonance instability of hot electrons, together with a much denser thermal background plasma. In particular, we analyse how the growth rate of the instability depends on the temperature of both the hot plasma and background plasma components.
Methods: We numerically integrated the analysed model equations, using Python and Wolfram Mathematica.
Results: We found that the growth-rate maxima of the upper-hybrid waves for non-zero temperatures of both the hot and background plasma are shifted towards lower frequencies comparing to the zero temperature case. This shift increases with an increase of the harmonic number s of the electron cyclotron frequency and temperatures of both hot and background plasma components. We show how this shift changes values of the magnetic field strength estimated from observed zebras. We confirmed that for a relatively low hot electron temperature, the dependence of growth rate vs. both the ratio of the electron plasma and electron cyclotron frequencies expresse distinct peaks, and by increasing this temperature these peaks become smoothed. We found that in some cases, the values of wave number vector components for the upper-hybrid wave for the maximal growth rate strongly deviate from their analytical estimations. We confirmed the validity of the assumptions used when deriving model equations. Title: Oscillation Maps in the Broadband Radio Spectrum of the 1 August 2010 Event Authors: Karlický, M.; Rybák, J. Bibcode: 2017SoPh..292....1K Altcode: 2016arXiv161102074K We search for indications of waves in the 25 - 2000 MHz radio spectrum of the 1 August 2010 event (SOL2010-08-01T08:57:00L075C013), where fast propagating waves in the solar corona with periods of 181, 69, and 40 seconds were detected in UV observations. Using the wavelet technique, we construct a new type of oscillation map for selected periods in the whole domain of the radio spectrum. While an oscillation with a period of 181 seconds was recognized in the whole 25 - 2000 MHz radio spectrum, oscillations with periods of 69 and 40 seconds were only confirmed in the 250 - 870 MHz frequency range. In the 800 - 2000 MHz range we found periods of 50 and 80 seconds. Moreover, in the 250 - 870 MHz frequency range, an oscillation with a period of about 420 seconds was detected. We also made maps of phases of the 181-second oscillations in order to analyze their frequency drift. At the beginning of the radio event, the phase of the 181-second oscillation in the 2000 - 500 MHz frequency range drifts toward lower frequencies. On the other hand, we found that the phase is nearly synchronous at frequencies 25 - 500 MHz. While the phase drift at higher frequencies can be interpreted as being caused by the UV wave, the synchronization of the phase on lower frequencies is explained by the fast electron beams, whose acceleration is modulated by the UV wave. Owing to this modulation, the electron beams are accelerated with the period of the UV wave (181 seconds). These beams propagate upward through the solar corona and generate the 25 - 500 MHz radio emission with the 181-second period. The 25 - 500 MHz radio emission, which corresponds to a large interval of heights in the solar corona, is nearly synchronous because of the high beam velocity (≈c /3 , where c is the light speed). Title: Origin of two extreme solar particle events Authors: Mishev, A.; Kocharov, L.; Pohjolainen, S.; Reiner, M. J.; Lee, J.; Laitinen, T.; Didkovsky, L. V.; Pizzo, V. J.; Kim, R.; Klassen, A.; Karlicky, M.; Choj, K. S.; Kovaltsov, G. A.; Usoskin, I. G.; Valtonen, E.; Vainio, R. Bibcode: 2017ICRC...35..146M Altcode: 2017PoS...301..146M No abstract at ADS Title: Torsional oscillations and observed rotational period variations in early-type stars Authors: Krtička, J.; Mikulášek, Z.; Henry, G. W.; Kurfürst, P.; Karlický, M. Bibcode: 2017MNRAS.464..933K Altcode: 2016arXiv160907914K Some chemically peculiar stars in the upper main sequence show rotational period variations of unknown origin. We propose that these variations are a consequence of the propagation of internal waves in magnetic rotating stars that lead to the torsional oscillations of the star. We simulate the magnetohydrodynamic waves and calculate resonant frequencies for two stars that show rotational variations: CU Vir and HD 37776. We provide updated analyses of rotational period variations in these stars and compare our results with numerical models. For CU Vir, the length of the observed rotational period cycle, Π=67.6(5) yr, can be well reproduced by the models, which predict a cycle length of 51 yr. However, for HD 37776, the observed lower limit of the cycle length, Π ≥ 100 yr, is significantly longer than the numerical models predict. We conclude that torsional oscillations provide a reasonable explanation at least for the observed period variations in CU Vir. Title: Differential rotation, flares and coronae in A to M stars Authors: Balona, L. A.; Švanda, M.; Karlický, M. Bibcode: 2016MNRAS.463.1740B Altcode: 2016MNRAS.tmp.1226B Kepler data are used to investigate flares in stars of all spectral types. There is a strong tendency across all spectral types for the most energetic flares to occur among the most rapidly rotating stars. Differential rotation could conceivably play an important role in enhancing flare energies. This idea was investigated, but no correlation could be found between rotational shear and the incidence of flares. Inspection of Kepler light curves shows that rotational modulation is very common over the whole spectral type range. Using the rotational light amplitude, the size distribution of star-spots was investigated. Our analysis suggests that stars with detectable flares have spots significantly larger than non-flare stars, indicating that flare energies are correlated with the size of the active region. Further evidence of the existence of spots on A stars is shown by the correlation between the photometric period and the projected rotational velocity. The existence of spots indicates the presence of magnetic fields, but the fact that A stars lack coronae implies that surface convection is a necessary condition for the formation of the corona. Title: Flares on A-type Stars: Evidence for Heating of Solar Corona by Nanoflares? Authors: Švanda, Michal; Karlický, Marian Bibcode: 2016ApJ...831....9S Altcode: 2016arXiv160803494S We analyzed the occurrence rates of flares on stars of spectral types K, G, F, and A, observed by Kepler. We found that the histogram of occurrence frequencies of stellar flares is systematically shifted toward a high-energy tail for A-type stars compared to stars of cooler spectral types. We extrapolated the fitted power laws toward flares with smaller energies (nanoflares) and made estimates for total energy flux to stellar atmospheres by flares. We found that, for A-type stars, the total energy flux density was at least four-times smaller than for G stars. We speculate that this deficit in energy supply may explain the lack of hot coronae on A-type stars. Our results indicate the importance of nanoflares for heating and formation of the solar corona. Title: Diagnosing the Source Region of a Solar Burst on 26 September 2011 by Using Microwave Type-III Pairs Authors: Tan, B. L.; Karlický, M.; Mészárosová, H.; Kashapova, L.; Huang, J.; Yan, Y.; Kontar, E. P. Bibcode: 2016SoPh..291.2407T Altcode: 2016SoPh..tmp..143T; 2016arXiv160605410T We report a peculiar and interesting train of microwave Type-III pair bursts in the impulsive rising phase of a solar flare on 26 September 2011. The observations include radio spectrometers at frequencies of 0.80 - 2.00 GHz from the Ondřejov radiospectrograph in the Czech Republic (ORSC), hard X-ray from the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and Gamma-Ray Burst Monitor onboard the Fermi Space Telescope (Fermi/GRB), EUV images from the Sun Watcher using APS detectors and image Processing instrument onboard the Project for Onboard Autonomy 2 (SWAP/PROBA2), and magnetograms from the Helioseismic and Magnetic Imager onboard the Solar Dynamic Observatory (SDO/HMI). By using a recently developed method (Tan et al., Res. Astron. Astrophys.16, 82, 2016a), we diagnosed the plasma density, temperature, plasma-β , magnetic field near the source region, the energy of energetic electrons, and the distance between the acceleration region and the emission start sites of Type-III bursts. From the diagnostics, we find that i) The plasma density, temperature, magnetic field, and the distance between the acceleration region and the emission start sites have almost no obvious variations during the period of Type-III pair trains, while the energy of electrons has an obvious peak value that is consistent with the hard X-ray emission. ii) The plasma-β is much higher than unity, showing a highly dynamic process near the emission start site of Type-III bursts. iii) Although the reversed-slope Type-III branches drift more slowly by one order of magnitude than that of the normal Type-IIIs, the related descending and ascending electrons still could have energy of the same order of magnitude. These facts indicate that both the ascending and descending electrons are possibly accelerated by a similar mechanism and in a small source region. These diagnostics can help us to understand the physics in the source region of solar bursts. Title: Shock-drift accelerated electrons and n-distribution Authors: Vandas, Marek; Karlicky, Marian Bibcode: 2016usc..confE.124V Altcode: Recently soft X-ray spectra observed during the impulsive phase of several solar flares have been explained by the presence of the n-distribution function of superthermal electrons. We examine if electrons with such a distribution function can be produced in a shock, e.g. in a flare termination shock. The distribution functions of reflected electrons at quasi-perpendicular shocks are analytically derived and compared with the n-distributions. We consider an influence of the electrostatic cross-shock potential, shock curvature, and a role of the upstream seed population on these distributions. We found that a high-energy part of the distribution of electrons reflected at a quasi-perpendicular shock could be very well fitted by the n-distribution. It gives a chance to detect the flare termination shock. Title: Physical Conditions in the Source Region of a Zebra Structure Authors: Yasnov, L. V.; Karlický, M.; Stupishin, A. G. Bibcode: 2016SoPh..291.2037Y Altcode: 2016SoPh..tmp..118Y We analyze the physical conditions in the source region of a zebra structure, observed with the Ondřejov radiospectrograph during the 1 August 2010 solar flare. To determine the gyro-frequency harmonic numbers of the observed zebra lines, we compute the magnetic field strength, the electron density, and their spatial scales in the source region of the zebra structure. The region where the flare occurred is analyzed using EUV (171 Å and 335 Å) observations. To determine the conditions in the zebra source region, the magnetic field structure is reconstructed using observed photospheric magnetic field data. By computing the dependence of the magnetic field vs. height in this reconstruction and by comparing the magnetic field strength derived from the zebra structure, we determine the dependence of the electron density vs. height in the zebra source-region. We identify the loops where the zebra structure was generated at heights of about 2.5 - 3.3 Mm. Assuming the barometric law for the electron density, we determine the temperature in the zebra source-region to be T ≈2.0 ×104K. Comparing the obtained values of the temperature and electron density in the zebra source-region with a model of the solar atmosphere, we find that the zebra structure was generated in the transition region, in agreement with our previous results. Title: Shock-drift accelerated electrons and n-distribution Authors: Vandas, Marek; Karlicky, Marian Bibcode: 2016cosp...41E1982V Altcode: Recently soft X-ray spectra observed during the impulsive phase of several solar flares have been explained by the presence of the n-distribution function of superthermal electrons. We examine if electrons with such a distribution function can be produced in a shock, e.g. in a flare termination shock. The distribution functions of reflected electrons at quasi-perpendicular shocks are analytically derived and compared with the n-distributions. We consider an influence of the electrostatic cross-shock potential, shock curvature, and a role of the upstream seed population on these distributions. We found that a high-energy part of the distribution of electrons reflected at a quasi-perpendicular shock could be very well fitted by the n-distribution. It gives a chance to detect the flare termination shock. Title: Shock-drift accelerated electrons and n-distribution Authors: Vandas, M.; Karlický, M. Bibcode: 2016A&A...591A.127V Altcode:
Aims: By analyzing soft X-ray spectra observed during the impulsive phase of several solar flares, the n-distribution function of superthermal electrons has been detected. In the paper we try to answer the question of whether electrons with this type of distribution function can be produced in a shock, e.g. in a flare termination shock.
Methods: We use analytical and numerical methods to compute distribution functions of electrons accelerated by a shock.
Results: We analytically derive the distribution functions of reflected electrons at quasi-perpendicular shocks. We also consider the influence of the electrostatic cross-shock potential, shock curvature, and the role of the upstream seed population on these distributions. The computed distributions are compared with the n-distributions. We found that a high-energy part of the distribution of electrons reflected at a quasi-perpendicular shock can be very well fitted by the n-distribution in all the cases we studied. This provides a chance to detect the flare termination shock. Title: Diagnosing physical conditions near the flare energy-release sites from observations of solar microwave type III bursts Authors: Tan, Bao-Lin; Karlický, Marian; Mészárosová, Hana; Huang, Guang-Li Bibcode: 2016RAA....16...82T Altcode: 2016RAA....16e..13T; 2015arXiv151108863T In the physics of solar flares, it is crucial to diagnose the physical conditions near the flare energy-release sites. However, so far it is unclear how to diagnose these physical conditions. A solar microwave type III burst is believed to be a sensitive signature of primary energy release and electron accelerations in solar flares. This work takes into account the effect of the magnetic field on the plasma density and develops a set of formulas which can be used to estimate the plasma density, temperature, magnetic field near the magnetic reconnection site and particle acceleration region, and the velocity and energy of electron beams. We apply these formulas to three groups of microwave type III pairs in an X-class flare, and obtained some reasonable and interesting results. This method can be applied to other microwave type III bursts to diagnose the physical conditions of source regions, and provide some basic information to understand the intrinsic nature and fundamental processes occurring near the flare energy-release sites. 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: Quasi-periodic processes in the flare loop generated by sudden temperature enhancements at loop footpoints Authors: Karlický, M.; Jelínek, P. Bibcode: 2016A&A...590A...4K Altcode:
Aims: During the impulsive flare phase, the plasma at the flare loop footpoints is rapidly heated by particle beams. In the present paper, we study processes that occur after this sudden heating in a two-dimensional magnetic loop.
Methods: We adopt a 2D magnetohydrodynamic (MHD) model, in which we solve a full set of the ideal time-dependent MHD equations by means of the FLASH code, using the adaptive mesh refinement (AMR) method. Periods in the processes are estimated by the wavelet analysis technique.
Results: We consider a model of the solar atmosphere with a symmetric magnetic loop. The length of this loop in the corona is approximately 21.5 Mm. At both loop footpoints, at the transition region, we initiate the Gaussian temperature (pressure) perturbation with the maximum temperature 14, 7, or 3.5 times higher than the unperturbed temperature. In the corona, the perturbations produce supersonic blast shocks with the Mach number of about 1.1, but well below Alfvén velocities. We consider cases with the same perturbations at both footpoints (symmetric case) and one with different perturbations (asymmetric case). In the symmetric case, the shocks move along both loop legs upwards to the top of the loop, where they interact and form a transient compressed region. Then they continue in their motion to the transition region at the opposite side of the loop, where they are reflected upwards, and so on. At the top of the loop, the shock appears periodically with the period of about 170 s. In the loop legs during this period, a double peak of the plasma parameters, which is connected with two arrivals of shocks, is detected: firstly, when the shock moves up and then when the shock, propagating from the opposite loop leg, moves down. Increasing the distance of the detection point in the loop leg from the top of the loop, the time interval between these shock arrivals increases. Thus, at these detection points, the processes with shorter periods can be detected. After ~500 s the process with the periodically interacting shocks slowly changes to slow mode magnetosonic free oscillation. Furthermore, we detected quasi-periodic processes, even in the chromosphere under the location of the pressure perturbation. These processes can be observed in intensities and Doppler shifts of optical chromospheric lines. In the case with the asymmetric perturbations, we found that the processes are even more complex. Title: Solar Science with the Atacama Large Millimeter/Submillimeter Array—A New View of Our Sun Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu, B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin, P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz, A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.; Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary, D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.; Selhorst, C. L.; Barta, M. Bibcode: 2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere—a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases. Title: Magnetohydrodynamic Oscillations in the Solar Corona and Earth's Magnetosphere: Towards Consolidated Understanding Authors: Nakariakov, V. M.; Pilipenko, V.; Heilig, B.; Jelínek, P.; Karlický, M.; Klimushkin, D. Y.; Kolotkov, D. Y.; Lee, D. -H.; Nisticò, G.; Van Doorsselaere, T.; Verth, G.; Zimovets, I. V. Bibcode: 2016SSRv..200...75N Altcode: 2016SSRv..tmp....2N Magnetohydrodynamic (MHD) oscillatory processes in different plasma systems, such as the corona of the Sun and the Earth's magnetosphere, show interesting similarities and differences, which so far received little attention and remain under-exploited. The successful commissioning within the past ten years of THEMIS, Hinode, STEREO and SDO spacecraft, in combination with matured analysis of data from earlier spacecraft (Wind, SOHO, ACE, Cluster, TRACE and RHESSI) makes it very timely to survey the breadth of observations giving evidence for MHD oscillatory processes in solar and space plasmas, and state-of-the-art theoretical modelling. The paper reviews several important topics, such as Alfvénic resonances and mode conversion; MHD waveguides, such as the magnetotail, coronal loops, coronal streamers; mechanisms for periodicities produced in energy releases during substorms and solar flares, possibility of Alfvénic resonators along open field lines; possible drivers of MHD waves; diagnostics of plasmas with MHD waves; interaction of MHD waves with partly-ionised boundaries (ionosphere and chromosphere). The review is mainly oriented to specialists in magnetospheric physics and solar physics, but not familiar with specifics of the adjacent research fields. Title: Quasi-periodic fast-mode magnetosonic wave trains within coronal waveguides associated with flares and CMEs Authors: Liu, Wei; Ofman, Leon; Broder, Brittany; Karlický, Marian; Downs, Cooper Bibcode: 2016AIPC.1720d0010L Altcode: 2015arXiv151207930L Quasi-periodic, fast-mode, propagating wave trains (QFPs) are a new observational phenomenon recently discovered in the solar corona by the Solar Dynamics Observatory with extreme ultraviolet (EUV) imaging observations. They originate from flares and propagate at speeds up to ∼2000 km s-1 within funnel-shaped waveguides in the wakes of coronal mass ejections (CMEs). QFPs can carry suffcient energy fluxes required for coronal heating during their occurr ences. They can provide new diagnostics for the solar corona and their associated flares. We present recent observations of QFPs focusing on their spatio-temporal properties, temperature dependence, and statistical correlation with flares and CMEs. Of particular interest is the 2010-Aug-01 C3.2 flare with correlated QFPs and drifting zebra and fiber radio bursts, which might be different manifestations of the same fast-mode wave trains. We also discuss the potential roles of QFPs in accelerating and/or modulating the solar wind. Title: Microwave Type III Pair Bursts in Solar Flares Authors: Tan, Baolin; Mészárosová, Hana; Karlický, Marian; Huang, Guangli; Tan, Chengming Bibcode: 2016ApJ...819...42T Altcode: 2016arXiv160105312T A solar microwave type III pair burst is composed of normal and reverse-sloped (RS) burst branches with oppositely fast frequency drifts. It is the most sensitive signature of the primary energy release and electron accelerations in flares. This work reports 11 microwave type III pair events in 9 flares observed by radio spectrometers in China and the Czech Republic at a frequency of 0.80-7.60 GHz during 1994-2014. These type III pairs occurred in flare impulsive and postflare phases with separate frequencies in the range of 1.08-3.42 GHz and a frequency gap of 10-1700 MHz. The frequency drift increases with the separate frequency (fx), the lifetime of each burst is anti-correlated to fx, while the frequency gap is independent of fx. In most events, the normal branches are drifting obviously faster than the RS branches. The type III pairs occurring in flare impulsive phase have lower separate frequencies, longer lifetimes, wider frequency gaps, and slower frequency drifts than that occurring in postflare phase. Also, the latter always has strong circular polarization. Further analysis indicates that near the flare energy release sites the plasma density is about {10}10{--}{10}11 cm-3 and the temperature is higher than 107 K. These results provide new constraints to the acceleration mechanism in solar flares. Title: Sources of Quasi-periodic Pulses in the Flare of 18 August 2012 Authors: Altyntsev, A.; Meshalkina, N.; Mészárosová, H.; Karlický, M.; Palshin, V.; Lesovoi, S. Bibcode: 2016SoPh..291..445A Altcode: 2016SoPh..tmp...41A; 2016arXiv160102332A We analyzed spatial and spectral characteristics of quasi-periodic pulses (QPP) for the limb flare on 18 August 2012, using new data from a complex of spectral and imaging instruments developed by the Siberian Solar Radio Telescope team and the Wind/Konusγ -ray spectrometer. A sequence of broadband pulses with periods of approximately ten seconds were observed in X-rays at energies between 25 keV and 300 keV, and in microwaves at frequencies from a few GHz up to 34 GHz during an interval of one minute. The QPP X-ray source was located slightly above the limb where the southern legs of large and small EUV loop systems were close to each other. Before the QPPs occurred, the soft X-ray emission and the Ramaty High Energy Solar Spectroscopic Imager signal from the energy channels below 25 keV were gradually arising for several minutes at the same location. It was found that each X-ray pulse showed a soft-hard-soft behavior. The 17 and 34 GHz microwave sources were at the footpoints of the small loop system, the source emitting in the 4.2 - 7.4 GHz band in the large system. The QPPs were probably generated by modulated acceleration processes in the energy-release site. We determined the plasma parameters in the radio sources by analyzing the spectra. The microwave pulses might be explained by relatively weak variations of the spectral hardness of the emitting electrons. Title: Flare evolution and polarization changes in fine structures of solar radio emission in the 2013 April 11 event Authors: Chernov, Gennady; Sych, Robert; Tan, Bao-Lin; Yan, Yi-Hua; Tan, Cheng-Ming; Fu, Qi-Jun; Karlický, Marian; Fomichev, Valery Bibcode: 2016RAA....16...28C Altcode: 2016RAA....16b...8C; 2015arXiv150906487C The measurement of positions and sizes of radio sources in observations is important for understanding of the flare evolution. For the first time, solar radio spectral fine structures in an M6.5 flare that occurred on 2013 April 11 were observed simultaneously by several radio instruments at four different observatories: Chinese Solar Broadband Radio Spectrometer at Huairou (SBRS/Huairou), Ondřejov Radio Spectrograph in the Czech Republic (ORSC/Ondřejov), Badary Broadband Microwave Spectropolarimeter (BMS/Irkutsk), and spectrograph/IZMIRAN (Moscow, Troitsk). The fine structures included microwave zebra patterns (ZPs), fast pulsations and fiber bursts. They were observed during the flare brightening located at the tops of a loop arcade as shown in images taken by the extreme ultraviolet (EUV) telescope onboard NASA's satellite Solar Dynamics Observatory (SDO). The flare occurred at 06:58-07:26 UT in solar active region NOAA 11719 located close to the solar disk center. ZPs appeared near high frequency boundaries of the pulsations, and their spectra observed in Huairou and Ondřejov agreed with each other in terms of details. At the beginning of the flare's impulsive phase, a strong narrowband ZP burst occurred with a moderate left-handed circular polarization. Then a series of pulsations and ZPs were observed in almost unpolarized emission. After 07:00 UT a ZP appeared with a moderate right-handed polarization. In the flare decay phase (at about 07:25 UT), ZPs and fiber bursts become strongly right-hand polarized. BMS/Irkutsk spectral observations indicated that the background emission showed a left-handed circular polarization (similar to SBRS/Huairou spectra around 3 GHz). However, the fine structure appeared in the right-handed polarization. The dynamics of the polarization was associated with the motion of the flare exciter, which was observed in EUV images at 171 Å and 131 Å by the SDO Atmospheric Imaging Assembly (AIA). Combining magnetograms observed by the SDO Helioseismic and Magnetic Imager (HMI) with the homologous assumption of EUV flare brightenings and ZP bursts, we deduced that the observed ZPs correspond to the ordinary radio emission mode. However, future analysis needs to verify the assumption that zebra radio sources are really related to a closed magnetic loop, and are located at lower heights in the solar atmosphere than the source of pulsations. Title: Comparison of 30 THz impulsive burst time development to microwaves, Hα, EUV, and GOES soft X-rays Authors: Miteva, R.; Kaufmann, P.; Cabezas, D. P.; Cassiano, M. M.; Fernandes, L. O. T.; Freeland, S. L.; Karlický, M.; Kerdraon, A.; Kudaka, A. S.; Luoni, M. L.; Marcon, R.; Raulin, J. -P.; Trottet, G.; White, S. M. Bibcode: 2016A&A...586A..91M Altcode: 2015arXiv151201763M The recent discovery of impulsive solar burst emission in the 30 THz band is raising new interpretation challenges. One event associated with a GOES M2 class flare has been observed simultaneously in microwaves, Hα, EUV, and soft X-ray bands. Although these new observations confirm some features found in the two prior known events, they exhibit time profile structure discrepancies between 30 THz, microwaves, and hard X-rays (as inferred from the Neupert effect). These results suggest a more complex relationship between 30 THz emission and radiation produced at other wavelength ranges. The multiple frequency emissions in the impulsive phase are likely to be produced at a common flaring site lower in the chromosphere. The 30 THz burst emission may be either part of a nonthermal radiation mechanism or due to the rapid thermal response to a beam of high-energy particles bombarding the dense solar atmosphere. Title: Frequency Oscillations of Drifting Pulsating Structures Authors: Karlický, M.; Jiřička, K.; Bárta, M. Bibcode: 2016CEAB...40...93K Altcode: Analyzing the solar radio spectra in the 0.8-4.5 GHz frequency range observed at the Ondřejov Observatory during 2000-2015 we found 118 drifting pulsating structures (DPSs). Among them we found 8 DPSs with distinct quasi-periodic oscillations in frequency. Periods of these oscillations are in the range of 4-75 s. Based on the model of DPS and numerical simulations we interpret these oscillations as a result of merging of two plasmoids into one larger plasmoid that after merging start to oscillate. The period of the plasmoid oscillation, P, can be estimated as P ≈ L/v_A, where L is the characteristic size of the plasmoid and v_A is the mean Alfvén speed in the plasmoid. This enables us to roughly estimate the mean magnetic field strength in the oscillating plasmoid (2.9-38.3 G). Title: Numerical RHD simulations of flaring chromosphere with Flarix Authors: Heinzel, Petr; Kašparová, Jana; Varady, Michal; Karlický, Marian; Moravec, Zdeněk Bibcode: 2016IAUS..320..233H Altcode: 2016arXiv160200016H Flarix is a radiation-hydrodynamical (RHD) code for modeling of the response of the chromosphere to a beam bombardment during solar flares. It solves the set of hydrodynamic conservation equations coupled with NLTE equations of radiative transfer. The simulations are driven by high energy electron beams. We present results of the Flarix simulations of a flaring loop relevant to the problem of continuum radiation during flares. In particular we focus on properties of the hydrogen Balmer continuum which was recently detected by IRIS. Title: SSALMON - The Solar Simulations for the Atacama Large Millimeter Observatory Network Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu, B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.; Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.; Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier, A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M. Bibcode: 2015AdSpR..56.2679W Altcode: 2015arXiv150205601W The Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) was initiated in 2014 in connection with two ALMA development studies. The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful new tool, which can also observe the Sun at high spatial, temporal, and spectral resolution. The international SSALMONetwork aims at co-ordinating the further development of solar observing modes for ALMA and at promoting scientific opportunities for solar physics with particular focus on numerical simulations, which can provide important constraints for the observing modes and can aid the interpretation of future observations. The radiation detected by ALMA originates mostly in the solar chromosphere - a complex and dynamic layer between the photosphere and corona, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere. Potential targets include active regions, prominences, quiet Sun regions, flares. Here, we give a brief overview over the network and potential science cases for future solar observations with ALMA. Title: Thermal Fronts in Solar Flares Authors: Karlický, Marian Bibcode: 2015ApJ...814..153K Altcode: We studied the formation of a thermal front during the expansion of hot plasma into colder plasma. We used a three-dimensional electromagnetic particle-in-cell model that includes inductive effects. In early phases, in the area of the expanding hot plasma, we found several thermal fronts, which are defined as a sudden decrease of the local electron kinetic energy. The fronts formed a cascade. Thermal fronts with higher temperature contrast were located near plasma density depressions, generated during the hot plasma expansion. The formation of the main thermal front was associated with the return-current process induced by hot electron expansion and electrons backscattered at the front. A part of the hot plasma was trapped by the thermal front while another part, mainly with the most energetic electrons, escaped and generated Langmuir and electromagnetic waves in front of the thermal front, as shown by the dispersion diagrams. Considering all of these processes and those described in the literature, we show that anomalous electric resistivity is produced at the location of the thermal front. Thus, the thermal front can contribute to energy dissipation in the current-carrying loops of solar flares. We estimated the values of such anomalous resistivity in the solar atmosphere together with collisional resistivity and electric fields. We propose that the slowly drifting reverse drift bursts, observed at the beginning of some solar flares, could be signatures of the thermal front. Title: Electric Current Filamentation at a Non-potential Magnetic Null-point Due to Pressure Perturbation Authors: Jelínek, P.; Karlický, M.; Murawski, K. Bibcode: 2015ApJ...812..105J Altcode: An increase of electric current densities due to filamentation is an important process in any flare. We show that the pressure perturbation, followed by an entropy wave, triggers such a filamentation in the non-potential magnetic null-point. In the two-dimensional (2D), non-potential magnetic null-point, we generate the entropy wave by a negative or positive pressure pulse that is launched initially. Then, we study its evolution under the influence of the gravity field. We solve the full set of 2D time dependent, ideal magnetohydrodynamic equations numerically, making use of the FLASH code. The negative pulse leads to an entropy wave with a plasma density greater than in the ambient atmosphere and thus this wave falls down in the solar atmosphere, attracted by the gravity force. In the case of the positive pressure pulse, the plasma becomes evacuated and the entropy wave propagates upward. However, in both cases, owing to the Rayleigh-Taylor instability, the electric current in a non-potential magnetic null-point is rapidly filamented and at some locations the electric current density is strongly enhanced in comparison to its initial value. Using numerical simulations, we find that entropy waves initiated either by positive or negative pulses result in an increase of electric current densities close to the magnetic null-point and thus the energy accumulated here can be released as nanoflares or even flares. Title: Determination of plasma parameters in solar zebra radio sources Authors: Karlický, M.; Yasnov, L. V. Bibcode: 2015A&A...581A.115K Altcode:
Aims: We present a new method for determining the magnetic field strength and plasma density in the solar zebra radio sources.
Methods: Using the double plasma resonance (DPR) model of the zebra emission, we analytically derived the equations for computing the gyroharmonic number s of selected zebra lines and then solved these equations numerically.
Results: The method was successfully tested on artificially generated zebras and then applied to observed ones. The magnetic field strength and plasma density in the radio sources were determined. Simultaneously, we evaluated the parameter Lnb = 2Lb/ (2Ln - Lb), where Ln and Lb are the characteristic scale-heights of the plasma density and magnetic field strength in the zebra source, respectively. Computations show that the maximum frequency of the low-polarized zebras is about 8 GHz, in very good agreement with observations. For the high-polarized zebras, this limit is about four times lower. Microwave zebras are preferentially generated in the regions with steep gradients of the plasma density, such as in the transition region. In models with smaller density gradients, such as those with a barometric density profile, the microwave zebras cannot be produced owing to the strong bremsstrahlung and cyclotron absorptions. We also show that our DPR model is able to explain the zebras with frequency-equidistant zebra lines. Title: Numerical simulations of flaring loops with Flarix Authors: none Heinzel, Petr; Karlicky, Marian; Varady, Michal; Kasparova, Jana; Moravec, Zdenek Bibcode: 2015IAUGA..2258466N Altcode: Flarix is the radiation-hydrodynamical code for simulation of the flare evolution. It solves the set of hydrodynamicval equations coupled to NLTE equations of radiative transfer. The simulation is driven by the accelerated electron beams. We present new results of Flarix simulations for various types of flare loops, incorporating new features like effects of the return current and particle re-acceleration in the chromosphere. Title: On the Visibility of Prominence Fine Structures at Radio Millimeter Wavelengths Authors: Heinzel, P.; Berlicki, A.; Bárta, M.; Karlický, M.; Rudawy, P. Bibcode: 2015SoPh..290.1981H Altcode: 2015SoPh..tmp...87H Prominence temperatures have so far mainly been determined by analyzing spectral line shapes, which is difficult when the spectral lines are optically thick. The radio spectra in the millimeter range offer a unique possibility to measure the kinetic temperature. However, studies in the past used data with insufficient spatial resolution to resolve the prominence fine structures. The aim of this article is to predict the visibility of prominence fine structures in the submillimeter/millimeter (SMM) domain, to estimate their brightness temperatures at various wavelengths, and to demonstrate the feasibility and usefulness of future high-resolution radio observations of solar prominences with ALMA (Atacama Large Millimeter-submillimeter Array). Our novel approach is the conversion of Hα coronagraphic images into microwave spectral images. We show that the spatial variations of the prominence brightness both in the Hα line and in the SMM domain predominantly depend on the line-of-sight emission measure of the cool plasma, which we derive from the integrated intensities of the observed Hα line. This relation also offers a new possibility to determine the SMM optical thickness from simultaneous Hα observations with high resolution. We also describe how we determine the prominence kinetic temperature from SMM spectral images. Finally, we apply the ALMA image-processing software Common Astronomy Software Applications (CASA) to our simulated images to assess what ALMA would detect at a resolution level that is similar to the coronagraphic Hα images used in this study. Our results can thus help in preparations of first ALMA prominence observations in the frame of science and technical verification tests. Title: Regions of Generation and Optical Thicknesses of dm-Zebra Lines Authors: Yasnov, L. V.; Karlický, M. Bibcode: 2015SoPh..290.2001Y Altcode: 2015SoPh..tmp...88Y Using a new model based on the double plasma resonance (DPR), we show that the zebra structure seen in solar radio bursts is generated in the transition region and at the tops of the magnetic arcade. The magnetic field in zebra sources is probably weaker than 150 gauss. According to this model, a generation of zebras in stronger magnetic fields is improbable. The high-frequency boundary of decimetric zebras depends on the background electron plasma density, but not on the magnetic field strength in the generation regions. The bremsstrahlung absorption in atmospheric layers above the DPR zebra generation region and the cyclotron absorption in the DPR region and in the gyroresonance layers at higher altitudes limit the spectrum of zebras from both high-frequency and low-frequency sides. While the bremsstrahlung reduces the emission from the high-frequency side, the cyclotron absorption limits the low-frequency side. The observed frequency range and the number of observed zebra lines are determined not only by these absorptions, but also by appropriate distribution functions of superthermal electrons and plasma conditions in this region. Low-frequency (metric) zebra emissions can be generated at high altitudes. Computations show that such emissions can escape from the DPR generation region only at high gyro-harmonics (s >10 ) and with many zebra lines. 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: The 2014 ALMA Long Baseline Campaign: An Overview Authors: ALMA Partnership; Fomalont, E. B.; Vlahakis, C.; Corder, S.; Remijan, A.; Barkats, D.; Lucas, R.; Hunter, T. R.; Brogan, C. L.; Asaki, Y.; Matsushita, S.; Dent, W. R. F.; Hills, R. E.; Phillips, N.; Richards, A. M. S.; Cox, P.; Amestica, R.; Broguiere, D.; Cotton, W.; Hales, A. S.; Hiriart, R.; Hirota, A.; Hodge, J. A.; Impellizzeri, C. M. V.; Kern, J.; Kneissl, R.; Liuzzo, E.; Marcelino, N.; Marson, R.; Mignano, A.; Nakanishi, K.; Nikolic, B.; Perez, J. E.; Pérez, L. M.; Toledo, I.; Aladro, R.; Butler, B.; Cortes, J.; Cortes, P.; Dhawan, V.; Di Francesco, J.; Espada, D.; Galarza, F.; Garcia-Appadoo, D.; Guzman-Ramirez, L.; Humphreys, E. M.; Jung, T.; Kameno, S.; Laing, R. A.; Leon, S.; Mangum, J.; Marconi, G.; Nagai, H.; Nyman, L. -A.; Radiszcz, M.; Rodón, J. A.; Sawada, T.; Takahashi, S.; Tilanus, R. P. J.; van Kempen, T.; Vila Vilaro, B.; Watson, L. C.; Wiklind, T.; Gueth, F.; Tatematsu, K.; Wootten, A.; Castro-Carrizo, A.; Chapillon, E.; Dumas, G.; de Gregorio-Monsalvo, I.; Francke, H.; Gallardo, J.; Garcia, J.; Gonzalez, S.; Hibbard, J. E.; Hill, T.; Kaminski, T.; Karim, A.; Krips, M.; Kurono, Y.; Lopez, C.; Martin, S.; Maud, L.; Morales, F.; Pietu, V.; Plarre, K.; Schieven, G.; Testi, L.; Videla, L.; Villard, E.; Whyborn, N.; Zwaan, M. A.; Alves, F.; Andreani, P.; Avison, A.; Barta, M.; Bedosti, F.; Bendo, G. J.; Bertoldi, F.; Bethermin, M.; Biggs, A.; Boissier, J.; Brand, J.; Burkutean, S.; Casasola, V.; Conway, J.; Cortese, L.; Dabrowski, B.; Davis, T. A.; Diaz Trigo, M.; Fontani, F.; Franco-Hernandez, R.; Fuller, G.; Galvan Madrid, R.; Giannetti, A.; Ginsburg, A.; Graves, S. F.; Hatziminaoglou, E.; Hogerheijde, M.; Jachym, P.; Jimenez Serra, I.; Karlicky, M.; Klaasen, P.; Kraus, M.; Kunneriath, D.; Lagos, C.; Longmore, S.; Leurini, S.; Maercker, M.; Magnelli, B.; Marti Vidal, I.; Massardi, M.; Maury, A.; Muehle, S.; Muller, S.; Muxlow, T.; O'Gorman, E.; Paladino, R.; Petry, D.; Pineda, J. E.; Randall, S.; Richer, J. S.; Rossetti, A.; Rushton, A.; Rygl, K.; Sanchez Monge, A.; Schaaf, R.; Schilke, P.; Stanke, T.; Schmalzl, M.; Stoehr, F.; Urban, S.; van Kampen, E.; Vlemmings, W.; Wang, K.; Wild, W.; Yang, Y.; Iguchi, S.; Hasegawa, T.; Saito, M.; Inatani, J.; Mizuno, N.; Asayama, S.; Kosugi, G.; Morita, K. -I.; Chiba, K.; Kawashima, S.; Okumura, S. K.; Ohashi, N.; Ogasawara, R.; Sakamoto, S.; Noguchi, T.; Huang, Y. -D.; Liu, S. -Y.; Kemper, F.; Koch, P. M.; Chen, M. -T.; Chikada, Y.; Hiramatsu, M.; Iono, D.; Shimojo, M.; Komugi, S.; Kim, J.; Lyo, A. -R.; Muller, E.; Herrera, C.; Miura, R. E.; Ueda, J.; Chibueze, J.; Su, Y. -N.; Trejo-Cruz, A.; Wang, K. -S.; Kiuchi, H.; Ukita, N.; Sugimoto, M.; Kawabe, R.; Hayashi, M.; Miyama, S.; Ho, P. T. P.; Kaifu, N.; Ishiguro, M.; Beasley, A. J.; Bhatnagar, S.; Braatz, J. A., III; Brisbin, D. G.; Brunetti, N.; Carilli, C.; Crossley, J. H.; D'Addario, L.; Donovan Meyer, J. L.; Emerson, D. T.; Evans, A. S.; Fisher, P.; Golap, K.; Griffith, D. M.; Hale, A. E.; Halstead, D.; Hardy, E. J.; Hatz, M. C.; Holdaway, M.; Indebetouw, R.; Jewell, P. R.; Kepley, A. A.; Kim, D. -C.; Lacy, M. D.; Leroy, A. K.; Liszt, H. S.; Lonsdale, C. J.; Matthews, B.; McKinnon, M.; Mason, B. S.; Moellenbrock, G.; Moullet, A.; Myers, S. T.; Ott, J.; Peck, A. B.; Pisano, J.; Radford, S. J. E.; Randolph, W. T.; Rao Venkata, U.; Rawlings, M. G.; Rosen, R.; Schnee, S. L.; Scott, K. S.; Sharp, N. K.; Sheth, K.; Simon, R. S.; Tsutsumi, T.; Wood, S. J. Bibcode: 2015ApJ...808L...1A Altcode: 2015arXiv150404877P A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

. 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: Particle Acceleration in Plasmoid Ejections Derived from Radio Drifting Pulsating Structures Authors: Nishizuka, N.; Karlický, M.; Janvier, M.; Bárta, M. Bibcode: 2015ApJ...799..126N Altcode: 2014arXiv1412.7904N We report observations of slowly drifting pulsating structures (DPSs) in the 0.8-4.5 GHz frequency range of the RT4 and RT5 radio spectrographs at Ondřejov Observatory, between 2002 and 2012. We found 106 events of DPSs, which we classified into four cases: (I) single events with a constant frequency drift (12 events), (II) multiple events occurring in the same flare with constant frequency drifts (11 events), (III) single or multiple events with increasing or decreasing frequency drift rates (52 events), and (IV) complex events containing multiple events occurring at the same time in a different frequency range (31 events). Many DPSs are associated with hard X-ray (HXR) bursts (15-25 keV) and soft X-ray (SXR) gradient peaks, as they typically occurred at the beginning of HXR peaks. This indicates that DPS events are related to the processes of fast energy release and particle acceleration. Furthermore, interpreting DPSs as signatures of plasmoids, we measured their ejection velocity, their width, and their height from the DPS spectra, from which we also estimated the reconnection rate and the plasma beta. In this interpretation, constant frequency drift indicates a constant velocity of a plasmoid, and an increasing/decreasing frequency drift indicates a deceleration/acceleration of a plasmoid ejection. The reconnection rate shows a good positive correlation with the plasmoid velocity. Finally we confirmed that some DPS events show plasmoid counterparts in Solar Dynamics Observatory/Atmospheric Imaging Assembly images. Title: Structured mass density slab as a waveguide of fast magnetoacoustic waves Authors: Jelínek, P.; Karlický, M. Bibcode: 2015CEAB...39...51J Altcode: Coronal loops are waveguides for magnetohydrodynamic (MHD) waves. These loops are expected to be structured. Therefore, in the present paper, we numerically studied the propagation of the fast MHD waves in the structured density slab (composed from a broad density slab with one axisymmetric narrow sub-slab superposed), and analysed the wave signals. Then, this structured slab was divided into its components, i.e., to simple broad and narrow slabs and the same analysis was made. We compared results of both these cases. For the calculations we adopted a two-dimensional (2D) magnetohydrodynamic (MHD) model, in which we solved a full set of ideal time-dependent MHD equations using the FLASH code, applying the adaptive mesh refinement (AMR) method. To initiate the fast sausage magnetoacoustic waves, we used axisymmetric Gaussian velocity perturbation. Wave signals were detected in different locations along the slab and as a diagnostic tool of these waves, the wavelet analysis method has been used. We found that for the structured density slab with sufficiently sharp boundaries, i.e., for good quality waveguides (without an energy leakage), the guided waves in the structured slab behave similarly as in its separated (simple slab) components. Title: High-frequency reverse drift bursts in 2012-2014 solar flares Authors: Jiřička, K.; Karlický, M. Bibcode: 2015CEAB...39...59J Altcode: During observations by the Ondřejov high-time resolution 0.8-2.0 GHz radio spectrograph in years 2012-2014, 33 high-frequency reverse drift bursts with frequency drift less than 500 MHz s-1 were found. In 23 cases these bursts were observed before the GOES flare maximum, while the remaining 10 after this GOES maximum. Using the Aschwanden's density model of the solar atmosphere and assuming the radio emission on the harmonic plasma frequency, the corresponding velocities of the agents generating these bursts are less than 7000 km s-1. These velocities are too slow for electron beams, therefore we propose that these bursts are generated by thermal conduction fronts or by magnetohydrodynamic shocks. Title: Solar Radio Bursts with Spectral Fine Structures in Preflares Authors: Zhang, Yin; Tan, Baolin; Karlický, Marian; Mészárosová, Hana; Huang, Jing; Tan, Chengming; Simões, Paulo J. A. Bibcode: 2015ApJ...799...30Z Altcode: 2014arXiv1411.4766Z Good observations of preflare activities are important for us to understand the origin and triggering mechanism of solar flares, and to predict the occurrence of solar flares. This work presents the characteristics of microwave spectral fine structures as preflare activities of four solar flares observed by the Ondřejov radio spectrograph in the frequency range of 0.8-2.0 GHz. We found that these microwave bursts which occurred 1-4 minutes before the onset of flares have spectral fine structures with relatively weak intensities and very short timescales. They include microwave quasi-periodic pulsations with very short periods of 0.1-0.3 s and dot bursts with millisecond timescales and narrow frequency bandwidths. Accompanying these microwave bursts are filament motions, plasma ejection or loop brightening in the EUV imaging observations, and non-thermal hard X-ray emission enhancements observed by RHESSI. These facts may reveal certain independent, non-thermal energy releasing processes and particle acceleration before the onset of solar flares. They may help us to understand the nature of solar flares and to predict their occurrence. Title: New Eyes Looking at Solar Activity: Challenges for Theory and Simulations - Placing It into Context Authors: Pohjolainen, S.; Karlický, M.; van Driel-Gesztelyi, L.; Mandrini, C. H. Bibcode: 2015SoPh..290....1P Altcode: 2014SoPh..tmp..190P Solar Cycle 24 has opened a new era in solar radio physics as we now have instruments that can probe solar processes from submillimeter to kilometer waves. New and upgraded instruments provide data that enable studies of both energetic particles and thermal plasma, enhancing our knowledge of solar eruptions and acceleration and propagation of particles, through the solar chromosphere and corona and into the interplanetary space. In this Topical Issue we highlight the new observational capabilities and discuss the theoretical issues connected to solar radio emission and interplanetary radio physics. Title: Fourier Analysis of Radio Bursts Observed with Very High Time Resolution Authors: Da̧browski, B. P.; Karlický, M.; Rudawy, P. Bibcode: 2015SoPh..290..169D Altcode: Numerous solar radio bursts were observed in 2000 - 2001 using the Toruń radio spectrograph with its unique time resolution of 80 microseconds. This high time resolution enables an in-depth analysis of the time evolution of the power spectra and Fourier spectral indices of selected short radio bursts. We analyze the power-spectrum parameters and variability for two millisecond radio dm-spike events and one drifting pulsation structure (DPS) event, for which the structures of the recorded signals were analyzed with an effective time resolution of 0.0008 s in five adjacent frequency bands of their radio spectra. Title: MHD flows at astropauses and in astrotails Authors: Nickeler, D. H.; Wiegelmann, T.; Karlický, M.; Kraus, M. Bibcode: 2014ASTRP...1...51N Altcode: 2015arXiv150105122N The geometrical shapes and the physical properties of stellar wind - interstellar medium interaction regions form an important stage for studying stellar winds and their embedded magnetic fields as well as cosmic ray modulation. Our goal is to provide a proper representation and classification of counter-flow configurations and counter-flow interfaces in the frame of fluid theory. In addition we calculate flows and large-scale electromagnetic fields based on which the large-scale dynamics and its role as possible background for particle acceleration, e.g., in the form of anomalous cosmic rays, can be studied. We find that for the definition of the boundaries, which are determining the astropause shape, the number and location of magnetic null points and stagnation points is essential. Multiple separatrices can exist, forming a highly complex environment for the interstellar and stellar plasma. Furthermore, the formation of extended tail structures occur naturally, and their stretched field and streamlines provide surroundings and mechanisms for the acceleration of particles by field-aligned electric fields. Title: Self-consistent stationary MHD shear flows in the solar atmosphere as electric field generators Authors: Nickeler, D. H.; Karlický, M.; Wiegelmann, T.; Kraus, M. Bibcode: 2014A&A...569A..44N Altcode: 2014arXiv1407.3227N Context. Magnetic fields and flows in coronal structures, for example, in gradual phases in flares, can be described by 2D and 3D magnetohydrostatic (MHS) and steady magnetohydrodynamic (MHD) equilibria.
Aims: Within a physically simplified, but exact mathematical model, we study the electric currents and corresponding electric fields generated by shear flows.
Methods: Starting from exact and analytically calculated magnetic potential fields, we solved the nonlinear MHD equations self-consistently. By applying a magnetic shear flow and assuming a nonideal MHD environment, we calculated an electric field via Faraday's law. The formal solution for the electromagnetic field allowed us to compute an expression of an effective resistivity similar to the collisionless Speiser resistivity.
Results: We find that the electric field can be highly spatially structured, or in other words, filamented. The electric field component parallel to the magnetic field is the dominant component and is high where the resistivity has a maximum. The electric field is a potential field, therefore, the highest energy gain of the particles can be directly derived from the corresponding voltage. In our example of a coronal post-flare scenario we obtain electron energies of tens of keV, which are on the same order of magnitude as found observationally. This energy serves as a source for heating and acceleration of particles. Title: Quasi-Periodic Pulsations with Varying Period in Multi-Wavelength Observations of an X-class Flare Authors: Huang, Jing; Tan, Baolin; Zhang, Yin; Karlický, Marian; Mészárosová, Hana Bibcode: 2014ApJ...791...44H Altcode: This work presents an interesting phenomenon of the period variation in quasi-periodic pulsations (QPPs) observed during the impulsive phase of a coronal mass ejection-related X1.1 class flare on 2012 July 6. The period of QPPs was changed from 21 s at soft X-rays (SXR) to 22-23 s at microwaves, to ~24 s at extreme ultraviolet emissions (EUV), and to 27-32 s at metric-decimetric waves. The microwave, EUV, and SXR QPPs, emitted from flare loops of different heights, were oscillating in phase. Fast kink mode oscillations were proposed to be the modulation mechanism, which may exist in a wide region in the solar atmosphere from the chromosphere to the upper corona or even to the interplanetary space. Changed parameters of flare loops through the solar atmosphere could result in the varying period of QPPs at different wavelengths. The first appearing microwave QPPs and quasi-periodic metric-decimetric type III bursts were generated by energetic electrons. This may imply that particle acceleration or magnetic reconnection were located between these two non-thermal emission sources. Thermal QPPs (in SXR and EUV emissions) occurred later than the nonthermal ones, which would suggest a some time for plasma heating or energy dissipation in flare loops during burst processes. At the beginning of flare, a sudden collapse and expansion of two separated flare loop structures occurred simultaneously with the multi-wavelength QPPs. An implosion in the corona, including both collapse and expansion of flare loops, could be a trigger of loop oscillations in a very large region in the solar atmosphere. Title: A Very Small and Super Strong Zebra Pattern Burst at the Beginning of a Solar Flare Authors: Tan, Baolin; Tan, Chengming; Zhang, Yin; Huang, Jing; Mészárosová, Hana; Karlický, Marian; Yan, Yihua Bibcode: 2014ApJ...790..151T Altcode: 2014arXiv1406.5209T Microwave emission with spectral zebra pattern structures (ZPs) is frequently observed in solar flares and the Crab pulsar. The previous observations show that ZP is a structure only overlapped on the underlying broadband continuum with slight increments and decrements. This work reports an unusually strong ZP burst occurring at the beginning of a solar flare observed simultaneously by two radio telescopes located in China and the Czech Republic and by the EUV telescope on board NASA's satellite Solar Dynamics Observatory on 2013 April 11. It is a very short and super strong explosion whose intensity exceeds several times that of the underlying flaring broadband continuum emission, lasting for just 18 s. EUV images show that the flare starts from several small flare bursting points (FBPs). There is a sudden EUV flash with extra enhancement in one of these FBPs during the ZP burst. Analysis indicates that the ZP burst accompanying an EUV flash is an unusual explosion revealing a strong coherent process with rapid particle acceleration, violent energy release, and fast plasma heating simultaneously in a small region with a short duration just at the beginning of the flare. Title: Solar flares: radio and X-ray signatures of magnetic reconnection processes Authors: Karlický, Marian Bibcode: 2014RAA....14..753K Altcode: This review summarizes new trends in studies of magnetic reconnection in solar flares. It is shown that plasmoids play a very important role in this primary flare process. Using the results of magnetohydrodynamic and particle-in-cell simulations, we describe how the plasmoids are formed, how they move and interact, and how a flare current sheet is fragmented into a cascade of plasmoids. Furthermore, it is shown that during the interactions of these plasmoids electrons are not only very efficiently accelerated and heated, but electromagnetic (radio) emission is also produced. We also describe possible mechanisms for the triggering of magnetic reconnection. The relevant X-ray and radio signatures of these processes (such as radio drifting pulsation structures, narrowband dm-spikes, and the loop-top and above-the-loop-top X-ray sources) are then described. It is shown that plasmoids can also be formed in kinked magnetic ropes. A mapping of X-points of the magnetic reconnection on the chromosphere (as e.g. a splitting of flare ribbons) is mentioned. Supporting EUV and white-light observations of plasmoids are added. The significance of all these processes for the fast magnetic reconnection and electron acceleration is outlined. Their role in fusion experiments is briefly mentioned. Title: Magnetoacoustic Waves Propagating along a Dense Slab and Harris Current Sheet and their Wavelet Spectra Authors: Mészárosová, Hana; Karlický, Marian; Jelínek, Petr; Rybák, Ján Bibcode: 2014ApJ...788...44M Altcode: Currently, there is a common endeavor to detect magnetoacoustic waves in solar flares. This paper contributes to this topic using an approach of numerical simulations. We studied a spatial and temporal evolution of impulsively generated fast and slow magnetoacoustic waves propagating along the dense slab and Harris current sheet using two-dimensional magnetohydrodynamic numerical models. Wave signals computed in numerical models were used for computations of the temporal and spatial wavelet spectra for their possible comparison with those obtained from observations. It is shown that these wavelet spectra allow us to estimate basic parameters of waveguides and perturbations. It was found that the wavelet spectra of waves in the dense slab and current sheet differ in additional wavelet components that appear in association with the main tadpole structure. These additional components are new details in the wavelet spectrum of the signal. While in the dense slab this additional component is always delayed after the tadpole head, in the current sheet this component always precedes the tadpole head. It could help distinguish a type of the waveguide in observed data. We present a technique based on wavelets that separates wave structures according to their spatial scales. This technique shows not only how to separate the magnetoacoustic waves and waveguide structure in observed data, where the waveguide structure is not known, but also how propagating magnetoacoustic waves would appear in observations with limited spatial resolutions. The possibilities detecting these waves in observed data are mentioned. Title: High-Resolution Time Profiles of Fiber Bursts at 1420 and 2695 MHz Authors: Zlobec, P.; Karlický, M. Bibcode: 2014SoPh..289.1683Z Altcode: To obtain constraints for models of fiber bursts, high-resolution time (0.01 s) profiles of the fiber bursts recorded at 1420 and 2695 MHz by the Trieste radiometers are studied in detail. The fiber bursts were identified using Ondřejov radio spectra. During the years 2000 - 2005, 18 intervals with fiber bursts were selected; 26 groups were defined and about 700 fibers were analyzed in detail. More than 300 pulsations, present almost simultaneously with the fibers, were also selected and studied in order to find similarities or differences between these two types of fine structures. It was found that the polarization of the associated continuum, both for fiber bursts and pulsations, is practically the same. Evaluating the ratio between absorption over emission of many single fibers we found that this parameter is very different even for nearby bursts; however, we realized that this ratio shows a tendency to decrease with time. Finally, the time profile of one selected fiber burst was fitted using a recent model based on the modulation of the broadband radio emission by fast magnetoacoustic waves. The results are discussed. 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: Modifications of thick-target model: re-acceleration of electron beams by static and stochastic electric fields Authors: Varady, M.; Karlický, M.; Moravec, Z.; Kašparová, J. Bibcode: 2014A&A...563A..51V Altcode: 2014arXiv1401.3329V Context. The collisional thick-target model (CTTM) of the impulsive phase of solar flares, together with the famous Carmichael, Sturrock, Hirayama, and Kopp-Pneuman (CSHKP) model, presented for many years a "standard" model, which straightforwardly explained many observational aspects of flares. On the other hand, many critical issues appear when the concept is scrutinised theoretically or with the new generation of hard X-ray (HXR) observations. The famous "electron number problem" or problems related to transport of enormous particle fluxes though the corona represent only two of them. To resolve the discrepancies, several modifications of the CTTM appeared.
Aims: We study two of them based on the global and local re-acceleration of non-thermal electrons by static and stochastic electric fields during their transport from the coronal acceleration site to the thick-target region in the chromosphere. We concentrate on a comparison of the non-thermal electron distribution functions, chromospheric energy deposits, and HXR spectra obtained for both considered modifications with the CTTM itself.
Methods: The results were obtained using a relativistic test-particle approach. We simulated the transport of non-thermal electrons with a power-law spectrum including the influence of scattering, energy losses, magnetic mirroring, and also the effects of the electric fields corresponding to both modifications of the CTTM.
Results: We show that both modifications of the CTTM change the outcome of the chromospheric bombardment in several aspects. The modifications lead to an increase in chromospheric energy deposit, change of its spatial distribution, and a substantial increase in the corresponding HXR spectrum intensity.
Conclusions: The re-acceleration in both models reduces the demands on the efficiency of the primary coronal accelerator, on the electron fluxes transported from the corona downwards, and on the total number of accelerated coronal electrons during flares. Title: Statistics and Classification of the Microwave Zebra Patterns Associated with Solar Flares Authors: Tan, Baolin; Tan, Chengming; Zhang, Yin; Mészárosová, H.; Karlický, M. Bibcode: 2014ApJ...780..129T Altcode: 2013arXiv1311.5305T The microwave zebra pattern (ZP) is the most interesting, intriguing, and complex spectral structure frequently observed in solar flares. A comprehensive statistical study will certainly help us to understand the formation mechanism, which is not exactly clear now. This work presents a comprehensive statistical analysis of a big sample with 202 ZP events collected from observations at the Chinese Solar Broadband Radio Spectrometer at Huairou and the Ondŕejov Radiospectrograph in the Czech Republic at frequencies of 1.00-7.60 GHz from 2000 to 2013. After investigating the parameter properties of ZPs, such as the occurrence in flare phase, frequency range, polarization degree, duration, etc., we find that the variation of zebra stripe frequency separation with respect to frequency is the best indicator for a physical classification of ZPs. Microwave ZPs can be classified into three types: equidistant ZPs, variable-distant ZPs, and growing-distant ZPs, possibly corresponding to mechanisms of the Bernstein wave model, whistler wave model, and double plasma resonance model, respectively. This statistical classification may help us to clarify the controversies between the existing various theoretical models and understand the physical processes in the source regions. Title: Frequency variations of solar radio zebras and their power-law spectra Authors: Karlický, M. Bibcode: 2014A&A...561A..34K Altcode: Context. During solar flares several types of radio bursts are observed. The fine striped structures of the type IV solar radio bursts are called zebras. Analyzing them provides important information about the plasma parameters of their radio sources. We present a new analysis of zebras.
Aims: Power spectra of the frequency variations of zebras are computed to estimate the spectra of the plasma density variations in radio zebra sources.
Methods: Frequency variations of zebra lines and the high-frequency boundary of the whole radio burst were determined with and without the frequency fitting. The computed time dependencies of these variations were analyzed with the Fourier method.
Results: First, we computed the variation spectrum of the high-frequency boundary of the whole radio burst, which is composed of several zebra patterns. This power spectrum has a power-law form with a power-law index -1.65. Then, we selected three well-defined zebra-lines in three different zebra patterns and computed the spectra of their frequency variations. The power-law indices in these cases are found to be in the interval between -1.61 and -1.75. Finally, assuming that the zebra-line frequency is generated on the upper-hybrid frequency and that the plasma frequency ωpe is much higher than the electron-cyclotron frequency ωce, the Fourier power spectra are interpreted to be those of the electron plasma density in zebra radio sources. Title: Statistical Moments of Active-Region Images During Solar Flares Authors: Šimberová, S.; Karlický, M.; Suk, T. Bibcode: 2014SoPh..289..193S Altcode: We present new temporal-evolution diagnostics of solar flares. The high-order statistical moments (skewness and kurtosis) of the Hα images of active regions during solar flares were computed from their initial phases up to their maxima. The same method was used for quiet active regions for tests and comparison. We found that temporal profiles of the Hα statistical moments during flares roughly correspond to those observed in soft X-rays by the GOES satellite. Maxima of the cross-correlation coefficients between the skewness and the GOES X-rays were found to be 0.82 - 0.98, and the GOES X-rays are delayed 0 - 144 seconds against the skewness. We recognized that these moments are very sensitive to pre-flare activities. Therefore we used them to determine the flare starting-time and to study the pre-flare quasi-periodic processes. We determined the periods of these pre-flare processes in an interval of 20 - 400 seconds by using special convolution filters and Fourier analysis. We propose to use this method to analyze active regions during the very early phases of solar flares, and even in real time. Title: Role of plasmoids in energy cascade in magnetic reconnection in solar Authors: Bárta, Miroslav; Büchner, Jörg; Karlicky, Marian; Skala, Jan Bibcode: 2014cosp...40E.222B Altcode: The key role of plasmoids for current sheet fragmentation and filamentation in magnetic reconnection in high Lundquist-number systems has been recently revealed. Their dynamics and mutual interaction can provide efficient mechanism for energy cascade towards the small scales where the fast kinetic reconnection process comes into play. We will present results of our recent MHD and PIC simulations in this direction. It will be shown that at medium and small scales additional effect has to be taken into account: The mutual interaction of plasmoids with reconnection flows. We shall also demonstrate that formation and interaction of plasmoids is naturally involved in the real solar flares. We will present an extension of the MHD simulations providing simulated observations in optical, UV/EUV and radio domains and their comparison with the data really observed during the solar flares. The comparison clearly shows that the theory and modelling of plasmoid-dominated regime of magnetic reconnection is applicable to the physics of solar flares. Title: Report on the 2nd Solar ALMA Workshop Authors: Dąbrowski, B.; Karlický, M. Bibcode: 2013Msngr.153...38D Altcode: The Czech node is one of the ALMA European Regional Centres and is the only one to support solar observations. The second workshop in the series is briefly described: the main themes were the scope of solar observation with ALMA, planning observations and the science that can be achieved. Title: Flare line impact polarization. Na D2 589 nm line polarization in the 2001 June 15 flare Authors: Hénoux, J. C.; Karlický, M. Bibcode: 2013A&A...556A..95H Altcode: Context. The impact polarization of optical chromospheric lines in solar flares is still being debated. For this reason, additional observations and improved flare atmosphere models are needed still.
Aims: The polarization-free telescope THEMIS used in multiline 2 MulTiRaies (MTR) mode allows accurate simultaneous linear polarization measurements in various spectral lines.
Methods: In the 2001 June 15 flare, Hα, Hβ, and Mg D2 lines linear impact polarization was reported as present in THEMIS 2 MTR observations. In this paper, THEMIS data analysis was extended to the Na D2 line. Sets of I ± U and I ± Q flare Stokes S 2D-spectra were corrected from dark-current, spectral-line curvature and from transmission differences. Then, we derived the linear polarization degree P and polarization orientation angle α 2D-spectra. No change in relative positioning could be found that would reduce the Stokes parameters U and Q values. No V and I crosstalks could explain our results either.
Results: The Na D2 line is linearly polarized with a polarization degree exceeding 5% at some locations. The polarization was found to be radial at outer ribbons edges, and tangential at their inner edges. This orientation change may be due to differences in electron distribution functions on the opposite borders of flare chromospheric ribbons. Electron beams propagating along magnetic field lines, together with return currents, could explain both radial and tangential polarization. At the inner ribbon edges, intensity profile-width enlargements and blueshifts in polarization profiles are observed. This suggests chromospheric evaporation.

Appendix A is available in electronic form at http://www.aanda.org Title: Fragmentation of electric currents in the solar corona by plasma flows Authors: Nickeler, D. H.; Karlický, M.; Wiegelmann, T.; Kraus, M. Bibcode: 2013A&A...556A..61N Altcode: 2013arXiv1306.5155N
Aims: We consider a magnetic configuration consisting of an arcade structure and a detached plasmoid, resulting from a magnetic reconnection process, as is typically found in connection with solar flares. We study spontaneous current fragmentation caused by shear and vortex plasma flows.
Methods: An exact analytical transformation method was applied to calculate self-consistent solutions of the nonlinear stationary magnetohydrodynamic equations. The assumption of incompressible field-aligned flows implies that both the Alfvén Mach number and the mass density are constant on field lines. We first calculated nonlinear magnetohydrostatic equilibria with the help of the Liouville method, emulating the scenario of a solar eruptive flare configuration with plasmoids (magnetic ropes or current-carrying loops in 3D) and flare arcade. Then a Mach number profile was constructed that describes the upflow along the open magnetic field lines and implements a vortex flow inside the plasmoid. This Mach number profile was used to map the magnetohydrostatic equilibrium to the stationary one.
Results: We find that current fragmentation takes place at different locations within our configuration. Steep gradients of the Alfvén Mach number are required, implying the strong influence of shear flows on current amplification and filamentation of the magnetohydrostatic current sheets. Crescent- or ring-like structures appear along the outer separatrix, butterfly structures between the upper and lower plasmoids, and strong current peaks close the lower boundary (photosphere). Furthermore, impressing an intrinsic small-scale structure on the upper plasmoid results in strong fragmentation of the plasmoid. Hence fragmentation of current sheets and plasmoids is an inherent property of magnetohydrodynamic theory.
Conclusions: Transformations from magnetohydrostatic into magnetohydrodynamic steady-states deliver fine-structures needed for plasma heating and acceleration of particles and bulk plasma flows in dissipative events that are typically connected to magnetic reconnection processes in flares and coronal mass ejections. Title: Observational consequences of the local re-acceleration thick-target model Authors: Varady, M.; Moravec, Z.; Karlický, M.; Kašparová, J. Bibcode: 2013JPhCS.440a2013V Altcode: In our contribution we compare the efficiency of the hard X-ray production and the vertical sizes and positions of the hard X-ray sources for the classical collisional thick-target model and for its recently proposed modification, the local re-acceleration thick-target model. The latter model has been proposed in order to ease some of the severe theoretical problems of the collisional thick-target model related to interpretation of the observational properties of the foot-point HXR sources in solar flares. The results are obtained using a relativistic test-particle approach for a fully ionised atmosphere with a converging magnetic field and a single (compact) flare loop. Title: Modeling of Hα Eruptive Events Observed at the Solar Limb Authors: Kotrč, P.; Bárta, M.; Schwartz, P.; Kupryakov, Y. A.; Kashapova, L. K.; Karlický, M. Bibcode: 2013SoPh..284..447K Altcode: 2012SoPh..tmp..290K; 2012SoPh..tmp..269K We present spectra and slit-jaw images of limb and on-disk eruptive events observed with a high temporal resolution by the Ondřejov Observatory optical spectrograph. Analysis of the time series of full width at half-maximum (FWHM) in Hα, Hβ, and radio and soft X-ray (SXR) fluxes indicates two phenomenologically distinct types of observations which differ significantly in the timing of FWHM and SXR/radio fluxes. We investigated one such unusual case of a limb eruptive event in more detail. Synthesis of all observed data supports the interpretation of the Hα broadening in the sense of regular macroscopic plasma motions, contrary to the traditional view (emission from warm dense plasma). The timing and observed characteristics indicate that we may have actually observed the initiation of a prominence eruption. We test this scenario via modeling of the initial phase of the flux rope eruption in a magnetohydrodynamic (MHD) simulation, calculating subsequently - under some simplifying assumptions - the modeled Hα emission and spectrum. The modeled and observed data correspond well. Nevertheless, the following question arises: To what extent is the resulting emission sensitive to the underlying model of plasma dynamics? To address this issue, we have computed a grid of kinematic models with various arbitrary plasma flow patterns and then calculated their resulting emission. Finally, we suggest a diagnostics based on the model and demonstrate that it can be used to estimate the Alfvén velocity and plasma beta in the prominence, which are otherwise hard to obtain. 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: Radio continua modulated by waves: Zebra patterns in solar and pulsar radio spectra? Authors: Karlický, M. Bibcode: 2013A&A...552A..90K Altcode:
Aims: We aim to answer the question how waves with plasma density variations affect the radio continua generated by the plasma emission mechanism.
Methods: We built a simple semi-empirical model of the radio continuum modulation. Assuming that the waves with density variations are in the source of this radio continuum, we modeled the artificial radio spectrum, which we compared with observed spectra.
Results: We show that the waves with density variations modulate the radio continua generated by the plasma emission mechanism. Considering a single slow magnetoacoustic wave, we model the radio spectra, which resemble solar zebra patterns. We show that this modulation generates zebra effects even when the radio continuum is composed of many spiky bursts. Generalizing from one single wave to a wave turbulence we find that the computed radio spectrum is similar to so-called lace bursts. Finally, using the same procedure, but for fast magnetoacoustic waves, we modeled the radio spectrum similar to that observed during the interpulse phase of the radio emission of the Crab Nebula pulsar. 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: Radio fiber bursts and fast magnetoacoustic wave trains Authors: Karlický, M.; Mészárosová, H.; Jelínek, P. Bibcode: 2013A&A...550A...1K Altcode: 2012arXiv1212.2421K
Aims: We present a model for dm-fiber bursts that is based on assuming fast sausage magnetoacoustic wave trains that propagate along a dense vertical filament or current sheet.
Methods: Eight groups of dm-fiber bursts that were observed during solar flares were selected and analyzed by the wavelet analysis method. To model these fiber bursts we built a semi-empirical model. We also did magnetohydrodynamic simulations of a propagation of the magnetoacoustic wave train in a vertical and gravitationally stratified current sheet.
Results: In the wavelet spectra of the fiber bursts computed at different radio frequencies we found the wavelet tadpoles, whose head maxima have the same frequency drift as the drift of fiber bursts. It indicates that the drift of these fiber bursts can be explained by the propagating fast sausage magnetoacoustic wave train. Using new semi-empirical and magnetohydrodynamic models with a simple radio emission model we generated the artificial radio spectra of the fiber bursts, which are similar to the observed ones. Title: Fragmented Reconnection and Narrowband Decimetric Spikes Authors: Karlický, M.; Bárta, M.; Jiřička, K. Bibcode: 2013CEAB...37..521K Altcode: Using numerical simulations, the fragmented reconnection process is described. It is shown that during this reconnection process plasmoids in a broad range of spatial scales are generated and form a cascade of interacting plasmoids. These interactions then produce electromagnetic waves. It is proposed that the observed narrowband dm-spikes are radio signatures of these processes. Some properties of these cascades of plasmoids are derived. Finally, it is discussed how these processes can generate the above-the-loop-top hard X-ray sources as well as the hard X-ray emission at footpoints of flare magnetic ropes. Title: Simulations of HXR Foot-point Source Sizes for Modified Thick-target Models Authors: Moravec, Z.; Varady, M.; Karlický, M.; Kašparová, J. Bibcode: 2013CEAB...37..535M Altcode: We study vertical sizes of foot-point hard X-ray (HXR) sources using a relativistic test particle approach in a flare loop with a converging magnetic field. We compare results for the Collisional Thick Target Model (CTTM) with recently proposed modifications of the CTTM comprising a secondary acceleration of beam electrons. Our preliminary results indicate that none of the proposed modifications of the CTTM can explain the observed sizes of the HXR sources in a single loop flare scenario. Title: Observing the Sun with ALMA Authors: Benz, A. O.; Brajsa, R.; Shimojo, M.; Karlicky, M.; Testi, L. Bibcode: 2012IAUSS...6E.205B Altcode: The Atacama Large Millimeter Array (ALMA) is in the commissioning phase for solar observations. A filter reduces the solar radiation to a level suitable for solar observations. First observations with one antenna have mapped the Sun by scanning. The results look promising. The image of the quiet chromosphere shows large spatial variations in emissivity. Interferometry is much more demanding and not yet achieved. The current state and problems will be summarized. It is clear that solar ALMA observations will take more developing time, but will eventually be possible. The goal is subarcsecond resolution of the quiet and active submillimeter continuum radiation originating in the chromosphere and possibly in the flaring corona. A limiting factor will be the temporal variability of the solar emission. Title: Magnetoacoustic waves in a vertical flare current-sheet in a gravitationally stratified solar atmosphere Authors: Jelínek, P.; Karlický, M.; Murawski, K. Bibcode: 2012A&A...546A..49J Altcode:
Aims: We numerically studied evolution of impulsively generated magnetoacoustic waves in the vertical flare current-sheet that is embedded in the gravitationally stratified solar atmosphere and compared it with its gravity-free counterpart.
Methods: We adopted a two-dimensional (2D) magnetohydrodynamic (MHD) model, in which we solved a full set of ideal time-dependent MHD equations by means of the FLASH code, using the adaptive mesh refinement (AMR) method. To initiate the fast sausage magnetoacoustic waves, we used axisymmetric Gaussian velocity perturbation. As a diagnostic tool of these magnetoacoustic waves, we used the wavelet analysis method.
Results: We present a model of magnetoacoustic wave propagation with a gravity that is more realistic than that presented in previous studies. We compare our results with those of a gravity-free case. In equilibrium the current-sheet with gravity requires a non-zero horizontal component of the magnetic field, contrary to the gravity-free case. This causes differences in the parameters of the wave signal that propagates along the current sheet. In addition to these differences we find that wave signal variations and their wavelet tadpoles are more complex in the case with gravity than in the gravity-free case. Furthermore, for a shorter scale-height we found a prolongation of the wavelet tadpoles. These differences result from a variation of the dispersive properties and group velocities of the propagating magnetoacoustic waves with height in the solar atmosphere in the gravitational case. We show that these results can affect the diagnostics of physical processes in solar flares. Title: Formation of Balmer Lines in Impulsively Heated Flare Atmosphere by Neutral Beams Authors: Varady, M.; Kašparová, J.; Moravec, Z.; Karlický, M.; Heinzel, P. Bibcode: 2012ASPC..454..341V Altcode: In the context of interpreting non-thermal hard X-ray emission and γ lines emanating from the footpoints of flare loops, most contemporary flare models assign a fundamental role during the flare energy release, transport and deposition to the high energy non-thermal particle beams. In this contribution we concentrate on modelling of the spectroscopic properties of chromospheric flare emission in optical hydrogen lines generated due to the bombardment of the chromosphere and photosphere by neutral beams with power-law spectra. In order to obtain an estimate of the neutral beam flare heating in the solar atmosphere we produced a simple model describing the propagation and thermalisation of neutral beams. We compare the neutral beam flare heating with the flare heating produced by corresponding pure electron and proton beams. Further we compare the contribution functions for Hα line obtained for neutral and electron beam heating. Title: Electron acceleration during three-dimensional relaxation of an electron beam-return current plasma system in a magnetic field Authors: Karlický, M.; Kontar, E. P. Bibcode: 2012A&A...544A.148K Altcode: 2012arXiv1207.6248K
Aims: We investigate the effects of acceleration during non-linear electron-beam relaxation in magnetized plasma in the case of electron transport in solar flares.
Methods: The evolution of electron distribution functions is computed using a three-dimensional particle-in-cell electromagnetic code. Analytical estimations under simplified assumptions are made to provide comparisons.
Results: We show that, during the non-linear evolution of the beam-plasma system, the accelerated electron population appears. We found that, although the electron beam loses its energy efficiently to the thermal plasma, a noticeable part of the electron population is accelerated. For model cases with initially monoenergetic beams in uniform plasma, we found that the amount of energy in the accelerated electrons above the injected beam-electron energy varies depending the plasma conditions and could be around 10-30% of the initial beam energy.
Conclusions: This type of acceleration could be important for the interpretation of non-thermal electron populations in solar flares. Its neglect could lead to the over-estimation of accelerated electron numbers. The results emphasize that collective plasma effects should not be treated simply as an additional energy-loss mechanism, when hard X-ray emission in solar flares is interpreted, notably in the case of RHESSI data. Title: Radio Diagnostics of Plasmoids in a Flare Current Sheet Authors: Karlický, M.; Bárta, M. Bibcode: 2012ASPC..454..287K Altcode: Examples of the drifting pulsating structures observed in solar dm-radio spectra are presented. Their relationship to plasmoids in a flare current sheet, and to their motions is explained. Then effects of the plasmoids, especially those moving downwards and interacting with an underlying flare-loop arcade, on a formation of flare ribbons are shown. Finally, using a 2.5-D particle-in-cell modelling we present the spectrum of the electromagnetic (radio) emission generated during a coalescence of the plasmoids. Title: Processes of fragmentation cascade in large-scale magnetic reconnection Authors: Bárta, Miroslav; Büchner, Jörg; Karlicky, Marian Bibcode: 2012cosp...39..101B Altcode: 2012cosp.meet..101B Magnetic field reconnection is now generally accepted as the key mechanism for energy release in solar flares and other eruptive events in astrophysical and space plasmas. However, direct application of magnetic-reconnection theory to the physics of solar flares (and other large-scale events) faces a crucial issue for a long time: All known micro-physical processes leading to the change of magnetic field topology (i.e. the reconnection) require very thin current sheets (~1 m in the solar corona). On the other hand, the typical flare current-layer width, estimated either from observations or from the dimensional considerations, is about six orders of magnitude larger. It is thus clear that some mechanisms of consecutive fragmentation of the current density (and corresponding magnetic field) structure have to play a role. In this contribution we aim at identifying all such possible processes and studying some of them in more detail. In order to cover a large range of scales we use high-resolution MHD simulations combined with larger-scale kinetic (PIC) modelling. Our recent research has shown that the cascade towards small scales is the result of mutual positive feedback between the Lorentz-force driven instabilities (such as tearing and the fragmenting coalescence), and their flow- and pressure-field driven counterparts (typically Kelvin-Helmholtz and ballooning instabilities). Title: Plasmoids in solar flares and their radio and X-ray diagnostics Authors: Karlicky, Marian; Bárta, Miroslav Bibcode: 2012cosp...39..883K Altcode: 2012cosp.meet..883K After introduction about a role of plasmoids in solar flare reconnection, a concept of the successive merging of plasmoids and fragmentation in the current sheet in the standard flare model is presented. Using a 2.5-D electromagnetic particle-in-cell model these processes are simulated. We recognized a formation of plasmoids and their mutual interactions. During these interactions the electrons are very effectively accelerated and heated. We recognized a fragmentation in the current sheet formed between two merging plasmoids. We found that this fragmentation is due to the tearing-mode instability in this current sheet as well as by plasma flows and vortices. It is shown that simultaneously the electromagnetic (radio) emission is produced. Relevant X-ray, radio and H-alpha signatures of these processes as e.g. the above-the-loop-top hard X-ray sources, merging of X-ray source with the loop-top kernel, drifting pulsating structures, narrowband dm-spikes, H-alpha ribbon motions are discussed. Title: Singularity spectra of decimetric solar bursts: The role of higher spatial resolution observations Authors: Rosa, Reinaldo; Karlicky, Marian; Sawant, Hanumant; Alves Bolzan, Maur&ício José; Fernandes, Francisco Bibcode: 2012cosp...39.1624R Altcode: 2012cosp.meet.1624R No abstract at ADS Title: The ALMA Regional Centre in the Czech Republic and the ALMA Winter School in Prague Authors: Dabrowski, B.; Karlický, M. Bibcode: 2012Msngr.148...47D Altcode: The scope of the work of the Atacama Large Millimeter/submillimeter Array (ALMA) Regional Centre in the Czech Republic is briefly outlined and a short report is presented on the recent Winter School held in Prague. Title: Fragmentation during merging of plasmoids in the magnetic field reconnection Authors: Karlický, M.; Bárta, M.; Nickeler, D. Bibcode: 2012A&A...541A..86K Altcode: Context. Application of the magnetic-reconnection theory onto large-scale events, such as solar flares, requires formation of very thin (kinetic-scale) current sheets within the rather thick flare current layer. Hence, some fragmentation/filamentation mechanisms has to be in action.
Aims: We aim at identifying fragmentation mechanisms for magnetic field and current density structures. Namely, we focus at detailed study of the processes during the merging of plasmoids that had been formed in the current layer.
Methods: A 2.5-D electromagnetic particle-in-cell model is used and its results analysed.
Results: It is shown that the merging process of plasmoids is not a simple process as presented in some previous studies. On the contrary, this process leads to a complex fragmentation. We found two types of fragmentation processes: a) fragmentation in the current sheet generated between the merging plasmoids and b) fragmentation at the boundary of plasma outflow from the reconnection between these plasmoids. While the first type of fragmentation is generated by the tearing-mode (plasmoid) instability of the secondary current sheet, the second one looks to be connected with an increase of the plasma β parameter during these processes. Thus, sheared high-β plasma flows produce this additional fragmentation.
Conclusions: The fragmentation and energy transport from large to small scales in a large-scale magnetic reconnection seem to be the result of interplay and positive feedback between instabilities driven by high gradients in both magnetic (intense current density) and velocity (high vorticity) fields. 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: Influence of Static and Stochastic Electric Fields on Electron Beams Bombarding the Chromosphere Authors: Varady, M.; Karlický, M.; Moravec, Z.; Kašparová, J. Bibcode: 2012ASPC..456..203V Altcode: Using a relativistic test-particle code we study and compare the influence of static and stochastic electric fields on propagation of electron beams along the magnetic fieldlines through the solar atmosphere given by the VAL C model from the primary acceleration site in the corona downwards to the chromosphere. The results are compared with the most common, classical model of electron beam propagation, scattering and thermalisation given by Emslie (1978). The effects of the fields on the chromospheric heating and hard X-ray emission are discussed. Title: The n-distribution of Electrons and Double Layers in the Electron-beam-Return-current System of Solar Flares Authors: Karlický, Marian Bibcode: 2012ApJ...750...49K Altcode: We investigate processes in the electron-beam-return-current system in the impulsive phase of solar flares to answer a question about the formation of the n-electron distribution detected in this phase of solar flares. An evolution of the electron-beam-return-current system with an initial local density depression is studied using a three-dimensional electromagnetic particle-in-cell model. In the system the strong double layer is formed. Its electric field potential increases with the electron beam flux. In this electric field potential, the electrons of background plasma are strongly accelerated and propagate in the return-current direction. The high-energy part of their distribution at the high-potential side of the strong double layer resembles that of the n-distribution. Thus, the detection of the n-distributions, where a form of the high-energy part of the distribution is the most important, can indicate the presence of strong double layers in solar flares. The similarity between processes in solar flare loops and those in the downward current region of the terrestrial aurora, where the double layers were observed by FAST satellite, supports this idea. 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: Magnetoacoustic waves in diagnostics of the flare current sheets Authors: Jelínek, P.; Karlický, M. Bibcode: 2012A&A...537A..46J Altcode:
Aims: To obtain diagnostics tools for solar flare current sheets, we numerically studied impulsively generated magnetoacoustic waves in the Harris current sheet.
Methods: We used two-dimensional (2-D) magnetohydrodynamic (MHD) and wave dispersion models. Tests of these models were performed for waves in the density slab, where analytical solutions are known. In the MHD model, we solved the full set of ideal MHD equations by means of the modified two-step Lax-Wendroff algorithm. The initial perturbation was chosen to generate preferentially the fast sausage magnetoacoustic waves. To determine the dispersion characteristics of MHD waves in the Harris current sheet, we numerically solved the equation of plasma motions by means of the Runge-Kutta fourth order method together with the bisection iteration one. To establish some diagnostics of these waves and their corresponding flare current sheets, we used the wavelet analysis method.
Results: We find that the results of tests of our 2-D MHD and wave dispersion models for the density slab are in good agreement with analytical results. We analyze the magnetoacoustic waves in the current sheet and compare them with those in the density slab. In both cases, for similar geometrical and plasma parameters, we find that wave trains were generated and propagated in a similar way. Their signals registered at selected locations of the Harris current sheet and density slab are also similar. Nevertheless, a dependence of the period of the magnetoacoustic waves on the width of the Harris current sheet differs from that for the density slab. The form of the wave front inside the current sheet similarly differs from that in the density slab. We find that the wavelet spectra of the signals of incoming magnetoacoustic waves at selected locations in the current sheet have the form of wavelet tadpoles. We distinguish that the form of these wavelet tadpoles becomes longer and the heads of the wavelet tadpoles are detected later in time as the distance of the detection point from that of the initial wave perturbation increases. We also find that the wavelet tadpole period depends on the plasma beta parameter. The results are discussed from the point of view of their use as diagnostics of the flare current sheets or flare loops. Title: Millisecond Radio Spikes in the Decimetric Band Authors: Dąbrowski, B. P.; Rudawy, P.; Karlický, M. Bibcode: 2012esrs.book...71D Altcode: We present the results of the analysis of thirteen events consisting of dm-spikes observed in Toruń between 15 March 2000 and 30 October 2001. The events were obtained with a very high time resolution (80 microseconds) radio spectrograph in the 1352 - 1490 MHz range. These data were complemented with observations from the radio spectrograph at Ondřejov in the 0.8 - 2.0 GHz band. We evaluated the basic characteristics of the individual spikes (duration, spectral width, and frequency drifts), as well as their groups and chains, the location of their emission sources, and the temporal correlations of the emissions with various phases of the associated solar flares. We found that the mean duration and spectral width of the radio spikes are equal to 0.036 s and 9.96 MHz, respectively. Distributions of the duration and spectral widths of the spikes have positive skewness for all investigated events. Each spike shows positive or negative frequency drift. The mean negative and positive drifts of the investigated spikes are equal to -776 MHz s-1 and 1608 MHz s-1, respectively. The emission sources of the dm-spikes are located mainly at disk center. We have noticed two kinds of chains, with and without frequency drifts. The mean durations of the chains vary between 0.067 s and 0.509 s, while their spectral widths vary between 7.2 MHz and 17.25 MHz. The mean duration of an individual spike observed in a chain was equal to 0.03 s. While we found some agreement between the global characteristics of the groups of spikes recorded with the two instruments located in Toruń and Ondřejov, we did not find any one-to-one relation between individual spikes. Title: Magnetoacoustic Wave Trains in the 11 July 2005 Radio Event with Fiber Bursts Authors: Mészárosová, H.; Karlický, M.; Rybák, J. Bibcode: 2012esrs.book...87M Altcode: A dm-radio emission with fiber bursts observed on 11 July 2005 was analyzed using wavelet filtration and spectral methods. In filtered radio spectra we found structures with different characteristic period P and frequency drift FD: i) fiber substructures (composed of dot emissions) with P 1≈ 0.5 s, FD1=- 87 MHz s-1 on average, ii) fiber structures with P 2≈1.9 s, and iii) drifting structures with P 3≈81.4 s, FD2=- 8.7, + 98.5, and - 21.8 MHz s-1. In the wavelet spectra we recognized patterns having the form of tadpoles. They were detected with the same characteristic periods P as found for the filtered structures. The frequency drift of the tadpole heads is found to be equal to the frequency drift of some groups of fibers for the long-period wavelet tadpoles (P 3) and to the frequency drift of individual fibers for the short-period tadpoles (P 2). Considering these wavelet tadpoles as signatures of propagating magnetoacoustic wave trains, the results indicate the presence of several wave trains in the fibers' source. While the long-period wave trains trigger or modulate a whole group of fibers, the short-period ones look like being connected with individual fiber bursts. This result supports the model of fibers based on magnetoacoustic waves. Using a density model of the solar atmosphere we derived the velocities of the magnetoacoustic waves, 107 and 562 km s-1, and setting them equal to the Alfvén ones we estimated the magnetic field in the source of fiber bursts as 10.7 and 47.8 G. Title: Magnetoacoustic Wave Trains in the 11 July 2005 Radio Event with Fiber Bursts Authors: Mészárosová, H.; Karlický, M.; Rybák, J. Bibcode: 2011SoPh..273..393M Altcode: 2011SoPh..tmp..128M; 2011SoPh..tmp..183M; 2011SoPh..tmp..252M A dm-radio emission with fiber bursts observed on 11 July 2005 was analyzed using wavelet filtration and spectral methods. In filtered radio spectra we found structures with different characteristic period P and frequency drift FD: i) fiber substructures (composed of dot emissions) with P1≈ 0.5 s, FD1=− 87 MHz s−1 on average, ii) fiber structures with P2≈1.9 s, and iii) drifting structures with P3≈81.4 s, FD2=− 8.7, + 98.5, and − 21.8 MHz s−1. In the wavelet spectra we recognized patterns having the form of tadpoles. They were detected with the same characteristic periods P as found for the filtered structures. The frequency drift of the tadpole heads is found to be equal to the frequency drift of some groups of fibers for the long-period wavelet tadpoles (P3) and to the frequency drift of individual fibers for the short-period tadpoles (P2). Considering these wavelet tadpoles as signatures of propagating magnetoacoustic wave trains, the results indicate the presence of several wave trains in the fibers' source. While the long-period wave trains trigger or modulate a whole group of fibers, the short-period ones look like being connected with individual fiber bursts. This result supports the model of fibers based on magnetoacoustic waves. Using a density model of the solar atmosphere we derived the velocities of the magnetoacoustic waves, 107 and 562 km s−1, and setting them equal to the Alfvén ones we estimated the magnetic field in the source of fiber bursts as 10.7 and 47.8 G. Title: Millisecond Radio Spikes in the Decimetric Band Authors: Da̧browski, B. P.; Rudawy, P.; Karlický, M. Bibcode: 2011SoPh..273..377D Altcode: 2011SoPh..tmp..162D; 2011SoPh..tmp..231D; 2011SoPh..tmp...85D We present the results of the analysis of thirteen events consisting of dm-spikes observed in Toruń between 15 March 2000 and 30 October 2001. The events were obtained with a very high time resolution (80 microseconds) radio spectrograph in the 1352 - 1490 MHz range. These data were complemented with observations from the radio spectrograph at Ondřejov in the 0.8 - 2.0 GHz band. We evaluated the basic characteristics of the individual spikes (duration, spectral width, and frequency drifts), as well as their groups and chains, the location of their emission sources, and the temporal correlations of the emissions with various phases of the associated solar flares. We found that the mean duration and spectral width of the radio spikes are equal to 0.036 s and 9.96 MHz, respectively. Distributions of the duration and spectral widths of the spikes have positive skewness for all investigated events. Each spike shows positive or negative frequency drift. The mean negative and positive drifts of the investigated spikes are equal to −776 MHz s−1 and 1608 MHz s−1, respectively. The emission sources of the dm-spikes are located mainly at disk center. We have noticed two kinds of chains, with and without frequency drifts. The mean durations of the chains vary between 0.067 s and 0.509 s, while their spectral widths vary between 7.2 MHz and 17.25 MHz. The mean duration of an individual spike observed in a chain was equal to 0.03 s. While we found some agreement between the global characteristics of the groups of spikes recorded with the two instruments located in Toruń and Ondřejov, we did not find any one-to-one relation between individual spikes. Title: Diagnostics of non-thermal distributions in solar flare spectra observed by RESIK and RHESSI Authors: Kulinová, A.; Kašparová, J.; Dzifčáková, E.; Sylwester, J.; Sylwester, B.; Karlický, M. Bibcode: 2011A&A...533A..81K Altcode: 2011arXiv1109.1011K Context. During solar flares an enormous amount of energy is released, and the charged particles, like electrons, are accelerated. These non-thermal electrons interact with the plasma in various parts of solar flares, where the distribution function of electrons can therefore be non-Maxwellian.
Aims: We focus on the non-thermal components of the electron distribution in the keV range and analyse high-energy resolution X-ray spectra detected by RESIK and RHESSI for three solar flares.
Methods: In the 2-4 keV range we assume that the electron distribution can be modelled by an n-distribution. Using a method of line-intensity ratios, we analyse allowed and satellite lines of Si observed by RESIK and estimate the parameters of this n-distribution. At higher energies we explore RHESSI bremsstrahlung spectra. Adopting a forward-fitting approach and thick-target approximation, we determine the characteristics of injected electron beams.
Results: RHESSI non-thermal component associated with the electron beam is correlated well with presence of the non-thermal n-distribution obtained from the RESIK spectra. In addition, such an n-distribution occurs during radio bursts observed in the 0.61-15.4 GHz range. Furthermore, we show that the n-distribution could also explain RHESSI emission below ~5 keV. Therefore, two independent diagnostics methods indicate the flare plasma being affected by the electron beam can have a non-thermal component in the ~2-5 keV range, which is described by the n-distribution well. Finally, spectral line analysis reveals that the n-distribution does not occupy the same location as the thermal component detected by RHESSI at ~10 keV.

Appendix A is available in electronic form at http://www.aanda.org Title: Filament destabilization and CME release during a long duration flare Authors: Zuccarello, F.; Contarino, L.; Farnik, F.; Karlicky, M.; Romano, P.; Ugarte-Urra, I. Bibcode: 2011A&A...533A.100Z Altcode: Context. During complex and long duration solar flares, several filament destabilizations or eruptions can occur that are often related to coronal mass ejections (CMEs).
Aims: We describe the study of an X3.8 long duration event (LDE) that occurred in NOAA 10720 on 17 January 2005 and was characterized by three filament destabilizations and two CMEs.
Methods: Using multi-wavelength data provided by both ground-based instruments and satellites, in addition to MDI magnetograms, we investigated the morphological and magnetic evolution of the active region before and during the LDE.
Results: Our analysis of Hα and 1600 Å images showed that initially a two-ribbon structure developed in the central part of the active region, where a filament was previously observed. At a later time, two bright ribbons (in the most eastern side) and a strong brightness increase (at the western outskirt of the active region) were simultaneously observed. In a subsequent time interval, a new pair of ribbons was observed in the western side of the active region. Moreover, a linear force-free field extrapolation helped identify a null point in the central part of the active region.
Conclusions: The initial filament destabilization that occurred in the central part of NOAA 10720 was probably due to magnetic flux emergence and photospheric shearing motions, which caused a slow tether-cutting process beneath the filament. The rearrangement of the magnetic field configuration, occurring in the same area as the location of the null point, changed the magnetic field connectivity in the active region, triggering two filament eruptions in the eastern and western part of the active region and two halo CMEs, in a kind of domino effect. Title: Spontaneous Current-layer Fragmentation and Cascading Reconnection in Solar Flares. I. Model and Analysis Authors: Bárta, Miroslav; Büchner, Jörg; Karlický, Marian; Skála, Jan Bibcode: 2011ApJ...737...24B Altcode: 2010arXiv1011.4035B Magnetic reconnection is commonly considered to be a mechanism of solar (eruptive) flares. A deeper study of this scenario reveals, however, a number of open issues. Among them is the fundamental question of how the magnetic energy is transferred from large, accumulation scales to plasma scales where its actual dissipation takes place. In order to investigate this transfer over a broad range of scales, we address this question by means of a high-resolution MHD simulation. The simulation results indicate that the magnetic-energy transfer to small scales is realized via a cascade of consecutively smaller and smaller flux ropes (plasmoids), analogous to the vortex-tube cascade in (incompressible) fluid dynamics. Both tearing and (driven) "fragmenting coalescence" processes are equally important for the consecutive fragmentation of the magnetic field (and associated current density) into smaller elements. At the later stages, a dynamic balance between tearing and coalescence processes reveals a steady (power-law) scaling typical of cascading processes. It is shown that cascading reconnection also addresses other open issues in solar-flare research, such as the duality between the regular large-scale picture of (eruptive) flares and the observed signatures of fragmented (chaotic) energy release, as well as the huge number of accelerated particles. Indeed, spontaneous current-layer fragmentation and the formation of multiple channelized dissipative/acceleration regions embedded in the current layer appear to be intrinsic to the cascading process. The multiple small-scale current sheets may also facilitate the acceleration of a large number of particles. The structure, distribution, and dynamics of the embedded potential acceleration regions in a current layer fragmented by cascading reconnection are studied and discussed. Title: Electron acceleration in a wavy shock front Authors: Vandas, M.; Karlický, M. Bibcode: 2011A&A...531A..55V Altcode: Context. It is known that electrons are accelerated at nearly perpendicular shocks by the drift mechanism. And it is also known that energy gain of electrons caused by this mechanism is not very high. Therefore it was suggested in the past that the energy gain might be increased if shocks had wavy fronts. For instance, there were attempts to explain coronal type II burst and their fine structure by electron acceleration in a wavy shock front.
Aims: We studied electron acceleration numerically at nearly perpendicular wavy shocks for coronal conditions and compared it with analytical results on electron acceleration at nearly perpendicular plane shocks.
Methods: An analytical model of a wavy shock front was used and trajectories of electrons in it and around it were calculated numerically in a guiding centre approximation.
Results: We found that energy gains of electrons at a wavy shock front and a corresponding smoothed-into-plane shock on the average were comparable. That is why they do not depend significantly on the shock thickness, magnetic field profile inside the shock, and shock wavy form. They do depend on the angle between the smoothed shock front and ambient magnetic field.
Conclusions: On average, a wavy shock front does not significantly increase an acceleration efficiency. Energy gain remarkably exceeds an average level for some combinations of initial parameters. Distribution functions of accelerated electrons have a patchy structure, which is prone to inducing plasma instabilities that will generate plasma waves. This may have relevance to the problem of type II burst origin. 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: Fluctuation analysis of solar radio bursts associated with geoeffective X-class flares Authors: Veronese, T. B.; Rosa, R. R.; Bolzan, M. J. A.; Rocha Fernandes, F. C.; Sawant, H. S.; Karlicky`, M. Bibcode: 2011JASTP..73.1311V Altcode: High temporal resolution solar observations in the decimetric range (1-3 GHz) can provide additional information on solar active regions dynamics and thus contribute to better understanding of solar geoeffective events as flares and coronal mass ejections. The June 6, 2000 flares are a set of remarkable geoeffective eruptive phenomena observed as solar radio bursts (SRB) by means of the 3 GHz Ondrejov Observatory radiometer. We have selected and analyzed, applying detrended fluctuation analysis (DFA), three decimetric bursts associated to X1.1, X1.2 and X2.3 flare-classes, respectively. The association with geomagnetic activity is also reported. DFA method is performed in the framework of a radio burst automatic monitoring system. Our results may characterize the SRB evolution, computing the DFA scaling exponent, scanning the SRB time series by a short windowing before the extreme event. For the first time, the importance of DFA in the context of SRB monitoring analysis is presented. Title: Electron acceleration by a wavy shock front: details on angular distribution Authors: Vandas, Marek; Karlický, Marian Bibcode: 2011IAUS..274..201V Altcode: We studied numerically electron acceleration by a perpendicular wavy shock. Distribution function of accelerated electrons is highly anisotropic, with many sharp peaks. The peaks are caused by (usually single) reflections of electrons by the shock and subsequent transmission. Title: ALMA and solar research Authors: Karlický, Marian; Bárta, Miroslav Bibcode: 2011IAUS..274..284K Altcode: The ALMA (Atacama Large Millimeter/sub-millimeter Array) is the large interferometer that will consist up to 64 high-precision antennas operating in the 31.3 - 950 GHz frequency range. In this range unique observations in cosmology, cold universe, galaxies, stars and their formations, and so on are expected. Among these objectives there is a unique possibility to observe the Sun and to address outstanding issues of solar physics. The ALMA is shortly described and then the new ESO-ALMA European node (ARC) built at Ondřejov Observatory is presented. The new ARC is the only one in Europe oriented to solar physics. The requirements and limitations for ALMA solar observations, as well as some examples of possible solar-oriented ALMA projects, are mentioned. Title: Electromagnetic emission by subsequent processes L->L'+S and L+L'->T Authors: Karlický, Marian; Bárta, Miroslav Bibcode: 2011IAUS..274..252K Altcode: Using a 2.5-D electromagnetic particle-in-cell (PIC) model, very early stages of a generation of the electromagnetic emission produced by a monochromatic Langmuir wave are studied. It is found that the electromagnetic emission, which is dominant on the harmonic of the plasma frequency, starts to be generated in a very small region of k-vectors. Later on the k-vectors of this emission are scattered around a `circle' (in our 2-D case), given by the relations for the L+L'->T process. Analytical analysis of two subsequent processes L->L'+S a L+L'->T confirms these results. Title: Separation of solar radio bursts in a complex spectrum Authors: Mészárosová, Hana; Rybák, Ján; Karlický, Marian; Jiřička, Karel Bibcode: 2011IAUS..274..150M Altcode: Radio spectra, observed during solar flares, are usually very complex (many bursts and fine structures). We have developed a new method to separate them into individual bursts and analyze them separately. The method is used in the analysis of the 0.8-2.0 GHz radio spectrum of the April 11, 2001 event, which was rich in drifting pulsating structures (DPSs). Using this method we showed that the complex radio spectrum consists of at least four DPSs separated with respect to their different frequency drifts (-115, -36, -23, and -11 MHz s-1). These DPSs indicate a presence of at least four plasmoids expected to be formed in a flaring current sheet. These plasmoids produce the radio emission on close frequencies giving thus a mixture of superimposed DPSs observed in the radio spectrum. Title: Successive Merging of Plasmoids and Fragmentation in a Flare Current Sheet and Their X-Ray and Radio Signatures Authors: Karlický, Marian; Bárta, Miroslav Bibcode: 2011ApJ...733..107K Altcode: 2011arXiv1101.4846K Based on our recent MHD simulations, a conception of the successive merging of plasmoids and fragmentation in the current sheet in the standard flare model is presented. Then, using a 2.5-dimensional electromagnetic particle-in-cell model with free boundary conditions, these processes are modeled on the kinetic level of plasma description. We recognize the plasmoids that mutually interacted and finally merged into one large plasmoid. Between interacting plasmoids, additional plasmoids and current sheets on smaller spatial scales were formed, congruent with the fragmentation found in MHD simulations. During interactions (merging-coalescences) between the plasmoids, the electrons were very efficiently accelerated and heated. We find that after a series of such merging processes, the electrons in some regions reached the energies necessary for emission in the hard X-ray range. Considering these energetic electrons and assuming a plasma density of 109-1010 cm-3 and a source volume equal to the 2007 December 31 flare, we compute the X-ray spectra as produced by the bremsstrahlung emission process. Comparing these spectra with observations, we think that these processes can explain the observed above-the-loop-top hard X-ray sources. Furthermore, we show that the process of fragmentation between two merging plasmoids can generate narrow-band dm-spikes. Formulae for schematic fractal reconnection structures are derived. Title: Quasi-periodic oscillations in solar X-ray sources Authors: Mészárosová, Hana; Karlický, Marian; Fárník, František Bibcode: 2011IAUS..274..255M Altcode: We have searched for quasi-periodic oscillations in the hard X-ray emission of solar flares. We have selected 14 flare events which were divided into two groups: a) the events with the X-ray sources located at the flare loop footpoints and b) the events with the X-ray source above the solar limb, i.e. with the loop-top X-ray source. We found that while in the case with the footpoints X-ray sources the quasi-periods of the recorded oscillations were in the interval 2-380 s, in the events with loop-top sources only the quasi-periods longer than 50 s were recognized. These results are probably connected with the MHD oscillation modes of the flaring loop. While the long periods, which are dominant in loop-top sources, are produced by acoustic oscillations along the whole long loop, in the layers close to the loop footpoints also the MHD wave modes in shorter structures with shorter periods are generated. Title: Magnetoacoustic waves in the narrowband dm-spikes sources Authors: Karlický, M.; Jelínek, P.; Mészárosová, H. Bibcode: 2011A&A...529A..96K Altcode:
Aims: A new type of analysis of the narrowband dm-spikes in solar radio radiation is introduced to look for magnetoacoustic waves in their sources.
Methods: The Fourier and wavelet methods were used. For the first time, the tadpole structures in the wavelet spectra of this radio emission were searched for.
Results: Fifteen groups of the narrowband dm-spikes, observed during solar flares, were selected and analyzed by the Fourier and wavelet analysis methods. We found that the mean Fourier spectra of these spikes in frequency space are the powerlaws with a power-law index in the range -1.2 --1.8. Furthermore, their wavelet spectra based on time series reveal tadpoles at some frequencies, which indicates the presence of magnetoacoustic waves. These waves are interpreted as propagating through a source of the narrowband dm-spikes. It is proposed that the spikes are generated by driven coalescence and fragmentation processes in turbulent reconnection outflow. This interpretation is supported by a simultaneous observation of drifting pulsating structures (DPSs) and spikes. Finally, modeling of the magnetoacoustic waves and tadpoles in the Harris current sheet supports this interpretation. 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: Spontaneous Current-layer Fragmentation and Cascading Reconnection in Solar Flares. II. Relation to Observations Authors: Bárta, Miroslav; Büchner, Jörg; Karlický, Marian; Kotrč, Pavel Bibcode: 2011ApJ...730...47B Altcode: 2010arXiv1011.6069B In a paper by Bárta et al., the authors addressed by means of high-resolution MHD simulations some open questions on the CSHKP scenario of solar flares. In particular, they focused on the problem of energy transfer from large to small scales in the decaying flare current sheet (CS). Their calculations suggest that magnetic flux ropes (plasmoids) are formed in a full range of scales by a cascade of tearing and coalescence processes. Consequently, the initially thick current layer becomes highly fragmented. Thus, the tearing and coalescence cascade can cause an effective energy transfer across the scales. In this paper, we investigate whether this mechanism actually applies in solar flares. We extend the MHD simulation by deriving model-specific features that can be searched for in observations. The results of the underlying MHD model show that the plasmoid cascade creates a specific hierarchical distribution of non-ideal/acceleration regions embedded in the CS. We therefore focus on the features associated with the fluxes of energetic particles, in particular on the structure and dynamics of emission regions in flare ribbons. We assume that the structure and dynamics of diffusion regions embedded in the CS imprint themselves into the structure and dynamics of flare-ribbon kernels by means of magnetic field mapping. Using the results of the underlying MHD simulation, we derive the expected structure of ribbon emission and extract selected statistical properties of the modeled bright kernels. Comparing the predicted emission and its properties with the observed ones, we obtain a good agreement between the two. Title: Radio Evidence of Break-out Reconnection? Authors: Aurass, H.; Mann, G.; Zlobec, P.; Karlický, M. Bibcode: 2011ApJ...730...57A Altcode: We reconsider the 2003 October 28 X17 flare/coronal mass ejection (CME), studying the five minutes immediately before the impulsive flare phase (not discussed in previous work). To this aim we examine complementary dynamic radio spectrograms, single frequency polarimeter records, radio images, space-based longitudinal field magnetograms, and ultraviolet images. We find widely distributed faint and narrowband meter wave radio sources located outside active regions but associated with the boundaries of magnetic flux connectivity cells, inferred from the potential extrapolation of the observed photospheric longitudinal field as a model for coronal magnetic field structures. The meter wave radio sources occur during the initial decimeter wave effects, which are well known to be associated with filament destabilization in the flaring active region (here NOAA 10486). Antiochos et al. predict in their break-out model for CME initiation that "... huge phenomena ... may be controlled by detailed plasma processes that occur in relatively tiny regions." They suggest that the expected faint energy release "... on long field lines far away from any neutral line ... may be detectable in radio/microwave emission from nonthermal particles..." In this paper, we describe meter wave sources whose properties correctly coincide with the quoted predictions of the break-out reconnection model of the CME initiation. 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: Separation of drifting pulsating structures in a complex radio spectrum of the 2001 April 11 event Authors: Mészárosová, H.; Rybák, J.; Karlický, M. Bibcode: 2011A&A...525A..88M Altcode:
Aims: We present new method of separating a complex radio spectrum into single radio bursts. The method is used in the analysis of the 0.8-2.0 GHz radio spectrum of the 2001 April 11 event, which was rich in drifting pulsating structures.
Methods: The method is based on the wavelet analysis technique, which separates different spatial-temporal components (radio bursts) that are difficult to recognize in the original radio spectrum.
Results: We show with this method that the complex radio spectrum observed during the 2001 April 11 event consists of at least four drifting pulsating structures (DPSs). These structures were separated with respect to their different frequency drifts. The DPSs indicate at least four plasmoids that are supposed to be formed in a flaring current sheet. Title: Solar Research with ALMA Authors: Karlický, M.; Bárta, M.; Da̧browski, B. P.; Heinzel, P. Bibcode: 2011SoPh..268..165K Altcode: 2010SoPh..tmp..231K; 2010SoPh..tmp..207K The Atacama Large Millimeter/sub-millimeter Array (ALMA) is a large interferometer that will consist up to 64 high-precision antennas operating in the 31.3 - 950 GHz frequency range. In this frequency range, which is largely unexplored, unique observations with a broad range of scientific objectives (cosmology, cold universe, galaxies, stars and their formation, planets and so on) are expected. Among these tasks there is a unique possibility to observe the Sun and to address several outstanding issues of solar physics. First, the ALMA is briefly described and then the new ESO-ALMA European node (ARC), built at Ondřejov Observatory, is presented. In Europe, this ARC is the only one oriented to solar physics. Consequently, the requirements and limitations for ALMA solar observations, as well as some examples of possible solar-oriented ALMA projects, are shown. A procedure of the preparation and submission of proposals for ALMA observations is mentioned. Title: Fine structures of radio bursts observed during the February 12, 2010 flare Authors: Jiřička, K.; Karlický, M. Bibcode: 2011CEAB...35..215J Altcode: Using the newly reconstructed Ondřejov radio spectrograph the radio emission of the February 12, 2010 flare was studied in details. The high-time resolution of the spectrograph (10 ms) reveals several interesting fine structures in (a) type III burst, (b) reverse drift burst and (c) drifting pulsating structures. Furthermore, an unique type of short-lasting and narrowband spikes was recognized. These fine structures give a more detailed information about superthermal electrons producing these bursts and about the electron acceleration. 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: Reconnection of a Kinking Flux Rope Triggering the Ejection of a Microwave and Hard X-Ray Source II. Numerical Modeling Authors: Kliem, B.; Linton, M. G.; Török, T.; Karlický, M. Bibcode: 2010SoPh..266...91K Altcode: 2010SoPh..tmp..149K; 2010arXiv1007.2147K Numerical simulations of the helical (m=1) kink instability of an arched, line-tied flux rope demonstrate that the helical deformation enforces reconnection between the legs of the rope if modes with two helical turns are dominant as a result of high initial twist in the range Φ≳6π. Such a reconnection is complex, involving also the ambient field. In addition to breaking up the original rope, it can form a new, low-lying, less twisted flux rope. The new flux rope is pushed downward by the reconnection outflow, which typically forces it to break as well by reconnecting with the ambient field. The top part of the original rope, largely rooted in the sources of the ambient flux after the break-up, can fully erupt or be halted at low heights, producing a "failed eruption." The helical current sheet associated with the instability is squeezed between the approaching legs, temporarily forming a double current sheet. The leg - leg reconnection proceeds at a high rate, producing sufficiently strong electric fields that it would be able to accelerate particles. It may also form plasmoids, or plasmoid-like structures, which trap energetic particles and propagate out of the reconnection region up to the top of the erupting flux rope along the helical current sheet. The kinking of a highly twisted flux rope involving leg - leg reconnection can explain key features of an eruptive but partially occulted solar flare on 18 April 2001, which ejected a relatively compact hard X-ray and microwave source and was associated with a fast coronal mass ejection. Title: Reconnection of a Kinking Flux Rope Triggering the Ejection of a Microwave and Hard X-ray Source I. Observations and Interpretation Authors: Karlický, M.; Kliem, B. Bibcode: 2010SoPh..266...71K Altcode: 2010arXiv1007.2146K; 2010SoPh..tmp..139K Imaging microwave observations of an eruptive, partially occulted solar flare on 18 April 2001 suggest that the global structure of the event can be described by the helical kink instability of a twisted magnetic flux rope. This model is suggested by the inverse gamma shape of the source exhibiting crossing legs of a rising flux loop and by evidence that the legs interact at or near the crossing point. The interaction is reflected by the location of peak brightness near the crossing point and by the formation of superimposed compact nonthermal sources most likely at or near the crossing point. These sources propagate upward along both legs, merge into a single, bright source at the top of the structure, and continue to rise at a velocity >1000 km s−1. The compact sources trap accelerated electrons which radiate in the radio and hard X-ray ranges. This suggests that they are plasmoids, although their internal structure is not revealed by the data. They exhibit variations of the radio brightness temperature at a characteristic time scale of ∼ 40 s, anti-correlated to their area, which also support their interpretation as plasmoids. Their propagation path differs from the standard scenario of plasmoid formation and propagation in the flare current sheet, suggesting the helical current sheet formed by the instability instead. Title: Modeling of Solar Flare Plasma and Its Radiation Authors: Varady, Michal; Kasparova, Jana; Moravec, Zdeněk; Heinzel, Petr; Karlicky, Marian Bibcode: 2010ITPS...38.2249V Altcode: No abstract at ADS Title: Tearing, coalescence and fragmentation processes in solar flare current sheet and drifting pulsating structures Authors: Karlický, M. Bibcode: 2010AdSpR..46..377K Altcode: The paper presents a summary of results from two different simulations which study the tearing, coalescence and fragmentation of current sheets, the associated production of energetic electrons and of plasma waves from these electrons which could explain drifting pulsation structures observed at radio wavelengths. Using a 2.5-D particle-in-cell (PIC) model of the current sheet it is shown that due to the tearing mode instability the current sheet tears into plasmoids and these plasmoids later on coalesce into larger ones. During these processes electrons are accelerated and they produce observable electromagnetic waves. Furthermore, the 3-D PIC model with two current sheets extended in the electric current direction shows their fast fragmentation associated with the exponential dissipation of the free magnetic field energy. An example of the drifting pulsating structure which is considered to be a radio signature of the above mentioned processes in solar flares is shown. Title: The X3.8 flare in NOAA 10720 : a new example of the domino effect Authors: Farnik, Frantisek; Contarino, L.; Romano, P.; Zuccarello, F.; Karlicky, M. Bibcode: 2010shin.confE..16F Altcode: We have studied an X3.8 flare occurred in NOAA 10720 on 17 January 2005 using chromospheric and photospheric images acquired at INAF - Catania Astrophysical Observatory, TRACE images acquired at 1600 ?, full disk MDI magnetograms, RHESSI hard X-ray data and Ondrejov radio data, in order to investigate the morphological and magnetic evolution of the active region before and during the flare. The analysis of H-alpha and 1600 ? images showed that initially a two-ribbon structure developed in the central part of the active region, later two bright ribbons (in the most eastern side) and a strong brightness increase (at the western boundary of the active region) were observed contemporarily. In the following time interval a new pair of ribbons was observed in the central-western side of the region. The analysis of the magnetic configuration and the location of a null point allowed us to single out the sites where magnetic reconnection processes were most likely to occur. Based on this result and on the analysis of H-alpha, TRACE, RHESSI and Ondrejov data, we interpreted this behavior as due to an initial filament eruption that occurred in the central part of NOAA 10720, where the null point was located, and later on, as in a domino effect, other filament destabilization or eruption took place in the eastern and western part of the active region. Title: Relation between the Spatial Distribution and Spectral Index of Superthermal Electron Distribution in Solar cm-Radio Sources Authors: Yasnov, L. V.; Karlický, M. Bibcode: 2010SoPh..264...93Y Altcode: 2010SoPh..tmp...90Y A series of solar cm-radio bursts are analyzed by a new inverse method estimating spatial changes of the superthermal electron distribution in solar cm-radio burst sources. It is found that the measure of the spatial change of superthermal electrons in the radio source νn is always greater than that for the magnetic field νB and it is linearly dependent on the spectral index of the electrons δ as νn≈0.5δ. This relation is explained in the simplified flare-loop model integrating the analytical solutions of the Fokker - Planck equation. The mean value of νB is found to be 0.36±0.04, which is very close to the value of νB=0.38±0.02 derived from the dependence of the magnetic field strength on the height in the active region measured by RATAN-600. Title: Radio spectra generated during coalescence processes of plasmoids in a flare current sheet Authors: Karlický, M.; Bárta, M.; Rybák, J. Bibcode: 2010A&A...514A..28K Altcode:
Aims: Motivated by observations of the drifting pulsating structures (DPSs) in solar radio spectra, we study the electromagnetic (radio) emission generated during tearing and coalescence processes in a flare current sheet.
Methods: For numerical simulations, we used a 2.5-D particle-in-cell electromagnetic relativistic code. Numerical data were analyzed by the wavelet methods.
Results: It is found that the electromagnetic emission is generated during a coalescence of plasmoids, and it has a quasi-periodic character. Detailed analysis reveals that the electromagnetic emission is produced around the interacting plasmoids just before their coalescence into a larger one. The period in variations of electromagnetic emission corresponds to that of magnetic field at the same region. Reflections of the electromagnetic waves between interacting plasmoids are recognized. The computed and observed periodicities are discussed. The similarity of the DPSs with some radio bursts observed during star flares indicates a broader applicability for this model. Title: Subsecond (0.1 s) Pulsations in the 11 April 2001 Radio Event Authors: Karlický, M.; Zlobec, P.; Mészárosová, H. Bibcode: 2010SoPh..261..281K Altcode: 2010SoPh..tmp....9K Radio pulsations observed during the 11 April 2001 event at six single frequencies (237, 327, 408, 610, 1420, and 2695 MHz) by the Trieste radio-polarimeter with a time resolution 10 ms are analyzed. A wavelet analysis method as well as time delay and polarization measurements are used. Both methods reveal pulsations with a period of about 0.1 s at all observed frequencies. Furthermore, the 0.1 s pulsations drift toward higher and lower frequencies, starting at about 1420 MHz. The polarization of pulsations increases with frequency and time. The remarkable fact that the detected 0.1 s period of pulsations does not depend on frequency in a very broad frequency range is discussed in terms of existing models of pulsations. Title: Nonlinear analysis of decimetric solar bursts Authors: Rosa, Reinaldo R.; Bolzan, Mauricio J. A.; Fernandes, Francisco C. R.; Sawant, H. S.; Karlický, Marian Bibcode: 2010IAUS..264..279R Altcode: The solar radio emissions in the decimetric frequency range (above 1 GHz) are very rich in temporal and spectral fine structures due to nonlinear processes occurring in the magnetic structures on the corresponding active regions. In this paper we characterize the singularity spectrum, f(α), for solar bursts observed at 1.6, 2.0 and 3 GHz. We interpret our findings as evidence of inhomogeneous plasma turbulence driving the underlying plasma emission process and discuss the nonlinear multifractal approach into the context of geoeffective solar active regions. Title: Singularity Spectra and Generalized Extreme Value Distributions of Decimetric Radio Bursts Associated with Flares Authors: Rosa, Reinaldo; Veronese, Thalita; José Alves Bolzan, Maurício; Fernandes, Francisco; Cecatto, José; Karlicky, Marian; Sawant, Hanumant Bibcode: 2010cosp...38.2841R Altcode: 2010cosp.meet.2841R The search for turbulent-like patterns and extreme dynamics from time series of solar radio burts has recently advanced due to high-resolution and high-sensitivity observations. Such so-lar radio emissions in the decimetric frequency range (above 1 GHz) are very rich in temporal and spectral fine structures due to nonlinear processes occurring in the magnetic structures on the corresponding active regions. In this paper we analize the decimetric fine structures of 8 X-Class Flares events observed from Brazilian Solar Spectroscope (1-2.5 GHz) and On-drejov radiospectrograph (3 GHz). The Singularity Spectra [1] and Generalized Extreme Value (GEV) distribution [2] are obtained and we interpret our findings as evidence of inhomogeneous lagrangian-like MHD turbulence driving the underlying non-gaussian plasma emission process. Once GEV statistical behavior was found for 75% of the events, the flare ocurrence is discussed into the context of solar extreme events. [1] Bolzan et al., Ann. Geophys., 27, 569-576, 2009. [2] S. Coles, An Introduction to Statistical Modeling of Extreme Values, Springer Series in Statistics, (2001) 228 pp., Springer-Verlag, Berlin, Germany. Title: Multi-scale MHD approach to the current sheet filamentation in solar coronal reconnection Authors: Bárta, M.; Büchner, J.; Karlický, M. Bibcode: 2010AdSpR..45...10B Altcode: Magnetic field reconnection - considered now as a key process in the commonly accepted standard scenario of solar flares - spans over many mutually coupled scales from the global flare dimensions (≈10 Mm) down to the scale, where non-ideal kinetic plasma effects takes place (≈10 m). Direct numerical simulation covering all the scales is, therefore, impossible. Nevertheless, the filamentary nature of the current sheet fragmentation together with rescalability of ideal-MHD equations - which governs the processes before reaching the scales of non-ideal plasma response - allow to describe the large- and intermediate-scale dynamics of reconnection flow with highly reduced request for number of grid points. Since the smaller-scale (and faster) dynamics sets-in only in regions of enhanced current sheet filamentation, we focus just on these areas, which occupy only a small fraction of the total volume. Generally, as the fragmentation continues, it forms a cascade of filamentation until kinetic non-ideal processes come to play. Information relevant for description of the smaller-scale physics occupies only a small fraction of grid-cells describing the large-scale dynamics. Thus, one can subsequently zoom-in onto the regions of continuing current filamentation. The current-sheet fragmentation cascade anticipated by Shibata and Tanuma [Shibata, K., Tanuma, S. Plasmoid-induced-reconnection and fractal reconnection. Earth, Planets, and Space 53, 473-482, 2001], creates multiple dissipative regions in a single current sheet, which can play a key role for DC-field particle acceleration in a flare reconnection. The main goal of the paper is to numerically investigate the relevance of cascading reconnection for solar flares. The numerical algorithm implemented for that purpose and first results are presented in this research note. Proposed algorithm - though motivated by the self-similar nature of MHD equations - belongs in fact to the class of block-structured Adaptive Mesh Refinement codes. Title: Spontaneous current sheet fragmentation and particle acceleration in cascading magnetic reconnection in solar flares Authors: Bárta, Miroslav; Büchner, Jörg; Karlicky, Marian Bibcode: 2010cosp...38.1955B Altcode: 2010cosp.meet.1955B The question how is the magnetic energy -accumulated in solar eruptive flares on relatively large scales (the thickness of the current layer behind ejected CME is supposed to be approx. 1000 km) -transported towards the dissipative scales (approx. 10 m in the solar corona) re-mains as one of the main open issues in the solar flare theory. To resolve this problem, Shibata and Tanuma (Earth, Planet Space 53, 2001) have suggested a concept of cascading (or 'fractal') reconnection. We studied this concept using numerical MHD simulations involving AMR tech-nique in order to gain broader range of resolved scales. The results of our simulations confirmed relevance of the mechanism of tearing cascade suggested by Shibata and Tanuma. In addition to that, we found further fragmentation of the current layer in the perpendicular direction: secondary current sheets are formed between interacting magnetic islands (plasmoids). These current layers are possibly subjected to the same kind of processes (tearing cascade + forced coalescence of tearing-formed plasmoids) as the original (global) current layer formed as conse-quence of CME ejection. Thus, we suggest to supplement the original cascading-reconnection scenario by the possibility of spontaneous current sheet fragmentation in the second dimen-sion. This finding is in agreement with general expectations of spontaneous isotropisation of the turbulent cascade. Propagation of the cascading process to he second dimension increases the efficiency of the reconnection process and has also clear consequences for theory of particle acceleration in the solar flares as such a fragmented current sheet can host many non-ideal regions capable to accelerate particles. Title: An Estimation of Spatial Variations of Magnetic Field and Superthermal Electron Distribution in cm-Radio Burst Sources Authors: Yasnov, L. V.; Karlický, M. Bibcode: 2009SoPh..260..363Y Altcode: The paper presents a new method of the estimation of spatial variations of the magnetic field and superthermal electron distribution in solar cm-radio burst sources. The method is based on minimization of the difference between the theoretical and observed radio fluxes and on the analysis of several burst spectra recorded in different moments of time. Several solar cm-radio bursts are analyzed by this method. It is found that the measure of the spatial variations of the superthermal electron distribution in the radio source is always larger than that for the magnetic field. Title: Electron beam - plasma system with the return current and directivity of its X-ray emission Authors: Karlický, M.; Kašparová, J. Bibcode: 2009A&A...506.1437K Altcode: 2009arXiv0909.0146K Aims: An evolution of the electron distribution function in the beam-plasma system with the return current is computed numerically for different parameters. The X-ray bremsstrahlung corresponding to such an electron distribution is calculated and the directivity of the X-ray emission is studied.
Methods: For computations of the electron distribution functions we used a 3-D particle-in-cell electromagnetic code. The directivity of the X-ray emission was calculated using the angle-dependent electron-ion bremsstrahlung cross-section.
Results: It was found that the resulting electron distribution function depends on the magnetic field assumed along the electron beam propagation direction. For small magnetic fields the electron distribution function becomes broad in the direction perpendicular to the beam propagation due to the Weibel instability and the return current is formed by the electrons in a broad and shifted bulk of the distribution. On the other hand, for stronger magnetic fields the distribution is more extended in the beam-propagation direction and the return current is formed by the electrons in the extended distribution tail. In all cases, the anisotropy of the electron distribution decreases rapidly due to fast collisionless processes. However, the magnetic field reduces this anisotropy decrease. The X-ray directivity shows the same trend and it is always closer to the isotropic case than that in a simple beaming model. 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: Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares Authors: Sych, R.; Nakariakov, V. M.; Karlicky, M.; Anfinogentov, S. Bibcode: 2009A&A...505..791S Altcode: 2010arXiv1005.3594S A phenomenological relationship between oscillations in a sunspot and quasi-periodic pulsations (QPP) in flaring energy releases at an active region (AR) above the sunspot is established. The analysis of the microwave emission recorded by the Nobeyama Radioheliograph at 17 GHz shows a gradual increase in the power of the 3-min oscillation train in the sunspot associated with AR 10756 before flares in this AR. The flaring light curves are found to be bursty with a period of 3 min. Our analysis of the spatial distribution of the 3-min oscillation power implies that the oscillations follow from sunspots along coronal loops towards the flaring site. It is proposed that QPP in the flaring energy releases can be triggered by 3-min slow magnetoacoustic waves leaking from sunspots. Title: Stationary stagnation point flows in the vicinity of a 2D magnetic null point: I. Systems with vanishing electric field and an X-type magnetic null point Authors: Nickeler, Dieter; Karlicky, Marian; Barta, Miroslav Bibcode: 2009arXiv0909.0836N Altcode: The appearance of eruptive space plasma processes, e.g., in eruptive flares as observed in the solar atmosphere, is usually assumed to be caused by magnetic reconnection. The process of magnetic reconnection is often connected with singular points of the magnetic field. We therefore analyse the system of stationary resistive/non-ideal magnetohydrodynamics (MHD) in the vicinity of singular points of flow and field to determine the boundary between reconnection solutions and non-reconnective solutions. We find conditions to enable the plasma to cross the magnetic separatrices also inside the current sheet, close to the current maximum. The results provide us with the topological and geometrical skeleton of the resistive MHD fields. We therefore have to perform a local analysis of almost all non-ideal MHD solutions with a generalized non-idealness. We use Taylor expansions of the magnetic field, the velocity field and all other physical quantities, including the non-idealness, and with the method of a comparison of the coefficients, the non-linear resistive MHD system is solved analytically. It turns out that not every non-ideal flow is a reconnective flow and that pure resistive/non-ideal MHD only allows for reconnection-like solutions, even if the non-idealness is localized to the region around the magnetic null point. It is necessary that the flow close to the magnetic X-point is also of X-point type to guarantee positive dissipation of energy and annihilation of magnetic flux. If the non-idealness has only a one-dimensional, sheet-like structure, only one separatrix line can be crossed by the plasma flow, similar to reconnective annihilation solutions. Title: Successive Solar Flares and Coronal Mass Ejections on 2005 September 13 from NOAA AR 10808 Authors: Liu, Chang; Lee, Jeongwoo; Karlický, Marian; Prasad Choudhary, Debi; Deng, Na; Wang, Haimin Bibcode: 2009ApJ...703..757L Altcode: 2009arXiv0908.0487L We present a multiwavelength study of the 2005 September 13 eruption from NOAA AR 10808 that produced total four flares and two fast coronal mass ejections (CMEs) within ~1.5 hr. Our primary attention is paid to the fact that these eruptions occurred in close succession in time, and that all of them were located along an S-shaped magnetic polarity inversion line (PIL) of the active region. In our analysis, (1) the disturbance created by the first flare propagated southward along the PIL to cause a major filament eruption that led to the first CME and the associated second flare underneath. (2) The first CME partially removed the overlying magnetic fields over the northern δ spot to allow the third flare and the second CME. (3) The ribbon separation during the fourth flare would indicate reclosing of the overlying field lines opened by the second CME. It is thus concluded that these series of flares and CMEs are interrelated to each other via magnetic reconnections between the expanding magnetic structure and the nearby magnetic fields. These results complement previous works made on this event with the suggested causal relationship among the successive eruptions. Title: ``Drifting tadpoles'' in wavelet spectra of decimetric radio emission of fiber bursts Authors: Mészárosová, H.; Karlický, M.; Rybák, J.; Jiřička, K. Bibcode: 2009A&A...502L..13M Altcode: Aims: The solar decimetric radio emission of fiber bursts was investigated searching for the “drifting tadpole” structures proposed by theoretical studies.
Methods: Characteristic periods with the tadpole pattern were searched for in the radio flux time series by wavelet analysis methods.
Results: For the first time, we have found drifting tadpoles in the wavelet spectra of the decimetric radio emission associated with the fiber bursts observed in July 11, 2005. These tadpoles were detected at all radio frequencies in the 1602-1780 MHz frequency range. The characteristic period of the wavelet tadpole patterns was found to be 81.4 s and the frequency drift of the tadpole heads is -6.8 MHz s-1. These tadpoles are interpreted as a signature of the magnetoacoustic wave train moving along a dense flare waveguide and their frequency drift as a motion of the wave train modulating the radio emission produced by the plasma emission mechanism. Using the Aschwanden density model of the solar atmosphere, only low values of the Alfvén speed and the magnetic field strength in the loop guiding this wave train were derived which indicates a neutral current sheet as the guiding structure. The present analysis supports the model of fiber bursts based on whistler waves. 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: Highlights of the Brazilian Solar Spectroscope Authors: Sawant, H. S.; Cecatto, J. R.; Mészárosová, H.; Faria, C.; Fernandes, F. C. R.; Karlický, M.; de Andrade, M. C. Bibcode: 2009AdSpR..44...54S Altcode: The digital, decimetric (950-2500 MHz) Brazilian Solar Spectroscope (BSS, Sawant, H.S., Subramanian, K.R., Faria, C., et al. Brazilian Solar Spectroscope (BSS). Solar Phys. 200, 167-176, 2001) with high time (10-1000 ms) and frequency (1-10 MHz) resolution is in regular operation since April, 1998, at the National Space Research Institute (INPE) at São José dos Campos, Brazil. The BSS has now been upgraded with a new digital data acquisition and data processing system. The new version of the BSS has improved the observational possibilities with the capability to record up to 200 frequency channels available in the selectable frequency range 950-2500 MHz. The GPS receiver permits the acquisition of data with time accuracy in the order of 0.1 ms. The software system of the BSS is composed by two distinct modules: the first, data acquisition system provides a flexible Graphical User Interface (GUI) that allows one to choose the observational parameters. The second module is the real time visualization system that permits real time visualization of the observed dynamic spectrum and additionally allows procedures for visualization and preliminary analysis of the recorded solar spectra. Using the new visualization system, we have realized two new types of dm-radio fine structures: narrow band type III bursts with positive as well as negative group frequency drift and dots emissions arranged in zebra-like and fiber-like chains. Furthermore, we have found flare generated fast wave trains according to their tadpole signature in wavelet power spectra for a decimetric type IV radio event (June 6, 2000 flare). Title: Response of optical hydrogen lines to beam heating. I. Electron beams Authors: Kašparová, J.; Varady, M.; Heinzel, P.; Karlický, M.; Moravec, Z. Bibcode: 2009A&A...499..923K Altcode: 2009arXiv0904.2084K Context: Observations of hydrogen Balmer lines in solar flares remain an important source of information on flare processes in the chromosphere during the impulsive phase of flares. The intensity profiles of optically thick hydrogen lines are determined by the temperature, density, and ionisation structure of the flaring atmosphere, by the plasma velocities and by the velocity distribution of particles in the line formation regions.
Aims: We investigate the role of non-thermal electrons in the formation regions of Hα, Hβ, and Hγ lines in order to unfold their influence on the formation of these lines. We concentrate on pulse-beam heating varying on a subsecond timescale. Furthermore, we theoretically explore possibility that a new diagnostic tool exists indicating the presence of non-thermal electrons in the flaring chromosphere based on observations of optical hydrogen lines.
Methods: To model the evolution of the flaring atmosphere and the time-dependent hydrogen excitation and ionisation, we used a 1-D radiative hydrodynamic code combined with a test-particle code that simulates the propagation, scattering, and thermalisation of a power-law electron beam in order to obtain the flare heating and the non-thermal collisional rates due to the interaction of the beam with the hydrogen atoms. To not bias the results by other effects, we calculate only short time evolutions of the flaring atmosphere and neglect the plasma velocities in the radiative transfer.
Results: All calculated models have shown a time-correlated response of the modelled Balmer line intensities on a subsecond timescale, with a subsecond timelag behind the beam flux. Depending on the beam parameters, both line centres and wings can show pronounced intensity variations. The non-thermal collisional rates generally result in an increased emission from a secondary region formed in the chromosphere.
Conclusions: Despite the clear influence of the non-thermal electron beams on the Balmer line intensity profiles, we were not able on the basis of our simulations to produce any unambiguous diagnostic of non-thermal electrons in the line-emitting region, which would be based on comparison of individual Balmer line intensity profiles. However, fast line intensity variations, well-correlated with the beam flux variations, represent an indirect indication of pulsating beams. Title: Tadpoles in Wavelet Spectra of a Solar Decimetric Radio Burst Authors: Mészárosová, H.; Karlický, M.; Rybák, J.; Jiřička, K. Bibcode: 2009ApJ...697L.108M Altcode: In the solar decimetric type IV radio event observed on 2001 June 13, we have found wavelet tadpole patterns for the first time. They were detected simultaneously at all radio frequencies in the 1.1-4.5 GHz frequency range. The characteristic period of the wavelet tadpole patterns was found to be 70.9 s. The parameters of the tadpoles on different frequencies are very similar and the correlations between individual radio fluxes are high. These tadpoles are interpreted as a signature of the magnetoacoustic wave train moving along the flare loop through the radio source and modulating its gyrosynchrotron emission. Title: Coronal fast wave trains of the decimetric type IV radio event observed during the decay phase of the June 6, 2000 flare Authors: Mészárosová, H.; Sawant, H. S.; Cecatto, J. R.; Rybák, J.; Karlický, M.; Fernandes, F. C. R.; de Andrade, M. C.; Jiřička, K. Bibcode: 2009AdSpR..43.1479M Altcode: The 22 min long decimetric type IV radio event observed during the decay phase of the June 6, 2000 flare simultaneously by the Brazilian Solar Spectroscope (BSS) and the Ondřejov radiospectrograph in frequency range 1200-4500 MHz has been analyzed. We have found that the characteristic periods of about 60 s belong to the long-period spectral component of the fast wave trains with a tadpole pattern in their wavelet power spectra. We have detected these trains in the whole frequency range 1200-4500 MHz. The behavior of individual wave trains at lower frequencies is different from that at higher frequencies. These individual wave trains have some common as well as different properties. In this paper, we focus on two examples of wave trains in a loop segment and the main statistical parameters in their wavelet power and global spectra are studied and discussed. Title: Kappa distribution and hard X-ray emission of solar flares Authors: Kašparová, J.; Karlický, M. Bibcode: 2009A&A...497L..13K Altcode: 2009arXiv0902.3574K Aims: We investigate whether the so-called kappa distribution, often used to fit electron distributions detected in situ in the solar wind, can describe electrons producing the hard X-ray emission in solar flares.
Methods: Using Ramaty High Energy Solar Spectroscopic imager (RHESSI) flare data we fit spatially- and feature-integrated spectra, assuming a kappa distribution for the mean electron flux spectrum.
Results: We show that a single kappa distribution generally cannot describe spatially integrated X-ray emission composed of both footpoint and coronal sources. In contrast, the kappa distribution is consistent with mean electron spectra producing hard X-ray emission in some coronal sources. Title: On spatial variations of magnetic field and superthermal electron distribution in cm-radio burst source Authors: Yasnov, Leonid V.; Karlický, Marian Bibcode: 2009IAUS..257..353Y Altcode: The paper presents a new method of an estimation of spatial variations of the magnetic field and superthermal electron distribution in solar cm-radio burst sources. The method is based on the analysis of several burst spectra recorded in the different moments of time and on the minimization of the difference between the theoretical and observed radio fluxes. It is found that the measure of the spatial variations of superthermal electron distribution in the radio source is always greater than that for the magnetic field. In most cases this measure has a minimum at the impulsive phase of cm-radio bursts. Title: Cyclic Magnetic Field Reconnection Authors: Karlický, Marian Bibcode: 2009ApJ...692L..72K Altcode: Using a 2.5D electromagnetic particle-in-cell model, we study the magnetic field reconnection around the rotating plasma embedded in a magnetic field. Considering plasma rotation driven by an external electric field, it was found that during one rotational cycle, first the magnetic field energy increases and then decreases to its initial value. The magnetic reconnection occurring during this cycle plays two roles: first, it produces the closed magnetic islands and later on it reopens them to the initial form of magnetic field lines. Thus, the magnetic reconnection can be cyclically repeated in following plasma rotations. Simultaneously, the kinetic particle energy in the system increases due to dissipative processes in this externally driven plasma system. We think that this cyclic reconnection can operate around rapidly rotating stars and in the plasma vortices formed in unstable plasma flows. Title: The X17.2 flare occurred in NOAA 10486: an example of filament destabilization caused by a domino effect Authors: Zuccarello, F.; Romano, P.; Farnik, F.; Karlicky, M.; Contarino, L.; Battiato, V.; Guglielmino, S. L.; Comparato, M.; Ugarte-Urra, I. Bibcode: 2009A&A...493..629Z Altcode: Context: It is now possible to distinguish between two main models describing the mechanisms responsible for eruptive flares : the standard model, which assumes that most of the energy is released, by magnetic reconnection, in the region hosting the core of a sheared magnetic field, and the breakout model, which assumes reconnection occurs at first in a magnetic arcade overlaying the eruptive features.
Aims: We analyze the phenomena observed in NOAA 10486 before and during an X17.2 flare that occurred on 2003 October 28, to study the relationship between the pre-flare and flare phases and determine which model is the most suitable for interpreting this event.
Methods: We performed an analysis of multiwavelength data set available for the event using radio data (0.8-4.5 GHz), images in the visible range (WL and Hα), EUV images (1600 and 195 Å), and X-ray data, as well as MDI longitudinal magnetograms. We determined the temporal sequence of events occurring before and during the X17.2 flare and the magnetic field configuration in the linear force-free field approximation.
Results: The active region was characterized by a multiple arcade configuration and the X17.2 flare was preceded, by ~2 h, by the partial eruption of one filament. This eruption caused reconnection at null points located in the low atmosphere and a decrease in magnetic tension in the coronal field lines overlaying other filaments present in the active region. As a consequence, these filaments were destabilized and the X17.2 flare occurred.
Conclusions: The phenomena observed in NOAA 10486 before and during the X17.2 flare cannot be explained by a simple scenario such as the standard or breakout model, but instead in terms of a so-called domino effect, involving a sequence of destabilizing processes that triggered the flare. Title: Drifting Pulsating Structure in the Post-maximum Phase of the May 13, 2005 Flare Authors: Jiřička, K.; Karlický, M. Bibcode: 2009CEAB...33..217J Altcode: A high-frequency drifting pulsating structure observed in the post-maximum flare phase is analysed in detail. Using the Aschwanden and Benz model (1997) of the solar atmosphere the altitude of the radio source of this structure is estimated and compared with the loop height derived from the distance of the Hα flare ribbons. It was found that for the emission on the harmonic frequency the radio source is close to the flare-loop top. It supports the idea that this drifting pulsating structure is generated in the so-called termination shock. Title: Multi-scale MHD Modelling of the Current Sheet Fragmentation in Turbulent Solar Flare Reconnection Authors: Bárta, M.; Karlický, M.; Büchner, J. Bibcode: 2009CEAB...33..299B Altcode: The concept of turbulent magnetic reconnection becomes now very attractive in solar flare research as it can address many open issues in that field. Nevertheless, it has not been explored yet by numerical simulation since it requires a model which spans over a broad scale-range of mutually coupled phenomena. Traditional simulation approaches are not capable to cover a range of scales from the global system dimensions down to the dissipation scale because of limited number of grid points. A solution could be the development of an appropriate recursive numerical algorithm which at different levels of recursion solves the processes in current sheet fragmentation on different spatial and temporal scales. For this sake we suggest a numerical scheme, where the data representing the system under study are stored in a dynamic hierarchically organized data structure (a tree) which should reflect the self-similar properties of the anticipated solution. To some extent such an algorithm can be considered as an alternative approach to Adaptive Mesh Refinement (AMR) codes. Title: Electron Beam-Plasma Interaction and the Return-Current Formation Authors: Karlický, Marian Bibcode: 2009ApJ...690..189K Altcode: Using a 3D electromagnetic particle-in-cell model, the plasma systems with electron beams are studied. The model parameters are chosen relevant to solar flares. To show the complexity of the problem studied, in the first model, we present an evolution of two oppositely propagating electron beams that escape from the localized acceleration region. Then due to the limitations of this model, in other models we consider a plasma system with one spatially homogeneous beam and a neutralizing return current. The models without the initial magnetic field revealed an importance of the Weibel instability that very efficiently transferred the beam energy to the heating of plasma electrons in the direction perpendicular to that of the beam propagation. In this case, the return current evolved from the initially shifted Maxwell distribution to the distribution with a broad flat maximum. However, in the models with a sufficiently strong magnetic field or those with shorter sizes of the numerical box (effectively the 1D case), the Weibel instability was reduced, and the electron distribution function mainly evolved in the beam-propagation direction and the return current was given by a shift of some bulk electrons and an extended tail. Title: Far-IR and Radio Thermal Continua in Solar Flares Authors: Kašparová, J.; Heinzel, P.; Karlický, M.; Moravec, Z.; Varady, M. Bibcode: 2009CEAB...33..309K Altcode: 2009arXiv0901.3465K With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO-ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radiation mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the thermal emission due to the energy deposit in the lower atmospheric layers. In this contribution we explore the time-dependent effects of beams on thermal FIR and radio continua. We show how and where these continua are formed in the presence of time dependent beam heating and non-thermal excitation/ionisation of the chromospheric hydrogen plasma. Title: Plasmoid Dynamics in Flare Reconnection and the Frequency Drift of the Drifting Pulsating Structure Authors: Bárta, M.; Karlický, M.; Žemlička, R. Bibcode: 2008SoPh..253..173B Altcode: 2008SoPh..tmp..131B In the paper by Kliem, Karlický, and Benz (Astron. Astrophys.360, 715, 2000) it was suggested, that plasmoids formed during the bursty regime of solar flare reconnection can be "visualised" in the radio spectra as drifting pulsating structures via accelerated particles trapped inside the plasmoid. In the present paper we investigate this idea in detail. First, simple statistical analysis supporting this hypothesis is presented. Then, by using the 2.5-D MHD (including gravity) model solar flare reconnection in the inhomogeneous, stratified atmosphere is simulated and the formation and subsequent ejection of the plasmoid is demonstrated. The ejected plasmoid, which is considered to be a trap for accelerated electrons, is traced and its plasma parameters are computed. To estimate the associated plasma radio emission we need to know locations of accelerated electrons and corresponding plasma frequencies. General considerations predict that these electrons should be distributed mainly along the magnetic separatrix surfaces and this was confirmed by using a particle-in-cell simulation. Finally, under some simplifying assumptions the model dynamic radio spectrum is constructed. The relation between the global frequency drift and the plasmoid motion in the inhomogeneous ambient atmosphere is studied. The results are discussed with respect to the observed drifting pulsation structures and their possible utilisation for flare magnetic field diagnostics. Title: Narrowband Pulsating Decimeter Structure Observed by the New Ondřejov Solar Radio Spectrograph Authors: Jiřička, K.; Karlický, M. Bibcode: 2008SoPh..253...95J Altcode: 2008SoPh..tmp...18J The new 0.8 - 2.0 GHz Ondřejov radio spectrograph with high time resolution (10 ms) is presented. As an example of first observations the 0.95 - 1.3 GHz narrowband pulsating structure with a characteristic quasi-period of about 150 ms, observed during the impulsive phase of the 9 June 2007 M1.0 flare, is shown. Some of the pulses show very fast but measurable frequency drift of about −17 GHz s−1. The model of this pulsating structure, based on the tearing and coalescence processes in the current sheet, is briefly discussed. Title: Decimetric radio dot emissions Authors: Mészárosová, H.; Karlický, M.; Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R.; de Andrade, M. C. Bibcode: 2008A&A...491..555M Altcode: Context: We study a rare type of solar radio bursts called decimetric dot emissions.
Aims: In the period 1999-2001, 20 events of decimetric dot emissions observed by the Brazilian Solar Spectroscope (BSS) in the frequency range 950-2640 MHz are investigated statistically and compared with radio fine structures of zebras and fibers.
Methods: For the study of the spectral characteristics of the dot emissions we use specially developed Interactive Data Language (IDL) software called BSSView and basic statistical methods.
Results: We have found that the dm dot emissions, contrary to the fine structures of the type IV bursts (i.e. zebras, fibers, lace bursts, spikes), are not superimposed on any background burst emission. In the radio spectrum, in most cases the dot emissions form chains that appear to be arranged in zebra patterns or fibers. Because some zebras and fibers, especially those observed with high time and high spectral resolutions, also show emission dots (but superimposed on the background burst emission), we compared the spectral parameters of the dot emissions with the dots being the fine structure of zebras and fibers. For both these dots, similar spectral characteristics were found. Some similarities of the dot emissions can be found also with the lace bursts and spikes. For some events the dot emissions show structural evolution from patterns resembling fibers to patterns resembling zebras and vice versa, or they evolve into fully chaotic patterns.
Conclusions: For the first time, we present decimetric dot emissions that appear to be arranged in zebra patterns or fibers. We propose that these emissions are generated by the plasma emission mechanism at the locations in the solar atmosphere where the double resonance condition is fulfilled. Title: Multi-scale Numerical Approach to Solar Flare Magnetic Reconnection Authors: Bárta, M.; Karlický, M.; Nickeler, D. Bibcode: 2008ESPM...12.3.49B Altcode: Magnetic reconnection - considered now commonly as the engine of solar flares - spans over many mutually coupled scales from the global flare dimensions (approximately 10 Mm) down to the scale, where dissipation through kinetic effects take place (approximately 10 m). Direct numerical simulation covering all the scales is therefore impossible for obvious reasons: full 3D numerical model would have to involve 1018 grid points. Nevertheless, the filamentary nature of the current sheet fragmentation give us the chance to describe the process of reconnection with highly reduced request for number of grid points. As the smaller-scale dynamics is interesting only in regions of enhanced current sheet filamentation, we can focus just on these areas, which occupy only a small fraction of the total volume. Generally, as the fragmentation continues, it forms a cascade (finished by the kinetic dissipation) where information relevant for description of the smaller-scale level occupies only a small fraction of grid points describing the higher level. Thus, one can subsequently zoom-in onto the regions of continuing current filamentation. Anticipated current-sheet-fragmentation cascade supposes multiple dissipative regions formed in a single current sheet - this fact can play a key role for direct particle acceleration in reconnection. The numerical algorithm implementing this 'zooming' technique and the first results will be presented. Title: Hydrogen Balmer Lines in the Solar Atmosphere Heated by Electron Beams Authors: Kasparova, J.; Varady, M.; Moravec, Z.; Heinzel, P.; Karlicky, M. Bibcode: 2008ESPM...12.3.16K Altcode: Accelerated particle beam are one of the mechanisms of the flare energy transport from the corona to the transition region and the chromosphere. Such beams heat ambient plasma and may affect atomic population via collisions. Using 1D NLTE radiative hydrodynamics we model influence of electron beams on hydrogen Balmer lines. In the contribution we focus on the effect of so-called non-thermal collisional rates on Halpha and Hbeta lines. Based on our results we discuss diagnostic methods for determination of beam presence in the formation regions of Halpha and Hbeta lines. Title: Gradient pattern analysis of short solar radio bursts Authors: Rosa, R. R.; Karlický, M.; Veronese, T. B.; Vijaykumar, N. L.; Sawant, H. S.; Borgazzi, A. I.; Dantas, M. S.; Barbosa, E. B. M.; Sych, R. A.; Mendes, O. Bibcode: 2008AdSpR..42..844R Altcode: We analyze the weak component of the localized temporal pattern variability of 3 GHz solar burst observed by the Ondrejov radiospectrograph. A complex, short and weak impulsive sample from the time series was analyzed by applying a method based on the gradient pattern analysis and discrete wavelet decomposition. By analyzing canonical temporal variability patterns we show that the new method can reliably characterize the phenomenological dynamical process of short time series (N ⩽ 103 measurements) as the radio burst addressed here. In the narrowest sense, by estimating the mutual information distance in the gradient spectra, we show that the fluctuation pattern of the short and weak 3 GHz impulsive solar burst, with energetic amplitudes <350 SFU, is closer to the intermittent and strong MHD turbulent variability pattern. Title: Far-IR and Radio Continua in Solar Flares Authors: Heinzel, P.; Kasparova, J.; Varady, M.; Karlicky, M.; Moravec, Z. Bibcode: 2008ESPM...12.3.20H Altcode: With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radition mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the thermal emission due to energy deposit in the lower atmospheric layers. The latter one was recently explored for the case of semiempirical flare models, without considering the temporal evolution. However, as the radiation-hydrodynamical simulations do show, the lower atmosphere heated by beams exhibits fast temporal changes which are typically reflected in variations of spectral-line intensities. In this contribution we explore the time-dependent effects of beams on FIR and radio continua. We show how and where these continua are formed in the presence of time dependent beam heating and non-thermal excitation/ionization of the chromospheric hydrogen plasma. Our results should contribute to planning of new observations in FIR and radio domain. Title: Flare Generated Coronal Fast Wave Trains of Decimetric Radio Pulsations Authors: Meszarosova, H.; Sawant, H. S.; Cecatto, J. R.; Rybak, J.; Karlicky, M.; Fernandes, F. C. R.; Jiricka, K.; Andrade, M. C. Bibcode: 2008ESPM...122.105M Altcode: The 22 minutes lasting interval of broadband dm-radio pulsations observed simultaneously during a decay phase of the June 6, 2000 flare by the Brazilian Solar Spectroscope (BSS) and Ondrejov radiospectrograph in frequency range 1200-4500 MHz has been analyzed. We have realized that dominant periods (32-64 s) belong to fast wave trains with a tadpole pattern in their wavelet power spectra. The whole time interval contains series of about 4 wave trains. These trains propagate in whole frequency range 1200-4500 MHz. The propagation of individual trains at lower levels of the solar atmosphere (higher frequencies) is different from propagation of individual trains at higher ones (lower frequencies). The wave trains at the same frequencies but in different time subintervals have some common as well as different properties. The main statistical parameters (periodical, quasi-periodical and decay phase) of these wave trains in their wavelet power spectra have been studied and the first results will be presented and discussed. Title: The Synthetic X-ray Flare Spectra for the Electron Beam and the Return Current Authors: Dzifcakova, E.; Karlicky, M. Bibcode: 2008ESPM...12.3.48D Altcode: The electron beams accelerated during flare in low corona create return currents of electrons in solar plasma. The accelerated electrons of the electron beam and return current influence the electron distribution function. The shape of the electron distribution which includes the interaction of the electron beam with plasma and formation of the return current has been modeled by PIC code. The synthetic X-ray spectra for a such kind of the electron distributions have been computed by using a modification of CHIANTI. The possibility to diagnose of the return current from X-ray spectra is discussed. Title: 2D Stationary Reconnection Solutions in the Vicinity of a Magnetic Null Point and a Stagnation Point Authors: Nickeler, D.; Karlicky, M. Bibcode: 2008ESPM...12.3.43N Altcode: The classical reconnection solutions propose an X-type inflow of the plasma into the X-point structure of the magnetic field. We analyse systematically the implications of the different magnetic field structures of a field which depends linearly on the spatial coordinates. The linear dependence is valid if the Jacobian matrix of the magnetic field does not vanish at the null point. We solve the complete set of the resistive MHD equations for the case that the stagnation point has only a small offset to the magnetic null point. We assume also that the Jacobian of the velocity field does not vanish. This leads to the question which topological and geometrical type of the flow corresponds to which type of magnetic field structure. 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: Return Current Formation in the Region of Escaping Electrons from the Acceleration Space Authors: Karlicky, M. Bibcode: 2008ESPM...12.3.47K Altcode: In a 3-D electromagnetic particle-in-cell model the particle distribution in the acceleration space with escaping accelerated electrons is initiated. Then an evolution of the electron beam penetrating into surrounding plasma and generating the return current is studied. Besides the electrostatic effects at the beam front and the beam-plasma instability a role of the Weibel instability is recognized. Finally, the effects found are discussed in connections to solar flares. Title: Numerical Modelling of Slow Standing Waves in a Solar Coronal Loop Authors: Jelinek, P.; Karlicky, M. Bibcode: 2008ESPM...12.3.59J Altcode: In the paper we numerically investigate slow standing waves that are impulsively generated in a solar coronal loop by the pressure and density pulse. The solved problem is considered as one- and two-dimensional and the results from both models are compared and discussed. The corresponding computer models are described by the ideal magnetohydrodynamic equations that are solved numerically on uniformly structured mesh by means of the Lax-Wendroff and flux limiter algorithms. The obtained numerical results show a time evolution of the velocity, mass density, pressure or plasma energy density in the model. Further results are the spatial profiles of velocity in fundamental or first harmonic modes, depending on the position of initial perturbations in the coronal loop, and for various positions in the work area. Our presented work is aimed at the explanation of coronal oscillations and its attenuation. These calculations are very important for the explanation of the problem of coronal heating and mechanisms of solar coronal oscillations. It is also important for an interpretation of observations because the density perturbations can produce corresponding perturbations in EUV or thermal X-ray emissions. Title: Influence of the Return Current on the EUV and X-Ray Flare Line Emissions Authors: Dzifčáková, Elena; Karlický, Marian Bibcode: 2008SoPh..250..329D Altcode: 2008SoPh..tmp..119D Electron beams accelerated during solar flares carry electric currents which should be neutralized by so-called return currents. Both the electron beam and return current modify the electron distribution function in the solar transition region and low corona. Thus, they influence the intensities of the spectral lines formed in these layers. Synthetic spectra for the solar flare atmosphere are computed from model conditions and the possibilities of diagnostics of the return current from the EUV and X-ray line spectra are discussed. Title: Particle-in-cell simulations of return current in solar flares Authors: Karlický, M.; Nickeler, D. H.; Bárta, M. Bibcode: 2008A&A...486..325K Altcode: Aims: We numerically study a formation of the return current generated in solar flares.
Methods: For simulations of the return current in the beam-plasma system, a 3D particle-in-cell electromagnetic code is used.
Results: In conditions of solar flares with the electron beam fluxes of EF = 9.1 × 109-4.55 × 1010 erg s-1 cm-2, the beam-plasma interaction with the return current is studied. We found that the electron beam relaxes to the plateau distribution function as known from electrostatic simulations. Simultaneously, due to electromagnetic effects and the Buneman instability of the prescribed Maxwell-shifted return current, the electron distribution function evolves to a new stationary state with a new form of the return current. In this final state the return current is formed not only by electrons in the bulk of the electron distribution function, but also by electrons in the extended tail. We use the results of simulations to estimate the critical beam fluxes for the processes under study in the low corona, the transition region and the upper chromosphere. Title: Solar Origin of the Radio Attributes of a Complex Type III Burst Observed on 11 April 2001 Authors: Reiner, M. J.; Klein, K. -L.; Karlický, M.; Jiřička, K.; Klassen, A.; Kaiser, M. L.; Bougeret, J. -L. Bibcode: 2008SoPh..249..337R Altcode: 2008SoPh..tmp...89R We report here on the solar origin of distinctive radiation characteristics observed for a decametric type III solar radio burst that was associated with a major solar flare and CME on 11 April 2001. The associated decimeter (Ondřejov) and meter (Potsdam) wavelength emissions, as well as the GOES soft X-ray lightcurve, suggest that there were two successive events of energy release and electron acceleration associated with this solar eruption. The Nançay radioheliograph images and additional evidence of plasmoid propagation suggest that the second event of electron acceleration resulted from coronal reconfigurations, likely caused by the erupting CME. These observational analyses provide new insights into the physical origin of the distinguishing characteristics of complex type III-like radio emissions that are typically observed at decameter wavelengths during major solar eruptive events. Title: Solar decimetric type III bursts in semi-closed magnetic field structures Authors: Mészárosová, H.; Karlický, M.; Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R.; de Andrade, M. C. Bibcode: 2008A&A...484..529M Altcode: Aims: We investigate statistically seventeen groups of solar type III bursts, observed in the frequency range 950-2500 MHz using the Brazilian Solar Spectroscope (BSS) during the period 1999-2002.
Methods: Using specially-developed Interactive Data Language (IDL) software called BSSView, the spectral characteristic properties of the bursts were investigated. For illustration a semi-closed magnetic field structure with trapped electron beams was modelled using the particle-in-cell model.
Results: Most of the type III bursts studied in this paper have starting frequencies in the range 1100-1400 MHz and their average bandwidth, half-power duration, and interval between adjacent bursts are 116 ± 59 MHz, 108 ± 41 ms, and 647 ± 643 ms, respectively. The number of bursts with negative frequency drift, which is on average -914 ± 684 MHz s-1, is greater than the number with positive frequency drift, which is on average +807 ± 675 MHz s-1. The type III bursts have power-law distribution function for their half-power duration H(f_start) = 4.79 × 108~f_start-2.145± 0.015, bandwidth B_1(f_start) = 1.95 × 10^7~f_start-1.697± 0.022 and B_2(f_start) = 7.07 × 10^5~f_start-1.154± 0.015, and frequency drift D(f_start) = 0.43~f_start1.040± 0.031. Most of the groups of type III bursts were also found to exhibit either positive or negative group frequency drifts of on average +53 ± 38 MHz s-1 and -46 ± 42 MHz s-1, respectively. The detailed statistical analysis suggests that in the frequency range studied there are two categories of type III bursts, the average parameters of which we provide in brackets for each type: a) numerous narrowband bursts (bandwidth ~100 MHz) with small frequency drift (~±500 MHz s-1) in groups with visible group drift (~±50 MHz s-1) and b) less numerous broader band bursts (bandwidth 171 MHz) with higher frequency drift (~±1800 MHz s-1) in groups without group drift. The statistics of the parameters of these drifting groups are presented for the first time. The drifting groups of type III bursts are interpreted as due to electron beams trapped in moving plasmoids, which are semi-closed magnetic field structures. Title: On the validity of ideal MHD in the vicinity of stagnation points in the heliosphere and other astrospheres Authors: Nickeler, D. H.; Karlický, M. Bibcode: 2008ASTRA...4....7N Altcode: The paradigm of ideal MHD is investigated in the vicinity of null points of flows and magnetic fields. These null points determine the location and geometrical shape of the heliopause (or other astropauses). We investigate the question whether regular and stable solutions of the ideal MHD equations in the vicinity of null points of flow and magnetic field exist. This is done to test the validity of ideal MHD in the vicinity of flow and magnetic field of the plasma boundaries of stellar winds and their local interstellar medium. We calculate the general solutions of ideal MHD in the vicinity of magnetic null points and use the standard form of stagnation point flows to analyse all possible time evolutions of these plasma environments. We show that the solution space in 2-D consists almost exclusively of either exponentially (in time) growing velocity or magnetic fields, or collapse solutions. Regular solutions must be three-dimensional and seem to be unstable with respect to small perturbations. This is an argument that reconnection has to take place in such regions and that therefore nonideal terms in Ohm's law are necessary, allowing for reconnection. We conclude that the use of ideal MHD in the vicinity of singular points of flow and magnetic field has to be analysed very carefully with respect to simulation results as those simulations show numerical dissipation (resistivity). These simulations can therefore produce unphysical reconnection regimes. Thus one has to search for a realistic Ohm's law, allowing for reconnection at the heliospheric boundaries. Title: Separation of Accelerated Electrons and Positrons in the Relativistic Reconnection Authors: Karlický, Marian Bibcode: 2008ApJ...674.1211K Altcode: 2007arXiv0709.0572K We study the acceleration of electrons and positrons in a relativistic magnetic field reconnection using a 2.5 dimensional particle-in-cell electromagnetic relativistic code. We consider a model with two current sheets and periodic boundary conditions. The electrons and positrons are very effectively accelerated during the tearing and coalescence processes of the reconnection. We found that near the X-points of the reconnection the positions of electrons and positrons differ. This separation process is in agreement with those studied in previous papers analytically or by test particle simulations. We expect that in dependence on the magnetic field connectivity this local separation can lead to global spatial separation of the accelerated electrons and positrons. A similar simulation in an electron-proton plasma with the proton-electron mass ratio mi/me = 16 is made. Title: Fragmentation of the Current Sheet, Anomalous Resistivity, and Acceleration of Particles Authors: Karlický, M.; Bárta, M. Bibcode: 2008SoPh..247..335K Altcode: 2008SoPh..tmp...11K The evolution of the current sheet in the electric current direction (in the guiding magnetic field direction) is studied numerically in the 3-D particle-in-cell model with two current sheets and periodic boundary conditions. In the regime with vD/v_{Te}≥ 1 (where vD and v_{Te} are the electric current drift and electron thermal velocities, respectively) the current sheets are unstable owing to the Buneman and kink instabilities and become strongly fragmented. During their evolution, in addition to an increase of the energy of the electric field component in the guiding magnetic field direction, the energies of the electric field components in the perpendicular direction are even more enhanced. In the current sheet the anomalous resistivity (ηanom/ηC∼7×105, where ηC is the classical resistivity) is generated and thus the magnetic field dissipates. Most of the dissipated magnetic energy is transformed into the electron kinetic energy in the direction of the electric current. The associated electric field accelerates the electrons from the tail of the distribution function. Title: Resonant Transition Radiation and Solar Radio Bursts Authors: Yasnov, L. V.; Karlický, M.; Modin, E. V. Bibcode: 2008SoPh..247..351Y Altcode: 2008SoPh..tmp....2Y This paper presents general relations for the intensity of the resonant transition radiation (RTR) and their detailed analysis. This analysis shows that the spectrum amplitude of the x-mode at some frequencies for high-energy electrons can grow with the magnetic field increase in some interval from zero value; it can even dominate over that for the o-mode. With further magnetic field increase, the intensity of the RTR x-mode decreases in comparison with the intensity of the o-mode and this decrease is higher for higher velocities of energetic electrons. The polarization of the RTR depends on the velocity of energetic electrons, too. For velocities lower than some velocity limit v<vi the RTR emission is unpolarized in a broad interval of magnetic field intensities in the radio source. For reasonable values of indices of the power-law distribution functions of energetic electrons, the RTR is broadband in frequencies (df/f≈0.2−0.4). Furthermore, we show various dependencies of the RTR and its spectral characteristics. Assuming the same radio flux of the transition radiation and the gyro-synchrotron one at the Razin frequency, we estimate the limit magnetic field in the radio source of the transition radiation. Then, we analyze possible sources of small-scale inhomogeneities (thermal density fluctuations, Langmuir and ion-sound waves), which are necessary for the transition radiation. Although the small-scale inhomogeneities connected with the Langmuir waves lead to the plasma radiation, which is essentially stronger than RTR, the inhomogeneities of the ion-sound waves are suitable for the RTR without any other radiation. Title: Modelling of Optical Emission in Solar Flares Authors: Varady, M.; Kašparová, J.; Heinzel, P.; Karlický, M.; Moravec, Z. Bibcode: 2008CEAB...32..101V Altcode: We present recent progress achieved by our group in the field of flare optical emission modelling. We concentrate on two problems. Firstly, on the possibility of modelling of the time evolution of several Balmer line profiles calculated for real electron fluxes obtained from the hard X--ray observations of a particular flare with the prospect to compare the theoretical results with the observed data for the corresponding flare. Secondly, we discuss the influence of the non--thermal electrons in the line emitting region on the formation and time evolution of Balmer hydrogen line profiles. Title: Diagnostics of Magnetic Field in Solar Flare Reconnection Using Authors: Bárta, M.; Karlický, M. Bibcode: 2008CEAB...32...51B Altcode: Simultaneous Radio and SXR Observations Based on detailed analysis of an earlier proposed relation between SXR plasmoid ejecta and Drifting Pulsating Structures (DPS) in radio spectra we suggested the method for the estimation of the magnetic field confining the plasmoid ejected during the solar flare reconnection. After a brief summary of the principles of the method, its applicability is demonstrated on the case of a limb flare on October 5, 1992. Using the method, the strength of the magnetic field confining the plasmoid/flux-rope was estimated to be ≤ 5× 10^{-4} T for this event. General applicability of the method is discussed at the end. Title: Dynamics of plasmoids formed by the current sheet tearing Authors: Bárta, M.; Vršnak, B.; Karlický, M. Bibcode: 2008A&A...477..649B Altcode: Context: Moving blob-like features observed in the soft X-ray and EUV range above flare-loops are often interpreted as signatures of plasmoids formed by the current sheet tearing in the flare-associated reconnection process.
Aims: We investigate the evolution of the flare-associated current sheet numerically in order to analyse the kinematics and dynamics of plasmoids. The goal is to explain the broad diversity of kinematical properties of the plasmoid signatures recorded by various observational techniques.
Methods: We performed a 2-dimensional resistive-MHD numerical simulation of the reconnection starting from the Harris-type current sheet. After identifying the plasmoids, we followed their motion to determine basic kinematical parameters (velocity and acceleration), and we analysed the associated magnetic field topology.
Results: The simulation reveals a broad variety of the kinematical/dynamical properties of plasmoids - after formation, a plasmoid can move upward, downward, or can even change its direction of propagation. The highest velocities, in the range of the ambient Alfvén speed, are found in the case of upward propagating plasmoids. The acceleration is determined by the net magnetic field tension of the reconnected field lines. Downwardly propagating plasmoids achieve only a fraction of the ambient Alfvén speed. They strongly decelerate during the coalescence with low-lying flare-loops, when distinct energy-release peaks occur and loop system oscillations are excited.
Conclusions: The presented results explain, qualitatively and quantitatively, the broad spectrum of kinematical properties of various observational features attributed to the current-sheet plasmoids. Title: Period variations of radio pulsations observed during decay phase of the June 06, 2000 flare Authors: Sawant, Hanumant; Meszarosova, Hana; Cecatto, José; Karlicky, Marian; Rybak, Jan; Fernandes, Francisco; Andrade, Maria; Jiricka, Karel Bibcode: 2008cosp...37.2758S Altcode: 2008cosp.meet.2758S The 22 minutes lasting interval of broadband dm-radio pulsations observed during decay phase of the June 6, 2000 flare by Brazilian Solar Spectroscope (BSS) and Ondrejov radiospectrograph in frequency range 1200-4500 MHz have been analyzed for its complex temporal variability. To understand the global relationship between radio fluxes on lower and higher frequencies and to recognize different emission mechanisms, we have made the cross-correlation of the radio fluxes at different frequencies during time intervals under study. We have realized that the dominant periods are not spread during whole 22 minutes time interval but their appearance is concentrated into 7 shorter time subintervals that we have then studied in detail. These subintervals last 9-33 s, on average 21 s. The pulsations inside the subintervals usually have higher intensity than the other ones and characteristic dominant periods of these quasi-regular pulsations are 0.5-78.8 s. We were interested in possible differences among dominant periods of individual time intervals as well as between the periods at frequencies below and above 2000 MHz. Periods > 60 s are rather rare. The periods < 40 s occur more frequently at frequencies below 2000 MHz than at frequencies above 2000 MHz. Occurrence of the periods > 40 s is similar at frequencies below and above 2000 MHz. Results are compared with TRACE and EIT/SOHO images and discussed in framework of multi-scaling flare loop interactions. Title: Return Current Simulations Authors: Karlický, M.; Nickeler, D. H. Bibcode: 2008CEAB...32...39K Altcode: The beam-plasma system is studied using a 3-D particle-in-cell model. Because the electromagnetic effects are included a return current is produced. The parameters are chosen to simulate a formation of the return-current in conditions relevant to the transition region and chromosphere during solar flares. Title: Separation of Accelerated Particles During Reconnection Processes Authors: Karlický, M.; Bárta, M. Bibcode: 2008CEAB...32...29K Altcode: Using a 2.5 D relativistic electromagnetic particle-in-cell code the acceleration of particles in the electron-positron and electron-"proton" plasmas during the reconnection process is studied. It is found that the electrons and positrons as well as electrons and protons appeared during the tearing and coalescence processes in different locations. In dependence on the local magnetic field connectivity it can lead to spatial separation of the accelerated electrons and positrons or electrons and protons. Title: The Interaction and Coalescence of a Loop-top Kernel with a Plasmoid Authors: Kołomański, S.; Karlický, M. Bibcode: 2008CEAB...32...93K Altcode: We study the interaction and coalescence between a downward moving plasmoid and a loop-top source recognized in the 30 Nov 2000 flare. Using observations from Yohkoh, GOES, SOHO and Ondřejov, we performed a multi-wavelength analysis of this event. We found that the interaction and coalescence of the two sources resulted in reconnection of their magnetic fields, particle acceleration and plasma heating. These observations are in agreement with predictions of numerical modelling. Title: Multi-scale numerical modelling of the current sheet fragmentation Authors: Bárta, Miroslav; Karlicky, Marian; Büchner, Jörg Bibcode: 2008cosp...37..196B Altcode: 2008cosp.meet..196B Magnetic reconnection - considered now commonly as the engine of solar flares - spans over many mutually coupled scales from the global flare dimensions (≈107 m) down to the scale, where dissipation through kinetic effects take place (≈10 m). Direct numerical simulation covering all the scales is therefore impossible for obvious reasons: full 3D numerical model would have to involve 1018 grid points. Nevertheless, the filamentary nature of the current sheet fragmentation give us the chance to describe the process of reconnection with highly reduced request for number of grid points. As the smaller-scale dynamics is interesting only in regions of enhanced current sheet filamentation, we can focus just on these areas, which occupy only a small fraction of the total volume. Generally, as the fragmentation continues, it forms a cascade (finished by the kinetic dissipation) where information relevant for description of the smaller-scale level occupies only a small fraction of grid points describing the higher level. Thus, one can subsequently zoom-in onto the regions of continuing current filamentation. Anticipated current-sheet-fragmentation cascade supposes multiple dissipative regions formed in a single current sheet - this fact can play a key role for direct particle acceleration in reconnection. The numerical algorithm implementing this 'zooming' technique and the first results will be presented. Title: Fragmentation of Current Sheet Authors: Karlický, M.; Bárta, M. Bibcode: 2008CEAB...32...35K Altcode: An evolution of the electric current in the current sheet along the electric current direction (along the guiding magnetic field direction) is studied numerically in the 3D PIC model of the current sheets. In the regime of the Buneman and kink instabilities the current sheet becomes strongly fragmented. Besides an increase of the energy of the electric field component in the guiding magnetic field direction, the energies of the electric field components in the perpendicular direction are also enhanced. These processes are found to be connected with the anomalous resistivity (η_{anom}/η_C = 10^5, where η_C is the classical resistivity) in the current sheet and the magnetic field dissipation. Title: Numerical simulations of solar flare processes Authors: Karlicky, Marian Bibcode: 2008cosp...37.1448K Altcode: 2008cosp.meet.1448K Using particle-in-cell models the processes of the current sheet fragmentation, return current formation and electron beam interaction with the current sheet are studied in details. Computations in the 3-D model with two current sheets in the Buneman instability regime and with the extended dimension in the electric current direction show that the current sheets become very fragmented. The anomalous resistivity is estimated. Furthermore, a formation of the return current due to electromagnetic effects is presented. Finally, it is shown that the electron beam can trigger the flare magnetic reconnection. Title: Interaction of non-thermal particles with solar chromosphere and solar corona plasma Authors: Radziszewski, Krzysztof; Rudawy, Pawel; Karlicky, Marian Bibcode: 2008cosp...37.2543R Altcode: 2008cosp.meet.2543R In our paper we present the results of the simultaneous high temporal resolution observations of the solar flares in the active region NOAA 10786 observed on 12 and 13 July 2005. The visual data were collected with the Multi-Channel Subtractive Double Pass (MSDP) spectrograph and Solar Eclipse Coronal Imaging System (SECIS) in Bialkow Observatory (University of Wroclaw, Poland) in H-alpha line with high temporal resolution of 0.04-0.075 s. The radio observations were collected in Ondrejov Observatory (Czech Republic) with 0.1 and 0.01 s cadence in 0.8- 2.0, 3.0 and 2.0-4.5 GHz bands using RT5, RT3 and RT4 radiotelescopes, respectively. The X-ray data were recorded with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite. We found high temporal correlation between the short lived radio emissions of type III, hard X-ray flux variations and short lasting variations of the brightness of the H- alpha flaring kernels observed simultaneously in line center and both wings. High cadence observations of solar flares has been used to investigate the interaction of non-thermal particles with solar chromosphere and solar corona plasma. Title: Highlights of the Brazilian Solar Spectroscope (bss) Authors: Sawant, Hanumant; Cecatto, José; Meszarosova, Hana; Faria, Claudio; Fernandes, Francisco; Karlicky, Marian; Andrade, Maria Bibcode: 2008cosp...37.2759S Altcode: 2008cosp.meet.2759S The digital, decimetric (1000-2500 MHz) Brazilian Solar Spectroscope (BSS) with high time (10- 1000 ms) and frequency (1-10 MHz) resolution is in regular operation since April, 1998, at the National Space Research Institute (INPE) at Sao Jose dos Campos, Brazil. The BSS has now been upgraded with a new digital data acquisition and data processing system. The new version of the BSS has a 14 bit A/D unit which permits improved combination of the observational parameters with a capability to record up to 200 frequency channels available in a selectable frequency range of 1000-2500 MHz. It permits data acquisition up to 5 ms time resolution with a limited number of frequency channels. The software system of the BSS is composed by two distinct modules: The first, data acquisition system provides a flexible Graphical User Interface (GUI) that allows one to choose a number of observational parameters. The second module is the real time visualization system that permits real time visualization of the observed dynamic spectrum and additionally has procedures for visualization and preliminary analysis of the recorded solar spectra. Using the new visualization system, we have realized two new types of dm-radio fine structures: narrow band type III bursts with positive/negative group frequency drift and dots-emissions arranged in zebras and fibers. Title: Particle-in-cell simulations of shocks and band splitting of type II solar radio bursts Authors: Sakai, J. I.; Karlický, M. Bibcode: 2008A&A...478L..15S Altcode: Aims:We investigate the emission process of electromagnetic waves from proton beams reflected by the front of a fast magnetosonic shock that propagates in a non-uniform density region, by changing the propagation angle with respect to a uniform magnetic field from 90° to 45°.
Methods: A two-dimensional, electromagnetic, relativistic particle-in-cell (PIC) code is used.
Results: Near the shock front, some protons are reflected and accelerated. The reflected protons can drag the background electrons to keep the charge neutrality, resulting in electron acceleration. Due to the accelerated electrons, the electrostatic waves (Z-modes in the oblique propagation) can be excited where the reflected protons are generated. It is found that for about 60° propagation, the extra-ordinary waves can be excited from the shock front with a double oscillating structure. These waves are excited both near the fundamental and second harmonic frequency region of the local plasma frequency. The second harmonic waves have a band splitting structure and the lower band is brighter than the upper band part. For 45° propagation, the fundamental frequency region has a band splitting structure. Title: Spike-like Bursts as Fine Structure of Zebras Authors: Zlobec, P.; Karlický, M. Bibcode: 2007SoPh..246..419Z Altcode: We studied the characteristics of the zebra-associated spike-like bursts that were recorded with high time resolution at 1420 MHz in four intervals (from 12:45 to 12:48 UT) during 5 August 2003. Our detailed analysis is based on the selection of more than 500 such spike-like bursts and it is, at least to our knowledge, the first study devoted to such short-lived bursts. Their characteristics are different from those pertinent to "normal" spike bursts, as presented in the paper by Güdel and Benz (Astron. Astrophys.231, 202, 1990); in particular, their duration (about 7.4 ms at half power) is shorter, so they should be members of the SSS (super short structures) family (Magdalenić et al., Astrophys. J.642, L77, 2006). The bursts were generally strongly R-polarized; however, during the decaying part of interval I a low R-polarized and L-polarized bursts were also present. This change of polarization shows a trend that resembles the peculiar form of the zebra lines in the spectral dominion ("V" like). A global statistical analysis on the bursts observed in the two polarimetric channels shows that the highest cross-correlation coefficient (about 0.5) was pertinent to interval I. The zebras and the bursts can be interpreted by the same double plasma resonance process as proposed by Bárta and Karlický (Astron. Astrophys.379, 1045, 2001) and Karlický et al. (Astron. Astrophys.375, 638, 2001); in particular, the spikes are generated by the interruption of this process by assumed turbulence (density or magnetic field variations). This process should be present in the region close to the reconnection site (e.g., in the plasma reconnection outflows) where the density and the magnetic field vary strongly. Title: Shock drift electron acceleration and generation of waves Authors: Karlický, M.; Vandas, M. Bibcode: 2007P&SS...55.2336K Altcode: An analytically derived distribution function of reflected and accelerated electrons at a nearly perpendicular shock is presented. Then this distribution in a simplified form is introduced into a 1.5-D relativistic electromagnetic particle-in-cell (PIC) model and a generation of waves is studied. Numerical modeling shows not only a generation of Langmuir and high-frequency electromagnetic waves as expected, but also an efficient generation of whistler waves. Their role in emission processes of type II solar radio bursts is discussed. Title: The Eruption from a Sigmoidal Solar Active Region on 2005 May 13 Authors: Liu, Chang; Lee, Jeongwoo; Yurchyshyn, Vasyl; Deng, Na; Cho, Kyung-suk; Karlický, Marian; Wang, Haimin Bibcode: 2007ApJ...669.1372L Altcode: 2007arXiv0707.2240L This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar NOAA AR 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at the TRACE 171 Å channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the sigmoid eruption, as evidenced by the multiwavelength data ranging from Hα, WL, EUV/UV, radio, and hard X-rays (HXRs). The most important finding is that the flare brightening starts in the core of the active region earlier than that of the rising motion of the flux rope. This timing clearly addresses one of the main issues in the magnetic eruption onset of sigmoid, namely, whether the eruption is initiated by an internal tether cutting to allow the flux rope to rise upward, or a flux rope rises due to a loss of equilibrium to later induce tether cutting below it. Our high time cadence SXI and Hα data show that the first scenario is relevant to this eruption. As in other major findings, we have the RHESSI HXR images showing a change of the HXR source from a confined footpoint structure to an elongated ribbon-like structure after the flare maximum, which we relate to the sigmoid-to-arcade evolution. The radio dynamic spectrum shows a type II precursor that occurred at the time of expansion of the sigmoid and a drifting pulsating structure in the flare rising phase in HXRs. Finally, type II and III bursts are seen at the time of maximum HXR emission, simultaneous with the maximum reconnection rate derived from the flare ribbon motion in UV. We interpret these various observed properties with the runaway tether-cutting model proposed by Moore et al. in 2001. Title: The interaction of a plasmoid with a loop-top kernel Authors: Kołomański, S.; Karlický, M. Bibcode: 2007A&A...475..685K Altcode: Aims:We study the interaction between a downward moving plasmoid and a loop-top kernel recognized in the 30 November 2000 flare. Such an interaction is predicted by some numerical models of solar flares.
Methods: Using X-ray observations from Yohkoh and GOES, EUV observations from SOHO, and radio observations from Ondřejov, we perform multi-wavelength analysis of this interaction.
Results: The Yohkoh/SXT and SOHO/EIT images indicate that the growing flare loop with the loop-top kernel and the above-lying plasmoid were formed as a result of the interaction of two extended arcade-loops. While the flare loop was growing upwards, the plasmoid moved downwards with the velocity of about 16 km s-1 and interacted with the loop-top kernel. Many details of this interaction are found, e.g., an increase of the X-ray and decimetric radio fluxes and an increase of the plasma temperature at the interaction site. Just after the coalescence of the plasmoid with the loop-top kernel, the 1-2 GHz pulsating radio structure and hard X-ray source above the coalescence site were observed. The analyzed temperature maps indicate flows of heated plasma around the plasmoid to the location of the X-ray and radio source. These observations are in agreement with predictions from numerical modelling. Title: On Solar Intermediate Drift Radio Bursts at Decimeter and Meter Wavelength Authors: Rausche, G.; Aurass, H.; Mann, G.; Karlický, M.; Vocks, C. Bibcode: 2007SoPh..245..327R Altcode: Fiber - or intermediate drift - bursts are a continuum fine structure in some complex solar radio events. We present the analysis of such bursts in the X17 flare on 28 Oct. 2003. Based on the whistler wave model of fiber bursts we derive the 3D magnetic field structures that carry the radio sources in different stages of the event and obtain insight into the energy release evolution in the main flare phase, the related paths of nonthermal particle propagation in the corona, and the involved magnetic field structures. Additionally, we test the whistler wave model of fiber bursts for the meter and the decimeter wave range. Radio spectral data (Astrophysikalisches Institut Potsdam, Astronomical Observatory Ondřejov) show a continuum with fibers for ≈ 6 min during the main flare phase. Radio imaging data (Nançay Radio Heliograph) yield source centroid positions of the fibers at three frequencies in the spectrometer band. We compare the radio positions with the potential coronal magnetic field extrapolated from SOHO/MDI data. Given the detected source site configuration and evolution, and the change of the fiber burst frequency range with time, we can also extract those coronal flux tubes where the high-frequency fiber bursts are situated even without decimeter imaging data. To this aim we use a kinetic simulation of whistler wave growth in sample flux tubes modeled by selected potential field lines and a barometric density model. The whistler wave model of fiber bursts accurately explains the observations on 28 Oct. 2003. A laterally extended system of low coronal loops is found to guide the whistler waves. It connects several neighboring active regions including the flaring AR 10486. For varying source sites the fiber bursts are emitted at the fundamental mode of the plasma frequency over the whole range (1200 - 300 MHz). The present event can be understood without assuming two different generation mechanisms for meter and decimeter wave fiber bursts. It gives new insight into particle acceleration and propagation in the low flare and post-CME corona. Title: Hydrogen Balmer line formation in solar flares affected by return currents Authors: Štepán, J. Å.; Kašparová, J.; Karlický, M.; Heinzel, P. Bibcode: 2007A&A...472L..55S Altcode: 2007arXiv0708.0265S Aims:We investigate the effect of the electric return currents in solar flares on the profiles of hydrogen Balmer lines. We consider the monoenergetic approximation for the primary beam and runaway model of the neutralizing return current.
Methods: Propagation of the 10 keV electron beam from a coronal reconnection site is considered for the semiempirical chromosphere model F1. We estimate the local number density of return current using two approximations for beam energy fluxes between 4 × 1011 and 1 × 1012 erg cm-2 s-1. Inelastic collisions of beam and return-current electrons with hydrogen are included according to their energy distributions, and the hydrogen Balmer line intensities are computed using an NLTE radiative transfer approach.
Results: In comparison to traditional NLTE models of solar flares that neglect the return-current effects, we found a significant increase emission in the Balmer line cores due to nonthermal excitation by return current. Contrary to the model without return current, the line shapes are sensitive to a beam flux. It is the result of variation in the return-current energy that is close to the hydrogen excitation thresholds and the density of return-current electrons. Title: Joint Discussion 1 Particle acceleration from solar system to AGN Authors: Karlický, Marian; Brown, John C. Bibcode: 2007HiA....14...79K Altcode: The scene is set for IAU JD01 on Cosmic Particle Acceleration: from Solar System to AGNs Title: Radio and X-ray diagnostics of electrons accelerated in solar flares Authors: Bárta, Miroslav; Karlický, Marian Bibcode: 2007HiA....14...88B Altcode: Starting from 2.5D MHD modelling of solar flares on a global scale we calculate (using the PIC and test-particle simulations) the radio and X-ray emissions generated in solar flare reconnection. Our results the radio and X-ray spectra and brightness distributions, and their dynamics are directly comparable with observations providing thus a test of particle acceleration models as well as of the ‘standard’ global flare scenario. Title: Electron acceleration in a post-flare decimetric continuum source Authors: Subramanian, P.; White, S. M.; Karlický, M.; Sych, R.; Sawant, H. S.; Ananthakrishnan, S. Bibcode: 2007A&A...468.1099S Altcode: 2007astro.ph..3612S Aims:To calculate the power budget for electron acceleration and the efficiency of the plasma emission mechanism in a post-flare decimetric continuum source.
Methods: We have imaged a high brightness temperature (∼ 109 K) post-flare source at 1060 MHz with the Giant Metrewave Radio Telescope (GMRT). We use information from these images and the dynamic spectrum from the Hiraiso spectrograph together with the theoretical method described in Subramanian & Becker (2006, Sol. Phys., 237, 185) to calculate the power input to the electron acceleration process. The method assumes that the electrons are accelerated via a second-order Fermi acceleration mechanism.
Results: We find that the power input to the nonthermal electrons is in the range 3× 1025-1026 erg/s. The efficiency of the overall plasma emission process starting from electron acceleration and culminating in the observed emission could range from 2.87× 10-9 to 2.38 × 10-8. Title: Hα with Heating by Particle Beams Authors: Kašparová, J.; Varady, M.; Karlický, M.; Heinzel, P.; Moravec, Z. Bibcode: 2007ASPC..368..441K Altcode: 2007astro.ph..3800K Using 1D NLTE radiative hydrodynamics we model the influence of the particle beams on the Hα line profile treating the beam propagation and the atmosphere evolution self-consistently. We focus on the influence of the non-thermal collisional rates and the return current. Based on our results, we propose a diagnostic method for determination of the particle beam presence in the formation regions of the Hα line. Title: Multiwavelength Study of the May 13, 2005 Flare Event Authors: Rovira, M. G.; Šimberová, S.; Karlický, M.; Luoni, M. L.; Fárnik Bibcode: 2007ASPC..368..461R Altcode: A global view to the flare evolution via the image data of various parts of electromagnetic spectra is introduced. Data from the ground-based observations in Hα (HASTA, El Leoncito, Argentina) and radio spectra in the 1-2-4.5 GHz range (Radiospectrographs, Ondřejov, Czech Republic) have been analyzed. As to the space observations, there were involved data of the event from SoHO (MDI, EIT, LASCO C2) and RHESSI (X-ray sources). Some results of possible relations among various layers of the Sun's atmosphere and following astrophysical interpretation are presented. Title: Return Current and Energy Deposit in Flares Authors: Varady, M.; Karlický, M.; Kašparová, J. Bibcode: 2007ASPC..368..473V Altcode: The return current (RC) related effects represent in flares one of the possible mechanisms of conversion of the kinetic energy of electron beams into the thermal energy of flare plasma. Using a 1-D current-in-cell model, details of formation and properties of the RC driven by monoenergetic electron beams are calculated. Based on results of the simulations, the influence of the RC on the energy deposit in flares is discussed. Title: The Radio-Coronal Mass Ejection Event on 2001 April 15 Authors: Maia, Dalmiro Jorge Filipe; Gama, Ricardo; Mercier, Claude; Pick, Monique; Kerdraon, Alain; Karlický, Marian Bibcode: 2007ApJ...660..874M Altcode: On 2001 April 15, the Nançay radioheliograph observed fast-moving, expanding loops in images taken in the wavelength range between 164 and 432 MHz. We were able to follow the progression of the radio loops, starting from a few tenths to more than 1 Rsolar above the solar limb, with a time cadence of order seconds. The loops seen in radio agree very well with the features of the coronal mass ejection (CME) seen later, more than 2.5 Rsolar above the limb, in white-light images by the Large Angle Spectrometric Coronagraph (LASCO) experiment on board the Solar and Heliospheric Observatory (SOHO) spacecraft. The event is well associated with an energetic electron event seen by the Electron, Proton, and Alpha Monitor (EPAM) experiment on board the Advanced Composition Explorer (ACE) spacecraft. A detailed transport model for the electrons shows that, not only the inferred onset at the Sun, but also the duration of the particle release, are similar for the radio loop and the in situ electron event detected near the Earth. Title: Drifting pulsating structures generated during tearing and coalescence processes in a flare current sheet Authors: Karlický, M.; Bárta, M. Bibcode: 2007A&A...464..735K Altcode: Aims:Based on particle-in-cell simulations, drifting pulsating structures are interpreted as the radio emission generated during tearing and coalescence processes in the current sheet of a flare.
Methods: A 2.5D particle-in-cell electromagnetic relativistic code was used considering two versions of the model: a) the model with one current sheet with free boundary conditions and b) the model with two current sheets and periodic boundary conditions. The dispersion diagrams of electromagnetic waves we then constructed using the 2D Fourier transform.
Results: It is found that electrons are accelerated most efficiently in the region near the x-point of the magnetic field structure in the phase at the end of tearing process and at the beginning of plasmoid coalescence. The most energetic electrons are distributed mainly along the x-lines of the magnetic field structure. During these processes, Langmuir waves are generated, along with the electromagnetic (radio) ones. It looks as these electromagnetic waves can be observed mainly on the second harmonics of the plasma frequencies corresponding to the plasma densities in the external parts of the plasmoids. Title: Collapsing magnetic trap as accelerator of electrons in solar flares Authors: Karlický, M.; Bárta, M. Bibcode: 2007AdSpR..39.1427K Altcode: A collapsing trap in the cusp topology of solar flares is simulated using a 2D MHD model. Then in this collapsing trap trajectories of test electrons and their acceleration are studied in detail. In the model we use the test particle technique with the guiding centre approximation including also collisional losses and scattering of test electrons. Computing the X-ray emission of the accelerated electrons it is shown that the acceleration process in the collapsing trap easily explains the formation of observed loop-top X-ray sources. Title: Magnetic reconnection in solar flares and corresponding radio bursts Authors: Karlický, M.; Bárta, M. Bibcode: 2007AdSpR..39.1415K Altcode: The 2D MHD model of the flare magnetic reconnection shows that a reconnection activity, changes of the magnetic field topology and generation of waves are connected. It is found that after the phase of a quasi-stationary reconnection in the extended current sheet above the flare arcade the tearing mode instability produces the plasmoids which then can interact and generate MHD waves. Results of particle-in-cell simulations of the tearing processes, which accelerate electrons, are mentioned. Then all these processes are discussed from the point of view of possible radio emissions. While shocks can contribute to the type II radio burst, the superthermal electrons trapped in plasmoids can generate so called drifting pulsating structures. Furthermore, regions with the MHD turbulence may manifest themselves as the lace or dm-spike bursts. Title: High-Frequency Fiber Bursts Observed during The July 11, 2005 Flare Authors: Karlický, M.; Jiřička, K.; Sawant, H. S.; Cecatto, J. R.; Fernandes, F. C. F.; Andrade, M. C. Bibcode: 2007CEAB...31..181K Altcode: A unique quasi-periodic activity of the 1-2 GHz fiber bursts observed during the July 11, 2005, B4.0 flare is presented. Groups of fibers and individual fibers occur with the period of about of 65 s and 1 s, respectively. The frequency drift of the fibers was found in the interval -40 - -160 MHz s^{-1}. Unique cases of a sudden start and sudden end of a group of fibers are shown. Considering the whistler or Alfvén wave velocities for the interpretation of the frequency drift of fibers and the Aschwanden's density model (2002) the magnetic field in the fiber radio source was estimated as 8-9 G or 25-60 G, respectively. Title: Flare-Associated X-Ray Plasma Ejections and Radio Drifting Structures Authors: Kołomański, S.; Tomczak, M.; Ronowicz, P.; Karlický, M.; Aurass, H. Bibcode: 2007CEAB...31..125K Altcode: A suggestion that radio drifting structures (DSs) are emitted by electrons trapped inside plasmoids that are seen as X-ray plasma ejections (e.g. Khan et al., 2002) was illustrated for a small group of events. We present preliminary results of a survey in which a list of DSs observed in Ondřejov and Potsdam has been confronted with Yohkoh Soft X-ray Telescope observations. Title: MHD Waves and Shocks Generated during Magnetic Field Reconnection Authors: Bárta, M.; Karlický, M.; Vršnak, B.; Goossens, M. Bibcode: 2007CEAB...31..165B Altcode: We use a 2D MHD model of magnetic field reconnection to investigate if and how bursts of reconnection activity, changes of the magnetic field and shock wave generation are related. We found that major bursts of power dissipated into Joule heat occur during topological transitions of the magnetic field structure. These bursts are followed by shocks and waves. Along the plasma outflow jet not only MHD waves, but also ion-sound shocks are formed. After the phase of more or less quiet reconnection (Petschek-type) the tearing mode produces plasmoids. The interactions of these plasmoids are associated with further bursts of the reconnection activity and a complex structure of shock waves. Finally, all these processes are discussed as possible sources of various radio bursts. Title: Spatial Structure and Spectra of X-Ray Sources During the 0.8 4.5 GHz Reverse Drift Bursts Observations Authors: Fárník, F.; Karlický, M. Bibcode: 2007SoPh..240..121F Altcode: In the years 2002 - 2005, 38 groups of the reverse drift bursts (RDBs) were observed in the 0.8 - 4.5 GHz frequency range by the Ondřejov radiospectrograph. In 21 cases, which were observed at the times of the RHESSI observations, spatial structure, positional changes, and spectra of X-ray sources during RDB observations are studied in detail. First, based on the frequency drift and the spatial structure of the associated X-ray source, the events are classified as: (a) fast drifting RDBs with a compact X-ray source, (b) fast drifting RDBs with a multiple X-ray source (FM), and slowly drifting RDBs. Then, the spectra of X-ray sources at the times of RDBs are analyzed. It is found that most fast drifting RDBs (16 of 17 cases) are associated with the spectra having a distinct power-law (non-thermal) component. In contrast, the X-ray spectra associated with the slowly drifting RDBs are predominantly purely thermal (in three out of four cases; in the 26 July 2004, case the X-ray spectrum is thermal and high temperature, with non-thermal component). Two special cases of RDBs observed during the 28 October 2003, and 23 July 2004, flares are added for comparison. The most frequent events are those with fast drifting RDBs, a compact short-lasting X-ray sources, and a power-law X-ray spectrum. The individual reverse drift bursts (∼1 s duration) do not show a clear temporal association with individual peaks of hard X-ray bursts. During slowly drifting RDBs the shape of the associated X-ray source changed or expanded. Among them the most interesting one was observed in 26 July 2004, when the very slowly drifting RDBs (+40 MHz s−1) were associated with an X-ray loop-like source continuously elongating in the southwest direction. In the most cases the model of RDBs with electron beams is compatible with the observations, but in flares on 26 July 2004, and 28 October 2003, the RDBs are probably generated by some other type of an agent; we propose here a thermal conduction front. Title: Long period variations of dm-radio and X-ray fluxes in three X-class flares Authors: Mészárosová, H.; Karlický, M.; Rybák, J.; Fárník, F.; Jiřička, K. Bibcode: 2006A&A...460..865M Altcode: Aims.Long period (≥60 s) variations of the radio (0.8-4.5 GHz) and X-ray fluxes observed during the July 14, 2000, April 12, 2001, and April 15, 2001 flares by the Ondřejov radiospectrograph and Yohkoh spacecraft are studied by statistical methods.
Methods: .In the flares under study, characteristic periods are searched for by the Fourier and wavelet methods. To understand the origin of the 0.8-4.5 GHz drifting burst with long period variations, observed at the beginning of the April 15, 2001 flare, cross-correlations, time shifts, coherence, and phase differences in its time series are computed.
Results: .The global statistical study of these flares revealed characteristic periods in the interval of 60-513 s in the radio (0.8-4.5 GHz) and 60-330 s in the X-ray Yohkoh fluxes. Cross-correlations between the radio fluxes at different frequencies helped us to determine the bursts generated by plasma or gyro-synchrotron mechanisms. In the April 12, 2001 flare, soft X-ray fluxes of the sources located at the loop-top and footpoints of a flare loop vary with the period of 60-320 s, and they are highly correlated. But their relation to the radio (1.1 GHz - plasma emission and 4.0 GHz - gyro-synchrotron emission) is complex. At the beginning of the April 15, 2001 flare, in the 0.8-4.5 GHz range, a broadband drifting radio burst with the time variation of 61-320 s was observed at times of flare loop ejection. Its detailed statistical analysis shows that this burst consists of two parts, and, that first part is generated by the plasma emission mechanism and the second, probably, by the gyro-synchrotron one. The characteristic period of about 300 s found in three X-class flares in their dm-radio and X-ray emissions is discussed.
Title: Are heliospheric flows magnetic line- or flux-conserving? Authors: Nickeler, D. H.; Karlický, M. Bibcode: 2006ASTRA...2...63N Altcode: This article discusses and tests the validity of the frozen in magnetic field paradigm (or 'ideal magnetohydrodynamics (MHD) constraint') which is usually adopted by many authors dealing with heliospheric physics.

To show the problem of using ideal MHD in such a counterflow configuration like the heliosphere, we first recapitulate the basic concepts of freezing-in of magnetic fields, respectively magnetic topology conservation and its violation (= magnetic reconnection) in 3-D, already done by other authors with different methods with respect to derivations and interpretations. Then we analyse different heliospheric plasma environments. As a model of the stagnation region/stagnation point in front of the heliospheric nose, we present and discuss the general solution of the ideal MHD Ohm's law in the vicinity of a 2-D stagnation point, which was found by us.

We show that ideal MHD either leads necessarily to a diverging magnetic field strength in the vicinity of such a stagnation point, or to a vanishing mass density on the heliopause boundaries. In the case that components of the electric field parallel to the magnetic field do not exist due to the chosen form of the non-ideal Ohm's law, it is always possible to formulate the transport equation of the magnetic field as a modified ideal Ohm's law.

We find that the form of the Ohm's law which is often used in heliospheric physics (see e.g. Baranov and Fahr, 2003), is not able to change magnetic topology and thus cannot lead to magnetic reconnection, which necessarily has to occur at the stagnation point. The diverging magnetic field, for instance, implies the breakdown of the flux freezing paradigm for the heliosphere. Its application, especially at the heliospheric nose, is therefore rather doubtful. We conclude that it is necessary to search for an Ohm's law which is able to violate magnetic topology conservation. Title: Stationary Reconnection Of 2.5D Magnetic Fields And Localized Non-Idealness In Incompressible MHD Flows Authors: Nickeler, D. H.; Barta, M.; Karlicky, M. Bibcode: 2006IAUJD...3E..55N Altcode: We construct 2D potential magnetic fields for modelling pre-flare magnetic field structures. We ask the question how the application of magnetic shear components, i.e. components of the magnetic field in the invariant direction, could be a source of stationary reconnection. We also ask how this is coupled to the localized non-idealness which produces field aligned electric field components, indicating that magnetic reconnection takes place. Title: Radio and X-ray Diagnostics of Electrons Accelerated in Solar Flares Authors: Bárta, M.; Karlický, M. Bibcode: 2006IAUJD...1E...7B Altcode: It is well known fact that solar flares are efficient particle accelerators - even several concurrent acceleration processes can take place in a single flaring volume. Using hybrid and particle simulations we study some of them, namely the direct acceleration in the current sheet torn during the magnetic reconnection, the acceleration in collapsing magnetic traps formed inside the cusp structure, and pinch-effects in non-equilibrium plasmoids newly created by the reconnection process. In order to relate our models more directly to the real world we not only calculate the dynamics of electron distribution functions but we extent our results to the form comparable with observations. As accelerated particles in the solar atmosphere manifest themselves most remarkably by the radio and X-ray emissions the final outputs of our modelling are radio and X-ray spectra and their dynamics as well as spatial structures of X-ray and radio sources. The obtained results are, of course, sensitive to the parameters of the used flare model. Conversely, fitting the observed and the modelled data provides us with the diagnostic tool for investigation of conditions under which the acceleration in the solar flares proceeds. Title: Electron Acceleration in a Wavy Shock Front Authors: Vandas, M.; Karlicky, M. Bibcode: 2006IAUJD...1E..39V Altcode: It is known that electrons are accelerated at nearly perpendicular shocks by the drift mechanism. And it is also known that energy gain of electrons caused by this mechanism is not very high. Therefore it was suggested in the past that the energy gain might be increased if shocks had wavy fronts. For instance, there were attempts to explain coronal type II burst and their fine structure by electron acceleration in a wavy shock front. We studied numerically electron acceleration at nearly perpendicular shocks. We found that energy gains of electrons at a wavy shock front and a corresponding smoothed plane shock were comparable. That is why they do not depend significantly on the shock thickness, magnetic field profile inside the shock, and shock wavy form; they depend on the angle between the smoothed shock front and ambient magnetic field. Title: Simulation of magnetic field dissipation in astrophysical jets Authors: Topinka, M.; Topinka, M.; Karlický, M. Bibcode: 2006IAUJD...1E..43T Altcode: We report first results of the numerical 3D MHD simulations of magnetic field dissipation applied to magnetically driven astrophysical jets. These simulations are considered to be a part of the gamma-ray burst model based on Poynting flux dominated outflow. Title: Quasi-Static Sequences Of 2D Magnetic Potential Fields In Barotropic Ideal MHD Flows Authors: Nickeler, D. H.; Barta, M.; Karlicky, M. Bibcode: 2006IAUJD...3E..56N Altcode: 2D potential fields for modelling pre-flare magnetic field structures have already often been used in the literature. The equation of motion is often neglected as the plasma beta is assumed to be very small in the regions above the photosphere. In contrast to that we analyse how magnetic potential fields do evolve in the frame of barotropic ideal MHD flows. Here neither the pressure gradient nor the equation of motion can be neglected. We show special solutions by solving the set of ideal MHD equations in the case of a quasi-static approach. This implies that the non-linear term in the equation of motion is neglected. Title: X-Ray Loop-Top Source Generated by Processes in a Flare Collapsing Trap Authors: Karlický, M.; Bárta, M. Bibcode: 2006ApJ...647.1472K Altcode: Using the two-dimensional MHD model of the magnetic reconnection, the cusp structure with the collapsing trap is simulated. Scaling these computational results into solar flare conditions, we study the electron acceleration in the collapsing trap. We use the test-particle technique with the guiding center approximation in which the collisional losses and scattering of accelerated electrons are included. We found that this ``secondary'' acceleration process essentially modifies the distribution function of electrons preaccelerated in the reconnection process. The collapsing trap consists of a structure with the return current, which influences the spatial structure of the loop-top X-ray source. The significance of the curvature drift of electrons in the electric field direction for the electron acceleration is confirmed. The acceleration is more efficient, and the X-ray loop-top source is more intense, but spatially more prolonged than the X-ray source computed in the model without this drift. Title: Collapsing magnetic trap as accelerator of electrons in solar flares Authors: Karlicky, M.; Barta, M. Bibcode: 2006IAUJD...1E..28K Altcode: A collapsing trap in the cusp topology of solar flares is simulated using a 2-D MHD model. Then in this collapsing trap trajectories of test electrons and their acceleration are studied in detail. In the model we use the test particle technique with the guiding centre approximation including also collisional losses and scattering of test electrons. Computing the X-ray emission of the accelerated electrons it is shown that the acceleration process in the collapsing trap easily explain a formation of observed loop-top X-ray sources. Title: Return Current And The Energy Deposit In Flares Authors: Varady, M.; Karlicky, M.; Kasparova, J. Bibcode: 2006IAUJD...1E..51V Altcode: The return current related effects in flares represent one of the possible mechanisms of conversion of the kinetic energy of electron beams into the thermal energy of flare plasma. Using a 1-D particle in cell model details of formation and properties of the return current driven by monoenergetic electron beams are calculated. Using the results of the simulations the influence of the return current on the energy deposit in flares are discussed. Title: Reverse Drift Bursts in the 0.8-4.5 GHz Band and their Relation to X-rays Authors: Fárnik, F.; Karlický, M. Bibcode: 2006ESASP.617E.127F Altcode: 2006soho...17E.127F No abstract at ADS Title: Waves generated by reflected and accelerated electrons at a nearly perpendicular shock Authors: Karlický, M.; Vandas, M. Bibcode: 2006A&A...453.1089K Altcode: Aims.We study a generation of waves by reflected and accelerated electrons at a nearly perpendicular shock.
Methods: .A shifted loss-cone distribution of reflected and accelerated electrons at a nearly perpendicular shock is derived analytically. Then in a simplified form called here "cone" beam, this distribution is incorporated into a 2D relativistic electromagnetic particle-in-cell model and the wave generation is studied.
Results: .Numerical modelling shows not only a generation of Langmuir and high-frequency electromagnetic waves, as expected, but also an efficient generation of whistler waves by the normal Doppler resonance process. While the intensity of Langmuir waves increases with the increase in the "cone" beam energy in a parallel direction to the magnetic field, the whistlers are most effectively generated for high values of the perpendicular beam energy. There are indications that the whistlers participate in conversion processes generating the high-frequency electromagnetic waves.
Conclusions: .Using a numerical model we found an efficient generation of Langmuir, whistler, and electromagnetic waves by electrons reflected and accelerated at a nearly perpendicular shock. Results are discussed in connection with the herringbone structure of type II radio bursts. The possible role of transmitted electrons is mentioned. 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: Electron Acceleration and Transport During the November 5, 1998 Solar Flare At ∼13:34 UT Authors: Trottet, G.; Correia, E.; Karlický, M.; Aulanier, G.; Yan, Y.; Kaufmann, P. Bibcode: 2006SoPh..236...75T Altcode: This paper deals with a detailed analysis of spectral and imaging observations of the November 5, 1998 (Hα 1B, GOES M1.5) flare obtained over a large spectral range, i.e., from hard X-rays to radiometric wavelengths. These observations allowed us to probe electron acceleration and transport over a large range of altitudes that is to say within small-scale (a few 103 km) and large-scale (a few 105 km) magnetic structures. The observations combined with potential and linear force-free magnetic field extrapolations allow us to show that: (i) Flare energy release and electron acceleration are basically driven by loop-loop interactions at two independent, low lying, null points of the active region magnetic field; (ii) <300 keV hard X-ray-producing electrons are accelerated by a different process (probably DC field acceleration) than relativistic electrons that radiate the microwave emission; and (iii) although there is evidence that hard X-ray and decimetric/metric radio-emitting electrons are produced by the same accelerator, the present observations and analysis did not allow us to find a clear and direct magnetic connection between the hard X-ray emitting region and the radio-emitting sources in the middle corona. Title: Evidence for Tether-Cutting Reconnection in a Quadrupole Magnetic Configuration in the April 9, 2001, M7.9 Flare Authors: Yurchyshyn, V.; Karlický, M.; Hu, Q.; Wang, H. Bibcode: 2006SoPh..235..147Y Altcode: We studied the M7.9 flare on April 9, 2001 that occurred within a δ-sunspot of active region NOAA 9415. We used a multi-wavelength data set, which includes Yohkoh, TRACE, SOHO, and ACE spacecraft observations, Potsdam and Ondřejov radio data and Big Bear Solar Observatory (BBSO) images in order to study the large-scale structure of this two-ribbon flare that was accompanied by a very fast coronal mass ejection (CME). We analyzed light curves of the flare emission as well as the structure of the radio emission and report the following: the timing of the event, i.e., the fact that the initial brightenings, associated with the core magnetic field, occurred earlier than the remote brightening (RB), argue against the break-out model in the early phase of this event. We thus conclude that the M7.9 flare and the CME were triggered by a tether-cutting reconnection deep in the core field connecting the δ-spot and this reconnection formed an unstable flux rope. Further evolution of the erupted flux rope could be described either by the "standard" flare model or a break-out type of the reconnection. The complex structure of flare emission in visible, X-ray, and radio spectral ranges point toward a scenario which involves multiple reconnection processes between extended closed magnetic structures. Title: Shrinking and Cooling of Flare Loops in a Two-Ribbon Flare Authors: Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid; Karlický, Marian; Lin, Jun Bibcode: 2006SoPh..234..273V Altcode: We analyze the evolution of the flare/postflare-loop system in the two-ribbon flare of November 3, 2003, utilizing multi-wavelength observations that cover the temperature range from several tens of MK down to 104 K. A non-uniform growth of the loop system enables us to identify analogous patterns in the height-time, h(t), curves measured at different temperatures. The "knees," "plateaus," and "bends" in a higher-temperature curve appear after a certain time delay at lower heights in a lower-temperature curve. We interpret such a shifted replication as a track of a given set of loops (reconnected field lines) while shrinking and cooling after being released from the reconnection site. Measurements of the height/time shifts between h(t) curves of different temperatures provide a simultaneous estimate of the shrinkage speed and cooling rate in a given temperature domain, for a period of almost ten hours after the flare impulsive phase. From the analysis we find the following: (a) Loop shrinkage is faster at higher temperatures - in the first hour of the loop-system growth, the shrinkage velocity at 5 MK is 20 - 30 km s−1, whereas at 1 MK it amounts to 5 km s−1; (b) Shrinking becomes slower as the flare decays - ten hours after the impulsive phase, the shrinkage velocity at 5 MK becomes 5 km s−1; (c) The cooling rate decreases as the flare decays - in the 5 MK range it is 1 MK min−1 in the first hour of the loop-system growth, whereas ten hours later it decreases to 0.2 MK min−1; (d) During the initial phase of the loop-system growth, the cooling rate is larger at higher temperatures, whereas in the late phases the cooling rate apparently does not depend on the temperature; (e) A more detailed analysis of shrinking/cooling around one hour after the impulsive phase reveals a deceleration of the loop shrinkage, amounting to ā ≈ 10 m s−2 in the T < 5 MK range; (f) In the same interval, conductive cooling dominates down to T ≈ 3 MK, whereas radiation becomes dominant below T ≈ 2 MK; (g) A few hours after the impulsive phase, radiation becomes dominant across the whole T < 5 MK range. These findings are compared with results of previous studies and discussed in the framework of relevant models. Title: Interference patterns in solar radio spectra: high-resolution structural analysis of the corona Authors: Bárta, M.; Karlický, M. Bibcode: 2006A&A...450..359B Altcode: Aims.We present a new method for high-resolution structural analysis of the solar corona.
Methods: .The relationship between the spectral features of various types of solar radio bursts and the physical properties of their sources have been extensively studied by many authors. On the other hand, it is plausible to accept that the spectral properties of the solar radio radiation received on the Earth are - besides the physics of the radio source - influenced by an inter-laying medium that radio waves propagate through. In particular, the regular structures in the solar corona - such as coronal waves, oscillations in shock fronts, the fine structures of coronal loops, streamer current sheets, etc. - might efficiently filter transferred radio radiation just as (broad-band) X-rays are filtered by a periodic atomic structure of crystals; the difference is only in the spatial scale. Using the wave optics methods, we investigate the prospective influence of considered coronal structures on the propagating radio waves originating in an external remote source.
Results: .Preliminary results have shown that the resulting modelled radio emission may recall the spectra of observed zebra patterns for the simple 1D density structure considered here and for a reasonable set of parameters. Conversely, it is suggested that the spectra of the zebra patterns might be used for an analysis of those coronal structures that made these traces on the radiation by methods similar to those used in crystallography. The possibility of the presence of such regular small scale structures in the solar corona is demonstrated. For completeness, a brief review of contemporary models of the zebra patterns is provided.
Title: Multi-wavelength study of coronal waves associated with the CME-flare event of 3 November 2003 Authors: Vršnak, B.; Warmuth, A.; Temmer, M.; Veronig, A.; Magdalenić, J.; Hillaris, A.; Karlický, M. Bibcode: 2006A&A...448..739V Altcode: The large flare/CME event that occurred close to the west solar limb on 3 November 2003 launched a large-amplitude large-scale coronal wave that was observed in Hα and Fe xii 195 Å spectral lines, as well as in the soft X-ray and radio wavelength ranges. The wave also excited a complex decimeter-to-hectometer type II radio burst, revealing the formation of coronal shock(s). The back-extrapolation of the motion of coronal wave signatures and the type II burst sources distinctly marks the impulsive phase of the flare (the hard X-ray peak, drifting microwave burst, and the highest type III burst activity), favoring a flare-ignited wave scenario. On the other hand, comparison of the kinematics of the CME expansion with the propagation of the optical wave signatures and type II burst sources shows a severe discrepancy in the CME-driven scenario. However, the CME is quite likely associated with the formation of an upper-coronal shock revealed by the decameter-hectometer type II burst. Finally, some six minutes after the launch of the first coronal wave, another coronal disturbance was launched, exciting an independent (weak) decimeter-meter range type II burst. The back-extrapolation of this radio emission marks the revival of the hard X-ray burst, and since there was no CME counterpart, it was clearly ignited by the new energy release in the flare. Title: X-ray sources and magnetic reconnection in the X3.9 flare of 2003 November 3 Authors: Veronig, A. M.; Karlický, M.; Vršnak, B.; Temmer, M.; Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W. Bibcode: 2006A&A...446..675V Altcode: Context: .Recent RHESSI observations indicate an apparent altitude decrease of flare X-ray loop-top (LT) sources before changing to the commonly observed upward growth of the flare loop system.
Aims: .We performed a detailed study of the LT altitude decrease for one well observed flare in order to find further hints on the physics of this phenomenon and how it is related to the magnetic reconnection process in solar flares.
Methods: .RHESSI X-ray source motions in the 2003 November 3, X3.9 flare are studied together with complementary data from SXI, EIT, and Kanzelhöhe Hα. We particularly concentrate on the apparent altitude decrease of the RHESSI X-ray LT source early in the flare and combine kinematical and X-ray spectral analysis. Furthermore, we present simulations from a magnetic collapsing trap model embedded in a standard 2-D magnetic reconnection model of solar flares.
Results: .We find that at higher photon energies the LT source is located at higher altitudes and shows higher downward velocities than at lower energies. The mean downward velocities range from 14 km s-1 in the RHESSI 10-15 keV energy band to 45 km s-1 in the 25-30 keV band. For this flare, the LT altitude decrease was also observed by the SXI instrument with a mean speed of 12 km s-1. RHESSI spectra indicate that during the time of LT altitude decrease the emission of the LT source is thermal bremsstrahlung from a "superhot" plasma with temperatures increasing from 35 MK to 45 MK and densities of the order of 1010 cm-3. The temperature does not significantly increase after this early (pre-impulsive superhot LT) phase, whereas the LT densities increase to a peak value of (3-4) × 1011 cm-3.
Conclusions: .Modeling of a collapsing magnetic trap embedded in a standard 2D magnetic reconnection model can reproduce the key observational findings in case that the observed emission is thermal bremsstrahlung from the hot LT plasma. This agrees with the evaluated RHESSI spectra for this flare. Title: X-Ray Emission from Flare Collapsing Trap Authors: Karlický, Marian Bibcode: 2006SSRv..122..161K Altcode: An acceleration process in the collapsing magnetic trap, formed in the flare with cusp magnetic field topology, is described. Computations show that high-energy electrons are accumulated in the central part of the collapsing magnetic trap due to an increase of their pitch angles. The effect explains in a natural way the formation of X-ray loop-top sources. Then, using the model with the collapsing trap and considering only the adiabatic heating process, a possible explanation for the motion of the X-ray loop-top source observed at the beginning of some cusp-type flares is presented. Title: Investigations of spatially resolved 1.28 GHz radio activity associated with solar X-Ray micro flares Authors: Sawant, H. S.; Krucker, S.; Madsen, F. R. H.; Kane, S.; Karlicky, M.; Ananthakrishnan, S.; Subramanian, P. Bibcode: 2006cosp...36.3365S Altcode: 2006cosp.meet.3365S On 20 and 22 November 2005 Solar observations at 1280 MHz were carried out from 04 00 to 11 30UT at the Giant Metrewave Radio Telescope -- GMRT - with time resolution of 512 ms and spatial resolution of sim 5 arc sec During GMRT observation time on both days micro flares have been observed by RHESSI satellites in the range of 3 -- 10 keV Detailed investigation of the X-ray emission shows the presence of both thermal and non-thermal components Imaging analysis of one of the micro flares in x ray shows the RHESSI data can produce image with resolution of 7 Here we report an investigation of simultaneous 1 28 GHz radio activity and 3-10 keV X-ray observations of solar X-ray micro flares as observed on 20 November during the interval 08 00-08 30 UT Title: Post-flare oscillation on November 17, 2001 flare at decimeter wavelength Authors: Sych, R.; Subramanian, P.; Karlicky, M.; Ananthakrishnan, S.; Sawant, H. Bibcode: 2006cosp...36.1160S Altcode: 2006cosp.meet.1160S On 17th November 2001 at GMRT observations were carried out at 1060 MHz with time resolution of 2 sec An M2 8 flare associated with active region was observed from 04 45 UT to 06 11 UT In the main phase of the flare the prominence eruption was observed at 17 GHz by the Nobeyama Radioheliograph associated with ejection of halo CME Type III of radio emission superimposed on drifting continuum was recorded by HIRAISO dynamic spectrum in the frequency range of 25-1500 MHz from 05 00 UT to 05 55 UT Post flare observations during the period 05 30-05 55 UT of GMRT light curve indicates the long duration oscillation From GMRT observation one can infer that these oscillations are originated in a southern compact source In order to investigate time evolution of GMRT radio sources we developed new method based on the continuous wavelet transform which shows periodicities of the order of 100 sec These results are discussed This research was supported by the grants of RFFI 04-02-39003 05-07-90147 Title: Model of Motion of the X-Ray Loop-Top Source at the Beginning of Cusp-Type Flares Authors: Karlický, M.; Veronig, A.; Vršnak, B. Bibcode: 2006CEAB...30...85K Altcode: A model with a 1-D collapsing magnetic trap is proposed for an explanation of the motion of the X-ray loop-top source at the beginning of cusp-type flares. Considering plasma heating due to the betatron mechanism an analytic formula for the temporal and spatial evolution of heated plasma temperature in the trap is derived. Using the formula and the relation for thermal bremsstrahlung flux, the time evolution of the X-ray intensity profile in the trap is computed numerically. The model explains not only the downward motion of the X-ray loop-top source observed at the beginning of cusp-type flares, but also the upward motion which follows. Title: Spectral and temporal properties of narrowband dm-spikes and broadband pulses in the August 5, 2003 flare Authors: Sych, R. A.; Sawant, H. S.; Karlický, M.; Mészárosová, H. Bibcode: 2006AdSpR..38..979S Altcode: On August 5, 2003 the Ondřejov radiospectrograph and the Brazilian Solar Spectrograph recorded simultaneously the narrowband dm-spikes superimposed on broadband pulses in the frequency ranges of 0.8-4.5 and 1.75-2.25 GHz, respectively. Using a new method of wavelet filtering broadband sub-second pulses with a frequency width of 0.48 GHz and narrowband millisecond spikes with a frequency width 0.13 GHz were recognized and analysed in detail. Filtered radio spectra showed that the spikes were clustered in stripes at different frequencies. These stripes drifted and their frequency ratios changed during short time intervals. Periods of the narrowband spikes and their stripes were ∼0.4 s and 4, 8-10, and 16 s, respectively. The main period of the broadband pulses was ∼4 s. Values of significant periods of the narrowband spikes coincided with those of the broadband pulses. We found significant peak-to-peak correlations with zero time lags among stripes of the narrowband spikes on different frequencies. The characteristics of the narrowband dm-spikes and broadband pulses indicate that mutually linked emission processes generate both fine structures. Title: Collapsing magnetic trap as accelerator of electrons Authors: Karlicky, M.; Barta, M. Bibcode: 2006cosp...36...20K Altcode: 2006cosp.meet...20K A quasi-stationary collapsing trap is simulated using a 2-D MHD model Then in this collapsing trap an acceleration of electrons is studied in detail We used a test particle technique in which collisional losses and pitch angle scattering of electrons in dense plasma are included We found that this secondary acceleration process efficiently accelerates electrons pre-accelerated in the reconnection This acceleration process explains a formation of flare loop-top X-ray sources in a very natural way Title: Harmonically related decimetric fine structures Authors: Sawant, H. S.; Fernandes, F. C. R.; Karlický, M.; Mészárosová, H.; Krishan, V.; Cecatto, J. R.; Madsen, F. R. H.; Andrade, M. C. Bibcode: 2006AdSpR..38..406S Altcode: We report rare events, above 1000 MHz, in which emission at the fundamental and at second harmonic frequencies show nearly identical fine structures. These high resolution observations are obtained from the Brazilian Solar Radio Spectrograph operating in the frequency range (2150 ± 100) MHz, and the Ondrejov observatory Solar Radio Spectrograph operating in the frequency range of (800-2000) MHz. These bursts have flux values of about 300 s.f.u. and total duration between 100 and 500 ms. The frequency and flux ratios of the harmonically related narrow band bursts varied from 1.76 to 2.29 and 1.28 to 3.57, respectively. The lower observed flux of the fundamental component in comparison to the second harmonic could be due to its higher collisional absorption assuming that the generation mechanism of these bursts is due to the beam plasma interaction. The heights of the acceleration regions estimated from the starting frequencies of the decimetric fine structures are ⩽10 4 km. Title: Magnetic field reconnection initiating waves and shocks and corresponding radio bursts Authors: Karlicky, M.; Barta, M. Bibcode: 2006cosp...36...18K Altcode: 2006cosp.meet...18K A 2D MHD model of the magnetic field reconnection shows that reconnection activity changes of the magnetic field topology and generation of waves and shocks are related For example it was found that after the phase of quiet reconnection the tearing mode instability produces plasmoids which then interact and generate MHD waves These processes are analyzed from the point of view of a possible radio emission While shocks can contribute to the type II radio burst the superthermal electrons trapped in plasmoids can generate so called drifting pulsating structures Furthermore possibly created turbulent structure of density and magnetic field may manifest itself as a lace or dm-spikes bursts Title: X-Ray Sources and Magnetic Reconnection in AN X-Class Flare Authors: Veronig, A. M.; Vršnak, B.; Karlický, M.; Temmer, M.; Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W. Bibcode: 2005ESASP.600E..32V Altcode: 2005ESPM...11...32V; 2005dysu.confE..32V No abstract at ADS Title: Two Examples of the Flare in the Flare: X14.4 April 15, 2001 and X17.2 October 28, 2003 Flares Authors: Karlický, M.; Fárník, F.; Mészárosová, H.; Jiřička, K. Bibcode: 2005ESASP.600E.125K Altcode: 2005ESPM...11..125K; 2005dysu.confE.125K No abstract at ADS Title: Hard X-Ray Emission and its Relation to Reverse Drift Bursts in the 0.8-4.5 GHZ Range Authors: Fárník, F.; Karlický, M. Bibcode: 2005ESASP.600E.122F Altcode: 2005ESPM...11..122F; 2005dysu.confE.122F No abstract at ADS Title: Problem of the Return Current in Energy Deposit in Flares Authors: Varady, M.; Karlický, M.; Kašparová, J. Bibcode: 2005ESASP.600E.146V Altcode: 2005ESPM...11..146V; 2005dysu.confE.146V No abstract at ADS Title: Current Sheet Dynamics at the Dissipation Scale Authors: Bárta, M.; Karlický, M. Bibcode: 2005ESASP.600E.110B Altcode: 2005dysu.confE.110B; 2005ESPM...11..110B No abstract at ADS Title: Hα Line in Solar Atmosphere Heated by Particle Beams Authors: Kašparová, J.; Varady, M.; Karlický, M.; Moravec, Z.; Heinzel, P. Bibcode: 2005ESASP.600E.127K Altcode: 2005dysu.confE.127K; 2005ESPM...11..127K No abstract at ADS Title: Statistical Analysis of Pulsations and Pulsations with Fibers in the Range 800-2000 MHZ Authors: Mészárosová, H.; Rybák, J.; Zlobec, P.; Magdalenić, J.; Karlický, M.; Jiřička, K. Bibcode: 2005ESASP.600E.133M Altcode: 2005dysu.confE.133M; 2005ESPM...11..133M No abstract at ADS Title: Multi-Wavelength Analysis of High-Energy Electrons in Solar Flares: A Case Study of the August 20, 2002 Flare Authors: Kašparová, Jana; Karlický, Marian; Kontar, Eduard P.; A. Schwartz, Richard; Dennis, Brian R. Bibcode: 2005SoPh..232...63K Altcode: 2005astro.ph..8636K A multi-wavelength spatial and temporal analysis of solar high-energy electrons is conducted using the August 20, 2002 flare of an unusually flat (γ1 = 1.8) hard X-ray spectrum. The flare is studied using RHESSI, Hα, radio, TRACE, and MDI observations with advanced methods and techniques never previously applied in the solar flare context. A new method to account for X-ray Compton backscattering in the photosphere (photospheric albedo) has been used to deduce the primary X-ray flare spectra. The mean electron flux distribution has been analysed using both forward fitting and model-independent inversion methods of spectral analysis. We show that the contribution of the photospheric albedo to the photon spectrum modifies the calculated mean electron flux distribution, mainly at energies below ∼100 keV. The positions of the Hα emission and hard X-ray sources with respect to the current-free extrapolation of the MDI photospheric magnetic field and the characteristics of the radio emission provide evidence of the closed geometry of the magnetic field structure and the flare process in low altitude magnetic loops. In agreement with the predictions of some solar flare models, the hard X-ray sources are located on the external edges of the Hα emission and show chromospheric plasma heated by the non-thermal electrons. The fast changes of Hα intensities are located not only inside the hard X-ray sources, as expected if they are the signatures of the chromospheric response to the electron bombardment, but also away from them. Title: Radio Diagnostics of the Solar Flare Reconnection Authors: Karlický, Marian; Bárta, Miroslav Bibcode: 2005SSRv..121..153K Altcode: First, high-frequency (HF) slowly drifting pulsating structures are interpreted as radio emissions of electron beams accelerated in the magnetic reconnection volume and injected into magnetic islands (plasmoids). Then, the time evolution of plasma parameters (density, magnetic field, etc.) in a 2-D MHD model of solar flare reconnection is computed numerically. Assuming plasma radio emission from locations where the “double-resonance’’ instability generates upper-hybrid (UH) waves due to unstable distribution function of suprathermal electrons, the radio spectra and spatial source structures in the reconnection region are modeled. By comparison of the modeled and observed spectra a remarkable similarity has been found between the computed narrow-band emission and the observed lace bursts. Finally, a new diagnostics of the reconnection process is proposed. Title: Non-thermal processes associated with rising structures and waves during a "halo" type CME Authors: Lehtinen, N. J.; Pohjolainen, S.; Karlický, M.; Aurass, H.; Otruba, W. Bibcode: 2005A&A...442.1049L Altcode: We analyse structures and events connected with a flare-associated "halo" type coronal mass ejection (CME) observed on December 18, 2000. A GOES C7.0 class X-ray flare started at 11:02 UT in NOAA Active Region 9269, located at N14 E03. Yohkoh SXT observed slowly rising soft X-ray loops already some 5 min before flare start. Hα images show a two-ribbon flare, remote brightenings, and a partly disappearing filament near the active region. A metric radio precursor was observed to start at 11:06:30 UT, simultaneously with impulsive emission in hard X-rays and microwaves. The frequency-drifting precursor envelope was superposed with J- and reverse drift bursts. The radio bursts traced large-scale soft X-ray loop structures about 160 000 km away from the flare core, and hard X-ray emission was observed at the ends of some of these loops. The precursor emission points to a rising structure where electron acceleration takes place. Later on, a radio type II burst (signature of a propagating shock, driven either by an ejecta or a blast wave) and an EIT wave were observed. We conclude that possible sources for the rising structure and accelerator of electron beams are (1) large-scale loops that connect the flare core region and the precursor site in the close vicinity of two separate rising filaments, and (2) a growing shock that accelerates electrons along closed field lines until the multipolar field is opened and the CME is lifted off. As neither X-ray nor EUV ejecta could be observed whether in the direction of the type II burst or near the radio precursor, we find some support for the shock wave scenario. Title: Magnetic Field Dissipation in GRBs Authors: Topinka, Martin; Spruit, Henk; Karlický, Marián Bibcode: 2005AIPC..801..141T Altcode: We report on the first steps towards the three-dimensional simulation of magnetic field dissipation in gamma-ray burst prompt emission. The model is based on magnetically driven Poynting flux outflow. Title: Electron Acceleration by Coronal Shocks and Solar Type II Bursts Authors: Vandas, M.; Karlický, M. Bibcode: 2005ESASP.592..453V Altcode: 2005ESASP.592E..80V; 2005soho...16E..80V No abstract at ADS Title: Characterization of solar multi-scaling magnetic loop interactions Authors: Rosa, Reinaldo R.; Karlický, Marian; Zanandrea, Ademilson; Sych, Robert A.; Sawant, Hanumant S.; Krishan, Vinod Bibcode: 2005AIPC..784..567R Altcode: Solar magnetic loop structures can exist in a broad range of spatio-temporal scales and their mutual interactions are described by nonlinear processes of magnetic reconnection triggered as a secondary regime by a primary MHD instability. From the application of wavelet analysis on decimetric time series as a counterpart of spatio-temporal flare loop observations we derive, using Tajima's model for quasi-periodic MHD coalescence, possible ranges of minimum Sagdeev potential. From this parameter we obtain the Alfven period of nonlinear oscillation for a typical mutual solar loop interaction observed by SOHO and TRACE. Title: Radio Signatures of Solar Flare Reconnection Authors: Bárta, M.; Karlický, M. Bibcode: 2005ApJ...631..612B Altcode: The time evolution of plasma parameters (density, magnetic field, etc.) in a two-dimensional MHD model of solar flare reconnection is computed numerically. Then assuming plasma radio emission from locations where the ``double-resonance'' instability generates upper hybrid waves due to unstable distribution function of suprathermal electrons, the radio spectra and spatial source structures in the reconnection region are modeled. By comparison of the modeled and observed spectra, a remarkable similarity has been found between the computed narrowband emission and the observed lace bursts. Finally, a new radio diagnostic of the reconnection process based on the model is proposed. Title: Multiwavelength Analysis of the Impact Polarization of 2001 June 15 Solar Flare Authors: Xu, Z.; Hénoux, J. -C.; Chambe, G.; Karlický, M.; Fang, C. Bibcode: 2005ApJ...631..618X Altcode: We report here on the temporal and spatial evolution of the impact polarization of the Hα and Hβ lines during an M6.3 solar flare observed on 2001 June 15 with the THEMIS telescope in the multiwavelength spectropolarimetric mode. Typical spectral intensity and polarization profiles are presented. Both lines are linearly polarized. The Hαline degree of polarization exceeds 4% at line center and in the near line wings. The Hβ line is also linearly polarized, with a degree of polarization reaching 6%. The directions of polarization are either parallel or perpendicular to the local transverse magnetic field (i.e., either radial or tangential because the transverse magnetic field is directed almost in the flare-to-disk center direction). However, contrary to Hα, the Hβ polarization direction is radial only. The Hα and Hβ polarization islands are located at the edges of flare kernels. Only for radial polarization are these islands cospatial. No Hβ polarization is found at the places where tangential Hα polarization is present. The origin of the observed polarization is discussed. Bombardment by low-energy protons or high-energy electrons associated with return currents can explain the radial polarization observed in the lowest flare kernel. The tangential Hα polarization observed in the surge near the upper flare location is interpreted as due to the electric current at the origin of the electromagnetic force that lifts the surge. Title: Simulation of magnetic field dissipation in gamma-ray bursts Authors: Topinka, M.; Karlický, M.; Hudec, R. Bibcode: 2005NCimC..28..455T Altcode: We report on the first steps in 3D simulation of magnetic field dissipation in gamma-ray burst (GRB) prompt emission. Our model is based on magnetically driven Poynting flux outflow. We study the evolution of multi-layered anti-parallel magnetic field in expanding self-accelerated systems. Title: Time scales of the slowly drifting pulsating structure observed during the April 12, 2001 flare Authors: Karlický, M.; Bárta, M.; Mészárosová, H.; Zlobec, P. Bibcode: 2005A&A...432..705K Altcode: First time scales of high-frequency (500-1500 MHz) slowly drifting pulsating structures observed during the April 12, 2001 flare by the Ondřejov (800-4500 MHz) and Potsdam (40-800 MHz) radiospectrographs and by the 1420 and 610 MHz Trieste radiopolarimeters (with high time resolution (1 ms)) are studied statistically. The Fourier method reveals periods in the range of 0.9-7.5 s. For shorter periods the power spectra show a power-law form, especially in the interval of about 0.06-0.2 s, where the power-law index is in the 1.3-1.6 range. The results are interpreted using the flare model with plasmoid ejections. For the first time, the multi-scale cascading reconnection process is included in the interpretation. Corresponding time scales are estimated analytically. Further, magnetic reconnection in the bursting regime is simulated in a 2-D MHD model and variations of the dissipation power and radio radiation measure are computed. Fourier spectra of these numerical variations are determined and compared with those obtained from observations. Title: Radio Diagnostics of Solar Flare Reconnection Authors: Bárta, M.; Karlický, M. Bibcode: 2005HvaOB..29..205B Altcode: A first attempt is made to describe theoretically a particular radio emission from solar flare reconnection in full complexity and to use obtained results for diagnostics of reconnection dynamics based on radio observations.

Firstly, the dynamics of flare reconnection is studied numerically in the 2-D MHD model. Time evolution of plasma parameters (density, magnetic field etc.) is found. Then, assuming plasma radio emission from locations where the ``double-resonance'' instability generates the upper-hybrid waves due to the unstable distribution function of suprathermal electrons, the radio spectra are modelled. Effects of the MHD turbulence in reconnection flows that have major influence on the radio spectra dynamics are studied. The resulting spectra are compared with those observed. It was found, that the observed spectra of lace bursts are qualitatively well reproduced. Finally, consequences of the model for plasma diagnostics are discussed. Title: Analysis of Radio Emission Mechanisms Generating Preferentially the Ordinary Mode of Electromagnetic Waves Authors: Yasnov, M. N.; Karlický, M. Bibcode: 2005HvaOB..29..225Y Altcode: Three radio emission mechanisms (radiation on the first and second harmonic of the plasma frequency, and the resonant transition radiation), which can preferentially generate electromagnetic waves of the o-mode, are analysed. For the case of the transition radiation various causes of density fluctuations (thermal, Langmuir and ion-sound waves) are considered. It was found that the radiation on the frequency of the upper-hybrid waves is always of the o-mode type. Radio emission on the second harmonic of the upper-hybrid frequency can also be polarized in the o-mode type, but this case is less probable than the previous one. In the transition radiation the preference of the o-mode type is also possible, but the small-scale turbulence in the radio source is necessary. The most probable case is the resonant transition radiation generated at density fluctuations produced by ion-sound waves. Title: Solar Narrowband Decimetric Spikes and Hard X-Rays Authors: Jiřička, K.; Karlický, M.; Fárník, F. Bibcode: 2005HvaOB..29..149J Altcode: Narrowband spikes observed by the Ondřejov radiospectrograph during solar flares in the decimetric (1-2 GHz) range were analysed together with the RHESSI observations. It was found that not the individual dm-spikes, but the dm-spikes as a whole, are closely related with the hard X-ray bursts (the correlation coefficient was 0.7-0.9) and their time delays after X-rays were 2-14 s. The Fourier spectra of spikes along the frequency were made and their spectral indices were found to be in the -0.67 to -1.6 range. No correlation between power-law spike and X-ray indices was found. The results were compared with those obtained by Aschwanden and Güdel (1992) for spikes observed on lower radio frequencies. Title: X-Ray and HαEmission of the 20 Aug 2002 Flare* Authors: Kašparová, J.; Karlický, M.; Schwartz, R. A.; Dennis, B. R. Bibcode: 2005ASSL..320..187K Altcode: 2005smp..conf..187K No abstract at ADS Title: Information on particle acceleration and transport derived from solar flare spectropolarimetry Authors: Xu, Z.; Hénoux, J. -C.; Chambe, G.; Karlický, M.; Fang, C. Bibcode: 2005AdSpR..35.1841X Altcode: The hydrogen H α line has been found to be linearly polarized at some locations and times during a June 15th 2001 flare observed with THEMIS. This flare was accompanied by radio pulses and hard X-ray emission. Linear polarization is below the noise level in the flare kernels. However, it is present at the edges of these kernels, in the line center and near wings where the polarization degree exceeds 4%. The directions of polarization are not random but close within ±15° to the tangential and radial directions. This polarization can be due either to electron beams and their associated return currents or to electron and proton beams. Title: Narrowband dm-spikes in the frequency range above 1 GHz and hard X-ray emission Authors: Fárník, F.; Karlický, M. Bibcode: 2005AdSpR..35.1799F Altcode: Narrowband dm-spikes observed in nine intervals during five solar flares in the 1-2 GHz range were analyzed together with the RHESSI and HXRS observations. It was found that the over-frequency integrated radio flux during the spike period is closely related with the hard X-ray bursts (the correlation coefficient was 0.7-0.9) and their time delays after X-rays were 2-14 s, with one exception (March 18, 2003) where the time delay was opposite -15 s. Association of spikes with X-ray spectral characteristics enabled us to divide the spikes into two groups: (a) those observed before the soft X-ray flare maximum and, (b) those observed after this maximum. While for the spikes observed after the flare maximum no systematic spectral characteristics were found, the spikes, observed before the flare maximum were at their beginning associated with relatively hard X-ray spectra and their hardness decreased with time. The RHESSI X-ray sources were compact, only in the March 18, 2003 event an additional X-ray source appeared just at the time of the dm-spikes observation. Fourier transformation of the dynamic spectra of spikes was done to compare their dynamics with the X-ray spectral indices. No correlation between power-law spike and X-ray indices were found. It indicates that the MHD turbulence, if it plays a role, does not represent a strong connection between the spectral characteristics of the dm-spikes and associated X-ray bursts. Furthermore, the results were compared with those obtained by (Aschwanden, M.J., Güdel, M. The coevolution of decimetric millisecond spikes and hard X-ray emission during solar flares. Astrophys. J. 401, 736-753, 1992) for spikes observed on lower radio frequencies. Contrary to their results, no monotonic dependence between time delays and X-ray intensities were found. Finally, the results were discussed using the model of the narrowband dm-spikes and model of electron acceleration in the collapsing magnetic trap. Title: Loop-Top Altitude Decrease in an X-Class Flare Authors: Veronig, A.; Vršnak, B.; Karlický, M.; Temmer, M.; Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W. Bibcode: 2005HvaOB..29..127V Altcode: We study RHESSI X-ray source motions in the X3.9 flare of 2003 November 3. Particular attention is drawn to the apparent altitude decrease of a distinct loop-top (LT) source at the early flare phase before then changing to the commonly observed upward expansion of the flare loop system. We obtain that the downward motion is more pronounced at higher X-ray energies (peak values up to 50 km s^{-1}) consistent with recent findings by Sui et al. (2004). RHESSI spectra indicate that the emission process in the LT source is thermal bremsstrahlung from a super hot plasma (∼40 MK) with high densities increasing from ∼10^{10} cm^{-3} early in the flare to several times 10^{11} cm^{-3} at the end of RHESSI observations. Title: X-Ray Emission of the April 6, 2001 Flare Modelled by Processes in a Collapsing Magnetic Trap Authors: Karlický, M. Bibcode: 2005HvaOB..29..137K Altcode: Using a test particle numerical model describing acceleration processes in the collapsing magnetic trap the X-ray emission of the April 6, 2001 flare was modelled. The Coulomb collisions and scattering were included. The basic parameters of the collapsing trap in the flare region was estimated from the potential magnetic field extrapolation. Although all parameters used in the modelling cannot be derived directly from observations a relatively good agreement between the modelled and observed X-ray observations was found when a) the collapse and trapping processes lasted 16 and 50 s, respectively, b) the scattering of superthermal electrons was enhanced (5 times greater than the Coulomb scattering), c) the injected electron distribution function had the double power law form (energy power-law indices γ_1^e = 8, γ_2^e = 1.3, the break energy E_{break}^e = 65 keV), and d) the rate of injected electrons was 8.73×10^{34} s^{-1}. Title: Numerical Simulation of the Formation of the Return Current Authors: Karlický, M. Bibcode: 2005HvaOB..29..215K Altcode: First, a new 1D particle numerical code computing the formation of the return-current is presented. Then the first results obtained by this code are shown. Although the computations are made for very short time intervals, they show details how the return current is formed. At the beam head the electric field oscillating at the background plasma frequency is generated. Their amplitude grows in time due to the two-stream instability. It is found that at positions near the beam injection the two-stream instability is forced by a continuation of the injected beam, which gives higher values of the electric field energy than in the normal saturation process due to the electron beam trapping. During the beam propagation the background electrons are accelerated in such a way that the electric current is neutralized. Most of the beam electrons are decelerated, forming thus with the accelerated background electrons a broad (in velocity space) distribution function. Title: Ten Types of Solar Radio Bursts and Fine Structures Observed by the Ondřejov 0.8-2.0 GHz Radio-Spectrograph Authors: Mészárosová, H.; Karlický, M.; Jiřička, K. Bibcode: 2005HvaOB..29..309M Altcode: 681 solar radio events observed by the Ondřejov 0.8--2.0 GHz radio-spectrograph during 1992--2000 are analysed and corresponding bursts and fine structures classified into ten different classes. A new type of fine structure (laces) and a new sub-class of zebra patterns were identified. Distribution of various types of fine structures in dependence on the changes of solar activity during the cycles 22 and 23 and occurrences of studied types of burst in association with GOES class flares are shown. Title: Influence of Electron Beam Pulses on Hα Line Formation Authors: Varady, M.; Kašparova, J.; Karlický, M.; Heinzel, P.; Moravec, Z. Bibcode: 2005HvaOB..29..167V Altcode: In this contribution we present results of our simulations focused on determination of spectroscopic signs of the presence of non--thermal electrons in the formation region of Hα using three mutually communicating codes. The originally autonomous and highly specialised codes model three simultaneously acting processes in flares: the precipitation and energy dissipation of the non-thermal power--law electron beams in the solar atmosphere, the hydrodynamic response of the atmosphere to the energy deposited by the beams, and the radiative transfer in chromosphere and photosphere which determines the hydrogen line profiles and their time evolution. The results show possible existence of a new diagnostic method on presence of electron beams in the formation region of the Hα line. Title: Loop-top gyro-synchrotron source in post-maximum phase of the August 24, 2002 flare Authors: Karlický, Marian Bibcode: 2004NewA....9..383K Altcode: A region with a 17 GHz radio source with a decreased microwave spectral index ( α∼-1.3) has been recognized at the top of the flare loop in the post-maximum phase of the August 24, 2002 flare. The radio emission from this region has been interpreted as optically thin gyro-synchrotron emission. It looks that the region appeared at the top of the flare loop as a consequence of the density decrease which reduced the free-free emission component and thus revealed the gyro-synchrotron one. The plasma parameters in the loop-top radio source are estimated. Together with associated gyro-synchrotron sources at the flare loop footpoints these phenomena indicate prolonged acceleration processes in the post-maximum phase of this flare. Title: Acceleration and heating processes in a collapsing magnetic trap Authors: Karlický, M.; Kosugi, T. Bibcode: 2004A&A...419.1159K Altcode: We study the acceleration processes in a collapsing magnetic trap formed in the cusp structure of the flare model, using a test-particle numerical method. Coulomb collisions and scattering are included. It was found that if the trap collapse is sufficiently fast and the energies of the injected electrons are sufficiently high, thus overcoming the collisional losses, electrons can be accelerated in this secondary acceleration process to very high energies depending on the initial magnetic trap ratio R =Bmax/Binit. The computations, made for R=10 and R=100 with isotropically injected 5-28.4 keV electrons and a background plasma density of about ne = 1010 cm-3, show that the high-energy electrons are accumulated in the central part of the collapsing magnetic trap where their velocities are nearly perpendicular to the magnetic field. This effect gives us a new possibility to explain the formation of loop-top sources observed in hard X-ray and radio emission. A further interesting aspect is that these electrons later on escape from this collapsing trap because its trap ratio decreases to R ->1. The time evolution of the energy of the trapped electrons and their energy flux at the end points of the trap (footpoints) are computed for cases without and with collisions. The effect of collisions on the energy spectrum of the accelerated electrons is also shown. The X-ray spectra along the collapsing trap are evaluated. Finally, we suggest a test of this model considering radio waves in the decimetric frequency range. Title: Multi-Wavelength Analysis of the 29 September 2002 M2.6/2N Flare Authors: Kulinová, Alena; Dzifčáková, Elena; Bujňák, Rastislav; Karlický, Marian Bibcode: 2004SoPh..221..101K Altcode: Using TRACE EUV 171 Å line, Hα line, Zürich radio, RHESSI, and HXRS observations the 29 September 2002 flare (M2.6), which occurred in AR NOAA 0134, was analyzed. Flaring structures were compared with a potential magnetic field model (field lines and quasi-separatrix layers) made from SOHO/MDI full-disk magnetogram. Series of high-resolution SOHO/MDI magnetograms and TRACE white-light images were used to find changes in the active region at the photosphere during the flare. The flare began with a rising of a small dark loop followed by the flare brightening observed in 171 Å with TRACE and Hα lines. In radio wavelengths, first type III bursts were observed 5 min prior to the start of hard X-ray emission, indicating a pre-flare coronal activity. The main hard X-ray emission peak (at 06:36 UT) was associated with the second type III burst activity and several slowly negatively drifting features, all starting from one point on the radio spectrum (probably a shock propagating through structures with different plasma parameters). After this time a huge loop formed and three minutes later it became visible in absorption both in Hα and 171 Å EUV lines. The phase of huge dark loop formation was characterized by long-lasting, slowly negatively drifting pulsations and drifting continuum. Finally, considering this huge loop as a surge an evolution of the event under study is discussed. Title: High-frequency slowly drifting structures and X-ray sources observed by RHESSI Authors: Karlický, M.; Fárník, F.; Krucker, S. Bibcode: 2004A&A...419..365K Altcode: Three solar flares (April 4, 2002, May 17, 2002, and August 30, 2002) with the 0.4-2.0 GHz slowly drifting structures were selected and analyzed together with RHESSI X-ray observations. Two events (April 4, 2002 and May 17, 2002) were observed above and one event (August 30, 2002) close to the solar limb. While in April 4, 2002 and August 30, 2002 the radio drifting structures with relatively high frequency drifts (-32- -25 MHz s-1) were recorded at times of the start of a motion of the X-ray flare source, in May 17, 2002 event a splitting of the X-ray source into two sources was observed before observation of the 0.8-1.8 GHz radio structure drifting with very slow frequency drift (-0.4 MHz s-1). The X-ray source of the May 17, 2002 was much softer (<40 keV) than those in April 4, 2002 and August 30, 2002 (>100 keV). Velocities of the X-ray sources in the image plane were estimated as 12 km s-1 for April 4, 2002 and 10 km s-1 for August 30, 2002. Analyzing GOES data and X-ray RHESSI spectra of the May 17, 2002 flare the plasma thermal and non-thermal electron densities in the X-ray sources were determined. For two cases (April 4, 2002 and May 17, 2002) it was found that the plasma density in the coronal X-ray source is higher than maximum one derived from the radio drifting structure. The cross-correlation of the radio drifting structure and hard X-ray flux for the August 30, 2002 event reveals that the hard X-ray emission is delayed 0.5-0.7 s after the radio and it is partly correlated with an enhanced background of the drifting structure. All these results are discussed and interpreted considering the flare model with the plasmoid ejection. Title: Series of high-frequency slowly drifting structures mapping the flare magnetic field reconnection Authors: Karlický, M. Bibcode: 2004A&A...417..325K Altcode: Rare series of the slowly drifting structures observed during two solar flares (April 11, 2001 and March 18, 2003) in the 0.8-4.5 GHz frequency range are studied. Their time-frequency evolution is compared with topological and X-ray characteristics of the flares. Based on recent modelling of the magnetic field reconnection in the bursting and intermittent regime, it is proposed that these slowly drifting structures map the flare magnetic field reconnection. In such a scenario the drifting structures correspond to the radio emission from primary and secondary plasmoids which are formed in the extended current sheet due to tearing and coalescence processes and they move upwards in the solar atmosphere. An increase and decrease of the frequency drifts of the drifting structures in the initial and decaying flare phases are interpreted as an increase and decrease of the reconnection rate, respectively. On the other hand, individual bursts in the drifting pulsating structures are considered to be radio manifestations of separate electron beams accelerated during the secondary tearing processes. The observed characteristic times are compared with those theoretically predicted and the basic plasma parameters in the flare process are estimated. Title: Collisional excitation and ionization of hydrogen by return current in solar flares Authors: Karlický, M.; Kašparová, J.; Heinzel, P. Bibcode: 2004A&A...416L..13K Altcode: First a problem of the transport of electron beams with high energy fluxes into the cold chromosphere during the flare is presented. Then it is shown that the problem might be solved by the return current formed by superthermal (runaway) electrons. In such a case the return current electrons could influence hydrogen excitations and ionizations. Therefore, we computed collisional rates of such a return current and compared them with those of the thermal plasma and of a monoenergetic (10 keV) electron beam with the energy flux FE = 1012 erg cm-2 s-1 penetrating into the flare atmosphere described by the F1 model (Machado et al. \cite{Machado1980}). We show that in this situation the return current collisional rates can be dominant for some transitions. Title: The Growth rate of upper-hybrid waves and dynamics of microwave zebra structures Authors: Yasnov, Leonid V.; Karlický, Marian Bibcode: 2004SoPh..219..289Y Altcode: The growth rate of the upper-hybrid waves with different velocities of superthermal electrons is computed considering a finite temperature of the background plasma and relativistic corrections. Based on these computations two examples of high-frequency zebra structures are interpreted. The sequence of the continuum, zebra structure, and continuum observed in the 29 October 2000, event is explained as an increase and following decrease of the velocity of superthermal electrons in the range of v=0.1-0.3 c. On the other hand, the zebra structure observed during the 18 March 2003 event represents an example with fast electron acceleration. Title: Collisional Excitation and Ionization of Hydrogen by Return Current in Solar Flares Authors: Kašparová, J.; Heinzel, P.; Karlický, M. Bibcode: 2004IAUS..219..760K Altcode: No abstract at ADS Title: Harmonically Related Decimetric Bursts Authors: Sawant, H. S.; Fernandes, F. C. R.; Karlický, M.; Meszarosova, H.; Krishan, V.; Cecatto, J. R.; Madsen, F. R. H. Bibcode: 2004cosp...35..528S Altcode: 2004cosp.meet..528S High frequency observations with 3 MHz frequency and 20 ms time resolutions were carried out in the frequency range of (2150 ± 100) MHz from August 2001 for about two months by the Brazilian Solar Spectroscope (BSS) totalling to of about 300 hours. About 30 groups of solar bursts were recorded. Some of them were also recorded by the Ondrejov Solar Spectroscopes. For the first time details of about 40 harmonically related decimetric narrowband type III bursts and unclassified fine structures above 1000 MHz are reported. Flux values are around 300 s.f.u. Total duration of all types of above bursts is in between 100 -- 500 ms. Frequency ratio of the harmonically related decimetric type III bursts including that of fine structures ranged between 1.76 -- 2.29, where as ratios of the fluxes varied between 1.28 to 3.57, except one case where ratio is ∼ 0.98. The lower observed flux of the fundamental component in comparison to the second harmonic could be due to its stronger collisional absorption near source. We have attempted to understand the formation of some of these structures in terms of the four-wave scattering processes assuming whistlers to be the low frequency waves. Title: What have we learned on non-thermal particle acceleration and transport by optical spectropolarimetry Authors: Hénoux, J. -C.; Karlicky, M.; Xu, Z.; Fang, C. Bibcode: 2004cosp...35..647H Altcode: 2004cosp.meet..647H Most of the information on non-thermal particles is derived from hard X-ray, gamma-ray or radio observations. Optical spectroscopic polarimetry provides complementary information on the particle nature and velocity distributions. Information is also provided on their propagation conditions at chromospheric level. We will report here on the information derived from measurements of the impact linear polarization made in the Halpha and Hbeta lines with the French-Italian solar telescope THEMIS. Title: Analysis of narrowband dm-spikes observed during the august 5,2003 flare. Authors: Sawant, H.; Sych, R.; Karlicky, M.; Meszarosova, H. Bibcode: 2004cosp...35.1604S Altcode: 2004cosp.meet.1604S Groups of narrowband dm-spikes superimposed on broadband pulsations, observed in the 1-2 GHz frequency range, simultaneously by the Brazilian Solar Spectroscope and Ondrejov radiospectrograph during the August 5, 2003 flare are presented. Two methods of an analysis of these spikes were used: a) The Fourier method searching frequency structures in time integrated data, and b) detailed analysis of the distribution of frequency and time structures using multiresolution wavelet analysis. While the first approach is conceptually connected with an expectation that the narrowband dm-spikes are generated in the MHD plasma turbulence without any preferential spatial scales, the wavelet analysis is searching for the preferential scales. Using the Fourier method the power spectra with the power-law indices in the range (-0.90 - -1.26) were found. On the other hand, the wavelet analysis revealed three significant frequency sizes: 1) wideband pulses (about 0.5 GHz), 2) narrowband pulses (0.12 and 0.04 GHz) and 3) small scale pulses (0.01 GHz). Moreover, the wavelet analysis shows a splitting and drifting of specific harmonics, an increase of significant periods of the narrowband pulses (e,g. from 3s to 7s, and from 9s to 19s), and simultaneous decrease of significant periods of broadband pulses (4.2s, 7.8s, 17.1s). But generally the significant periods of the narrowband pulses coincide with those of the broadband pulses. The results are interpreted within the model of spikes generated in a non-stationary MHD plasma turbulence. Title: Decimetric fine structures and associated X-ray flares Authors: Fernandes, F. C. R.; Kane, S. R.; Sych, R. A.; Andrade, M. C.; Cecatto, J. R.; Sawant, H. S.; Karlický, M.; Meszarosova, H. Bibcode: 2004cosp...35.2984F Altcode: 2004cosp.meet.2984F Brazilian Solar Spectroscope and Ondrejov radio spectrograph operate, respectively, in the frequency range of 1250-1750 MHz and 800-2500 MHz. On 4 July 2003 the two instruments observed simultaneously radio bursts associated with two solar flares, one at ∼ 1441 UT and the other at ∼ 1637 UT. In both flares the radio bursts were found to be rich in fine structures. The first flare was associated with a C7.1 soft X-ray flare recorded by the GOES satellite from 1435 to 1520 UT with a peak at 1455 UT. An optical flare of importance 1F occurred during 1435-1439 UT and was located at N05,E32 in the active region 10400. During the period 1442-1508 UT the hard X-ray imaging spectrometer on RHESSI recorded slowly decaying hard X-ray emission in 10-20 keV range. X-ray emission at higher energies could not be recorded due to the presence of terrestrial (magnetospheric) energetic particles. 6-50 keV X-ray emission associated with the second flare (1637 UT) was recorded by RHESSI during 1630-1650 UT. The emission was characterized by several distinct maxima. Although no optical flare has been reported at the time of this flare, hard X-ray images obtained by RHESSI indicate that this flare occurred in the same active region (10400) as the first flare. An analysis of the decimetric fine structures has revealed positively drifting bursts in the frequency range of 1380-2000 MHz with positive drift rates of 180-- 600 MHz/sec at the beginning of the pulsating structures. Periodicity of pulsation was found to be about 9 sec. Detailed radio and hard X-ray observations of the two flares will be presented and the implications of these observations with respect to the location of the electron acceleration region in solar flares will be briefly discussed. Title: Narrowband dm-spikes and associated X-ray emission Authors: Farnik, F.; Karlicky, M. Bibcode: 2004cosp...35.1166F Altcode: 2004cosp.meet.1166F Narrowband dm-spikes observed in nine intervals during five solar flares (20 May 2002, 18 March 2003, 10 June 2003, 22 June 2003 and 5 August 2003) were analyzed together with the RHESSI and HXRS observations. The height scale spectra of the spikes were derived and their spectral scale index was found to be between --0.67 and --1.6 . We divided the studied events into two groups: a) the spikes observed before the soft X-ray flare maximum and, b) the spikes observed after the maximum. While the events with spikes after the flare maximum manifested no specific characteristics, we found that during the events with spikes before the flare (X-ray) maximum (10 June 2003 and 5 August 2003) the spikes were associated with relatively hard X-ray spectra (spectral index gamma was 3.0 and 3.7, respectively) and the spectral slope was increasing afterwards (the X-ray spectrum was getting softer during the event approaching the thermal equilibrium). All the observational results are discussed in frame of our model of the narrowband dm-spikes. Title: High frequency decimetric pulsations and associated hard X-ray emission in the 5 August 2003 (1249 UT) flare Authors: Sawant, H. S.; Sych, R. A.; Kane, S. R.; Fernandes, F. C. R.; Andrade, M. C.; Karlický, M.; Meszarosova, H. Bibcode: 2004cosp...35.2328S Altcode: 2004cosp.meet.2328S The flare on 5 August 2003 (1243-1251 UT) was observed at a variety of wavelengths. The H-alpha flare (importance SN) was located at S16, E33 in the active region NOAA 10424. The soft X-ray flare observed by GOES has been classified as M1.7. The spatial and spectral characteristics of the hard X-ray source were observed by the imaging spectrometer on the RHESSI satellite. In addition, white light observations at 1600Å and EUV observations at 171Å (TRACE) and 195Å (EIT) are also available. Ondrejov and BSS radio spectroscopes, operating in the frequency ranges of 800-2000 MHz and 1750 - 2200 MHz respectively, observed four groups of dm pulsations which covered the entire frequency range and lasted for 30 to 50 sec. Wavelet and Fourier analysis have shown that these groups of pulsations are composed of broad band 0.5 GHz subsecond pulses and narrow band 0.12 MHz millisecond spikes. Periodicity of these groups of pulsations is about 4 sec and with 2 and 3 harmonics. The periodicity of the broad band component is also same. Early in the flare RHESSI observed a double hard X-ray source which later developed into a single source. The fluctuations in the hard X-ray emission are similar to those at decimetric wavelengths. Big and small loops are seen in TRACE data and their foot points are nearly coincident with the appropriate polarity of magnetic field as seen from MDI maps of the associated active region. An analysis of these multi-wavelength observations of the 5 August 2003 flare will be presented and their implications regarding the acceleration and escape of energetic electrons will be briefly discussed. Title: Hard x-ray Pulsations in the Initial Phase of Flares Authors: Fárník, F.; Karlický, M.; Švestka, Z. Bibcode: 2003SoPh..218..183F Altcode: When analyzing light curves of hard X-ray bursts recorded by the Hard X-Ray Spectrometer on board the MTI satellite, we have found three events (all associated with major solar flares, two of them in the same active region) which show pulsations in the very initial phase of the burst. Periods of the pulsations range from 25 to 48 s. We compare them with other observations of pulsations of radio waves and in X-rays and conclude that pulsations of this kind have not been observed before. We mention several possible causes and prefer interactions between current-carrying loops as the most likely interpretation of the observed variations. Title: The Unusual Hard X-ray Spectrum of the Flare of 20 August 2002 Authors: Schwartz, R. A.; Kasparova, J.; Dennis, B.; Karlicky, M. Bibcode: 2003AGUFMSH22A0171S Altcode: An M3 Class flare was observed in x-rays with RHESSI and in H-alpha with the Kanzelhohe Solar Observatory. The event was observed to several hundreds of keV in X-rays and was marked by an unusually flat spectrum observed from 20-70 keV. The measured power-law exponent of this component was about 1.7, very close to the theoretical limit for a thick-target injection of energetic electrons implying a near cutoff below 80 keV. We will bound any systematic effects that may be contributing to this result by analyzing the spectrum using multiple techniques. We will also forward model the spatial/spectral x-ray sources to further validate these observations. Title: Superluminal apparent velocities of relativistic electron beams in the solar corona Authors: Klassen, A.; Karlický, M.; Mann, G. Bibcode: 2003A&A...410..307K Altcode: We present spectral and imaging observations of high frequency type III bursts appearing in pairs: a primary fast drifting component and a secondary ``normal" drifting component. The primary bursts have generally higher frequency drift and start at higher frequencies. They show superluminal velocities up to 2.5 c (c, speed of light), while the secondary component shows the usual <0.5 c velocity expected for type III burst exciters. These superluminal velocities are explained as apparent velocities of relativistic electron beams propagating nearly along the line of sight towards the observer with velocities close to the speed of light. A model of type III burst pairs consisting of subsequent fast drifting and ``normal" drifting components is presented. Title: Radio manifestation of reconnection outflow jets Authors: Bárta, Miroslav; Karlický, Marian Bibcode: 2003ESASP.535..471B Altcode: 2003iscs.symp..471B As was already suggested in our previous models of the lace bursts and the narrow-band dm-spikes both these spectral types are formed in radio sources with MHD turbulence. Since such conditions are, as commonly accepted, in the reconnection out-flow jets, it is reasonable to locate radio sources of these bursts just there. The purpose of this paper is to present global view on relevant plasma processes. Starting from a 2-D MHD reconnection model the plasma density and magnetic field are determined. Assuming a propagation of an unstable distribution function outwards from the reconnection diffusion region along chosen magnetic field lines, contributions to the radio flux due to the double-resonance instability are computed. Integrating over an entire source volume the artificial radio spectra are obtained. It is shown that depending on MHD turbulence properties either the lace-burst or the dm-spikes are observed. Title: On group velocity delays in microwave millisecond oscillating events and radio spikes Authors: Yasnov, L. V.; Karlický, M. Bibcode: 2003A&A...408..737Y Altcode: Time delays between opposite polarizations, interpreted by a difference between the ordinary and extraordinary modes, are studied. Two different density and magnetic field models are used, and three emission mechanisms generating radio waves in double upper-hybrid, plasma, and gyro frequencies are considered. It is found that time delays and their spectra can reach various values and forms depending on plasma parameters in the radio wave emission and propagation. For the emission in double upper-hybrid frequency the considerable decrease of the time delay is due to an increase of the electron plasma density in the radio wave generation. In a dense flare plasma the power index a of the time delay spectrum is negative. On the other hand, in a diluted plasma a becomes positive, but in this case it is much lower than observed for dm-pulsations (a=3). Furthermore model values are compared with the time delays presented by Fleishman et al. (\cite{Fleishman02}), and it is shown that the best agreement is with the model assuming the emission on double gyro-frequency. But, in this case the gyro-resonant absorption limits the angle for escape of radio waves to Theta <3-10deg. Finally, an effect of the difference of the group and light velocities on the frequency drift is analyzed. It is shown that such an effect can be important for wave propagation along magnetic field lines at frequencies close to the plasma frequency. Title: Regular variations of 3 GHz radio flux and current-loop coalescence model of solar flares. Authors: Karlický, M.; Jiřička, K. Bibcode: 2003ESASP.535..499K Altcode: 2003iscs.symp..499K The 3 GHz radio flux records of two solar flares (April 7, 1997 and March 29, 2001) with regular variations are presented. While the 3 GHz flux record of the April 7, 1997 flare shows double-peaks periodicity, the 3 GHz record of the March 29, 2001 flare reveals regular radio flux steps at the ascending part of the radio burst. We interpret the observed phenomena using the current loop coalescence model of solar flares. In the case of the April 7, 1997 event we suggest that the main period of the 3 GHz radio flux (about 100 s) corresponds to the repetition of the current loop coalescence and the radio double peaks are associated with the maxima of the electric field component perpendicular to the interaction plane. In this case the plasma β parameter in the current loop coalescence process is estimated to be 0.63. An increase of the β parameter during the flare is recognized. On the other hand, the steps-like form of the 3 GHz flux record of the March 29, 2001 event expresses an increasing amount of accelerated electrons during periodic coalescence accelerations. Title: First detection of return currents in solar flares by spectropolarimetry with THEMIS Authors: Hénoux, J. -C.; Karlický, M. Bibcode: 2003A&A...407.1103H Altcode: Using THEMIS French-Italien telescope with the MTR mode, the Hydrogen Hα and Hβ lines have been observed to be linearly polarized up to a few percent by impact during the impulsive phase of two solar flares associated with high-frequency radio pulses. Two privileged directions of linear polarization are present, respectively radial (in the disk center to flare direction) and tangential (perpendicular to the radial direction). This 90 degree change in the linear polarization direction is interpreted as due to the chromospheric return current generated by the penetration of a non-thermal electron beam into the chromosphere. Title: Analysis of solar narrow band dm-spikes observed at 1420 and 2695 MHz Authors: Mészárosová, H.; Veronig, A.; Zlobec, P.; Karlický, M. Bibcode: 2003A&A...407.1115M Altcode: Using both linear and nonlinear methods, narrow band dm-spikes recorded at 1420 and 2695 MHz on June 6, 2000, July 8, 2000, July 12, 2000, July 20, 2000, and March 28, 2001 were analyzed. In particular their time profiles were studied statistically. The mean characteristic times of the ascending and of the decaying parts of their profiles are comparable, even if the dispersion of the values is very broad. For selected spikes at 1420 MHz a more precise fitting technique using exponential profiles was applied. While in the decaying part the exponential trend can be generally found, in the ascending part the exponential form can be confirmed only in few cases. The ascending and decaying phase of spikes presumably correspond to the source instability evolution and the plasma wave absorption. Furthermore, durations and polarization values of both 1420 and 2695 MHz spikes were determined and compared with the results in literature. All the analyzed spike events were located near the solar disk center. The polarization values and their trend in spike groups and the nearly constant duration suggest that the polarization originates at the source itself or near it. Selected time series of spikes were tested with respect to low-dimensional determinism and nonlinearity. We found that spikes recorded at fixed frequencies are not governed by a linear stochastic process, as the underlying physical system contains nonlinear signatures. Title: A Model of Zebra Emission in Solar Type IV Radio Bursts Authors: LaBelle, J.; Treumann, R. A.; Yoon, P. H.; Karlicky, M. Bibcode: 2003ApJ...593.1195L Altcode: Solar type IV radio bursts present a theoretical challenge because they are composed of both continuum emission and fine structures. The latter include ``zebra bursts,'' which appear as harmonically spaced multiplets that shift in frequency with time. Similarities between these features and terrestrial auroral emissions suggest a new model to explain zebra-structured type IV emissions. In this model, the basic generation mechanism is identical with that proposed by Winglee and Dulk: mode conversion of Z-mode waves generated by the cyclotron maser mechanism under the condition fuh=Nfce, with N an integer; however, we propose a twist on this model whereby the ``zebra bursts'' do not arise from multiple N-values. Rather, the presence of localized density irregularities within the type IV source region leads to trapping of the upper hybrid Z-mode waves in density enhancements, which results in a discrete spectrum of upper hybrid modes with nearly constant frequency spacing. The number m of quasi-harmonics is limited by the trapping (quantization) conditions. The problem is described by an equivalent Schrödinger equation for the trapped mode, which is solved for an (idealized) cylindrical square density irregularity. In this model, the eigenfrequency spacing matches the observed type IV frequency spacings for less than 10% density enhancements with individual scale sizes of 30-1000 thermal electron gyroradii, corresponding to 1-100 m scales in coronal loops. To produce the observed emitted power for a reasonable (<1%) efficiency requires a large number of such individual microscopic sources occurring over a portion of a magnetic type IV loop at a restricted altitude within which the magnetic field and density are approximately constant. The loop plasma in the zebra emission source is thus highly turbulent in the sense that it contains a large number of density fluctuations. In this case transition radiation can effectively contribute to the radiation background and may also provide the wave power required in the upper hybrid range for generating zebra emissions. Title: Evolução temporal da explosão solar de 06 de junho de 2000 apresentando estruturas finas em rádio freqüências Authors: Fernandes, F. C. R.; Sawant, H. S.; Cecatto, J. R.; Caracini, A. G.; Vats, H. O.; Karlický, M.; Meszarosova, H. Bibcode: 2003BASBr..23..174F Altcode: Em 06 de junho de 2000 (~15: 00-17: 00 UT), o Brazilian Solar Spectroscope (BSS) registrou uma explosão solar intensa no intervalo de freqüência de (1000-2000) MHz, com alta resolução temporal (100 ms) e espectral (5 MHz). A atividade solar relacionada a esta explosão associada à região ativa (AR) 9026 e classificada como X2.3 foi grande. O Ondrejov Observatory registrou rádio emissões até 4,5 GHz. O satélite SOHO registrou uma série de erupções solares, incluindo uma Ejeção de Massa Coronal (CME) tipo "full-halo" (~15: 54 UT). Explosões tipo II/IV também foram registradas. Na faixa de ondas decimétricas, este evento apresentou dois picos distintos (~15: 21 UT e ~16: 42 UT). O primeiro pico coincide com a explosão registrada em raios-X moles (GOES) e em raios-X duros (Yohkoh). Os espectros dinâmicos com alta resolução do BSS revelaram várias estruturas finas, principalmente emissões tipo "zebra" e "fibra", rádio pulsações, emissões tipo III e do único caso de emissões "zebra" harmônicas observado na faixa decimétrica. Neste trabalho, analisamos a evolução temporal e o comportamento global do evento de 06 de junho de 2000, com ênfase na identificação e associação da ocorrência de cada tipo de estrutura fina registrada em rádio com cada etapa da explosão. Resultados preliminares mostraram que, na fase pré-flare, as estruturas finas apresentaram taxa de deriva negativa (~ 70-190 MHz/s). As emissões tipo "zebra" concentram-se na fase de descida do primeiro pico impulsivo e na de subida do segundo pico. Enquanto que as emissões tipo "fibra" ocorrem em ambas fases, mas preferivelmente durante a fase de descida. Os resultados serão apresentados e discutidos. Title: Investigation of april 4th, 2002 solar flare observed simultaneously in X-rays and decimetric wavelengths Authors: Fernandes, F. C. R.; Sawant, H. S.; Cecatto, J. R.; Andrade, M. C.; Kane, S. R.; Karlický, M.; Meszarosova, H. Bibcode: 2003BASBr..23..173F Altcode: The Brazilian Solar Spectroscope (BSS) is in operation at INPE, in conjunction with a 9-m diameter antenna. BSS operates in the decimetric frequency range (1000-2500 MHz) with high temporal (10-1000 ms) and spectral (3 MHz) resolutions and the absolute timing accuracy of less than 3 ms. Data can be digitized up to 100 frequency channels. From March 2002, a couple of solar flares were simultaneous observed in X-rays by the "Ramaty High Energy Solar Spectroscopic Imager" (RHESSI) satellite and in radio frequencies by the BSS and by the Ondrejov Solar Spectrographs (OSS). These flares have been selected for multi-spectral investigations. The limb flare observed on April 4th, 2002, around 15: 28 UT was investigated. Hard X-ray and high frequency decimetric narrow-band ( < 200 MHz) type III-like radio bursts have been observed in association with the impulsive phase of this flare. The analysis of the RHESSI X-ray images indicates that the flare occurred behind the south-east solar limb (~ 6o). The estimated occultation height was ~4000 km. The X-ray spectrum (8-30 keV) was consistent with a power-law slope with a negative exponent of ~6. These results are presented and discussed. Moreover, we complement the analysis of the flare of 4th April, 2002, by including studies of correlation between radio structures and X-ray emission. A possible connection with the plasmoid injection is also investigated, since the observation of the limited frequency slowly drifting structures, as recorded by BSS and OSS, is an evidence that the type III-like bursts were generated inside the plasmoid. Title: High-Frequency Radio Signatures of Solar Eruptive Flares Authors: Karlický, Marian Bibcode: 2003SSRv..107...81K Altcode: Several examples of the radio emission of eruptive solar flares with high-frequency slowly drifting structures and type II bursts are presented. Relationships of these radio bursts with eruptive phenomena such as soft X-ray plasmoid ejection and shock formation are shown. Possible underlying physical processes are discussed in the framework of the plasmoid ejection model of eruptive solar flares. On the other hand, it is shown that these radio bursts can be considered as radio signatures of eruptive solar flares and thus used for the prediction of heliospheric effects. Title: X-ray and radio observations of the activation stages of an X-class solar flare Authors: Fárník, F.; Hudson, H. S.; Karlický, M.; Kosugi, T. Bibcode: 2003A&A...399.1159F Altcode: We report interesting developments prior to the impulsive phase of an X-class solar flare that occurred on September 24, 2001. Our multiwavelength study makes use of X-ray data from the Yohkoh satellite, the Ondřejov radio spectral observations in the decimetric band, and the new Hard X-Ray Spectrometer instrument (HXRS) on board the MTI satellite. The GOES time history of this event showed a ``precursor'' phase starting as early as two hours prior to the impulsive phase, and we have used various data sets to identify what parts of this development could be associated with the flare itself. The most interesting time interval was identified roughly one hour before the main peak when an unusual drifting radio continuum was observed together with two radio sources (at 327 and 164 MHz) in positions corresponding to expanding loops seen in Yohkoh/SXT and SOHO/EIT images, accompanied by a filament disappearence during the same period. Hard X-ray observations revealed a soft spectrum that we interpret as non-thermal, located within loop structures observed in soft X-rays along the magnetic neutral line. The hard X-ray emission continued for more than one hour, as observed in turn by the two spacecraft. In the initial phase of the flare itself, the hard X-ray emission arose in structures closely identifiable with the early soft X-ray loops, which appeared to evolve smoothly into the post-flare loop system of the flare maximum. The decimeter spectra showed loosely-correlated spiky emission at frequencies consistent with the densities inferred from soft X-rays, but with rapid drifts implying motions along field lines. From all these data we infer that the initiation of the flare involved non-thermal processes extending along the neutral line in the photosphere, systematically including open magnetic field lines as shown by the occurrence of interplanetary Type III bursts observed by the WAVES spectrometer on board the WIND spacecraft. Title: Plasma Resonance Surfaces in the Magnetic Field Reconnection and Radio Fine Structures Authors: Karlický, Marian Bibcode: 2003SoPh..212..389K Altcode: Using a 2-D MHD model, the magnetic field reconnection in the current sheet and corresponding plasma resonance lines (surfaces in 3-D), where the upper-hybrid frequency equals one of harmonics of the electron gyrofrequency, ωUH=(ωpe2+ωBe2)1/2=s ωBe (ωUH, ωpe, and ωBe are the upper hybrid, electron plasma, and cyclotron frequencies, respectively, and s is the integer harmonic number) are computed. Then at selected times and positions in the magnetic reconnection the spatial and time spectra of upper hybrid frequencies along the resonance lines are calculated. These spectra are discussed from the point of view of radio fine structures as narrowband dm-spikes, zebras, and lace bursts. It is shown that not only turbulent plasma outflows, suggested in the paper by Bárta and Karlický (2001), but also perturbed zones near the reconnection slow-mode shocks can be locations of the narrowband dm-spikes (and/or continua). Sources of the lace bursts (i.e. bursts with irregular lines) can be located in the reconnection space, too. On the other hand, the zebras (bursts with regular separations of zebra lines) need to be generated out of strongly perturbed reconnection areas. Title: Transport of Energy from the Corona to the Chromosphere During Flares Authors: Heinzel, P.; Karlický, M. Bibcode: 2003LNP...612..161H Altcode: 2003ecpa.conf..161H Hard X-ray (HXR) observations frequently exhibit fast temporal variations during the impulsive phase of solar flares and this is usually ascribed to the propagation of beams of accelerated particles and to the dissipation of their energy in lower layers of the solar atmosphere. As a result of fast heating and non-thermal processes, several chromospheric lines show significant impulsive brightenings. We first review observational attempts of detecting such fast (sub-second) variations of the line intensities, namely in the Halpha line, and discuss the problems associated with such observations. Second, we describe new radiation-hydrodynamical (RHD) simulations of the pulse-beam heating and show how they predict both HXR and optical-line intensity variations on very short time scales. We also discuss the effect of the return current on the energy deposit in the atmosphere. Using new spatially-resolved HXR observations (RHESSI) made simultaneously with a high-cadence detection of selected optical lines, one should be able to diagnose the properties of particle beams, provided that the response of the lower atmospheric layers to beam pulses is strong enough. Title: Time profile, duration and polarization of high frequency spikes Authors: Zlobec, P.; Mészárosová, H.; Veronig, A.; Karlický, M.; Magdaleníc, J. Bibcode: 2003HvaOB..27..115Z Altcode: We analysed a large data set of spikes observed at frequencies 1420 and 2695 MHz recorded with high time resolution by the Trieste Solar Radio System. Different types of analysis were performed in order to determine duration, polarization and time profiles of single spikes. Title: High-frequency slowly drifting structures in the November 25, 2000 and April 15, 2001 solar flares Authors: Karlický, M.; Fárník, F. Bibcode: 2003AdSpR..32.2539K Altcode: Three slowly drifting structures observed during the November 25, 2000 and April 15, 2001 solar flares arepresented. Their relationship to the hard X-ray emission is shown. While the April 15, 2001 X14.4 flare started with the high-frequency drifting structure associated with a plasmoid ejection observed by TRACE in the 171 Å line, the November 25, 2000 event commenced with two drifting structures in two different frequency ranges; the high-frequency one consists of fast positively drifting features with rapid frequency variations of their high-frequency boundary. Due to fast drifting features the slowly drifting structures are interpreted in the flare model with a sequence of fast electron beams accelerated in the current sheet below the ejected plasmoid. Drifting structures in the November 25, 2000 flare are explained by beams injected into the plasmoid and, at the same time, by beams propagating downwards against the evaporation or termination shocks. Title: High-Frequency Slowly Drifting Bursts and Plasmoid Ejections Authors: Karlický, M.; Jiřička, K. Bibcode: 2003HvaOB..27..123K Altcode: Two examples of radio emission of eruptive solar flares with high-frequency slowly drifting structures are presented. The relationship of these radio bursts with the soft X-ray plasmoid ejection is shown. Possible underlying physical processes are discussed in the framework of the model of eruptive solar flares. It is also shown that these radio bursts can be considered as radio signatures of eruptive solar flares and thus used for the prediction of heliospheric effects. Title: Hard X-ray and high-frequency decimetric radio observations of the 4 April 2002 solar flare Authors: Kane, S. R.; Sawant, H. S.; Cecatto, J. R.; Andrade, M. C.; Fernandes, F. C. R.; Karlicky, M.; Meszarosova, H. Bibcode: 2003AdSpR..32.2503K Altcode: Hard X-ray and high frequency decimetric type III radio bursts have been observed in association with the soft X-raysolar flare (GOES class M 6.1) on 4 April 2002 (∼1532 UT). The flare apparently occurred ∼ 6 degrees behind the east limb of the Sun in the active region NOAA 9898. Hard X-ray spectra and images were obtained by the X-ray imager on RHESSI during the impulsive phase of the flare. The Brazilian Solar Spectroscope and Ondrejov Radio Telescopes recorded type III bursts in 800-1400 MHz range in association with the flare. The images of the 3-6, 6-12, 12-25, and 25-50 keV X-ray sources, obtained simultaneously by RHESSI during the early impulsive phase of the flare, show that all the four X-ray sources were essentially at the same location well above the limb of the Sun. During the early impulsive phase, the X-ray spectrum over 8-30 keV range was consistent with a power law with a negative exponent of ∼ 6. The radio spectra show drifting radio structures with emission in a relatively narrow (Δf ≤ 200 MHz) frequency range indicating injection of energetic electrons into a plasmoid which is slowly drifting upwards in the corona. Title: Time-dependent Flare Models with MALI Authors: Kašparová, J.; Heinzel, P.; Varady, M.; Karlický, M. Bibcode: 2003ASPC..288..544K Altcode: 2003sam..conf..544K Temporal variations of Hα line profile intensities related to electron beams are presented. We show first results of time dependent simulations of a chromospheric response to a 1 sec monoenergetic electron beam. 1-D hydrodynamic code together with particle representation of the beam have been used to calculate atmospheric evolution. Time dependent radiative transfer problem has been solved for the resulting atmosphere in the MALI approach, using the Crank-Nicholson implicit scheme. Non-thermal collisional rates were included in linearised equations of statistical equilibrium. Title: Southern hemisphere solar radio heliograph Authors: Sawant, H. S.; Fernandes, F. C. R.; Neri, J. A. C. F.; Cecatto, J. R.; Faria, C.; Stephany, S.; Rosa, R. R.; Andrade, M. C.; Ludke, E.; Subramanian, K. R.; Ramesh, R.; Sundrarajan, M. S.; Sankararaman, M. R.; Ananthakrishnan, S.; Swarup, G.; Boas, J. W. V.; Botti, L. C. L.; Moron, C. E.; Saito, J. H.; Karlický, M. Bibcode: 2002ESASP.506..971S Altcode: 2002svco.conf..971S; 2002ESPM...10..971S The Brazilian Decimetric Array (BDA) is being developed at National Institute for Space Research (INPE) as an international collaborative program. Initially, the BDA will operate in the tuneable frequency range of 1.2-1.7 GHz. The initial planned baseline for BDA 'T' array is 256×144 m and will be extended to 2.2×1.1 km. In this paper, we present the results of developments concerning the prototype of BDA (PBDA). The PBDA will initially operate in the frequency range of 1.2-1.7 GHz, with a five-antenna array, using 4-meter parabolic dishes with altitude and azimuth mountings and complete tracking capability. The spatial resolution for solar images with the PBDA will be about 3.5 arc-minutes leading to a sensitivity of ≍2×104 mJy/beam for an integration time of 1 sec. The array will be installed at -22°41'19" latitude and 45°0'22" W longitude and it is under operation between 9 and 21 UT for continuous solar flux monitoring. Details of the PBDA system are presented. Title: Time dependent flare model with non-LTE radiative transfer Authors: Varady, M.; Karlický, M.; Kašparová, J.; Heinzel, P. Bibcode: 2002ESASP.506..521V Altcode: 2002svco.conf..521V; 2002ESPM...10..521V The first results of a time dependent simulation of chromospheric response to a high energy electron beam are presented. The hybrid code, i.e. a combination of a 1-D hydrodynamic code and a test particle code, has been used to calculate the energy losses of a high energy electron beam propagating through the solar atmosphere and the consequent response of the ambient solar plasma to the energy deposition. The resulting time evolution of the solar plasma temperature, density, velocity and energy deposit on hydrogen has then been used as an input for a time dependent radiative transfer code in the MALI approach to determine the time variation of the Hα line profile. Non-thermal collisional rates have been included in the linearised ESE. Title: Observation of harmonically related solar radio zebra patterns in the 1-4 GHz frequency range Authors: Sawant, H. S.; Karlický, M.; Fernandes, F. C. R.; Cecatto, J. R. Bibcode: 2002A&A...396.1015S Altcode: A unique case of two zebra patterns related harmonically with ratio of ~ 1:2 was observed by distant radio telescopes at São José dos Campos and Ondřejov Observatories. Accompanied zebras show that the ratio of frequencies of the neighboring zebra lines is in the range of 1.009-1.037. There is a tendency of a decrease of this ratio with decreasing frequency within the specific zebra pattern. Both facts speak in favour of plasma emission models for the zebra pattern fine structure in radio burst continua. Title: Statistical analysis of high-frequency narrowband dm-spikes Authors: Mészárosová, H.; Veronig, A.; Zlobec, P.; Karlický, M. Bibcode: 2002ESASP.506..347M Altcode: 2002ESPM...10..347M; 2002svco.conf..347M Using linear and nonlienar methods narrowband dm-spikes recorded at 1420 and 2695 MHz were analyzed. In particular their time profiles were studied statistically. For selected spikes at 1420 MHz a more precise fitting technique using exponential profiles was applied. Generally, while in the decaying part the exponential trend can be found, in the ascending part the exponential form can be confirmed only in few cases. Furthermore, durations of 1420 and 2695 MHz spikes were determined and compared with the results in literature. Selected time series of spikes were tested with respect to nonlinearity. We found that spikes at fixed frequencies are not governed by a linear stochastic process, as the underlying physical system contains nonlinear signatures. Title: Prolonged millimeter-wave radio emission from a solar flare near the limb Authors: Pohjolainen, S.; Hildebrandt, J.; Karlický, M.; Magun, A.; Chertok, I. M. Bibcode: 2002A&A...396..683P Altcode: We present a multi-wavelength analysis of a gradual radio flare on June 27, 1993 which showed emission at millimeter waves long after the soft X-ray flux had peaked. The radio flare located at S12 E75 was associated with a GOES class M3.6 flare that lasted for more than one hour and hard X-ray emission during the rising phase of the soft X-ray/radio emission. The maximum radio flux density at 35 GHz was 60 sfu, but the calculated thermal bremsstrahlung flux from the GOES soft X-rays was less than half of that. The possible explanations for this prolonged millimeter wave emission could be accelerated high-energy electrons gyrating along the field-lines (nonthermal gyrosynchrotron emission) or thermal bremsstrahlung from evaporating chromospheric warm and dense plasma (cool enough to go undetected by GOES), or a mixture of these. Our model calculations show that even an inhomogeneous source containing both kinds of particles would not be able to produce such a spectral shape. A second source with extremely high electron densities (>1016 m-3), large source dimensions (>1015 m2), and very low temperatures (<106 K) must be assumed to explain the observed radio spectra. Title: Interpretation of prolonged millimeter-wave emission from a flare using model calculations Authors: Hildebrandt, Joachim; Pohjolainen, Silja; Karlický, Marian Bibcode: 2002ESASP.506..299H Altcode: 2002svco.conf..299H; 2002ESPM...10..299H The long-duration radio flare on June 27, 1993 was characterized by strong emission at millimeter waves (up to 60 sfu at 35 GHz). It was not possible to fit the spectrum by model calculations assuming only one (even inhomogeneous and non-thermal) source because of the increasing flux between 10 and 35 GHz. Either the low-frequency part would be totally suppressed by the strong thermal bremsstrahlung of cool (<106K) plasma necessary for the high mm-flux or the spectral slope would be always negative for ν > 10 GHz if gyrosynchrotron emission dominates. The only way to achieve a sufficient fit was the assumption of two independent sources, one with energetic electrons and enhanced plasma temperature (loop-like structure), the other with rather high electron densities, large source dimensions, and low temperatures (evaporated plasma), both located inside the antenna beam of 2.4 arc min. Title: Radio signature of multi-scaling flare loop interactions Authors: Rosa, Reinaldo R.; Ramos, Fernando M.; Sawant, Hanumant S.; Fernandes, Francisco C. R.; Vijaykumar, Nandamudi L.; Zanandrea, Ademilson; Karlický, Marian Bibcode: 2002ESASP.506..737R Altcode: 2002ESPM...10..737R; 2002svco.conf..737R The solar radio emission at 3 GHz observed during the June 6, 2000 flare, at times when the EIT/SOHO and SXT/Yohkoh images indicate the flare loop interactions, has been analyzed for its complex temporal variability. Using the Fourier Power Spectrum (FPS) and the Global Wavelet Spectrum (GWS) techniques the power spectra of the 3 GHz signal, observed with time resolution of 0.6 s, have been determined: a 1/f1.66±0.16 power law. The presence of a characteristic power-law implies that the fluctuations are stochastically correlated without a dominant characteristic spatio-temporal scale and contain some self-similarity in time. Title: Sawtooth bursts: observations and model Authors: Karlický, M.; Bárta, M.; Klassen, A.; Aurass, H.; Mann, G. Bibcode: 2002ESASP.506..303K Altcode: 2002ESPM...10..303K; 2002svco.conf..303K An example of the sawtooth burst observed during the November 3, 1997 flare is shown. Basic parameters of the sawtooth bursts are summarized and compared with those of fibers, fiber chains, zebras, EEL bursts and lace bursts. The sawtooth bursts are found to be most similar to the lace bursts, therefore the lace bursts model is proposed also for them. Then using this model the dynamic spectrum with the sawtooth burst is modelled. The model considers accelerated electrons with an unstable distribution function on the double resonance frequency and quasi-periodic variations of the electron plasma density and/or magnetic field in the radio source. Title: The 1 October 2001 Eruptive Prominence: Observed and Modeled Structures Authors: Karlický, Marian; Kotrč, Pavel; Kupryakov, Yurij A. Bibcode: 2002SoPh..211..231K Altcode: Using TRACE 171 Å image observations and Hα spectra and images observed at the Ondřejov Observatory, the October 1, 2001, eruptive prominence is studied. The evolution of this prominence is described and velocities of specific parts of the prominence are determined. It was found that, after the rising phase of the cold loop-like prominence, its upper part expanded and below this expanding part, around one of its legs a `ring' structure, visible in the TRACE images, was formed. Then, at the same place, a tearing of the prominence leg was recognized. Simultaneous spectral observations of this structure reveal a very broad Hα line, which indicates strong turbulent motion at these positions. These processes were accompanied by an expanding Hα envelope. Due to the similarity of the observed `ring' and tearing structures with those modeled by Lau and Finn (1996), the prominence leg tearing is interpreted as a reconnection process between two parallel magnetic ropes having parallel electric currents, but anti-parallel axial magnetic fields. Title: Analysis of the expanding flare loops of C8.5/1F April 2, 2001 flare Authors: Kulinová, A.; Dzifčáková, E.; Klačka, J.; Karlický, M. Bibcode: 2002ESASP.506..677K Altcode: 2002svco.conf..677K; 2002ESPM...10..677K Evolution of the flare loops observed in TRACE 171 Å line, 1600 Å continuum and Hα line (Modra Observatory) during the C8.5/1F, April 2, 2001 flare is analyzed (NOAA AR 9393). The expansion of the flare loops at their tops is recognized nearly co-spatially at the hot TRACE 171 Å as well as cold Hα line and 1600 Å continuum. Due to the visibility of Hα structures in emission against the disc we assume that this demands relatively high plasma electron densities (~1012cm-3). Prior to the expansion of the loops a high density plasma injection into them was observed. Detailed analysis shows that plasma parameters are close to the ballooning instability threshold, especially in regions close to the null point of the extrapolated magnetic field. Title: Drifting decimetric pulsation structures in the initial phase of solar flares Authors: Karlický, M.; Kliem, B.; Mészárosová, H.; Jiřička, K. Bibcode: 2002ESASP.506..653K Altcode: 2002svco.conf..653K; 2002ESPM...10..653K Two new cases of slowly negatively drifting pulsation structures in the decimetric wavelength range are reported. It is shown that the August 18, 1998 flare started with a slowly drifting pulsation structure associated with a plasmoid ejection observed by Yohkoh/SXT. This drifting pulsation structure is an example of a narrow-band one, which even shows intensity enhancements at its high- and low-frequency edges. Using the cross-correlation method no significant relation between the radio emission of this drifting structure and the hard X-rays was found. On the other hand, the second drifting structure observed during the hard X-ray decay phase of the March 24, 2000 flare shows a clear separation from the large-scale coronal shock wave released by the flare (a partly simultaneous type II radio burst occurred at much lower frequencies). The slowly drifting structures are analyzed and possible underlying physical processes are discussed assuming the plasmoid ejection model of eruptive solar flares. Title: Radio observations of the July 13, 2000 transequatorial eruptive prominence Authors: Karlický, M.; Shibasaki, K. Bibcode: 2002ESASP.506..657K Altcode: 2002ESPM...10..657K; 2002svco.conf..657K Using the 17 and 34 GHz Nobeyama Radioheliograph observations the July 13, 2000 transequatorial eruptive prominence was studied. It was found that the eruption started near the bright equatorial feature, which reappeared in the post-eruption phase. During 7 hours of observations of this feature periodic variations of its brightness temperature were recognized, e.g. in the initial phase of the prominence eruption their characteristic period was about of 12 minutes. Circular loops and helical structures of different scales, indicating the presence of electric currents were observed during the whole prominence eruption. The velocity of the upper boundary of the prominence in the image plane, along the chosen line was estimated as 24 km s-1 in the first 15 minutes of the eruption and about of 66 km s-1 in following times. Finally, the observations are shortly discussed. Title: High-frequency slowly drifting structures in solar flares Authors: Karlický, M.; Fárník, F.; Mészárosová, H. Bibcode: 2002A&A...395..677K Altcode: Radio emission of four solar flares with high-frequency slowly drifting structures is presented. Three sub-classes of these structures were recognized. It is shown that the April 15, 2001 X14.4 flare started with the slowly drifting structure associated with a plasmoid ejection observed by TRACE in the 171 Å line. The August 18, 1998 event presents an example of the drifting pulsation structure (DPS) which is well limited in frequency extent at both sides. A further example of the DPS, but followed by clouds of the narrowband dm-spikes, was observed during the November 23, 2001 flare. Finally, in the case of the April 12, 2001 flare, the drifting pulsation-continuum structure was recorded at the same time as the metric type II radio burst, i.e. in different frequency ranges. The slowly drifting structures were analyzed and in two cases their relation to hard X-ray emission was studied. Possible underlying physical processes are discussed assuming the plasmoid ejection model of eruptive solar flares. Title: Magnetic fields, plasma densities, and plasma beta parameters estimated from high-frequency zebra fine structures Authors: Karlický, M.; Jiricka, K. Bibcode: 2002ESASP.505..437K Altcode: 2002solm.conf..437K; 2002IAUCo.188..437K Using the recent model of the radio zebra fine structures (Ledenev et al. 2001) the magnetic fields, plasma densities, and plasma beta parameters are estimated from high-frequency zebra fine structures. It was found that in the flare radio source of high-frequency (1-2 GHz) zebras the densities and magnetic fields vary in the intervals of (1-4)×1010 cm-3 and 40-230 G, respectively. Assuming then the flare temperature as about of 107K, the plasma beta parameters in the zebra radio sources are in the 0.05-0.81 interval. Thus the plasma pressure effects in such radio sources, especially in those with many zebra lines, are not negligible. Title: Flare loops destabilization and expansion during the April 2, 2001 flare Authors: Kulinová, A.; Dzifcáková, E.; Klacka, J.; Karlický, M. Bibcode: 2002ESASP.505..469K Altcode: 2002solm.conf..469K; 2002IAUCo.188..469K An evolution of the flare loops observed in TRACE 171 Å line, 1600 Å continuum and Hα line (Modra Observatory) during the C8.5/1F, April 2, 2001 flare is analyzed. The expansion of the flare loops at their tops is recognized co-spatially at the hot (TRACE 171 Å, 0.9 MK) as well as cold (Hα and 1600 Å, 0.01 - 0.02 MK) lines. The loop expansion started after an injection of the cold plasma into the loops. At some parts of the expanding loops helical features were found. At space of loop footpoints the umbrella handle shape features can be seen. It was found that these structures are 3-dimensional ones, i.e. not only layers in the chromosphere. Such an interpretation demands relatively high plasma densities (~1012 cm-3) in these structures due to their visibility in emission against the disc in the Hα. Furthermore the linear bright structure, perpendicular to the global magnetic field of the expanding loops, was observed. To understand the whole process under the study, the observed structures are compared with those extrapolated in the potential magnetic field approximation. A possible role of the "ballooning" instability, destabilizing the loops, is discussed. Title: X-ray and radio observations in the initial development of an X-class solar flare Authors: Fárnik, F.; Karlický, M.; Hudson, H.; Kosugi, T. Bibcode: 2002ESASP.508..441F Altcode: 2002soho...11..441F The EIT/SOHO and SXT/YOHKOH plasma ejecta accompanied by an unusual drifting radio continuum and early hard X-ray emission observed prior to the impulsive phase of the September 24, 2001, X-class flare are analyzed. The paper presents some of the first reported observations from the new Hard X-ray Spectrometer instrument (HXRS), as well as imaging data from YOHKOH plus radio spectral observations in the decimetric band. The early hard X-ray observations revealed a soft spectrum that we interpret as non-thermal, located within loop structures observed in soft X-rays along the magnetic neutral line. The hard X-ray emission continued for more than one hour. In the initial phase of the flare, the hard X-ray emission arose in structures closely identifiable with the early soft X-ray loops, which appeared to evolve smoothly into the post-flare loop system of the flare maximum. At this time the decimeter spectra showed loosely-correlated spiky emission at frequencies consistent with the densities inferred from soft X-rays, but with rapid drifts implying motions along magnetic field lines. Title: The EIT coil-like structure in the March 20, 2000 eruptive prominence Authors: Karlický, M.; Šimberová, S. Bibcode: 2002A&A...388.1016K Altcode: The evolution of the March 20, 2000 prominence eruption observed in the 195 Å(EIT/SOHO), Hα , (MDI/SOHO), 1-3 GHz radio and hard X-ray (BATSE) was analyzed. A unique EIT coil-like structure with a hot core, indicating an electric current, was observed at the beginning of the prominence eruption. This structure with about 5 turns was associated with the reverse drift radio bursts at 1.0-2.5 GHz and the 33-57 keV hard X-ray emission. The hot core observation confirmed our recent suggestion about heating inside the eruptive prominence. Comparing the form of the EIT filament in the pre-eruption phase with the magnetic field map the presence of the electric current was confirmed. It was suggested that the relatively slow drifts of the reverse drift bursts can be due to a beam propagating in a vertical coil-like (helical) structure. Plasma processes and parameters in the eruptive prominence were discussed. Title: Correlated Study of Decimetric Solar Radio Bursts and Solar X-Ray Bursts Observed by RHESSI Authors: Fernandes, F. C. R.; Cecatto, J. R.; Reinaldo, R. R.; Krishan, V.; Sawant, H. S.; Karlicky, M.; Liricka, K.; Kane, S. R. Bibcode: 2002AAS...200.7609F Altcode: 2002BAAS...34..777F High resolution sprectra and images of solar hard X-ray bursts in 3 keV -- 15 MeV range obtained by the recently launched RHESSI spacecraft are compared with decimetric solar radio bursts observed simultaneously with high time and frequency resolution with the Brazilian Solar Decimetric Telescope (1000 -- 2000 MHz) and Ondrejov Radio Telescope (800 -- 4500 MHz). Preliminary results from a correlated study of the type III bursts and other fine structures observed with the ground-based radio instruments and the impulsive hard X-ray bursts observed by RHESSI will be reported. These results are expected to lead to a better understanding of the acceleration and propagation of energetic electrons in the solar atmosphere. Title: A Mechanism for ZEBRA Burst Radio Emission in the Solar Corona Authors: LaBelle, J.; Yoon, P. H.; Karlicky, M.; Treumann, R. A. Bibcode: 2002AGUSMSH21D..02L Altcode: Solar ZEBRA radio bursts are one of the least understood solar radio emissions. They occur irregularly during solar Type IV radio bursts covering a relatively wide frequency range from 0.5-4 GHz. Their instantaneous total bandwidth is narrow of the order of a fraction of 1 GHz. As the name suggests, they consist of a limited but sometimes large number of emission lines which are about equally spaced in frequency. The spacing is of the same order as the width of each line emission. Their connection with type IV bursts suggests that they occur in relatively strong magnetic field regions in the source region of the type IV and are related to the generation of emission by the trapped electron component in magnetic loop configurations. We propose a mechanism which is based on trapping of the upper hybrid mode in plasma density fluctuations in the loop plasma. Upper hybrid waves are readily excited by the trapped electron populations in the loop, whose distribution functions are characterized by loss cones. Trapping causes a discrete spectrum of such modes and nearly constant frequency spacing with the number of quasi-harmonics limited by the trapping conditions. We derive an equivalent Schrödinger equation for the trapped mode and solve it in cylindrical symmetry, obtaining the eigenfrequencies. Trapping occurs for sufficiently large density modulations. The expected frequency spacing is as narrow as observed. The trapped upper hybrid modes may mode convert into radio emission in order to radiate away; such mode conversion occurs in several other space physics radio emissions, such as terrestrial continuum radiation and auroral electron cyclotron harmonic waves (``auroral roar''). This model of the ZEBRA emissions implies that they can be used to remotely sense the fluctuating density structure in the solar corona under type IV conditions. Title: Microwave Detection of Shock and Associated Electron Beam Formation Authors: Aurass, H.; Shibasaki, K.; Reiner, M.; Karlický, M. Bibcode: 2002ApJ...567..610A Altcode: We use complementary European and Japanese solar radio ground-based observations, together with Yohkoh soft X-ray and SOHO extreme-UV images, to search for the signature of flare-related waves at different heights above the Sun. The key data set for event selection is 40-800 MHz dynamic radio spectra from the Potsdam Astrophysical Institute, whose radio spectral polarimeter is sensitive to the coronal shock waves due to the associated type II radio bursts in the range between 0.2 and 1 Rsolar. Nobeyama Radio Heliograph images at 17 GHz show the chromosphere and the transition region to the corona with unprecedented sensitivity and time resolution (1 s image cadence). Here we focused on 17 GHz images in the time interval between flare onset and the start of the metric type II burst. The decametric-hectometric (Dm-Hm 1-14 MHz) radio experiment on board Wind completes the radio spectral coverage. The spectra are used to check if the coronal shock wave is also continuously visible in the range 3-8 Rsolar and if the corona is open or closed for electron beams exciting hectometric type III bursts. We selected two flare events that show metric type II bursts, but with different associated 17 GHz features. For both events we find flare disturbances in 17 GHz images that propagate earlier than the type II bursts: a hot, dense blob (event 1; 1997 April 2) or a cold, absorbing cloud (event 2; 1998 July 31). In event 1, the hot and dense blob preceded the formation of a wave front segment that appeared in SOHO/EIT images. In event 2, we observed the impact of the 17 GHz absorbing cloud on a preexisting quiescent prominence far out of the flaring active region after several minutes of propagation without being disturbed. We demonstrate that the spectral pattern, as well as the drift rate, of the given type II burst drastically changes shortly before the cloud's impact. The Dm-Hm spectra in event 2 reveal a typical shock-associated (SA) event in the outer corona during the interaction between the absorbing cloud and the prominence. Finally, we stress that there may be a common driver for the metric type II bursts and simultaneous decimeter reverse-drift bursts between 1 and 2 GHz recorded on the radio spectrograph of Astronomical Observatory Ondřejov. Title: Loop structures in the July 19, 1999 solar flare Authors: Kulinová, A.; Karlický, M. Bibcode: 2002ESASP.477..143K Altcode: 2002scsw.conf..143K Comparing the SOHO/EIT 195 Å and Hα images (Hvar and Modra Observatories) with the magnetic field extrapolations of SOHO/MDI magnetograms the loop structures of the July 19, 1999 flare were analyzed. The presence of the current-carrying flux rope was identified by its deviation from the current-free magnetic field extrapolation and "umbrella hand" shape of the Hα ribbons. After the flare start in the neighboring "cone" arcade this current-carrying flux rope interacts (reconnects) with this arcade, forming thus flare loops spanning over both these magnetic structures. During these processes several cross-loop structures appeared. One of them indicates the flare loop interaction. At this space the extended helical structure, possibly a remnant of some current-carrying flux rope, was found. The pitch angle of this helical thread θ = 61° was determined. Assuming then the magnetic field as 10-4 - 10-3T, the total electric current in the helical structure was estimated as J = 4.8×(109 - 1010)A. Title: Magnetic rope in the March 20, 2000 prominence eruption Authors: Karlický, Marian; Simberová, Stanislava Bibcode: 2002ESASP.477..127K Altcode: 2002scsw.conf..127K An evolution of the March 20, 2000 prominence eruption observed in the Hα and 195 Å EIT was analyzed using the image processing technique. The helical structure of the eruptive prominence (magnetic rope) with a hot core was recognized and the electric current of 3.7×1010 Å inside this rope was estimated. The hot core observation agrees with our recent spectroscopic observations. It is interesting that the pre-eruptive filament was located above the X-type photospheric magnetic field. During the eruption the magnetic field changes around this X-type configuration have been found. Title: Occurrences of different types of 0.8-2.0 GHz solar radio bursts and fine structures during the solar cycle Authors: Jiřička, K.; Karlický, M.; Mészárosová, H. Bibcode: 2002ESASP.477..351J Altcode: 2002scsw.conf..351J 681 solar radio events observed by the Ondřejov 0.8-2.0 GHz radiospectrograph during 1992-2000 are analyzed and corresponding bursts and fine structures classified into ten different classes. For all defined types of bursts and fine structures basic characteristics of their parameters are presented. Distributions of various types of bursts and fine structures in the years 1992-2000 in dependence on the changes of solar activity during the cycles 22 and 23, occurrences of studied types of bursts in association with GOES class flares as well as their relationship to GOES flare maxima are shown. Finally, the association of the analyzed bursts with the metric type III bursts is studied. Title: Impact Hα line polarization and return current Authors: Karlický, M.; Hénoux, J. C. Bibcode: 2002A&A...383..713K Altcode: Electron beams, bombarding the dense chromospheric layers during solar flares, carry electric currents which need to be neutralized by so-called return currents. Return currents are formed by background plasma electrons having an anisotropic velocity distribution. Thus they can generate impact Hα line polarization. First, a numerical method of computation of the impact Hα line polarization for an arbitrary electron distribution function is presented. Then the polarization due to return current electrons associated with beam electrons is computed. For low electron beam fluxes, the return current is low and the polarization is only due to the electron beam, i.e. it is perpendicular to the electron beam direction and it reaches -8.0%. Increasing the return current and the beam flux leads to a change of orientation of the polarization by 90deg and the polarization degree can even reach a maximum of +22.4%. But this change and the maximum of the polarization require very high electron beam fluxes of 1.79 x 1012 and 4.8 x 1012 ergs cm-2 s-1, respectively. Therefore plasma processes, which can reduce the high-energy flux requirement for the polarization change observations, are briefly discussed. Title: 3 GHz Flux Variations of the April 7, 1997 Flare and Current-Loop Coalescence Model Authors: Fárník, F.; Karlický, M. Bibcode: 2002mwoc.conf..169F Altcode: Very regular time variations of the 3 GHz radio flux observed during the 7 April 1997 flare are presented together with Yohkoh-SXT and SOHO-EIT observations. On lower frequencies (40-800 MHz) the variations were followed by several branches of type II radio burst. In the post-maximum phase of this flare the Yohkoh images indicate I-type of the flare loop interaction. The observations were analyzed and it was found that the data can be described by the current-loop coalescence model: the main period of the 3 GHz radio flux (about 100 s) corresponds to the repetition of the current-loop coalescence, and the radio double-peaks are associated with the maximum of the electric field component perpendicular to the interaction plane. The plasma beta-parameter in the current-loop coalescence process was estimated as 0.63. Indications of the beta-parameter increase during the flare are found. Title: Flare Changes Associated with Peaks of Hard X-Ray Bursts Authors: Farnik, F.; Svestka, Z.; Karlicky, M. Bibcode: 2002cosp...34E1403F Altcode: 2002cosp.meetE1403F Using the high-resolution records made in four energy channels by the Hard X-Ray Spectrometer (HXRS) on board the MTI spacecraft (launched on 12 March 2000) we try to refine the study made by Dwivedi et al. 18 years ago (Dwivedi, B.N., Hudson, H.S., Kane, S.R., and Svestka, Z.: 1984, Solar Phys. 90, 331) who looked for changes in the flare development associated with changes in the hard X-ray flux. In addition to H-alpha and SOHO data we can, at least for some flares, also use high-resolution TRACE images which make it possible to see fine changes which could not be detected before. We try to find, in particular, which parts of flares produce hard X ray peaks of various hardness in the HXRS records and we also- compare them with peaks in microwave records. Intense peaks often correspond to flaring structures penetrating into strong magnetic fields (penumbrae and umbrae of sunspots) which generally confirms Dwivedi et al.'s findings. However, we can provide more details than they were able to obtain from their data with worse space and time resolution. Title: High-Frequency Slowly Drifting Pulsation Structures in the November 25, 2000 and April 15, 2001 Solar Flares. Authors: Karlicky, M.; Farnik, F. Bibcode: 2002cosp...34E1404K Altcode: 2002cosp.meetE1404K Radio and X ray emissions of the November 25, 2000 and April 15, 2001 solar- flares exhibiting the high-frequency slowly drifting pulsation structures (DPS) are presented. The characteristic periods of the DPSs are determined and their relationship to the hard X-ray emission is analyzed. Possible physical processes are discussed under assumption of the plasmoid ejection model of eruptive solar flares. It is shown that the April 15, 2001 X14.4 flare started with the DPS which was associated with a plasmoid ejection seen in the 171 A line (TRACE). The November 25, 2000 event exhibits the DPS together with the bursts with rapid frequency variations, indicating a different origin of the DPS. Title: Decimetric dot-like structures Authors: Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R.; Vats, H. O.; Neri, J. A. C. F.; Portezani, V. A.; Martinon, A. R. F.; Karlický, M.; Jiřička, K.; Mészárosová, H. Bibcode: 2002AdSpR..29..349S Altcode: Various types of fine structures have been observed by the Brazilian Solar Spectroscope (BSS) in the frequency range of (1000 - 2000) MHz, since its regular operation from 1998. Here, we report for the first time statistical analysis of the 165 isolated dot-like emissions and their chains observed, from September 1999 to September 2000, in the decimetric band. Dots are observed in groups spread over the frequency - time plane. Rarely their chains are observed. Chains of dots cover the frequency range of ∼ 150 MHz and hardly cover the entire frequency range of observations. Isolated dot-like emission has been observed to the limit of the BSS resolutions (3 MHz, 50 ms). In 50 % of the cases the observed instantaneous bandwidth and flux values are 5 MHz and ∼ 20 sfu, respectively. Also, in 90 % of the cases total duration is of about 50 ms, equal to the limit of BSS time resolution. The groups of the dots have been found to be associated with the rising part of the impulsive flares and a radio-continuum. A model of dot-like emissions based on the anisotropic beam instability is suggested. Title: Decimetric Reverse Drift and U-Type Bursts in the April 9, 2001 Flare Authors: Cecatto, J. R.; Sawant, H. S.; Fernandes, F. C. R.; Krishan, V.; Rosa, R. R.; Karlický, M. Bibcode: 2002mwoc.conf..313C Altcode: No abstract at ADS Title: Electron acceleration, Decimetric Solar radio bursts and Solar hard X-ray bursts observed by RHESSI Authors: Kane, S.; Fernandes, F.; Cecatto, J.; Reinaldo, R.; Krishan, V.; Sawant, H.; Karlicky, M.; Liricka, K. Bibcode: 2002cosp...34E.574K Altcode: 2002cosp.meetE.574K Characteristics of the acceleration and propagation of electrons in the solar corona during a solar flare are deduced from a correlated study of decimetric radio bursts and impulsive hard X-ray bursts. Decimetric type III bursts and other fine structures in the frequency range of (1000-2000) MHz have been observed with the Brazilian Solar Decimetric Spectroscope. Corresponding radio observations in the (800-4500) MHz frequency range were made with the Ondrejov radio Telescopes. High resolution sprectra and images of solar hard X-ray bursts in 3 keV - 15 MeV range obtained by the recently launched RHESSI spacecraft are compared with the radio observations to determine the temporal relationship and its dependence on the characteristics of the radio bursts and hard X ray bursts. Early results from this- correlated study of ground-based radio observations and and spacecraft -observations of solar X-ray flares will be reported. Title: Radio Shocks from Reconnection Outflow Jet? - New Observations Authors: Aurass, H.; Karlicky, M.; Thompson, B. J.; Vršnak, B. Bibcode: 2002mwoc.conf..401A Altcode: The common analysis of dynamic radio spectrograms with Yohkoh X-ray images yields information about possible associations between nonthermal electron acceleration and changes in hot and dense plasma-magnetic field structures of the corona. Examples are correlated X-ray-jet--electron beam injections (type III/U bursts), motions of X-ray blobs and correlated shock-driven (type II) radio bursts, and sigmoid evolution associated with characteristic type IV burst spectral fine structures. Here, we demonstrate the first identification of the radio signature of a reconnection outflow termination shock during a dynamic flare. Reconnection of magnetic fields is one flare energy release mechanism. During dynamic flares there is formed a system of standing slow and - sometimes - also fast mode shock waves in the space around the diffusion region. This standing fast mode shock is revealed by a zero-drift type II burst between 300 and 400 MHz. It exists more than 30 min starting 1 hour after the impulsive flare on 07 April 1997 in AR 8027. It shows herringbone fine structure and 10% band splitted lanes. We argue for having detected fundamental mode emission. No fundamental-harmonic pattern was observed. Simultaneous imaging observations (Hα, Yohkoh SXT, SOHO EIT) show a postflare loop arcade with a bright soft X-ray cusp. Preferable conditions for the radio detection of the termination shock are a low plasma to magnetic pressure ratio eta upstream of the slow shocks, a low diffusion region rise velocity, and a low reconnection rate. The occurrence of the termination shock is most probable in late stage of flares. Title: The 1.0-4.5 GHz Zebras in the June 6, 2000 Flare Authors: Sawant, H. S.; Karlický, M.; Fernandes, F. C. R.; Cecatto, J. R. Bibcode: 2002mwoc.conf..315S Altcode: For the first time we are reporting harmonically related zebra structures above 1000 MHz, having ratio of 1:2. Zebra structures show up to 8 zebra lines. In individual zebra patterns the frequency ratio of the neighbouring zebra lines are less than 1.03 and these ratios decrease with the frequency decrease. The zebra patterns are analyzed and interpreted assuming double plasma resonance instability as the cause for their generation. The longitudinal upper hybrid waves are excited at positions of cyclotron resonances and then transformed into electromagnetic ones. Using this model the magnetic field strengths in the flaring loops are estimated in the range of 110-230 G. Title: Drifting Pulsations, 3 GHz Oscillations and Loop Interactions in the June 6, 2000 Flare Authors: Karlický, M.; Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R.; Fárník, F.; Mészárosová, H. Bibcode: 2002mwoc.conf..173K Altcode: During this long-lasting X2.3 flare (15:00-17:00 UT) two 3 GHz maxima (impulsive phases) were recognized at 15:06:46-15:07:00 and 16:26:34-16:26:42 UT. Quasi-periodic oscillations with the periods of 160 s and 11 s, respectively, were found, during both these impulsive phases. While in the first impulsive phase the 2.0-4.5 GHz broadband pulsations superimposed on the continuum were recorded, during the second one several quasi-periodic patches of narrowband spikes were observed in the frequency range of 2.5-3.5 GHz. Moreover, at the onsets of both impulsive phases the narrowband fast drift structures slowly drifting towards lower frequencies and indicating the plasmoid ejection were recorded. The SOHO and YOHKOH images of the flare show parallel loops with brightenings among them. It shows that the flaring loops interact. This view is supported by simultaneous observations of the quasi-periodic oscillations at 3 GHz and the narrowband pulsations in the second impulsive phase, which can be thus understood in the framework of the current loop coalescence model. Title: Turbulent plasma model of the narrowband dm-spikes Authors: Bárta, M.; Karlický, M. Bibcode: 2001A&A...379.1045B Altcode: Starting from radio spectrum features of the narrowband dm-spikes, it is suggested that they are generated at positions in the solar flare atmosphere where the upper hybrid frequency is equal to the low harmonics of the electron cyclotron frequency. It is assumed that a radio source plasma is in a turbulent state. The upper hybrid waves are generated by an anisotropic electron beam which propagates along magnetic loop lines. Collisional damping and turbulent changes of plasma parameters in the radio source cause strong intensity-frequency variations of the upper hybrid waves. These waves are then transformed into observed narrowband dm-spikes. Using this model, the artificial radio spectra are computed. It is shown that a chain of narrowband spikes is generated at a one cyclotron harmonic, in one turbulent magnetic flux tube. On the other hand, a cloud of spikes (or their harmonic clouds) results from a superposition of many chains of spikes generated in many turbulent magnetic flux tubes (in several cyclotron harmonics). Finally, further features of the narrowband dm-spikes are discussed in the framework of the proposed model. Title: Bastille Day Event: A Radio Perspective Authors: Reiner, M. J.; Kaiser, M. L.; Karlický, M.; Jiřička, K.; Bougeret, J. -L. Bibcode: 2001SoPh..204..121R Altcode: We describe the radio signatures that led up to and concluded the solar eruptive event of 14 July 2000 (Bastille Day Event). These radio signatures provide a means of remotely sensing the associated solar activity and transient phenomena. For many days prior to the Bastille Day Event kilometric Type III radio storm emissions were observed that were presumably associated with the active region NOAA 9077. These storm emissions continued until the X5.7 flare at ∼ 10 UT on 14 July 2000 that characterized the Bastille Day Event, then ceased abruptly. The Bastille Day Event itself produced very intense, complex, long-duration Type III-like radio emissions, which appear to have been associated with electrons generated (accelerated) deep in the solar corona. The coronal mass ejection (CME) associated with the Bastille Day Event generated decametric to kilometric Type II radio emissions as the CME propagated through the solar corona and interplanetary medium. The frequency drift of these Type II radio emissions are related to the dynamics of the propagating CME and indicate that the CME experienced significant deceleration as it propagated from the high corona into the interplanetary medium. Title: Radio bursts with rapid frequency variations - Lace bursts Authors: Karlický, M.; Bárta, M.; Jiřička, K.; Mészárosová, H.; Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R. Bibcode: 2001A&A...375..638K Altcode: The Ondřejov radiospectrograph operating in the 0.8-2.0 GHz frequency range recorded in recent years (1998-2000), three (August 10, 1998; August 17, 1999; June 27, 2000) unique bursts with rapid frequency variations (lace bursts) lasting for several minutes. On August 17, 1999, the same burst was recorded simultaneously by the Brazilian Solar Spectroscope in the 1.0-2.5 GHz frequency range. The frequency variations of these bursts in four time intervals were analyzed by the Fourier method and power-law spectra with power-law indices close to -2 were found. The Fourier spectra show the presence of frequency variations in the 0.01-3.0 Hz interval which indicate fast changes of plasma parameters in the radio source. Due to the similarities in the line features of these bursts with zebra pattern lines, a model similar to that of the zebra pattern was suggested. The model radio spectra, computed using this model with a turbulent state of the solar flare atmosphere, are similar to those observed by the radiospectrographs. Title: Global statistics of 0.8-2.0 GHz radio bursts and fine structures observed during 1992-2000 by the Ondřejov radiospectrograph Authors: Jiřička, K.; Karlický, M.; Mészárosová, H.; Snížek, V. Bibcode: 2001A&A...375..243J Altcode: 681 solar radio events observed by the Ondřejov 0.8-2.0 GHz radiospectrograph during 1992-2000 are analyzed and corresponding bursts and fine structures classified into ten different classes. A new rare type of fine structure with rapid frequency variation we called lace pattern was included. Drifting pulsation structures, observed usually at the beginning of the impulsive flare phase, were recognized among pulsations. Furthermore, a new sub-class of zebra patterns with many zebra lines ( ~ 30) superimposed on fibers was identified. For all defined types of burst and fine structures basic characteristics of their parameters are presented. Distributions of various types of burst and fine structures in the years 1992-2000 in dependence on the changes of solar activity during the cycles 22 and 23, occurrences of studied types of burst in association with GOES class flares as well as their relationship to GOES flare maxima are shown. Finally, the association of the analyzed bursts with the metric type III bursts observed at Potsdam-Tremsdorf Observatory was studied. Title: An Estimation of the Coronal Magnetic Field Strength From Spectrographic Observations in the Microwave Range Authors: Ledenev, V. G.; Karlický, M.; Yan, Y.; Fu, Q. Bibcode: 2001SoPh..202...71L Altcode: 2001astro.ph..1360L Solar radio emission observations in the microwave frequency range show fine structures consisting of a number of almost parallel narrow-frequency bands. We interpret these bands as plasma emission at cyclotron harmonics. This emission is generated by the anisotropic electron beam, which excites longitudinal waves at a normal Doppler effect resonance. Subsequently, the longitudinal waves convert to radio emission at the second harmonic of the longitudinal wave frequency, and sometimes to the fundamental harmonic. The magnetic field strength is estimated on the basis of such a model in the microwave burst sources at ∼ 100-200 G. Estimates of the density variations are also made. Title: Locations of Footpoints of Transequatorial Interconnecting Loops Authors: Fárník, František; Karlický, Marian; Švestka, Zdeněk. Bibcode: 2001SoPh..202...81F Altcode: We discuss footpoints of loops seen by Yohkoh in soft X-rays that connect active regions across the equator (transequatorial interconnecting loops - TILs). While most TILs are rooted in moderately strong fields at peripheries of active regions, there are also cases when these loops are anchored in very weak or very strong fields, ranging from < 30 G to several hundred gauss. Some have their footpoints near sunspot penumbrae, creating `X-ray fountains' in a combination with active region loops. But TILs are never rooted in sunspots. The most likely explanation is that magnetic field lines leave spots almost vertically so that TILs rooted in them extend high into the corona and density in them is below the limit of visibility in X-rays. The fact that in force-free modeling some TILs are rooted in sunspots is most probably due to the difference between field-line connections in `vacuum' and in the highly conductive plasma on the Sun. Some TILs end before they reach active regions which sometimes may indicate the real situation, but mostly this `gap' is probably due to a temperature decrease near the loop footpoints which makes them invisible in X-rays. In that case the fact that these cool lowest parts of TILs are never found in TRACE or SOHO EIT images indicates that plasma density in TILs must be very low. Still, the total absence of any counterparts of X-ray TILs in TRACE and EIT images is puzzling and, therefore, other possible interpretations of the `gap' origin are also briefly mentioned. Title: New Solar Broad-Band Hard X-Ray Spectrometer: First Results Authors: Fárník, František; Garcia, Howard; Karlický, Marian Bibcode: 2001SoPh..201..357F Altcode: The scientific and operational aims of the Czech-made Hard X-Ray Spectrometer (HXRS) launched onboard the U.S. Department of Energy Multispectral Thermal Imager satellite (MTI), on 12 March 2000 are discussed. The principal operating characteristics of the instrument such as the temporal resolution, energy band selection, spectral sensitivity, and the in-flight calibration procedure are described as well as the technical details of the spectrometer including detectors, shielding (against charged particles) and electronic design. The MTI host satellite and its orbit are briefly described. Recent observations by the 3 GHz Ondřejov radiometer are compared with HXRS data to demonstrate one example of the HXRS data utilization: the temporal relation between hard X-rays and radio emission. These results show relatively long time delays (2-14 s) of the GHz broadband radio pulses relative to the hard X-ray emission peaks. Access to the HXRS data base via the Internet is provided. Title: Holes in the Hα Eruptive Prominence Structure Authors: Šimberová, Stanislava; Karlický, Marian; Varady, Michal; Rank, Gerhard Bibcode: 2001SoPh..201..119S Altcode: The eruptive prominence observed on 27 May 1999 in Hα at Ondřejov Observatory is analyzed using image-processing techniques. To understand the physical processes behind the prominence eruption, heated structures inside the cold Hα prominence material are sought. Two local minima of intensity (holes), the first above and the second below the erupting Hα prominence, have been found in the processed Hα images. A comparison of Hα images with the SOHO/EIT and Yohkoh/SXT images showed: (a) the cold Hα prominence is visible as a dark feature in the EIT images, (b) the upper local minimum of intensity in the Hα image corresponds to a hot structure seen in EIT, (c) the lower minimum corresponds to a hot loop observed by SXT. The physical significance of the Hα intensity minima and their relation to the hot structures observed by EIT and SXT is discussed. The time sequence of observed processes is in favor of the prominence eruption model with the destabilization of the loop spanning the prominence. For comparison with other events the velocities of selected parts of the eruptive prominence are determined. Title: Some aspects of radio and hard X-ray emissions of solar flares Authors: Karlický, Marian Bibcode: 2001PBeiO..37...75K Altcode: Two examples of the 1-2 GHz radio observations made by the Ondrejov radiospectrograph are shown: a) The October 5, 1992 drifting pulsation structure, and b) the November 9, 1998 high-frequency type II-like burst. We propose a model in which the drifting pulsations are caused by quasi-periodic particle accelerations in the magnetic reconnection in space under the ejected plasmoid. Then a new model of the electron component heating during the neutral beam bombardment of the dense atmospheric layers is presented and its relevance to the hard X-ray emission is discussed. Title: On an estimation of the coronal magnetic field strength from spectrographic observations in the microwave range Authors: Ledenev, V. G.; Karlický, M.; Yan, Yihua; Fu, Qijun Bibcode: 2001PBeiO..37...81L Altcode: Observations of the solar radio emission in the microwave frequency range show fine structures consisting of s number of the almost parallel narrow frequency bands. We interpret these bands as the cyclotron harmonics plasma emission. This emission is generated by the anisotropic electron beam, which excites longitudinal waves on the normal Doppler effect resonance. Then the longitudinal waves convert into the radio emission on the second harmonic of the longitudinal waves frequency and sometimes into the fundamental one. Estimations of the magnetic field strength made on the basis of such a model give the values of the magnetic field in the microwave burst sources as ~100-200 G. Title: Drifting radio bursts and fine structures in the 0.8-7.6 GHz frequency range observed in the NOAA 9077 AR (July 10-14, 2000) solar flares Authors: Karlický, M.; Yan, Y.; Fu, Q.; Wang, S.; Jiřička, K.; Mészárosová, H.; Liu, Y. Bibcode: 2001A&A...369.1104K Altcode: The 0.8-7.6 GHz global and detailed radio spectra of the four most intense flares observed in the NOAA 9077 active region (July 10-14, 2000) are presented. The radio bursts of these flares and their sequence reveal features indicative of topological similarities among the flares under study. The drifting pulsation structures were found to be the typical signatures of these flares. Furthermore, many other fine structures such as narrowband drifting lines, drifting harmonic structure with zebra patterns, drifting branches of narrowband dm-spikes, and structures with fast positively and negatively drifting bursts are shown in the context of the whole radio flares. Some of them were observed for the first time. The relationships among them and the resulting interpretations are summarized. The characteristic periods of the drifting pulsation structures and the magnetic field in the zebra radio source are determined. Title: The Magnetic Rope Structure and Associated Energetic Processes in the 2000 July 14 Solar Flare Authors: Yan, Yihua; Deng, Yuanyong; Karlický, Marian; Fu, Qijun; Wang, Shujuan; Liu, Yuying Bibcode: 2001ApJ...551L.115Y Altcode: In the reconstructed nonlinear force-free magnetic field of NOAA Active Region 9077 before the X5.7/3B (10:24 UT) flare on 2000 July 14, we reveal for the first time the presence of a magnetic rope from the extrapolation of the three-dimensional magnetic field structure. This magnetic rope is located in a space above the magnetic neutral lines of the filament. The calculated field lines of the rope rotate around its axis for more than three turns. Overlying the rope are multilayer magnetic arcades with different orientations. These arcades are in agreement with the Transition Region and Coronal Explorer observations. The estimated free magnetic energy in this rope system is about 1.6×1032 ergs. Such magnetic field structure provides a favorable model for the interpretation of the energetic flare processes as revealed by Hα, EUV, and radio observations. In particular, the intermittent cospatial brightening of the rope in EUV 1600 Å image leading to the onset of the flare suggests that the rope instability may have triggered the flare event, and the drifting pulsation structure in the decimetric frequency range is considered to manifest the initial phase of the coronal mass ejection. Title: Axially-symmetric Velocities in the 15 May 2000 Eruptive Prominence Authors: Karlický, Marian; Kotrč, Pavel; Kupryakov, Yurij A. Bibcode: 2001SoPh..199..145K Altcode: Large Doppler velocities with unique, almost regular elliptical features were observed in the Hα spectra of the May 15, 2000 eruptive prominence. These features were interpreted in the frame of axially symmetric models of the eruptive prominence. The rotational (7-60 km s−1), expansion (30-44 km s−1), axial (3-19 km s−1), and global (66-160 km s−1) prominence plasma velocities were derived. The plasma velocity patterns were compared with the observed helical structures of the Hα prominence. The velocities of selected Hα blobs in the image plane were determined. The axially symmetric detwisting process of the magnetic flux rope of the eruptive prominence was recognized. Title: Shock Drift Electron Acceleration in a Wavy Shock Front Authors: Vandas, M.; Karlický, M. Bibcode: 2000SoPh..197...85V Altcode: It is commonly believed that solar type II bursts are caused by accelerated electrons at a shock front. Holman and Pesses (1983) suggested that electrons creating type II bursts are accelerated by the shock drift mechanism. Zlobec et al. (1993) dealt with a fine structure of type II bursts (herringbones) and suggested a qualitative model where electrons are accelerated by a nearly perpendicular wavy shock front. Using this idea, we developed a model of electron acceleration by such a wavy shock front. Electrons are accelerated by the drift mechanism in the shock layer. Under simplifying assumptions it is possible to obtain an analytical solution of electron motion in the wavy shock front. The calculations show that electrons are rarely reflected more than once at the wavy shock front and that their final energy is mostly 1-3 times the initial one. Their acceleration does not depend significantly on shock spatial parameters. In the present model all electrons are eventually transmitted downstream where they form two downstream beams. Resulting spectral and angular distributions of accelerated electrons are presented and the relevance of the model to the herringbone beams is discussed. Title: Hard X-Rays from Neutralized Ion Beams in Solar Flares Authors: Brown, J. C.; Karlický, M.; Mandzhavidze, N.; Ramaty, R. Bibcode: 2000ApJ...541.1104B Altcode: Under suitable conditions, hard X-rays (HXRs) may be emitted by a neutralized proton beam due to the ``heating'' of the electrostatically dragged electrons in collisions with a nearly neutral background atmosphere. A simple estimate is made generalizing this HXR emission mechanism to heavier ions dragging a neutralizing electron current. Recent gamma-ray results on the energy content of flare ions of >=1 MeV nucleon-1 are used to estimate the total HXR yield above 20 keV or so which would be expected from these processes, and in 19 flares the results are compared with HXR data in the same events. It is found that only in two flares are the neutral beam HXRs clearly important and that in a few others they may be significant. In most events, however, the neutral beam HXR contribution is small, though the ion energy is comparable with that of electrons. Title: Linear and nonlinear statistical analysis of narrow-band dm-spikes observed during the June 15, 1991 flare Authors: Mészárosová, H.; Karlický, M.; Veronig, A.; Zlobec, P.; Messerotti, M. Bibcode: 2000A&A...360.1126M Altcode: Narrow-band dm-spikes observed during the June 15, 1991 flare are statistically analysed. The character of their frequency distributions at 237, 327, 408 and 610 MHz in both L- and R-handed circular polarizations is studied. While for the complete time intervals no simple distributions of spikes (either exponential or power-law) are recognized, for shorter intervals both exponential and power-law distributions are observed. No significant difference is found in the distributions for L- and R-polarized data. Further analysis reveals that spikes appearing in dense groups and with high intensities preferentially have exponential distributions, while the sparse spikes with lower intensities are rather characterized by power-law distribution functions with high exponents. Groups of independent spikes (cases with low rates and low intensities) have power-law distributions trend in agreement with the coherent spike mechanisms. Tests are provided regarding statistical analyses. The nonlinear analysis reveals that the degree of complexity of the system varies. It decreases when the attractor dimensions and the Lyapunov exponents assume smaller values, which happens when very strong spikes are present. The changing characteristics of the statistical parameters are probably the result of a mutual interaction in the source environment or a product of propagation conditions. Title: Solar flare radio pulsations as a signature of dynamic magnetic reconnection Authors: Kliem, B.; Karlický, M.; Benz, A. O. Bibcode: 2000A&A...360..715K Altcode: 2000astro.ph..6324K Decimetric radio observations of the impulsive solar flare on October 5, 1992, 09:25 UT show a long series of quasi-periodic pulsations deeply modulating a continuum in the 0.6-2 GHz range that is slowly drifting toward lower frequencies. We propose a model in which the pulsations of the radio flux are caused by quasi-periodic particle acceleration episodes that result from a dynamic phase of magnetic reconnection in a large-scale current sheet. The reconnection is dominated by repeated formation and subsequent coalescence of magnetic islands (known as "secondary tearing" or "impulsive bursty" regime of reconnection), while a continuously growing plasmoid is fed by newly coalescing islands. Such a model, involving a current sheet and a growing plasmoid, is consistent with the Yohkoh observations of the same flare (Ohyama & Shibata ?). We present two-dimensional MHD simulations of dynamic magnetic reconnection that support the model. Within the framework of the proposed interpretation, the radio observations reveal details of plasmoid formation in flares. Title: Power-law spectra of 1-2 GHz narrowband dm-spikes Authors: Karlický, Marian; Jiřička, Karel; Sobotka, Michal Bibcode: 2000SoPh..195..165K Altcode: Twelve examples of clouds of narrowband dm-spikes, observed by the Ondřejov radiospectrograph in the 1-2 GHz frequency range, are analyzed. After transforming of the frequency scales to heights in the solar atmosphere, the indices of the power-law power spectra are determined. The derived power-law indices are scattered in a broad range of values (−0.80-−2.85). In some cases they considerably deviate from the previously found value of −5/3. A change of the power-law index above log k≈2.5 was also found in some cases. In the two longest events the time evolution of their power spectra as well as their indices were studied. While in most parts of the radio spectra the spectral index remains constant, in one part its absolute value increases with the spike intensity increase. Finally, the results, especially the broad range of power-law indices, are briefly discussed. Title: Propagation of shock waves in the solar corona with 2-D loop structures Authors: Odstrčil, D.; Karlický, M. Bibcode: 2000A&A...359..766O Altcode: Motivated by recent observations of type II radio bursts, we study propagation of shock waves by the two-dimensional numerical magnetohydrodynamic model. Explosion of a hot plasma is investigated for various ratios of the mass density and magnetic field intensity in a fan of coronal loops. Ducting of shock waves occurs along loop-like structure and ducting of possible radio emission in under-dense coronal loops is expected. This provides an alternative to classical explanation that two distinctly separated type II radio bursts are caused by two different shocks. The presented results support the idea that a single solar flare energy release with a single shock can generate coronal disturbances observed as two separate type II radio bursts. Title: Simultaneous SOHO and Ground-Based Observations of a Large Eruptive Prominence and Coronal Mass Ejection Authors: Plunkett, S. P.; Vourlidas, A.; Šimberová, S.; Karlický, M.; Kotrč, P.; Heinzel, P.; Kupryakov, Yu. A.; Guo, W. P.; Wu, S. T. Bibcode: 2000SoPh..194..371P Altcode: Coronal mass ejections (CMEs) are frequently associated with erupting prominences near the solar surface. A spectacular eruption of the southern polar crown prominence was observed on 2 June 1998, accompanied by a CME that was well-observed by the LASCO coronagraphs on SOHO. The prominence was observed in its quiescent state and was followed throughout its eruption by the SOHO EIT and later by LASCO as the bright, twisted core of the CME. Ground-based Hα observations of the prominence were obtained at the Ondřejov Observatory in the Czech Republic. A great deal of fine structure was observed within the prominence as it erupted. The prominence motion was found to rotate about its axis as it moved outward. The CME contained a helical structure that is consistent with the ejection of a magnetic flux rope from the Sun. Similar structures have been observed by LASCO in many other CMEs. The relationship of the flux rope to other structures in the CME is often not clear. In this event, the prominence clearly lies near the trailing edge of the structure identified as a flux rope. This structure can be observed from the onset of the CME in the low corona all the way out to the edge of the LASCO field of view. The initiation and evolution of the CME are modeled using a fully self-consistent, 3D axisymmetric, MHD code. Title: On the Solar Origin of Complex Type III-like Radio Bursts Observed at and below 1 MHZ Authors: Reiner, M. J.; Karlický, M.; Jiřička, K.; Aurass, H.; Mann, G.; Kaiser, M. L. Bibcode: 2000ApJ...530.1049R Altcode: By simultaneously analyzing decimetric, metric, and hectometric radio observations, we provide evidence that a class of hectometric type III-like radio events are associated with electrons accelerated during the primary flare energy release process. We do this by demonstrating that there is a good temporal correspondence between the hectometric and decimetric radio emissions that are believed to involve the acceleration of electrons in deep layers of the solar atmosphere at heights estimated to be from 10,000 to 30,000 km (0.014 to 0.043 Rsolar). This class of hectometric type III-like events may have simple or complex intensity-time profiles. When they have complex profiles of long duration, the decimeter emissions also have complex long-duration profiles. In this latter case they are also often associated with metric type II radio bursts and coronal mass ejections (CMEs). However, we argue on the basis of the observations that the hectometric radio emissions are not necessarily associated with the metric phenomena. Specifically, they are not likely generated by a secondary acceleration process associated with the shock generating a metric type II burst or with a shock driven ahead of the CME despite the fact that the hectometric emission time profiles would (erroneously) be morphologically classified as shock-accelerated (SA) events. Title: Collisional Heating of the Electron Component of Neutral Beams Authors: Karlicky, M. Bibcode: 2000HvaOB..24...57K Altcode: Using a 1-D test particle model with the collisional scattering the numerical simulations of the collisional heating of the electron component of neutral beams is studied. Namely, beam electrons lag behind the protons, due to differential drag in collisions with the background, but their longitudinal velocities are closely tied to the beam protons by the electric field generated. However, collisions with the background also scatter the beam electrons resulting in the beam electron heating. The heating of these electrons up to 0.0125 of the initial proton energy was found. But, due to a decrease of the energetic electron density to about of 0.11 of the initial one, the real mean energy gain of these energetic electrons is 1/0.11 times greater. Moreover, the electron distribution function deviates strongly from the Maxwellian one. Title: Variations of 3 GHz Daily Radio Flux during the Years 1995-2000 Authors: Jiricka, K.; Karlicky, M.; Meszarosova, H. Bibcode: 2000ESASP.463..345J Altcode: 2000sctc.proc..345J No abstract at ADS Title: Hard X-Rays from MeV Neutral Beams Authors: Brown, J. C.; Karlicky, M.; Mandzhavidze, N.; Ramaty, R. Bibcode: 2000ASPC..206..210B Altcode: 2000hesp.conf..210B No abstract at ADS Title: The 1-2 GHz Slowly Positively Drifting Bursts at the Beginning of the May 2, 1998, September 23, 1998, and November 9, 1999 Solar Flares Authors: Kaltman, T.; Karlicky, M.; Jiricka, K. Bibcode: 2000HvaOB..24...35K Altcode: At the beginning of three solar flares: May 2, 1998, September 23, 1998, and November 9, 1999, slowly positively drifting bursts were observed in the Ondrejov radiospectra frequency range 0.8-2.0 GHz. The frequency drifts were estimated as 65-180 MHz s^-1, 20-40 MHz s^-1 and 40-125 MHz s^-1, respectively. Using the Aschwanden and Benz (1995) density model for the low solar atmosphere, the corresponding velocities of disturbances were determined as 650-1350 km s^-1, 120-340 km s^-1 and 300-850 km s^-1 respectively in the case of the fundamental radiation and 1150-2440 km s^-1, 200-600 km s^-1 and 550-1550 km s^-1 in the case of the harmonic radiation. These velocities are too low to be associated with particle beams. Therefore, downwards propagating shock waves, e.g. thermal conduction shock fronts, are suggested as possible radio sources. Title: Energy mode distribution at the very beginning of parametric instabilities of monochromatic Langmuir waves Authors: Bárta, M.; Karlický, M. Bibcode: 2000A&A...353..757B Altcode: Starting from a general form of the Zakharov equations the relations for electric fields and wave energy distributions at the very beginning of parametric instabilities are derived in dependence on initial Langmuir wave parameters. The corresponding dispersion equations in general and approximative forms are presented. These equations of the order up to eleven, with a different level of physical effects included (hydrodynamic-like, L_2 and L_3 distributions, non-linear denominators, quasi-neutrality violation approximations) are solved numerically. The growth rates, real frequencies and energy mode distributions are obtained in five regimes of the modulational and decay instabilities. A new description which is expressed by the energy mode distribution clearly shows energies transferred into up- and down-converted Langmuir and electromagnetic modes. Results confirming those from previous studies as well as new and more general ones are presented. Furthermore, it is found that in some commonly used approximations of the dispersion equation, in the decay regime, non-physically high real frequencies appear. It is shown that for more general approximations this problem is effectually reduced. The role of wave damping is considered, too. Finally, for a constant parent Langmuir wave, it is found that the conversion efficiency into the electromagnetic mode sharply increases with the temperature increase. Title: Radio Emission from Turbulent Flare Plasma Authors: Barta, M.; Karlicky, M. Bibcode: 2000HvaOB..24...69B Altcode: A model of radio emission from a localized turbulent flare plasma based on the plasma emission mechanism is presented. This work is aimed mainly to the transformation of wave modes, while incoming Langmuir waves, generated by particle beams, are described phenomenologically by various wave packets. The wave transformation is described by means of the Zakharov equations, but, in contrast to previous studies, where interacting wave modes filled the whole space, here only a limited interaction area is supposed. Due to this approach the wave energy movement effects are included. Our modelling starts with a Langmuir wave packet moving toward the interaction region, where the hydrodynamic turbulence, driven by outer (e.g. plasma outflows from the magnetic field line reconnection site) rather than ponderomotive forces, is supposed. The time evolution of the high-frequency electric field is then governed by the first Zakharov equation. The electromagnetic mode time dependence is calculated not only in the interaction region, but also at some selected distant point, which represents the Earth radiotelescope position. The aim of this modelling is the computation of the model dynamic spectrum, which can be directly compared with observed data, especially with the narrowband dm-spikes. Title: Global Coronal Waves: Implications for HESSI Authors: Hudson, H. S.; Karlický, M. Bibcode: 2000ASPC..206..268H Altcode: 2000hesp.conf..268H No abstract at ADS Title: Flare hard X-rays from neutral beams Authors: Karlický, Marian; Brown, John C.; Conway, Andrew J.; Penny, Gail Bibcode: 2000A&A...353..729K Altcode: A new mechanism is presented for the production of bremsstrahlung radiation from neutral beams (p+,e-) and its possible relevance to flare heating and production of hard x-ray bursts is discussed. Beam electrons lag behind the protons, due to differential drag in collisions with the background, but their longitudinal velocities are closely tied to the protons by the electric field generated. However, collisions with the background also scatter the beam electrons resulting in rms (quasi-thermal) transverse velocities well in excess of the proton speed. We demonstrate the initial development of this effect using an electrostatic particle simulation with scaled collision rate and then study its full development using an approximate analytic treatment. In particular, the heating of the beam electrons under the bombardment effect of the background is limited by the warm target effect but mean electron energies (`temperatures') of up to E_e =~ 0.02Ep0 result during the propagation of a neutral beam of initial proton energy Ep0. Thus, for example, HXR bremsstrahlung in the range 20-200 keV can be generated by protons in the range 1MeV-10MeV. The energy efficiency of the bremsstrahlung production is also limited by the warm target effect but, depending on the HXR spectrum, can exceed =~ 0.2 of the efficiency of the standard thick target electron beam model. This suggests that the MeV neutral beam model is, in terms of power requirements, unlikely to be the source of `HXR-rich' flare bursts but that neutral beams able to provide the impulsive flare heating will yield easily detectable HXR burst signatures. Also, while the neutral beam model needs more power ( =~ 5x) than an electron beam to yield a given HXR burst flare, it requires a much smaller beam number flux ( =~ 0.07 x). The issue of the HXR spectral distribution expected from the neutral beam model is also discussed. Title: Chromospheric Response to a Short-Duration Beam Heating: Observing Programme and Numerical Simulations Authors: Heinzel, P.; Karlický, M.; Kotrč, P.; Kupryakov, Yu. A. Bibcode: 2000ASPC..206..289H Altcode: 2000hesp.conf..289H No abstract at ADS Title: The 1-4 GHz Zebras, Fibers, Reverse Drift Bursts and Slowly Drifting Lanes Observed during the March 18, 1999 Flare Authors: Zlobec, P.; Messerotti, M.; Karlický, M.; Mészárosová, H. Bibcode: 1999ESASP.448.1075Z Altcode: 1999ESPM....9.1075Z; 1999mfsp.conf.1075Z No abstract at ADS Title: High-frequency Intermediate Drift Bursts and Zebra Patterns Authors: Jiricka, K.; Karlický, M.; Mészárosová, H. Bibcode: 1999ESASP.448..829J Altcode: 1999ESPM....9..829J; 1999mfsp.conf..829J No abstract at ADS Title: Radio Emission from Early Stages of Strong Langmuir Turbulence Authors: Bárta, M.; Karlický, M. Bibcode: 1999ESASP.448..753B Altcode: 1999mfsp.conf..753B; 1999ESPM....9..753B No abstract at ADS Title: Power-law and Exponential Distributions of Narrowband dm-Spikes Observed During the June 15, 1991 Flare Authors: Meszarosova, H.; Karlický, M.; Veronig, A.; Zlobec, P.; Messerotti, M. Bibcode: 1999ESASP.448.1025M Altcode: 1999mfsp.conf.1025M; 1999ESPM....9.1025M No abstract at ADS Title: Indications of Plasmoid Injection at the Beginning of an Eruptive Flare Authors: Fárnik, F.; Karlický, M.; Khan, J. I. Bibcode: 1999ESASP.448..791F Altcode: 1999ESPM....9..791F; 1999mfsp.conf..791F No abstract at ADS Title: Physical Characteristics of the September 23, 1998 Solar Flare Authors: Kotrc, P.; Karlický, M.; Kupryakov, Yu. A.; Kaltman, T. I.; Kasparova, J.; Rompolt, B. Bibcode: 1999ESASP.448..841K Altcode: 1999ESPM....9..841K; 1999mfsp.conf..841K No abstract at ADS Title: On a Herringbone Structure of Solar Type II Bursts Authors: Vandas, M.; Karlický, M. Bibcode: 1999ESASP.448.1071V Altcode: 1999ESPM....9.1071V; 1999mfsp.conf.1071V No abstract at ADS Title: Transequatorial Interconnecting Loops and Increase of Their Length in the New Cycle Authors: Fárnik, F.; Ŝvestka, Z.; Karlický, M.; Hudson, H. S. Bibcode: 1999ESASP.446..305F Altcode: 1999soho....8..305F Using Yohkoh SXT data, we show that active regions of the new solar cycle, appearing at high latitudes, can be connected across the solar equator by loops as long as 60 heliographic degrees (730000 km). This length greatly exceeds the limit of 37 degrees found for transequatorial interconnecting loops on Skylab and implies that the Skylab limit was simply due to the low latitudes of active regions during the period of Skylab observations. By modelling the loops in force-free approximation using Kitt Peak magnetograms, we find strong support for the interpretation that these long interconnecting loops originate through reconnection of magnetic field lines which extend from the two active regions towards and beyond the equator, and confirm the earlier finding by Canfield, Pevtsov, and McClymont that a favourable condition for the reconnection is the same chirality (i.e., same sign of the force-free parameter alpha and same direction of current flow) in the two active regions. As we were unable to find any longitudinal (i.e., east-west) loops of a comparable length, we suggest that an important component of the driving force for the reconnection of transequatorial interconnecting loops may be the differential solar rotation. It can help to drive the reconnection of loops extending in the north- south direction, whereas it does not help in the case of longitudinal loops. These conclusions are based on loop observations in December 1997 and May 1998, when only short-lived transequatorial loops connected the high-latitude active regions on the northern and southern hemispheres. However, in February 1999 a rich system of transequatorial loops as long as 550 000 km could be observed during its whole transit across the visible solar disk. We are now studying this system (not all supporting data have been available yet when writing this Abstract), comparing it with a similar system of much shorter transequatorial loops which crossed the solar disk in March/April 1992 during the preceeding cycle. We again try to model these long-lived loop systems in current-free approximation, using both Kitt Peak and Big Bear magnetograms and, for the February 1999 transit, also the more frequent, high-resolution full-disk magnetic maps from SOHO. This modelling verifies the location of the footpoints of interconnecting loops in low magnetic fields at peripheries of the interconnected active regions, indicates how some of the loops have been formed, and provides information about some of the reasons which lead to the shape and brightness variations in the loops system. Title: Acceleration Of Photoelectrons In A Return-Current Electric Field And Ha Polarization Authors: Karlický, Marian; Hénoux, Jean-Claude Bibcode: 1999ESASP.446..369K Altcode: 1999soho....8..369K Chromospheric hydrogen Balmer Ha and Hb lines have been found to be linearly polarized in the gradual phase of some solar flares. This impact polarization is believed to be caused by low energy protons (E< 200 keV). However, we still must examine if low energy electrons (E< 200 eV) with an anisotropic velocity distribution function, if presents, could also generate impact polarisation . In a recent paper by H noux and Karlicky (1999), the evolution, in chromospheric layers, of the ve-locity distribution function of high energy photoelectrons produced by flare X-ray irradiation, was studied. A significant anisotropy was found. However, due to the dominance of local electrons in the line formation process, the resulting impact polarization was one order of magnitude lower than ob-served. In this paper, we look for the change of the photoelectrons anisotropy that could result from the pre-sence of a return-current electric field. A 1-D test particle code is used for computating both the re-turn-current electric field generated by monoenergetic electron beams in flaring chromospheric layers and the evolution of the photoelectron distribution function. Using a 100 keV electron beam with a density of 2 and the MAVH flare atmosphere, it is found that, at chromospheric level, low-energy photoelectrons (E at 150 eV), produced by flare X-ray irradiation, can be accelerated by the return-current electric field. This acceleration is very sensi-tive to the exact density and temperature profile of the solar atmosphere and the resulting effect as generation of impact Ha polarization is discussed. Title: On two distinct shocks during the flare of 9 July 1996 Authors: Klassen, A.; Karlický, M.; Aurass, H.; Jiřička, K. Bibcode: 1999SoPh..188..141K Altcode: Due to the emission of shock-accelerated electrons, broadband radio observations display propagating super Alfvénic shock waves in the low corona ('type II bursts'). We study the 9 July 1996 flare (AR NOAA 7978) focusing on the aspect of shock generation. This event's radio spectrogram shows two different type II bursts in sequence. Radio imaging data (Paris, Meudon Observatory) reveal that both bursts appear at different sites above the Hα flare. The driver of the first type II burst seems to propagate with twice the speed of the second one. The projected source site of the first type II burst (seen earlier and at higher frequencies) is spatially situated further away from the Hα flare site than the source of the second type II burst. We try to understand this by comparing with Yohkoh soft X-ray images. The first shock source occurs near the top of high soft X-ray loop structures. Its driver can be a guided fast mode magnetic disturbance. The second type II source appears in-between two high soft X-ray loop systems. This might be a piston-driven disturbance powered by an evaporation front. We get a consistent picture only by assuming a very inhomogeneous Alfvén speed in the active region's atmosphere. Title: Fourier and wavelet analysis of type 42 SER and 41 F solar radio bursts Authors: Mészárosová, H.; JiřiČka, K.; Karlický, M. Bibcode: 1999A&A...348.1005M Altcode: 19 radio bursts (0.01 s time resolution) classified as 42 SER and 41 F types were selected from observations made by the Ondřejov 3 GHz radiometer during 1990-1998. On the 2-4 GHz dynamic radio spectrum in most cases these bursts were identified as decimetric DCIM and in the metric range were accompanied by type III radio bursts indicating the plasma emission origin of these bursts. This set of 3 GHz bursts was analyzed by both the Fourier and the wavelet transform methods searching for characteristic periodicities. Statistical parameters of selected bursts were very similar and almost no difference between 42 SER and 41 F was found. The analysis of the 42 SER and 41 F radio bursts on 3 GHz shows that the number of periods is increasing with decreasing periods, forming a power-law distribution. The dominant periods of the 3 GHz radiation are discussed in the framework of the recent RLC-circuit model with current-carrying magnetic loops. On the basis of this interpretation the electric current densities in the magnetic loops were estimated in the 0.01-0.1 A m(-2) range. Title: The Radio-Silent Start of an Intense Solar Gamma-Ray Flare Authors: Rieger, Erich; Treumann, Rudolf A.; Karlický, Marian Bibcode: 1999SoPh..187...59R Altcode: Radio-silent γ-ray flares are solar flares that lack any significant emission in the (non-thermal) radio wave band during their impulsive hard X-ray and γ-ray emission phases. Flares with extremely suppressed long-wavelength spectra have previously been reported by White et al. (1992) and have been discussed in different context by Hudson and Ryan (1995). A striking example of a radio-silent flare was observed by SMM during the onset of the 6 March 1989 energetic γ-ray flare. We argue that the absence of radio emission at wavelengths longer than microwave wavelengths is an indication of the compactness of the flare rather than that the flare did not exhibit non-thermal properties. Probably the flare site was restricted to altitudes above the photosphere in a newly emerging loop configuration lower than the equivalent altitude corresponding to an emission frequency of 1.4 GHz. This implies the presence of a dense and highly magnetized closed field configuration confining the electron component which causes the impulsive γ-ray continuum. Reconnection in such a configuration did not lead to open magnetic fields and streamer formation. Acceleration of particles in the γ and hard X-ray bursts was restricted to closed field lines. Thermal expansion of the loop system may subsequently lead to the generation of radially propagating blast waves in the solar corona which are accompanied by type II solar radio bursts and decimetre emissions. The emission during the onset of the flare was dominated by a continuum originating from electron bremsstrahlung at X-ray and γ-ray energies with only little evidence for the presence of energetic ions. It is, therefore, concluded that energetic electrons have been primary and not secondary products of the particle acceleration process. Title: Solar type II bursts and shock drift electron acceleration Authors: Vandas, M.; Karlický, M. Bibcode: 1999AIPC..471..657V Altcode: 1999sowi.conf..657V It is generally believed that type II bursts are caused by electrons accelerated at a shock front. Holman and Pesses (1) suggested that type II bursts can be caused by electrons accelerated by the shock drift mechanism. In order to explain a fine structure of type II bursts (herringbones), Zlobec et al. (2) presented a qualitative model where electrons are accelerated by a nearly perpendicular wavy shock front. We discuss this possibility quantitatively, namely we present an analytical solution of electron motion in a wavy shock front. Then we perform a parametric study in order to determine which parameters of the model are necessary for an appropriate electron energy gain. The calculations show that electrons are rarely reflected more than once at the wavy shock front and their final energy is mostly 1-3 times the initial one. This is similar to the theoretical acceleration gain of reflected electrons at the Earth's bow shock. In the present case all electrons are eventually transmitted downstream where they form two downstream beams. Title: Long transequatorial interconnecting loops of the new solar cycle Authors: Fárník, F.; Karlický, M.; Švestka, Z. Bibcode: 1999SoPh..187...33F Altcode: We study two long transequatorial loops connecting high-latitude regions of the new solar cycle. These loops (with lengths of 47 and 61 heliographic degrees) provide evidence that the upper length limit of 37° found by Chase et al. (1976) from Skylab data was determined simply by the typical distances between northern and southern active regions during the period of Skylab observations. We find strong support for the idea that these long interconnecting loops originate through reconnection of field lines extending from the two active regions towards and beyond the equator, and confirm the earlier finding by Canfield, Pevtsov, and McClymont (1996) that only field lines from active regions with the same chirality reconnect. As we are not aware of any longitudinal (E-W) loops of comparable lengths, we suggest that it is mainly the solar differential rotation which drives the reconnection of latitudinal (N-S) field lines. Title: A spectropolarimetric estimate of energy deposition into the chromosphere during solar flares Authors: Kazantsev, S. A.; Karlicky, M.; Petrashen', A. G.; Hénoux, J. -C. Bibcode: 1999ARep...43..340K Altcode: The dependence of the degree of polarization of Hα and Hβ emission in the solar chromosphere during solar flares on the energy of an incident proton beam is calculated assuming that the origin of the observed linear polarization is collisional. Estimates of the lower boundary for the energy of the proton beam are obtained using a model for the kinetics of the propagation of fast protons inside solar-flare magnetic loops together with spectropolarimetric Hα and Hβ observations. Title: Velocity distribution function anisotropy of soft X-ray generated photoelectrons and resulting Hα polarization in solar flares Authors: Hénoux, J. -C.; Karlický, M. Bibcode: 1999A&A...341..896H Altcode: Soft X-rays irradiation of the solar atmosphere during solar flares generates photoelectrons which have an anisotropic velocity distribution. Using a 1-D test particle code, the anisotropy of the photoelectrons velocity distribution is derived, and the maximum degree of linear polarization in the hydrogen Hα and Hβ lines that photoelectrons could generate by impact is estimated. Over a band pass of 0.75 and 0.5 Angstroms, the net polarization degree expected in both lines is predicted not to exceed 0.2%. Therefore, soft X-ray irradiation cannot explain the one order of magnitude higher degree of linear polarization observed in solar flares. Title: Intensity Distributions of Peak Fluxes of Radio Bursts at Different Frequencies Authors: Mészárosová, H.; Karlický, M.; Jiricka, K. Bibcode: 1999ASSL..239..243M Altcode: 1999msa..proc..243M In this paper intensity distributions of peak fluxes of radio bursts at frequencies of 3.0, 3.2, 5.2 and 8.4 GHz are studied. The exponents of power-law distribution function are found in the range from -1.2 to -1.5. Comparisons of these results with results published for other frequencies and with those predicted by avalanche models are made. Title: The NOAA AR 6718 magnetic field extrapolation with localized current filaments. Authors: Karlický, M.; Démoulin, P.; Aulanier, G.; van Driel-Gesztelyi, L.; Hénoux, J. C.; Jirička, K. Bibcode: 1999joso.proc...97K Altcode: The 3-D extrapolation of magnetic field lines of the July 11, 1991 Kitt Peak magnetogram shows a differential magnetic field shear in the NOAA 6718 active region. A new combined extrapolation technique, which includes localized current filaments is suggested and applied in modelling of this shear. First, the potential field extrapolation is made and then force-free current paths for several current filaments in specific positions are computed. It is shown that with the electric current increase the localized magnetic field shear is increasing. The total electric current in 16 current filaments is considered up to 1.2×1012A. Title: Statistical analysis of 3 GHz solar radio bursts and estimation of electric current densities in flare loops. Authors: Mézsárosová, H.; Karlický, M.; Jiřička, K. Bibcode: 1999joso.proc..166M Altcode: From observations made by the Ondřejov 3 GHz radiometer during 1990-1998, 15 radio bursts classified as 42 SER and 41 F types were selected. (Most of these bursts were on the radio spectrum identified with a group of high-frequency type III radio bursts). On the selected bursts both the Fourier and the wavelet analyses were applied to determine the periodicities. Then, using the RLC-circuit analog of current-carrying magnetic loops the authors estimated electric current densities in the acceleration space. As example they present results for the radio burst of April 15, 1998. Title: Correction [to “A shock associated (SA) radio event and related phenomena observed from the base of the solar corona to 1 AU”] Authors: Bougeret, J. -L.; Zarka, P.; Caroubalos, C.; Karlický, M.; Leblanc, Y.; Maroulis, D.; Hillaris, A.; Moussas, X.; Alissandrakis, C. E.; Dumas, G.; Perche, C. Bibcode: 1998GeoRL..25.4103B Altcode: No abstract at ADS Title: Evidence of Magnetic Field Reconnection in the Hα Eruptive Prominence on 18 september 1995 Authors: Kotrč , P.; Karlický, M.; Šimberová, S.; Knížek, M.; Varady, M. Bibcode: 1998SoPh..182..393K Altcode: In this paper we present a detailed study of a violent evolution of the 18 September 1995 eruptive prominence observed by the Hα telescope and the Multichannel Optical Flare Spectrograph in Ondřejov. The fast changes of the prominence structure started immediately after a weak radio burst at 3 GHz. This circumstance shows the presence of non-thermal processes. In the later phase of the prominence evolution a comparison of the Hα filtergrams with the Yohkoh Soft X-ray Telescope pictures was made. For a search of fine structures in the Hα images, an image processing technique was used. A detailed analysis of observations indicates magnetic field line reconnection, mainly in space below the rising Hα prominence. These reconnection processes are manifested not only by structural changes of the Hα prominence and X-ray loops but also by the character of Doppler velocities. Evidence of splitting and rotation was found in the Hα spectrum formed close to the reconnection space, and the typical velocities of such plasma movement were evaluated. We estimated amplitudes of rotational velocities, giving evidence about the rearrangement of helical structures during the process of the eruptive prominence activation. In the conclusion we discuss some implications of our results. Title: Narrowband dm-SPIKES Observed during the 15 June 1991 Flare Authors: Zlobec, Paolo; Karlický, Marian Bibcode: 1998SoPh..182..477Z Altcode: We performed a statistical analysis of the dm-spikes that were present for an exceptionally long period (more than 10 min) during the 15 June 1991 flare. We realized that the polarization degree, the duration and the mutual delay of the R- and L-components were nearly the same for both CW and ACW cases. CW (ACW) means the clockwise (anti-clockwise) sense of the loop in the R−L versus L+R plots, when the data of a single spike are considered according to the time sequence. The presence of such a loop is determined by the delay of the weaker (stronger) polarimetric component in respect to the other one. The increase of the polarization percentage started first at 610, then at 408 and afterwards at 327 MHz. It was found that the duration of spikes was almost completely independent from the polarization degree. The mean duration of spikes at different frequencies corresponds to that computed using the formula of Güdel and Benz. Like the mean duration, also the mean delay decreased with increasing frequency. The CW/ACW ratio varied simultaneously for the frequencies we recorded during an interval of about three minutes. Spikes were considered as the radio manifestation of superthermal electrons accelerated in the MHD cascading waves. The evolution of spikes and their parameters were qualitatively interpreted within the flare reconnection model with turbulent plasma outflows. Title: Chromospheric evaporation shock and reduced optical thickness drifting in the 1-4.5 GHz range Authors: Karlicky, Marian Bibcode: 1998A&A...338.1084K Altcode: Using a 1-D numerical hydrodynamic model, the evaporation shock evolution is computed in the solar atmosphere having the density profile derived from radioastronomical observations. Then the optical thickness of the 1-4.5 GHz plasma emission on harmonic frequency is computed. It is found that the optical thickness of the radio emission is reduced at the evaporation shock. With a motion of this shock the optical thickness reduction drifts towards lower frequencies with the frequency drift which depends on the evaporation shock speed. The theoretical radio spectrum caused by this optical thickness reduction is presented and discussed in comparison with the July 9, 1996 radio spectrum. Title: Frequency gap between fast drift and type III associated bursts. Authors: Karlicky, M.; Zajtsev, V. V. Bibcode: 1998R&QE...41..639K Altcode: The frequency gap between the high-frequency fast drift bursts and metric type III associated bursts is interpreted using the collisional absorption of the radio emission in dense layers of the solar atmosphere. Studying the absorption of radio emission from the narrow, cold and dense filament which is embedded in hotter plasma and heated from the corona, it was found that the absorption causing the frequency gap has a maximum at about 2 GHz, in agreement with observations. Similar results were obtained also for the current sheet structure. Title: The Solar Minimum Active Region 7978, Its X2.6/1B Flare, CME, and Interplanetary Shock Propagation of 9 July 1996 Authors: Dryer, M.; Andrews, M. D.; Aurass, H.; DeForest, C.; Galvin, A. B.; Garcia, H.; Ipavich, F. M.; Karlický, M.; Kiplinger, A.; Klassen, A.; Meisner, R.; Paswaters, S. E.; Smith, Z.; Tappin, S. J.; Thompson, B. J.; Watari, S. I.; Michels, D. J.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.; Lamy, P.; Mann, G.; Arzner, K.; Schwenn, R. Bibcode: 1998SoPh..181..159D Altcode: The first X-class flare in four years occurred on 9 July 1996. This X2.6/1B flare reached its maximum at 09:11 UT and was located in active region 7978 (S10° W30°) which was an old-cycle sunspot polarity group. We report the SOHO LASCO/EIT/MDI and SOONSPOT observations before and after this event together with Yohkoh SXT images of the flare, radio observations of the type II shock, and GOES disk-integrated soft X-ray flux during an extended period that included energy build-up in this active region. Title: A shock associated (SA) radio event and related phenomena observed from the base of the solar corona to 1 AU Authors: Bougeret, J. -L.; Zarka, P.; Caroubalos, C.; Karlický, M.; Leblanc, Y.; Maroulis, D.; Hillaris, A.; Moussas, X.; Alissandrakis, C. E.; Dumas, G.; Perche, C. Bibcode: 1998GeoRL..25.2513B Altcode: We present for the first time an almost complete frequency coverage of a Shock Associated (SA) radio event and related phenomena observed on May 6, 1996 at 9:27 UT. It is observed from the base of the solar corona up to almost 1 Astronomical Unit (AU) from the Sun by the following radio astronomical instruments: the Ondřejov spectrometer operating between 4.5 GHz and 1 GHz (radiation produced near the chromosphere); the Thermopyles Artemis-IV spectrograph operating between 600 MHz and 110 MHz (distance range about 1.1-1.4 R⊙ from sun center); the Nançay Decameter Array operating between 75 and 25 MHz (distance range about 1.4-2 R⊙) and the RAD2 and RAD1 radio receivers on the WIND spacecraft covering the range from 14 MHz to about 20 kHz (distance range between 3 R⊙ and about 1 AU). Observations at the Nançay Decameter Array clearly show that the SA event starts from a coronal type II radio burst which traces the progression of a shock wave through the corona above 1.8 R⊙-2 R⊙ from the sun center. This SA event has no associated radio emission in the decimetric-metric range, thus there is no evidence for electron injection in the low/middle corona. Title: Optical Thickness of the 2-4.5 GHz SOLAR PLASMA EMISSION Authors: Karlický, Marian Bibcode: 1998SoPh..179..421K Altcode: For radio emission at the frequency corresponding to the second harmonic of the local plasma frequency, the optical thickness in the solar atmosphere is calculated. Three types of models are assumed: the model with radio emission from the narrow transition region, and models with radio emission from a cool and dense plasma filament embedded in hotter plasma at the transition region and in the corona. The optical thickness is computed by integration of the collisional (free-free) absorption along a radio-ray path radial in the solar atmosphere. In all models considered the optical thickness can be sufficiently low for appropriate parameters. For example, in the narrow (<100 km) transition region where the density scale height is much less than that of the pressure one, the optical thickness can be lower than 1. Furthermore, the optical thickness can be decreased if the radio emission is generated in the cool and dense plasma filament surrounded by hotter and thinner plasma. But the models differ in density scale heights and thus in distances between plasma emission levels. This difference is essential for the interpretation of high-frequency type III radio bursts. Title: Electrostatic effects during neutral beam propagation through plasmas Authors: Brown, John C.; Karlicky, Marian; Conway, Andrew J.; Martland, Suzanne Bibcode: 1998A&A...331.1147B Altcode: In this paper several aspects of the interaction of 1-D neutral beams with plasmas are considered. In order to clearly understand the dual roles of a background plasma in collisionally decelerating the beam and its response to the consequently generated E-field, we examine two cases: an artificial unresponsive background plasma, that corresponds closely to the case of an unionized gas; and a realistic background plasma, whose charges respond to the presence of any E-field. In the former case, the electric field results solely in extremely small scale oscillation of the beam electrons about the protons as both decelerate collisionally and, although electron runaway is possible, the numbers involved are found to be negligibly small. However, collisional separation of the beam electrons and protons does occur in the case of a realistic background plasma, since E easily drives a neutralizing dense plasma electron current. Despite the charge separation, runaway is found to be impossible in this case because of the masking effect that the background plasma electrons have on the separated charges unless the plasma is extremely tenuous compared to the beam, where the plasma behaviour is close to that of a near-neutral gas. These effects are shown by approximate analytic mean particle solutions and confirmed by simulations from an electrostatic particle code, which can deal with collective effects. Additional numerical simulations are also performed to investigate the generation of Langmuir waves by a neutral beam. The consequences of these results are discussed for flare neutral beams and corresponding radiation signatures. As regards hard X-ray production by runaways, although some very high energy electrons may result, the number is far too small to be relevant to solar flare HXR burst production. The beam and plasma oscillations may however be relevant to radio bursts. Title: Interaction of Weak Shock Waves with Current Sheets in an Active Region to Produce Nanoflares and Chains of Type I Radio Bursts Authors: Odstrčil, Dušan; Karlický, Marian Bibcode: 1998SoPh..177..415O Altcode: Interaction of weak shock waves with a current sheet is investigated by a two-dimensional numerical magnetohydrodynamic model. In accordance with solar coronal conditions, a ratio of thermal to magnetic pressures of 0.1 and a shock Alfvén Mach number slightly above 1 are considered. It is found that even weak shock waves trigger magnetic field reconnection in current sheets. Based on this result, it is suggested that drifting chains of type I radio bursts are radio manifestations of the interactions of weakly super-Alfvénic shock waves with pre-existing current sheets distributed in an active region. This model of type I noise storms is then discussed in connection with the concept of nanoflares (localized reconnections) and the heating of the solar corona. Title: On the source height of decimetre-wave burst emission (abstract) Authors: Krüger, A.; Kliem, B.; Hildebrandt, J.; Karlický, M.; Zlobec, P. Bibcode: 1998PAICz..88...93K Altcode: No abstract at ADS Title: Magnetic Field Reconnection in the H-alpha Eruptive Prominence on September 18, 1995 Authors: Karlicky, M.; Kotrc, P.; Simberova, S.; Knizek, M.; Varady, M. Bibcode: 1998ASPC..150..310K Altcode: 1998IAUCo.167..310K; 1998npsp.conf..310K No abstract at ADS Title: Generation of Langmuir waves in neutral beam-plasma system Authors: Karlický, M.; Messerotti, M.; Zlobec, P. Bibcode: 1998PAICz..88..133K Altcode: No abstract at ADS Title: The narrowband dm-spikes observed during the 15 June 1991 flare Authors: Zlobec, P.; Karlicky, M. Bibcode: 1998cee..workE..69Z Altcode: We performed a statistical analysis of the dm-spikes that were present for an exceptionally long period (more than 10 m) during the 15 June 1991 flare. We realized that the polarization degree, the duration and the mutual delay of the R- and L-components were nearly the same for both CW and ACW cases. CW (ACW) means clock-wise (anti-clock-wise) sense of the loop in the R-L versus L+R plots when the data of a single spike are considered according to the time sequence. The presence of such a loop is determined by the delay of the weaker (stronger) polarimetric component in respect to the other one. The increase of the polarization percentage started first at 610, then at 408 and afterwards at 327 MHz. It was found that the duration of spikes was almost completely independent from the polarization degree. The mean duration of spikes at different frequencies corresponds to that computed using the formula of Gudel and Benz. Like the mean duration, also the mean delay was decreasing with increasing frequency. The CW/ACW ratio varied simultaneously for the frequencies we recorded during an interval of about three minutes. Spikes were considered as the radio manifestation of superthermal electrons accelerated in the MHD cascading waves. Evolution of spikes and their parameters were qualitatively interpreted within the flare reconnection model with the turbulent plasma outflows. Title: Force-free Electric Current Rope in the Solar Atmosphere Authors: Karlický, M. Bibcode: 1998ESASP.417..301K Altcode: 1998cesh.conf..301K No abstract at ADS Title: The narrowband dm--spikes observed during the September and November 1997 solar flares Authors: Karlicky, M.; Jivrivcka, K.; Aurass, H.; Klassen, A.; Mann, G. Bibcode: 1998cee..workE..44K Altcode: During coordinated observations by radio spectrographs at AO Ondvrejov (0.8 - 4.3 GHz) and AI Potsdam (40 - 800 MHz sweep and 693-740 MHz high resolution multi-channel spectrometer) three flares were observed with narrowband decimeter spikes clustered within a bandwidth of about 2 GHz. In all three cases the dm-spikes appear during the impulsive flare phase above and near to the starting frequency range of meter type III bursts. Date: || Associated Flare: || Narrowband Spikes: September 12, 1997 || SF/--, N24W20, AR8084 || 0.6 -- 2.7 GHz; 16:05:35 -- 16:07 UT November 03, 1997 || 1B/M1.4, S20W15, AR 8100 || 0.4 -- 2 GHz; 9:05:40 -- 9:09:30 UT November 03, 1997 || --/M4.2 || 0.25 -- 1.2 GHz; 10:25:50 -- 10:27:40 UT The time coincidence found between the narrowband dm-spikes and type III radio bursts show that dm-spikes manifest the particle acceleration processes. Figure 1. The 03 November 1997, 10:25 UT event. 1 second with 0.01 s resolution; left-spectrum, right--the time derivative of the spectrum. Title: Triggering of magnetic reconnection in the current sheet by shock waves. Authors: Odstrcil, D.; Karlicky, M. Bibcode: 1997A&A...326.1252O Altcode: Interaction of a shock wave with a current sheet is investigated by the two-dimensional numerical magnetohydrodynamic model. In accordance with the solar coronal conditions, the ratio of the thermal to magnetic pressures of 0.1 and the shock Alfven Mach number of about 1.25 are used. It is found that the shock wave initiates magnetic reconnection process in the current sheet. Further, it is found that the post-shock situation rather than the shock compression is a cause of the magnetic reconnection. Interaction of the shock with the current sheet results in formation of two shocks that propagate away from the current sheet on opposite sides followed by a rarefaction waves region. This dynamic situation causes the current sheet to become gradually thinner and the magnetic reconnection process is initiated probably due to the tearing-mode instability. Presented results support the idea that the solar flare can be triggered by the shock wave from a distant flare. Title: Optical and Radio Spectral Analysis of a Recurrent Surge Authors: Kotrč, Pavel; Schmieder, Brigitte; Karlický, Marian; Heinzel, Petr Bibcode: 1997SoPh..172..199K Altcode: 1997ESPM....8..199K Coordinated observations obtained at Meudon (MSDP) and at Ondřejov provide surge spectra in optical range (Hα, Hβ, Hγ, Hµ, Ca H and K lines) and in radio range. The MSDP data allowed us to follow the time evolution of the surge. The spectra of Balmer lines were used to derive the electron density of the expelled cool material. The radio bursts indicate that the acceleration of electrons took place in the low and dense atmosphere, giving a good argument for a reconnection near the transition region. Title: Ring Current Formed During the Bombardment of a Rotating Gas Torus by Neutral Beams Authors: Karlický, Marian Bibcode: 1997Ap&SS.257..249K Altcode: A new mechanism for the generation of the electric ring current is presented. During the radial bombardment of a rotating gas torus by a neutral beam, electrons and protons are dragged by rotating gas. Due to collisions electrons obtain the torus velocity faster than protons, therefore in some layer there is a difference in electron and proton beam toroidal velocities; the electric current is thus generated. This current is discussed as the seed magnetic field in early stages of evolving galaxies, which is then amplified by the dynamo process to present values of the magnetic field. Title: Evolution of force-free electric currents in the solar atmosphere. Authors: Karlicky, M. Bibcode: 1997A&A...318..289K Altcode: The new 3-D numerical model studying evolution of force-free electric currents in the solar atmosphere is presented. The initial dipole magnetic field is considered in a simplified active region. Starting from a low electric current, which penetrates the photosphere, and increasing the current intensity, the path of force-free electric current and the corresponding magnetic field are computed. The virtual mirror current representing the effect of the inertial photosphere is considered. The single and the multiple current paths are compared. For the single path case, it was found that an arch-shape electric current is sheared with the increasing current intensity, then screwed into a current loop with the helical structure and when the electric current generates a magnetic field greater than the initial dipole magnetic field the current path becomes unstable. During all this process the current path moves upwards. Although the multiple current paths show more complex internal structures of electric currents, the global aspect of these processes remains the same. The relevance of this modelling for processes in the solar atmosphere is discussed. Title: Effects of Particle Beams in the Solar Atmosphere Authors: Karlicky, M. Bibcode: 1997HvaOB..21...43K Altcode: This work addresses the observational and physical effects of particle beams in the solar atmosphere. Mainly electron beams are considered. Describing acceleration mechanisms of superthermal particles, the main attention is devoted to effects influencing the particle beam propagation. The collisional energy losses and pitch angle scattering, the return current effects, and the mirroring in the converging magnetic field in specific situations are considered. Furthermore, the processes connected with the particle beam bombardment of dense layers of the solar atmosphere are briefly described. Finally, some open questions are summarized. Title: The Solar Minimum X2. 6/1B Flare and CME of 9 July 1996; Part 2: Propagation Authors: Dryer, M.; Andrews, M. D.; Aurass, H.; DeForest, C.; Karlicky, M.; Kiplinger, A.; Klassen, A.; Meisner, R.; Ipavich, F. M.; Galvin, A. B.; Paswaters, S. E.; Smith, Z.; Tappin, S. J.; Thompson, B. J.; Watari, S. -I.; Michels, D. J.; Brueckner, G. E.; Howard, R. A.; Koomen, M. J.; Lamy, P.; Mann, G.; Arzner, K.; Schwenn, R. Bibcode: 1997ESASP.404..331D Altcode: 1997cswn.conf..331D No abstract at ADS Title: Shear Magnetic Field Reconnection near the 3-D Null Point Authors: Karlicky, M. Bibcode: 1997HvaOB..21...91K Altcode: Using a 3-D MHD numerical code the shear magnetic field reconnection near the 3-D null point is studied. To demonstrate the topological changes of magnetic field lines during the shear reconnection two cases: (a) without and (b) with the anomalous resistivity are compared. For simplicity a high beta plasma is assumed. It was found that during this process magnetic field lines on one side of the "fan" structure are reconnected with those on the opposite side of the fan. Thus, the magnetic field lines reconnect places in a very broad range of angles in the plane of the fan layer. Title: Triggering of Magnetic Reconnection in the Current Sheet by Shock Waves - Nanoflares, and Chains of Type I Radio Bursts Authors: Karlicky, M.; Odstrcil, D. Bibcode: 1997ESASP.404..451K Altcode: 1997cswn.conf..451K No abstract at ADS Title: Effects of Particle Beams in the Solar Atmosphere Authors: Karlicky, Marian Bibcode: 1997SSRv...81..143K Altcode: This work addresses the observational and physical effects of particle beams in the solar atmosphere. Mainly electron beams are considered, but also some effects of proton and neutral beams are mentioned. Briefly describing acceleration mechanisms of superthermal particles, the main attention is devoted to effects influencing the particle beam propagation. The collisional energy losses and pitch-angle scattering, return current effects, mirroring in the converging magnetic field, and the scattering in the Alfven and whistler wave turbulence in specific situations are considered. The role of quasi-linear relaxation is discussed. Examples of observations showing effects of particle beams in the solar atmosphere are presented. Separate chapters are devoted to processes connected with particle beam bombardment of dense layers of the solar atmosphere: hard X-ray and gamma-ray flare emissions, evaporation process, asymmetry of optical chromospheric lines, and impact linear H-alpha line polarization. The beam induced energy release processes are also included. The presented effects of particle beams are summarized. Title: Interaction of shocks with a current sheet and reconnection in the solar corona Authors: Odstrcil, D.; Karlicky, M. Bibcode: 1997AdSpR..19.1895O Altcode: Interaction of shocks with a current sheet is investigated within a 2D MHD model based on an improved FCT numerical scheme. Basic parameters of the problem are chosen to correspond to situations in the solar corona with low plasma beta and moderate shock strength. Slow and fast MHD shocks are introduced with shock normal parallel to magnetic field lines. The interaction with the current sheet causes distortion of the shock front and this distorts the magnetic field lines and generates electric current. Large current densities are generated especially when the fast MHD shock becomes the intermediate MHD shock at the current sheet. Then peak values of the current density are about 3-4 times larger than the initial undisturbed values in the current sheet. Title: Narrowband dm-Spikes in the 2 GHz Frequency Range and MHD Cascading Waves in Reconnection Outflows Authors: Karlický, Marian; Sobotka, Michal; Jiřička, Karel Bibcode: 1996SoPh..168..375K Altcode: Two examples of clouds of narrowband dm-spikes, observed by the Ondřejov radiospectrograph in the 1-2 GHz frequency range, are analyzed. After transformation of the frequency scales to distances in the solar atmosphere, the power spectra analysis of size scales reveals a spectral index of −5/3, resembling that of Kolmogorov spectra of turbulent cascades. The narrowband dm-spikes are interpreted as radio emission from electrons accelerated in MHD cascading waves, probably generated in plasma outflows from magnetic field reconnection. Title: Transport of superthermal electrons in coronal loops and U(N)-type solar radio bursts. Authors: Karlicky, M.; Mann, G.; Aurass, H. Bibcode: 1996A&A...314..303K Altcode: Electron beams travelling with about 1/3 of the velocity of light along closed coronal loops can manifest themselves in decimeter and meter wave solar type U or U(N) radio bursts. Using a 1-D test particle model, we study trajectories of superthermal electrons in coronal loops with the aim of understanding recently published detailed radio spectral and imaging data about type U(N) bursts. The computations are carried out in a static semi-circular loop of 1 solar radius length. For modeling transport processes Coulomb collisions, mirroring of electrons in the loop magnetic field, and scattering in zones of enhanced whistler wave turbulence are taken into account. The formation of a finite zone of enhanced whistler turbulence in the loop top is consistently explained by the properties of loss-cone instability of a weak preexisting energetic particle component. In a model run initially electrons are injected upwards along the loop axis in one leg. Scanning the trajectories of electrons through the loop and representing them in space vs time and plasma frequency vs time plots, respectively, we get synthetic radio source distributions and radio spectra. The results can be analyzed in dependence on loop and particle parameters including the strength of whistler turbulence. Thus, we are able to model the essential aspects of observed U(N) bursts. We find that in a zone of sufficiently strong whistler turbulence near the loop top the initial electron beam is splitted up into two beams propagating from the top back and forward into both loop legs. Thus two widely separated radio sources brighten during the descending branch of U burst spectra. Moreover, we find that U(N) type radio bursts can be excited not only due to mirroring but also by scattering of electrons in whistler turbulence near a leg of the loop. For demonstrating the strength of the present model a simulation of an observed U(N) burst (February 23, 1993) is given. Title: Proton transport in a magnetic loop and Hα impact line linear polarization. Authors: Karlicky, M.; Henoux, J. -C.; Smith, D. Bibcode: 1996A&A...310..629K Altcode: Using a 1-D test particle model with 350000 numerical protons, we study the evolution of the proton distribution function in a magnetic loop. A continuous injection of low-energy 200-1500keV protons with a distribution function proportional to a E^-3^ power-law is considered. The acceleration region is assumed to be at the top of a flare loop where the protons are injected into a cone of pitch angles centered along the loop axis. The computations are made for a static loop of length 20880km with the parameters in the chromosphere corresponding to the VAL-C model of the solar atmosphere. Coulomb collisions, mirroring, and Alfven wave scattering in an intermediate regime (W_a_^tot^=10^-1^erg/cm^3^) relative to prior analyses corresponding to saturated scattering are taken into consideration. The proton distribution function in the chromosphere at the Hα formation layer is computed. The resulting anisotropy of the proton distribution function in a quasi-stationary state of proton bombardment is analyzed from the point of view of its expected effects on the impact linear polarization of chromospheric lines. Title: Evidence for prolonged acceleration based on a detailed analysis of the long-duration solar gamma-ray flare of June 15, 1991 Authors: Akimov, V. V.; Ambrož, P.; Belov, A. V.; Berlicki, A.; Chertok, I. M.; Karlický, M.; Kurt, V. G.; Leikov, N. G.; Litvinenko, Yu. E.; Magun, A.; Minko-Wasiluk, A.; Rompolt, B.; Somov, B. V. Bibcode: 1996SoPh..166..107A Altcode: Gamma-ray emission extending to energies greater than 2 GeV and lasting at least for two hours as well as 0.8-8.1 MeV nuclear line emission lasting 40 min were observed with very sensitive telescopes aboard the GAMMA and CGRO satellites for the well-developed post-flare loop formation phase of the 3B/X12 flare on June 15, 1991. We undertook an analysis of optical, radio, cosmic-ray, and other data in order to identify the origin of the energetic particles producing these unusual gamma-ray emissions. The analysis yields evidence that the gamma-rays and other emissions, observed well after the impulsive phase of the flare, appear to be initiated by prolonged nonstationary particle acceleration directly during the late phase of the flare rather than by a long-term trapping of energetic electrons and protons accelerated at the onset of the flare. We argue that such an acceleration, including the acceleration of protons up to GeV energies, can be caused by a prolonged post-eruptive energy release following a coronal mass ejection (CME), when the magnetic field above the active region, strongly disturbed by the CME eruption, relaxes to its initial state through magnetic reconnection in the coronal vertical current sheet. Title: Observations and Analysis of Surges in Chromosphere and Lower Corona Authors: Kotrc, P.; Schmieder, B.; Karlický, M.; Heinzel, P. Bibcode: 1996RoAJ....6...69K Altcode: No abstract at ADS Title: H-alpha Eruptive Prominence and Evolution of Force-Free Electric Currents in the Solar Atmosphere Authors: Karlicky, M. Bibcode: 1996ASPC..111..365K Altcode: 1997ASPC..111..365K Hα observations of the 18 Sep 1995 eruptive prominence indicating magnetic field reconnection or electric current coalescence are presented. To explain some aspects of these observations a 3-D numerical model of the evolution of force-free electric currents in the solar atmosphere was built. Title: Pinch Processes near the Transition Region and Electron Bombardment of the Chromosphere in the Presence of Electric Current Authors: Karlicky, M. Bibcode: 1996mpsa.conf..591K Altcode: 1996IAUCo.153..591K No abstract at ADS Title: 1 4 GHz type II-like radio bursts and pinch processes near the transition region Authors: Karlický, Marian; Jiřička, Karel Bibcode: 1996SoPh..163..171K Altcode: Analyzing 205 radio bursts observed by the Ondřejov radiospectrograph in the 1-4 GHz frequency range during 1992 and 1993, we found 6 examples of type II-like radio bursts coinciding with impulsive phases of solar flares. These bursts were interpreted as radio manifestations of MHD (shock) waves generated during impulsive phases of flares in the vicinity of the transition region. Assuming a magnetic-field perturbation origin of these waves, we studied pinch processes in the current sheet near the transition region. In the 2-D MHD numerical model of this current sheet we demonstrated that 2-D pinch processes induced by radiative losses can trigger the impulsive phase of some flares and so generate the observed high-frequency type II-like radio bursts. Title: Solar flares and related processes in active regions. Authors: Karlický, M. Bibcode: 1996joso.proc..100K Altcode: No abstract at ADS Title: Isolated narrowband dm-spikes in the 1 - 2 GHz frequency range. Authors: Jiřička, K.; Mészárosová, H.; Karlický, M. Bibcode: 1996joso.proc..149J Altcode: No abstract at ADS Title: Phenomena related to electron beams in solar flares Authors: Karlický, Marian Bibcode: 1995CzJPh..45.1063K Altcode: Starting from basic observational characteristics of solar flares the flare physical processes are briefly described. The role of electron beams in such a flare scenario is expressed. The observational manifestations of electron beams as, e.g., type III and U radio bursts are presented. Then results of numerical modelling of these processes are shown. Besides the magnetic field-line reconnection process which is considered to be a primary flare one, the main attention is devoted to the evolution of electron beams in flare loops, to the interpretation of U bursts, to the electron beam bombardment of deep and dense layers of the solar atmosphere and to accompanied processes as the evaporation process and the asymmetry of optical chromospheric lines. Title: Repeated activity of the 0.8 1.2 GHz radio source of March 20, 1993 Authors: Karlický, Marian; Jiřička, Karel Bibcode: 1995SoPh..160..121K Altcode: During March 20, 1993, from 12:00 to 16:00 UT, repeated radio burst activity was observed in the 0.8-1.2 GHz frequency range. `Periods' in intervals 0.1-0.5, 0.7-1.0, 2.8-3.9, 75-170 s, and 15-25 min were recognized. This long-lasting narrowband activity consisted mainly of pulsations and continua. In some intervals it was accompanied not only by spikes, broadband pulsations, and fibers in the 1-2 GHz frequency range, but also by type III and U burst activity at lower frequencies as well as by hard X-ray bursts. From several radio bursts, two characterized by different fine structures were selected and compared. The observed differences are explained by different distribution functions of superthermal electrons. The position of the 0.8-1.2 GHz radio source above the photosphere and the magnetic field in the fiber burst source were estimated to be 66 000-75 000 km and 120-135 G, respectively. Title: Electron beam bombardment of the chromosphere in a flare loop with electric currents. Authors: Karlicky, M. Bibcode: 1995A&A...298..913K Altcode: In a flare loop with electric current and corresponding Ohm electric field the electron beam bombardment of chromospheric layers is considered. It is assumed that the electric current, which is generated during the slow evolution before a flare, flows along current filaments in the flare loop and all current densities in these filaments are below any thresholds of current instabilities. The convergence of magnetic field below transition region and its influence on current densities in current filaments are considered. The Ohm electric field in the VAL-model chromosphere is determined and compared with the electric field equivalent to collisional losses of the 30-100keV electrons at these layers. It was found that for sufficiently high current densities and electron energies the Ohm electric field can be greater than that of collisional one, mainly at upper chromosphere. Using a numerical model of electron beam bombardment in a flare loop, the energy changes of initially 100keV electrons during their penetration into the chromosphere in the case with and without the presence of electric current are computed. The significance of these effects and their influences on interpretations of hard X-ray emission and evaporation process are discussed. Title: The generation of MHD shock wave during the impulsive phase of the February 27, 1992 flare Authors: Karlický, M.; Odstrcil, D. Bibcode: 1994ESASP.373..325K Altcode: 1994soho....3..325K No abstract at ADS Title: Chromospheric and transition-region heating phenomena: coordinated GBO and SOHO observations Authors: Heinzel, P.; Kotrc, P.; Karlicky, M.; Nejezchleba, T.; Knizek, M. Bibcode: 1994ESASP.373..369H Altcode: 1994soho....3..369H No abstract at ADS Title: The Generation of Magnetohydrodynamic Shock Waves during the Impulsive Phase of the 1992FEB27 Flare Authors: Karlicky, Marian; Odstrcil, Dusan Bibcode: 1994SoPh..155..171K Altcode: In this paper a unique 2.3-4.2 GHz radio spectrum of the flare impulsive phase, showing fast positively drifting bursts superimposed on a slowly negatively drifting burst, is presented. Analyzing this radio spectrum it was found that the flare started somewhere near the transition region, where upward propagating MHD waves were generated during the whole impulsive phase. Moreover, it was found that behind a front of these ascending MHD waves the downward propagating electron beams, which bombarded dense layers of the solar atmosphere, were accelerated. It seems that, simultaneously with the increase of beam bombardment intensity, the intensity of MHD waves was increasing and thus the MHD shock wave generation and the electron beam acceleration and bombardment formed a self-consistently amplifying flare process. At higher coronal heights this process was followed by a type II radio burst, i.e. by the MHD flare shock. To verify this concept, the numerical modeling of the shock-wave generation and propagation in space from a flare site near the transition region up to 3 solar radii was made. Comparing the thermal and magnetic field disturbances, it was found that those of magnetic origin are more relevant in this case. Combining the results of interpretation and numerical simulation, a model of the February 27, 1992 flare is suggested and new aspects of this model are discussed. Title: Magnetic field estimation in microwave radio sources Authors: Ai-hua, Zhou; Karlický, M. Bibcode: 1994SoPh..153..441A Altcode: Eliminating the termN L, useful formulae for the magnetic field estimation in microwave radio sources are presented. Applications of these formulae to observed solar microwave radio bursts are shown. Title: Magnetic field estimation in microwave radio sources Authors: Zhou, Ai-Hua; Karlicky, M. Bibcode: 1994SoPh..153..441Z Altcode: Eliminating the term N L, useful formulae for the magnetic field estimation in microwave radio sources are presented. Applications of these formulae to observed solar microwave radio bursts are shown. Title: On the Occurrence of Blue Asymmetry in Chromospheric Flare Spectra Authors: Heinzel, Petr; Karlicky, Marian; Kotrc, Pavel; Svestka, Zdenek Bibcode: 1994SoPh..152..393H Altcode: We present observations of optical spectra of a flare in which blue line asymmetry was seen for more than 4 min close to the flare onset. The maximum blue asymmetry coincided with the maximum of a hard X-ray and microwave burst. We discuss possible interpretations of the blue asymmetry and conclude that the most plausible one is electron-beam heating with return current. Although this process predicts downflows in the lower transition region and upper chromosphere, its ultimate effect on the line profiles can be blue asymmetry: the upper layers moving away from us absorb the radiation of the red peak thus lowering its intensity in comparison to the blue one. Title: Space and time distribution of hard X-ray emission in a loop at the beginning of a flare Authors: Karlicky, Marian; Henoux, Jean-Claude Bibcode: 1994A&A...283..202K Altcode: Using a 1-D hybrid model of the electron bombardment in flare loops, we study not only the evolution of densities, plasma velocities and temperatures in the loop, but also the temporal and spatial evolution of hard X-ray emission. In the present paper a continuous bombardment by electrons isotropically accelerated at the top of flare loop with a power-law injection distribution function is considered. The computations included the effects of the return-current that reduces signifcantly the depth of the chromospheric layer which is evaporated. These computations were made to study the contribution of various processes - chromospheric evaporation, mirroring and high pitch angle of superthermal electrons - to the hard X-ray emission at the top of a loop at the very beginning of flares. Therefore the present modelling was made with superthermal electron parameters coresponding to the classical resistivity regime for an input energy flux of superthermal electrons of 109 erg cm-2/sec. Chromospheric evaporation density waves generated at both feet of the loop propagate up to the top, where they collide and cause a temporary electron density enhancement. Electron mirroring at magnetic mirrors increases the population of superthermal electrons at the top loop. These two processes lead to hard X-ray emission at the top of the loop and dominate over the effect of high pitch-angle superthermal electrons. Title: Fast Drift Bursts; Spikes; and Continua Ohservations in the 100-4200 MHz Band Authors: Jiricka, K.; Karlicky, M.; Kepka, O.; Tlamicha, A. Bibcode: 1994scs..conf..285J Altcode: 1994IAUCo.144..285J New Ondřejov solar radio observational system consisting of a high-time resolution 3000 MHz receiver and of a 100 - 4200 MHz radiospectrograph is described and some results of observation of fast drift bursts, spikes, and continua are presented. Title: Space and Time Distribution of Hard X-Ray Emission in a Loop at the Beginning of a Flare Authors: Karlicky, M.; Henoux, J. -C. Bibcode: 1994scs..conf..275K Altcode: 1994IAUCo.144..275K Using a new 1D hybrid model of the electron bombardment in flare loops, the authors study not only the evolution of densities, plasma velocities and temperatures in the loop, but also the temporal and spatial evolution of hard X-ray emission. In this paper a continuous bombardment by electrons isotropically accelerated at the top of flare loop with a power-law injection distribution function is considered. Title: The Superthermal Electrons in Flare Loops (Invited) Authors: Karlicky, M. Bibcode: 1994scs..conf..235K Altcode: 1994IAUCo.144..235K In this paper the collisional, return current, mirroring and wave-particle interaction effects on the propagation of superthermal electrons in flare loops are reviewed. Moreover, the electron bombardment of dense layers of the solar atmosphere and corresponding atmospheric response are presented. The accompanied X-ray, radio and Hα emissions during the evaporation process are discussed. Title: Electron acceleration due to beam flux increase in a converging magnetic field Authors: Karlicky, M.; Henoux, J. -C. Bibcode: 1993A&A...278..627K Altcode: The effects of the magnetic field mirroring and backscattering of beam electrons in a time varying return-current electric field are studied with a 1-D hybrid test particle model of the electron bombardment in flare loops. These effects are analyzed for monoenergetic electron beams with an energy flux increasing with time, for different widths of their pitch-angle distribution. The consequence of a weak linear increase of the magnetic field from the apex to the feet of the loop is considered. The number and therefore the role of mirroring electrons are increasing with the broadening of the pitch-angle distribution. While in the case of bombardment by an unidirectional beam only few particles are reflected by back-scattering in the dense layers of the loop and then accelerated in the return-current electric field, in the case of a broader pitch-angle distribution of beams much more electrons are mirrored and accelerated. Part of them are accelerated to energies higher than the initial ones. Consequently, a collisionless return-current is formed, which decreases the beam return-current losses. The possible role of these effects in the solar flare scenario is shortly discussed. Title: Fast drift burst observations with the new Ondřejov radiospectrograph Authors: Jiricka, K.; Karlicky, M.; Kepka, O.; Tlamicha, A. Bibcode: 1993SoPh..147..203J Altcode: The new 100-4200 MHz Ondřejov radiospectrograph and the high-time resolution 3 GHz radiometer are described and the observations of fast drift bursts during the increased solar activity of September 5-7, 1992 are presented and analyzed. Title: Return current losses in pulse beam heating of the solar atmosphere Authors: Karlický, Marian; Hénoux, Jean-Claude Bibcode: 1993AdSpR..13i.195K Altcode: 1993AdSpR..13..195K The influence of return current losses on pulse beam heating of the solar atmosphere is studied using a 1 D-hybrid code. While heating of the coronal plasma by the penetrating electron beam is obtained, as expected, strong return current losses of beam electrons at the resistivity jump in the transition region are also found. The electron beam energy is deposited at greater heights in the solar atmosphere than in the case of pure collisional losses. At the starting time of the flare, due to a strong return current heating, a very steep transition region is formed where upwards and downwards plasma flows are generated. However, this state has a transitory character. The atmosphere is heated and a channel of hot, low resistivity plasma is formed, by which the following electron beams can penetrate more easily to deep chromospheric levels, where they are then thermalized. Title: An Analysis of SKYLAB X-Ray Pictures of a Giant Coronal Arch Authors: Simberova, Stanislava; Karlicky, Marian; Svestka, Zdenek Bibcode: 1993SoPh..146..343S Altcode: The limb event of 13/14 August, 1973, imaged by Skylab in soft X-rays, proved to be a giant arch, quite similar to those observed in 1980-1986 on SMM. High spatial resolution (by a factor of 4-5 better than in SMM data) made it possible to see the internal structure of the arch. Its brightest part consisted of loops very similar to, but higher than, post-flare loops, surrounded by a rich system of weak loop structures extending up to altitudes of 260 000 km. While the main brightest structure of the arch was newly formed, the weak very large loops had existed above the active region before and were only enhanced during the event. Title: New aspects of the April 27, 1981 flare Authors: Karlicky, M.; Zhou, Ai-Hua Bibcode: 1993SoPh..146..199K Altcode: Very interesting radio bursts, observed during the well-known solar flare of April 27, 1981 are presented. While the sequence of reverse drift bursts, U-bursts and radio flux depression on 9.375 GHz can be explained within the beam bombardment and evaporation model, the narrowband dm-spikes uniquely organized in "necklace" structures seem to indicate the interaction of flare loops. Arguments in favour of the plasma emission model of narrowband dm-spikes were found. Title: The acceleration of back-scattered beam electrons in a return-current electric field Authors: Karlicky, Marian Bibcode: 1993SoPh..145..137K Altcode: Using a 1-D hybrid model of the electron beam bombardment in a flare loop, it is demonstrated that beam electrons, back-scattered in dense layers of the solar atmosphere, are accelerated in the return-current electric field. This effect is shown in two regimes of the electron beam bombardment: (a) with a monoenergetic quasi-steady beam, and (b) with a sequence of 4 pulse beams. It is suggested that the mirroring of electrons at loop magnetic mirrors can amplify this process. The role of such acceleration for the formation of a collisionless return-current, and thus for a decrease of return-current losses, is discussed. Title: Fine Structures in Time Profiles of Type-II Bursts at Frequencies above 200-MHZ Authors: Zlobec, P.; Messerotti, M.; Karlicky, M.; Urbarz, H. Bibcode: 1993SoPh..144..373Z Altcode: We studied the properties of fine structures in 23 type II bursts recorded at the Trieste Astronomical Observatory at frequencies above 200 MHz. Title: Pulse Beam Heating of the Solar Atmosphere (Abstract) Authors: Karlicky, M. Bibcode: 1993HvaOB..17...33K Altcode: No abstract at ADS Title: Mass motion of a heated plasma blob in a coronal loop. Authors: Karlicky, M.; Simnett, George M. Bibcode: 1992ESASP.348..205K Altcode: 1992cscl.work..205K A problem of the gravitational fall of dense plasma blob in the semicircular coronal magnetic loop is studied using a 1-D hydrodynamic code. Considering the thermal conduction and radiative losses are fully compensated by an appropriate heating, it is shown that the falling dense plasma blob compresses the underlying coronal plasma and thus the blob is decelerated and reflected. This process together with a decompression in the opposite side of coronal loop leads to the oscillation movement of dense plasma blob and eventually to the stop of this blob in some equilibrium position, in which the blob is supported by the pressure of an underlying plasma. This process is very sensitive to the deviation from full compensation of heating, radiative and thermal conduction losses. Nevertheless, it seems that the pressure with the appropriate heating can support the dense and cold plasma, e.g. in solar prominences, where their magnetic field is stabilizing the Rayleigh-Taylor instability of heavy gas above the lighter one. Title: Pulse-beam heating in flare loops. Authors: Heinzel, Petr; Karlicky, M. Bibcode: 1992ESASP.348..237H Altcode: 1992cscl.work..237H Using a 1D hydbrid code, the authors evaluate a response of the flare loop atmosphere to a series of very short electron beam pulses with subsecond duration. Loop dynamics and energy balance are treated by solving the standard set of hydrodynamic equations, while the beam deceleration in denser atmospheric layers is evaluated by using a particle simulation technique. Ionization of hydrogen below T ≍ 104K is obtained by solving simultaneously the time-dependent non-LTE problem for a three-level hydrogen atom with continuum. The resulting electron densities are then used to compute radiation losses at each time step. The authors discuss the behaviour of time-dependent heating, the ionization structure of the chromosphere, and the role of relaxation processes. A series of short-duration electron beam pulses represents schematically the non-stationary heating in the flare loops. However, the time-dependent radiation-hydrodynamical approach used in this paper can also be applied to study other processes taking place in coronal loops. Title: Return current losses in pulse beam heating of the solar atmosphere Authors: Karlicky, M.; Henoux, J. -C. Bibcode: 1992A&A...264..679K Altcode: A 1D-hybrid code is employed to examine the influence of return current losses on pulse beam heating of the solar atmosphere. While heating of the coronal plasma by the penetrating electron beam is obtained as expected, strong return current losses of beam electrons at the resistivity jump in the transition region are also found. The electron beam energy is deposited at greater heights in the solar atmosphere than in the case of pure collisional losses. At the starting time of the flare, due to a strong return current heating, a very steep transition region is formed where upward and downward plasma flows are generated. The atmosphere is heated and a channel of hot low-resistivity plasma is formed by which the following electron beams can penetrate more easily to deep chromospheric levels where they are then thermalized. Title: A simulation approach to neutral beam-plasma systems: analysis of Langmuir waves generation Authors: Messerotti, M.; Karlicky, M. Bibcode: 1992pdta.proc..115M Altcode: Many authors suggested the acceleration of neutral beams in the primary energy release site of solar flares (Simnett, 1986; Simnett and Heines, 1990; Martens and Young, 1990); such neutral beams would consist of electrons and protons with the same drift velocity, so that the protons carry the bulk of kinetic energy, and this would also overcome most of the problems connected with the propagation of pure proton and pure electron beams (Brown et Al., 1989). Numerical simulations in a preliminary work (Karlicky, 1989) indicate that neutral beams can be the result of current neutralization in accelerated proton beams or, according to the model by Martens and Young (1990), their formation can be due to the non-collisional, direct acceleration of protons and electrons through the action of the electric field in the current sheet formed at the top of a post-flare loop. Actually the real existence of neutral beams in solar flares has to be proved yet and, among the possible signatures, the emission of electromagnetic radiation was considered in the literature. Proton beams were suggested by Benz and Simnett (1986) as exciters of slowly-drifting solar radio bursts and Smith and Benz (1989) proposed a model based on high-energy proton beams to explain non-drifting radio emissions observed in the frequency band 1 - - 3 GHz with a lifetime ranging from 2 to 4 s, but many questions concerning this point remain open (Messerotti, 1990). With regard to that in the present work the generation of Langmuir waves in neutral beam-plasma systems was studies using a 1-D electrostatic and a 1-D electromagnetic particle code. For a weak and monoenergetic neutral beam-plasma system a two-step saturation process of the electrostatic beam instability was found to be operating, firstly driven by beam electrons till their trapping and mixing in the phase space, when beam protons undertake the role. The addition of a thermal spread in the neutral beam resulted in the disappearance of the electron trapping phase. The effect of an external magnetic field was also analyzed and the simulations show that the saturation levels decrease according to a square cosine law in the angle between the considered and the beam propagation direction. Furthermore it was tried to estimate the influence of electromagnetic waves on the generated Langmuir waves using a 1-D electromagnetic relativistic code. Numerical results indicate that such influence is negligible, as the level of em waves corresponds roughly to the noise level of the background plasma. A comparison of the parameters derived from the numerical experiments with those from the theoretical estimations confirm the adequate accuracy of the above results. In particular, the most relevant conclusion is that a real neutral beam with monoenergetic protons can generate Langmuir waves with a saturation level 150 times higher than that due to a pure electron beam with the same density and velocity and this suggests that observable radio emission could be produced. Title: Parametric model of interplanetary shock wave propagation Authors: Voros, Z.; Karlicky, M. Bibcode: 1992sws..coll..675V Altcode: The free parameters of the present simple model for the propagation of a driven interplanetary shock wave are discussed, and the physically meaningful range of 2D MHD numerical model input parameters is noted, in view of experimentally obtained time intervals of soft, long-duration X-radiation and type IVm radiation. It appears possible to improve blast wave propagation forecasts by considering actual anisotropy features of shock wave propagation. Title: Subsecond Variations of HXR and Hα Flare Emission Authors: Heinzel, P.; Karlicky, M. Bibcode: 1992LNP...399..359H Altcode: 1992esf..coll..359H; 1992IAUCo.133..359H For a series of electron beam pulses, we have computed the time-dependent chromospheric heating and the corresponding hard X-ray (HXR) flux. Moreover, by solving the time-dependent NLTE problem for hydrogen, we theoretically predict the Ha-line intensity variations on sub-second time scales. Both HXR-fluxes and Ha wing intensities do exhibit a spiky behaviour, consistent with short pulse-beam heating. However, the spikes in Ha are unexpectedly inverse, i.e. the line intensity decreases during the beam heating. They correlate rather well with HXR emission peaks computed for 24 keV channel. We compare our theoretical results with recent observations of Kiplinger et al. (1991). Title: Radio Emission of Eruptive Flares Authors: Karlicky, M. Bibcode: 1992LNP...399..171K Altcode: 1992esf..coll..171K; 1992IAUCo.133..171K Radio spectra of some eruptive flares are described. Most of them do not conform to the classical spectrum schema. Both the type I burst chains associated with the filament activation phase of the May 16, 1981 flare, and the slow negative drift of the group of type III and U bursts in the July 12, 1982 and June 15,1991 flares illustrate the upwards expansion of complete magnetic structures. In some eruptive flares, e.g. April 24, 1985, reverse drift bursts are observed prior to the upwards expansion. In addition, narrowband dm-spikes and a variety of positively drifting features are frequently observed. These are believed to be radio signatures of localized reconnections and of the spreading of flare dissipative processes. Results of numerical simulations supporting these ideas are presented. Title: Radio Emission of the February 27, 1992 Flare Authors: Karlicky, M.; Tlamicha, A.; Jiricka, K.; Aurass, H.; Zlobec, P. Bibcode: 1992HvaOB..16...23K Altcode: No abstract at ADS Title: Comparison of 2-Dimensional MHD and Semiempirical Models of Interplanetary Shock Wave Propagation Authors: Karlicky, M.; Smith, Z.; Dryer, M. Bibcode: 1991BAICz..42..320K Altcode: A comparison was made between the 2D version of the 2 1/2-D MHD model by Wu et al.(1983) and the semiempirical model of Voros and Karlicky (1988). Although agreement in the exponential dependence (N is about 0.5) of shock wave velocities was found, the compared models differ in the early stages of shock wave propagation and in the shock shapes. A small E-W asymmetry of shock wave propagation was found in the MHD simulations. Title: The Negative Frequency Drift of Microwave Bursts Due to Collisional and Radiative Losses of Superthermal Electrons Authors: Karlicky, M. Bibcode: 1991BAICz..42..260K Altcode: An analytical estimate of negative frequency drift is compared to observed values of microwave radio spectra with attention given to the effects of microwave bursts. Observations of fast drift bursts (FDBs) in the range 2-4.5 GHz are examined in terms of both radiative and collisional losses, and the electron densities in the radio source are reasonable and coincide with microwave bursts. Classical collisions are sufficient to explain the negative frequency drift of FDBs, but the frequency drift of the bursts from compact radio sources can be used to estimate the plasma density in those sources. Title: Pulse Beam Heating of Solar Atmosphere Authors: Karlicky, M.; Henoux, C. Bibcode: 1991BAICz..42...22K Altcode: The response of the solar atmosphere to pulse beam heating was computed using a one-dimensional hybrid code. Whereas the hydrodynamic part of this program was used to compute the atmospheric response, the pulse beam decelerated by electron-electron interactions in the dense layers of the solar atmosphere is represented by particles. In this new description of the electron beam, the finite transit time of electrons accelerated in flare loops is taken into account and the hard X-ray radiation has been computed directly. Title: The Role of the Magnetic Field in Intensity and Geometry in the Type-Iii Burst Generation Authors: Zlobec, P.; Ruždjak, V.; Vršnak, B.; Karlický, M.; Messerotti, M. Bibcode: 1990SoPh..130...31Z Altcode: We study the association of type III bursts related to Hα flares in different magnetic environments in the period 1970-1981. Special attention is paid to flares which partly cover a major spot umbra (Z-flares). In particular we consider the location of the spots in the active regions and the magnetic field intensities of spots covered by a ribbon. The association rate with type III bursts decreases to 17% when the flare is located inside the bipolar pattern of a large active region, compared with an association rate of 54% when the flare is situated outside it. The association rate increases with the magnetic field intensity of the spot covered by Hα emission; this is most clearly revealed for the flares occurring outside the bipolar pattern of active regions. Ninety-three percent of the flare-associated type III burst were accompanied by 10 cm radio bursts. For the most general case in which a flare is developing anywhere in an active region, the association with type III bursts generation increases with the increasing magnetic field intensity of the main spot of the group. Title: Analysis of the Time Profile of Type-Iii Bursts at Meter Wavelengths Authors: Abrami, A.; Messerotti, M.; Zlobec, P.; Karlicky, M. Bibcode: 1990SoPh..130..131A Altcode: The time profile of two sets of isolated type III bursts, observed in the meter wavelength range at the Trieste Astronomical Observatory, was analyzed using a Fourier transform technique in order to accurately determine the decay constant of the exponential phase and to derive the exciter time profile. The decay constant (τ) was found to be correlated with the exciter duration (De), suggesting that the damping of plasma waves is not of collisional origin and confirming results obtained by previous authors at lower frequencies. In particular, two distributions can be identified in the (τ − De) plane and fitted by two nearly parallel lines, which could be the signature of different decay processes. Moreover, the damping constant observed at higher frequencies (327 and 408 MHz) has the same dependence on exciter duration as that at the lower frequency (237 MHz), also in disagreement with the collisional hypothesis. Title: Pulse Beam Heating of the Solar Atmosphere Authors: Karlicky, Marian Bibcode: 1990SoPh..130..347K Altcode: A response of the solar atmosphere to pulse beam heating is computed using a 1-D hybrid code. While the hydrodynamic part of this program is used to compute the atmospheric response, the pulse beam decelerated by electron-electron and electron-neutral hydrogen interactions in the dense layers of the solar atmosphere is represented by particles. In this new description of an electron beam, the finite transit time of accelerated electrons in the flare loops is taken into account and the hard X-ray radiation is computed directly. Four different pulse beams are considered and their effects are compared. Moreover, the return current losses of the pulse beam are discussed. Title: Particle beams as a source of noise storm depression? Authors: Aurass, H.; Boehme, A.; Karlicky, M. Bibcode: 1990SoPh..130...19A Altcode: The February 5, 1986 flare-related radio continuum depression is studied, compared with other noise storm depression events and discussed in the framework of current type I storm models. The influence of flare plasma flow or shocks and of superthermal electrons on noise storm radiation is considered. The presence of fast drifting emission features just before and during the decrease of the intensity, the association between the depression onset and the microwave burst maximum, the simultaneous appearance of the intensity minimum over a broad spectral range as well as preflare evidence of an interconnection of the flare site and the noise storm source are arguments for a preference of the role of beams of superthermal electrons. We distinguish abrupt and slow depressions (Figure 5). The abrupt depressions are in agreement with Melrose's (1980) predictions. Slow depressions can only be understood by invoking the diffusion of super-thermal electrons through the magnetic field carrying the storm source. Title: Return Current and Collisional Effects in Nonthermal Electron Beams with Pulsed Injection Authors: Karlicky, M.; Alexander, D.; Brown, J. C.; MacKinnon, A. L. Bibcode: 1990SoPh..129..325K Altcode: The evolution of a pulse of nonthermal electrons, with a truncated power-law spectrum, injected into a uniformly dense coronal plasma, is studied by the 1-D particle simulation of return current and direct collisional effects. The beam pulse injection profile varies gradually enough for total current neutrality, and a steady-state Ohm's law for the return current, to apply at each point and time. Quasi-linear relaxation of the beam is deliberately ignored in order to isolate the modification of return current effects by pulsed injection. Title: Beam Heating in Solar Flares: Electrons or Protons? Authors: Brown, J. C.; Karlicky, M.; MacKinnon, A. L.; van den Oord, G. H. J. Bibcode: 1990ApJS...73..343B Altcode: The current status of electron and proton beam models as candidates for the impulsive phase heating of solar flares is discussed in relation to observational constants and theoretical difficulties. It is concluded that, while the electron beam model for flare heating still faces theoretical and observational problems, the problems faced by low and high energy proton beam models are no less serious, and there are facets of proton models which have not yet been studied. At the present, the electron beam model remains the most viable and best developed of heating model candidates. Title: A survey of the peculiar radio emission of the solar behind-limb event on 16th February 1984 Authors: Chertok, I. M.; Fomichev, V. V.; Gorgutsa, R. V.; Markeev, A. K.; Podstrigach, T. S.; Aurass, H.; Hildebrandt, J.; Kliem, B.; Krüger, A.; Kurths, J.; Karlický, M.; Tlamicha, A.; Urbarz, H. W.; Zlobec, P. Bibcode: 1990AN....311...55C Altcode: This paper presents radio emission measurements, taken from different European stations, of the February 16th, 1984 solar behind-limb burst, which started in the active region AR 4408 at a longitude of about 130 deg W. The event was related to a very strong relativistic particle emission, the presence of cm-wave radiation from altitudes above 200,000 km above the photosphere, and an unusual U-shaped type II burst pattern consisting of four simultaneous emission bands. The spectrum in the cm-dm range exhibited different stages of evolution related to the burst onset, the burst maximum, and the postburst increase. It appears possible that, at dm-waves during the burst maximum, a partial overlapping of plasma radiation with gyrosynchroton radiation governing the cm-wave range took place. Title: Solar Flares and the Dynamics of Langmuir Waves in Current-Carrying Plasmas Authors: Karlicky, M.; Jungwirth, K. Bibcode: 1989SoPh..124..319K Altcode: The dynamics of intense Langmuir waves in current-carrying plasmas is studied both analytically and numerically. Starting with the widely used Zakharov equations, adapted to these systems, specific features of this problem are pointed out. Further, the role of resonant particles is analyzed. By using 1-D macroparticle numerical code, nonlinear regimes of the modified-decay and modulational instabilities are then modelled. Efficient cooperation of essentially ponderomotive and electron-ion drift effects its demonstrated. Title: Interpretation of a Special Fine Structure in Type-Iv Solar Radio Bursts Authors: Mann, G.; Baumgaertel, K.; Chernov, G. P.; Karlicky, M. Bibcode: 1989SoPh..120..383M Altcode: A special fine structure (slowly drifting chains of narrowband fiber bursts), firstly observed during the solar type-IV radio burst on April 24, 1985, is interpreted as the radio signature of whistler waves periodically excited by a switch-on/switch-off process of a loss-cone instability in a localized wave packet of the fast magnetoacoustic mode. Title: The Route to Chaos during a Pulsation Event Authors: Kurths, Juergen; Karlicky, Marian Bibcode: 1989SoPh..119..399K Altcode: A time series analysis of a pulsation event in solar radio emission provides an evolution from a regular doubly periodic phase to an irregular behaviour. Applying some techniques developed in the theory of nonlinear dynamic systems to this irregular stage suggests that there exists a low-dimensional attractor. Estimates of the maximum Lyapunov exponent give some evidence to deterministic chaos. The sudden transition from a regular to a chaotic structure is identified as a part of the Ruelle-Takens-Newhouse route to chaos which is typical in nonlinear systems. It is checked whether this pulsation event may be interpreted in terms of known pulsation models. Consequences for models, which are suitable to describe such an evolution, are discussed. Title: Solar flares and dynamics of Langmuir waves in current-carrying plasmas Authors: Jungwirth, K.; Karlicky, M. Bibcode: 1989STIN...9021710J Altcode: The dynamics of intense Langmuir waves in current-carrying plasmas is studied both analytically and numerically. Starting with the widely used Zakharov equations, adapted to these systems, specific features of this problem are pointed out. Further, the role of resonant particles is analyzed. By using 1-D macroparticle numerical code, nonlinear regimes of the modified-decay and modulational instabilities are then modelled. Efficient cooperation of essentially ponderomotive and electron-ion drift effects is demonstrated. It appears that the heating of a current-carrying plasma can be activated through releasing of the inductively stored energy, due to the enhanced conversion of energy associated with the electron drift motion. The underlying physics is discussed and its relationship to the solar flare theory is suggested. Title: Effects of Shear Plasma Flow on Externally Induced Magnetic Field Line Reconnection Authors: Karlicky, M. Bibcode: 1989BAICz..40...23K Altcode: A numerical study of the response of a current sheet to resistivity enhancement in the presence of shear plasma flow is presented. Simulations were conducted with two-dimensional model of the current sheet and comparisons were made between cases with and without the shear flow. The results show that the shear plasma flow in the adjacent magnetic flux tubes forming the current sheet on their tangential surface influences the resultant velocity field. Also, it is found that the reconnection process in the vicinity of the X-point becomes slower in the presence of shear flow. Title: The application of a 1-D electrostatic code for the analysis of beam-plasma systems in the solar corona Authors: Messerotti, M.; Zlobec, P.; Karlicky, M. Bibcode: 1989MmSAI..60..187M Altcode: A one-dimensional electrostatic particle simulation code used for the analysis of beam-plasma systems is investigated. The use of the code in the preliminary study of an electrostatic streaming instability (bump-on-tail type) in the nonlinear regime and the related choice of system parameters is explained. The saturation of the instability is analyzed for a proton as well as for an electron weak beam having the same density and velocity in the cold approximation; the corresponding energy levels are then compared to test the efficiency of the process. The saturation level for protons was revealed to be larger than that of electrons, thus suggesting possible radio emission by protons. Title: Solar flares and dynamics of Langmuir waves in current-carrying plasmas. Authors: Karlický, M.; Jungwirth, K. Bibcode: 1989BAAS...21Q1027K Altcode: No abstract at ADS Title: Chaotic Radiopulsations and Coronal Magnetic Field Estimates Authors: Kurths, J.; Karlicky, M. Bibcode: 1989ESASP.285..175K Altcode: No abstract at ADS Title: A simple model of propagation of driven interplanetary shock waves and prediction of sudden commencements of geomagnetic storms. Authors: Voros, Z.; Karlicky, M. Bibcode: 1988BAICz..39..250V Altcode: On the basis of the results of magnetohydrodynamic models, observations of type II radio burst and measurements of the interplanetary plasma parameters of shock waves, a simple model relation has been suggested for propagation of driven shock wave. The free parameters in this relation, which has been constructed for a quick and simple prediction of SSC, are determined and discussed with the aid of cases of interplanetary shock waves already recorded. Title: Impulsive 6-cm Spikes and Langmuir Turbulence Caused by Thick-target Electron Beams Authors: Karlicky, M. Bibcode: 1988BAICz..39..146K Altcode: The possibility that the 6-cm spikes observed during the May 16, 1981, solar flare are the microwave signature of Langmuir turbulence generated by thick-target electron beams is discussed. The Langmuir turbulence in the spike sources are estimated and compared with the results of Emslie and Smith (1984). The short duration and small extent of these 6-cm spikes are explained by the short lifetime of the highly collimated thick-target electron beams in the small volumes of the solar flare. It is suggested that the effects of gyroresonance absorption must be taken into account with the increase of the magnetic field in the spike sources. Title: Response of the Current Sheet to a Time-Limited Enhancement of Electrical Resistivity Authors: Karlicky, M. Bibcode: 1988BAICz..39...13K Altcode: The initiation of a solar flare by an electron beam from a distant previous flare via the mechanism proposed by Farnik et al. (1983) is investigated by means of numerical simulations, extending the analysis of Ugai (1980, 1982, and 1983) to focus on the evolution of the current sheet after a rectangular pulse of increased electrical resistivity has ended. The derivation of the governing equations is recalled, and the simulation results are presented in extensive graphs. The reconnection of magnetic-field lines after the pulse is found to be associated with local field-line diffusion, an X-type field configuration, locally enhanced Joule heating, and vortex formation near the X point (leading to quasi-steady plasma flow). The current at the X point decreases and changes sign during the period of vortex flow but then increases rapidly when the vortex disappears. Title: On the Intermediate Drift Burst Model Authors: Mann, G.; Karlicky, M.; Motschmann, U. Bibcode: 1987SoPh..110..381M Altcode: A modification of the presently existing intermediate drift burst model by Kuijpers (1975) and Bernold (1983) is suggested. It is shown that whistler solitons cannot be responsible for intermediate drift bursts. Here, they are interpreted as the radio signature of localized formstable whistler wave packets propagating along the magnetic field in a coronal loop. In the frame of this modified model, the magnetic field strengths derived from fiber burst data agree with previous estimates by Dulk and McLean (1978). Title: Hα diagnostics of (post)-flare loops based on narrow-band filtergram observations Authors: Heinzel, P.; Karlicky, M. Bibcode: 1987SoPh..110..343H Altcode: Using narrow-band Hα filtergrams, we develop a quantitative non-LTE approach to determine the physical conditions prevailing at the tops of (post)-flare loops observed against the solar disc. At temperatures 10000-15000 K, the tops of flare loops turn to emission at Hα line center when the gas pressure Pg reaches 1 dyn cm−2 and should be clearly visible for Pg≳ 3 dyn cm−2, independently of the loop diameter. This situation corresponds to the electron density of the order 1012 cm−3. The contrast of flare-loops (in projection on the disc) at Hα line center is mainly the function of Pg, while in the line wings (Hα ± 1 Å) the loop can be visible in absorption or emission only when rather strong microturbulence is present or for unrealistically high gas pressures. Finally, we briefly discuss our diagnostical results in frame of the latest (post)-flare loop model. Title: On a sequence of remarkable fine structures in the type IV burst of 24 April, 1985 Authors: Aurass, H.; Chernov, G. P.; Karlický, M.; Kurths, J.; Mann, G. Bibcode: 1987SoPh..112..347A Altcode: During the type IV burst on 24 April, 1985 we observed at 234 MHz an untypical, strong, nearly six hours lasting continuum emission incorporating several groups of broadband pulsations, zebra patterns, fiber bursts, and a new fine structure phenomenon. The power spectra of the groups of broadband pulsations reveal no simple structure. There is only one common periodic component between 0.3 s and 0.4 s. Slowly drifting chains of narrowband fiber bursts are described as a new fine structure by spectrograms and simultaneously recorded single frequency intensity profiles. A qualitative model of this new fine structure is suggested. Title: Book Review: Radio continua during solar flares. / Reidel, 1986. Authors: Karlicky, M. Bibcode: 1987SSRv...45..411K Altcode: 1987SSRv...45..411B No abstract at ADS Title: Effects of Impulsively Heated Electrons in Solar Flares Authors: Karlicky, M. Bibcode: 1987BAICz..38..201K Altcode: Using a one-dimensional particle code, the evolution of impulsively heated electrons in the flare loop is examined. The processes are studied in two regimes: with and without the electric current. One run was made for the system with the constant electric current, simulating the large inductance of the current loop. It was shown that impulsive electron heating leads to the formation of a double layer. Moreover, this heating can trigger the ion-acoustic instability in the current system of a flare loop. Both these effects increase the flare energy release. The generated electrostatic high-frequency waves can be observed as a radio burst. Title: Estimate of Plasma Parameters in a Coronal Loop by Means of a Fiber Burst Authors: Aurass, H.; Kurths, J.; Mann, G.; Chernov, G. P.; Karlicky, M. Bibcode: 1987SoPh..108..131A Altcode: Analyzing a fiber burst occurring in the event on 19 August, 1981, plasma parameters of the burst source volume are estimated by means of Kuijpers' (1975) fiber burst model. The derived height dependence of the density in a coronal loop agrees with an isothermal barometric loop atmosphere. Title: Dm-Spikes and Their Relation to Other Flare Phenomena in the October 14, 1983 Event Authors: Karlický, M.; Messerotti, M.; Ruždjak, V.; Slottje, C.; Tlamicha, A.; Urpo, S.; Zlobec, P. Bibcode: 1987BAICz..38...42K Altcode: By using observations in H-alpha and radio frequencies between 169 MHz and 37 GHz, the October 14, 1983 two ribbon flare was analysed. A coherent picture of the event is given using the standard topology for two-ribbon flares and describing the dm-spikes as manifestations of electron acceleration in a reconnection process (with stationary shock wave). The drifting chains of these spikes are explained by the movement of this "stationary" shock wave. It is shown that the behaviour with time of the number density of the spikes is in agreement with that of the 37 GHz flux and hence that the same population of accelerated electrons that gave rise to the spikes, also produced the 37 GHz radiation. Title: Solar Radio Continua and the X-Ray Emission during Flares Authors: Fárník, F.; Karlický, M.; Tlamicha, A. Bibcode: 1987BAICz..38...36F Altcode: Radio continua measured by the Ondřejov solar radio spectrograph in the frequency band of 100 - 1000 MHz are compared with the X-ray flux in the 2 - 320 keV region, measured by the Czechoslovak photometer aboard the Prognoz 8 satellite. The authors have chosen 20 flare-associated events, recorded by both instruments from March to August 1981, and, using the Solar Geophysical Data, they have determined source flares and their optical characteristics. Title: Radio wave diagnostics of solar active regions. Part I - mm-cm bands,part II - dm-m bands. Authors: Karlicky, M.; Krueger, A. Bibcode: 1987PAICz..66..237K Altcode: 1987eram....1..237K The results of different methods of observation of solar active regions at mm and cm wavelengths when exploring the source structures and parameters in the chromosphere and corona are reviewed. Calculations of emission models which take into account bremsstrahlung and gyromagnetic radiation are summarized. Diagnostic uses of different kinds of microwave burst emission are briefly discussed. Decimetric and metric radio spectral observations as diagnostic tools for the determination of plasma parameters in the coronal areas of solar active regions are also reviewed. Attention is given to the radio diagnostics of solar flares. The most important types of dm and m radio bursts are presented, and the most recent theoretical and observational results are summarized. Title: Magnetic field line reconnection by localized enhancement of resistivity and its interruption. Authors: Karlicky, Marian Bibcode: 1987PAICz..66..253K Altcode: 1987eram....1..253K The nonlinear development of magnetic reconnection in a current-sheet system is studied numerically. The reconnection process, developing from an initial localized enhancement of electrical resistivity, is at some instants interrupted by a sharp decrease in electrical resistivity. The development of this process is studied and the results discussed within the scope of the solar flare theory. Title: Effects of Impulsively Heated Electrons in Solar Flares Authors: Karlicky, M. Bibcode: 1987HvaOB..11..109K Altcode: For the full text see Abstr. 44.073.004. Title: Electrical conductivity in the solar photosphere and chromosphere Authors: Kubat, J.; Karlicky, M. Bibcode: 1986BAICz..37..155K Altcode: The method of computing of isotropic, Pedersen, Hall and Cowling conductivities for the model of a quiet photosphere and chromosphere (C-model of VAL) is developed. Numerical results and graphs are calculated for magnetic fields of 10-2T and 10-4T using new values of the proton-hydrogen scattering cross-section. In addition, the graph of conductivities in the solenoid magnetic field model is presented. A table of the Braginski coefficients calculated from VAL is also presented. Title: Radio observations of the solar neutron flare of 3 June, 1982 Authors: Karlicky, M.; Aurass, H.; Mann, G. Bibcode: 1986SoPh..104..165K Altcode: In this paper the solar neutron and white-light flare is studied on the basis of radioastronomical observations. It is shown that the 3 June, 1982 flare had an impulsive character. A strong shock wave (MA ≥ 2.9) was observed unusually soon after the impulsive phase of the flare. The radio spectrum of this event shows that the primary acceleration process probably occurred in the region with an electron density of ne = 4.4 × 1015 m−3. The pulsations of the type IV radio burst, observed 15 min after the mass ejection process, manifest the reconnection process in the post-flare stage. Title: Plasma diagnosis by means of fiber bursts Authors: Aurass, H.; Kurts, J.; Mann, G.; Chernov, G. P.; Karlický, M. Bibcode: 1986CoSka..15..327A Altcode: During the type IV solar radio burst on August 19, 1981 a lot of fiber bursts were observed. One of them is used for plasma diagnostic in the source volume. The great frequency extension of the considered fiber burst allows to estimate the height dependence of the plasma parameters. Title: Neutron increase at Lomnický štít, (June 3 1982) and character of source flare Authors: Křivský, L.; Karlický, M.; Kudela, K. Bibcode: 1986CoSka..15..161K Altcode: No abstract at ADS Title: The role of narrowband dm-spikes in solar flares. Authors: Karlicky, Marian Bibcode: 1986NASCP2449..155K Altcode: 1986rfsf.nasa..155K The main observational characteristics of narrowband dm-spikes are summarized. Since the spikes are observed in typical sequences of radio bursts, a global model of these bursts is presented. The intensity of the magnetic field in the spike source region, which is of principal importance, is discussed. Title: White-light flare of 26 July 1981. Authors: Gesztelyi, L.; Karlicky, M.; Farnik, F.; Gerlei, O.; Valnicek, B. Bibcode: 1986lasf.conf..163G Altcode: 1986lasf.symp..163G Making use of series of white light heliograms the authors studied the development of a flare-active sunspot group in Hale region 17760, where a white-light flare (WLF) was observed on 26 July 1981. The WLF appeared in a disintegrating delta-configuration, where rapid motion of newly emerged spots and of separating fragments of older umbrae was shearing and distorting the magnetic field. On the basis of optical, X-ray and radio observations the authors analysed the WLF event. Some observational indications exist supporting the hypothesis that the WLF knots are situated in the places of concentrated electric current which electrically couples sub-photospheric, photospheric and higher layers. Provided this is true the WL emission has been interpreted as the response of deep layers of the solar atmosphere to the dissipation-spreading process propagating along the electric current system. Intensity of the WLF knots relatively to the photosphere has been deduced and the power emitted between 545 and 555 nm estimated. The total energy emitted by the WLF knots is roughly estimated. Title: Narrowband dm-Spikes, Intermediate Drift Bursts and Pulsations in the Solar Flare of August 19, 1981 Authors: Karlicky, M. Bibcode: 1986BAICz..37....1K Altcode: In the initial phase (12.51-12.53 UT) of the flare of August 19, 1981, an interesting group of narrowband dm-spikes, intermediate drift bursts and pulsations was observed. This paper tries to explain this group of bursts by an uniform model. It is shown that all these bursts have connections with acceleration and trapping of superthermal electrons in the flare loop. The parameters of the flare loop and the electric field in the acceleration process were estimated. The same 'period' of intermediate drift bursts and pulsations has been explained. In the following time, the flare loop under study explodes and a shock wave (type II radio burst) is generated at the relatively high altitude of about 100,000 km above the photosphere. This process was connected with the radio flux decrease on 10 cm. Title: Analysis of the Flare of May 16th, 1981 with a Complex Space-Time Structure Using Optical, X-Ray Data and Radio Observations Authors: Ishkov, V. N.; Markeev, A. K.; Fomichev, V. V.; Chernov, G. P.; Chertok, I. M.; Likin, O. B.; Pisarenko, N. F.; Karlický, M.; Tlamicha, A.; Fárník, F.; Valniček, B.; Kalman, B. Bibcode: 1985BAICz..36...81I Altcode: A comprehensive analysis of the flare event of May 16, 1981 was carried out using burst records, heliograms, and dynamic spectra of radio emission in the frequency band 1000-45 MHz. Observations of X-ray emission obtained from the Prognoz-8 satellite were also used in the analysis. Attention is given to the location and dynamic characteristics of the H-alpha knots accompanied by a complicated multicomponent time profile and a strongly varying spectrum of X-ray and microwave bursts. A substantial change in the frequency spectrum of the microwave emission was observed during the development of the flare, with the maximum shifting towards the short-wave part of the cm band when H-alpha emission approached the sunspots. In the pre-maximum phase of the flare, sharp changes in the rate of increase of soft X-rays were correlated with the brightening of existing and upsurging new knots of H-alpha emission. The radio spectra for different frequency bands are reproduced in photographic form. Title: Narrowband DM Spikes as Indication of Flare Mass Ejection Authors: Karlicky, M. Bibcode: 1984SoPh...92..329K Altcode: The paper presents the radio spectra of seven solar flares (May 16, 1981; August 19, 1981; January 31, 1982; February 1, 1982; June 3, 1982; June 7, 1982; and July 12, 1982), whose common feature is the presence of narrowband dm-spikes. A close relationship was found among dm-spikes, dm-pulsations and type II radio bursts. Moreover, all flares under study showed indications of a mass ejection process. Based both on these facts and on the theory of dm-spikes (Kuijpers et al., 1981), our observations can be explained by runaway processes in several small regions within the ejected and tearing magnetic structure of the flare. Title: On a model of relationship between type I and type III bursts activity. Authors: Karlicky, M. Bibcode: 1984ost1.conf..149K Altcode: No abstract at ADS Title: Flare of March 28, 1980 and its Coronal Radio and Transient Effects Authors: Krivsky, L.; Karlicky, M.; Tlamicha, A.; Ruzdjak, V.; Urbarez, H. Bibcode: 1984sii..conf..217K Altcode: No abstract at ADS Title: X-ray, Hα, and radio observations of the two-ribbon flare of 16 May, 1981 Authors: Fárník, F.; Kaastra, J.; Kálmán, B.; Karlický, M.; Slottje, C.; Valniček, B. Bibcode: 1983SoPh...89..355F Altcode: The paper is a contribution to the study of two-ribbon flares. A variety of observational material, i.e. Hα pictures, radio spectrum in the frequency band of 150-1000 MHz, radio map at 6 cm, fluxes at other frequencies, magnetograms and X-ray flux in a broad energy interval, enabled us to study the development of the 16 May, 1981 flare. The onset of the flare could be described by the model of Van Tend and Kuperus. A diminishing of the magnetic shear during the activation of the filament was observed. From radio and X-ray data it was found that pulsed acceleration took place in the region under the rising filament, the electrons propagating in a limited region both upwards to greater heights and downwards into the footpoints. Internal oscillations of the filament were observed. A manifestation of the primary process of interplanetary shock-wave generation was found. The 6 cm radio sources could be localized in the footpoints of magnetic loops. Title: Book-Review - Solar Magnetohydrodynamics Authors: Priest, E. R.; Karlicky, M. Bibcode: 1983BAICz..34..378P Altcode: No abstract at ADS Title: Radio Spectrum and Model of White-Light Flare of July 4, 1974 Authors: Karlicky, M. Bibcode: 1983BAICz..34..355K Altcode: The paper suggests a model of the white-light flare of July 4, 1974 which satisfies both the theoretical considerations and the actual observations. The observed radio spectrum is interpreted as an eruptive process that started at heights of more than 50000 km above the photosphere and was activated by an electron beam. The radio spectrum further shows that the activation is followed by a dissipation-spreading process (Heyvaerts, 1981) propagating through an electric current system towards the photosphere, to the place of the emission in continuum. In conclusion the radio spectrum of the white-light flare (1353 UT, July 4, 1974) is compared with the radio spectrum of its "homologous" flare (0647 UT, July 4, 1974). Title: Magnetic Field Potential Approximation and Penumbral Fine Structure before the White-Light Flare of July 4, 1974 Authors: Karlicky, M.; Suda, J. Bibcode: 1983BAICz..34..282K Altcode: A comparison is made of the horizontal solar magnetic field component distribution calculated at the photosphere, with the penumbral fine structure of the large active group in the McMath active region 13 043 before the white-light flare of July 4, 1974. The magnetic field is calculated as a potential approximation taking into account the shape of individual spots in the group. Good agreement was found for the peripheral portions of the flare activity regions, although strong deviations were found in and near the location of white-light flare. The discrepancies in the flare location support the conclusion that the magnetic field structure in these regions before the white-light flare have a non-potential component: that electric currents are present even at the photospheric level. The disappearance of the discrepancies implies that the direction of the penumbral fibrils after the flare corresponds more to that of the potential magnetic field approximation. Title: Book-Review - Classics in Radio Astronomy Authors: Sullivan, W. T., III; Karlicky, M. Bibcode: 1983BAICz..34..253S Altcode: No abstract at ADS Title: Method of Estimating Langmuir's Turbulence in a Solar Flare Authors: Karlicky, M. Bibcode: 1983BAICz..34..100K Altcode: In principle, the theory of X hard and microwave solar bursts makes it possible to determine the development of the 'mean' distribution function of hot or superthermal electrons during the impulse phase of a flare. On the basis of this development of the distribution function of electrons, the method described in this paper can be used to determine the parameters of Langmuir's turbulence, assumed to exist in a solar flare. Title: Evolutionary Electron Beam and MHD Two Stream Instability in Solar Radio Burst Models Authors: Karlicky, M.; Krlin, L. Bibcode: 1983BAICz..34...18K Altcode: This paper represents a contribution to the theory of type III and IIIb solar radio bursts. It tries to clarify the role of the MHD two stream instability in the case of the evolutionary electron beam. It is shown that, in this case, the generation of the MHD two stream instability depends on strong depression of quasilinear relaxation (caused by a bump-on-tail instability). The results of this paper are compared with the ideas used in Smith's and de la Noë's (1976) model of type IIIb burst. Title: Drifting chains of type I radio bursts in the early stage of the two-ribbon flare of May 16, 1981. Authors: Karlický, M.; Jiřička, K. Bibcode: 1983ITABO..57...81K Altcode: In the early stage of the two-ribbon flare of May 16, 1981, a close relation between drifting chains of type I radio bursts and an activated rising filament was found. The generation of a weak shock wave is very probable in this phase of the flare, i.e. the model of type I radio bursts by Spicer et al. (1981) is in good agreement with the observations. Title: Peculiarities of the development of flare on May 16, 1981 as observedin optical, X-rays and radio waves. Authors: Ishkov, V. N.; Markeev, A. K.; Fomichev, V. V.; Chernov, G. P.; Chertok, I. M.; Likin, O. B.; Pisarenko, N. F.; Valníček, V.; Karlický, M.; Tlamicha, A.; Fárník, F.; Kálmán, B. Bibcode: 1983PDHO....5..193I Altcode: 1984PDHO....5..193I On the basis of X-ray, visual and radio observations of the large flare of 16 May 1981 the conclusion may be drawn that a large flare is a long duration energy release process, and it can be interpreted as a sum of smaller flares throughout the active region. Title: On the Relationship between the Chromospheric Flares and Type I Noise Storm Authors: Karlicky, M.; Kotrc, P.; Urbarz, H. Bibcode: 1982BAICz..33..331K Altcode: No abstract at ADS Title: Radio Observation of Sudden Shock Wave Deceleration above Solar Flare Authors: Karlicky, M.; Jiricka, K.; Kepka, O.; Krivsky, L.; Tlamicha, A. Bibcode: 1982BAICz..33...72K Altcode: Sudden changes in frequency drift accompanied by broadening of the frequency spectra and herringbone structure were observed in the initial phase in three different cases of type II burst observations. The phenomenon is interpreted as a sudden shock wave deceleration, which is found to be the limiting factor for the existence of fast shock waves under coronal conditions, and which may be connected with the second phase of acceleration in the flare. Type II bursts with a frequency ratio of about 1.5 and occasionally with a herringbone structure, correspond to shock waves in turbulent states, while the laminar stage corresponds to a narrow-band type II burst. Title: Drifting chains of Type I radio bursts in the early stage of the Two Ribbon Flare of May 16, 1981 Authors: Karlicky, M.; JiřiČka, K. Bibcode: 1982nsco.work...81K Altcode: No abstract at ADS Title: Five decades of radio astronomy. Authors: Grygar, J.; Karlický, M. Bibcode: 1982Rise...63...45G Altcode: No abstract at ADS Title: Type-Iii Bursts and Coronal Temperature Authors: Karlicky, M. Bibcode: 1981SoPh...71..381K Altcode: Numerical solution of the interaction of evolutionary electron beam with coronal plasma shows that the velocity of packet of the generated Langmuir's waves increases with the increase of coronal temperature. This effect can be manifested by a dependence of the drift of type III bursts on the coronal temperature. Title: Periodic Fluctuations in the Solar Millimeter Wave Burst Associated with the Solar Flare on 1978SEP22 Authors: Urpo, S.; Tiuri, M.; Tlamicha, A.; Pracka, M.; Karlicky, M. Bibcode: 1981A&A....93..121U Altcode: On September 22, 1978 the Sun was mapped at a wavelength of 8 mm (37 GHz) at the Radio Research Station of the Helsinki University of Technology in Finland. Enhanced radiation was found in the active region McMath 15,551. This region was monitored and the time variation of the radio flux was measured. During the observation a radio burst occurred between 11 56 and 13 06 UT. It corresponded in time to a flare observed in this region at N30 E49. The brightness temperature of the burst was 7900±800 K. The spectrum analysis of the burst indicates that there were pulsations with periodicities of 2.1 to 2.4s. Compatible periodicities were also found from the sequence of type III radio bursts which accompanied this flare. It is proposed that the observed burst was caused by quasi-periodically accelerated electron beams. Title: Estimate of the Spectrum of Langmuir's Turbulence in a Solar Flare from the X-emission Spectrum Authors: Karlicky, M.; Farnik, F. Bibcode: 1980BAICz..31..111K Altcode: With regard to estimating the spectrum and level of Langmuir's turbulence in the region of a solar flare, the X-spectra of the flare of October 12, 1977 is considered. Using Brown's (1971) model, the distribution function of fast electrons has been determined from three X-emission spectra derived at consecutive (10-second interval) times. The monotonic increase of the distribution function of electrons entering the X-emission area indicates that the electrons are continuously accelerated in the region of the flare. The acceleration is analyzed in the case where the effect of collision processes was neglected, and for the case of a strong effect of the collision processes. For the latter case, a model is outlined in which the required distribution functions are accelerated by Langmuir's turbulence in the acceleration region with a filamentary structure. Title: The Acceleration of the Electrons with Distribution Function ƒ ~(v_{0)/v)^δ by Langmuir's Flare Turbulence Authors: Karlicky, M. Bibcode: 1980BAICz..31..182K Altcode: The process of acceleration of an evolutionary electron beam by Langmuir's flare turbulence is studied in two ways. By means of the diffusion equation in velocity space, Langmuir's turbulence (LT) is described by the spectrum of a strong LT, and secondly, using the Fokker-Planck equation, the LT is described by a soliton gas. In addition, the time in which the original Maxwell distribution function is accelerated to a distribution function is estimated with the aid of a computed spectrum and of the soliton gas under the conditions of the acceleration space. It is suggested that the acceleration space has a filamentary structure, oriented in the direction of the magnetic field and vertically. Title: Analysis and Interpretation of the Quasiperiodical Structure of a Type IV Burst Authors: Pracka, M.; Karlicky, M. Bibcode: 1979BAICz..30..257P Altcode: This paper deals with the analysis of the type IV radio burst (with a quasiperiodical structure), observed in the 270 to 470 MHz frequency range with the radio spectrograph of the Ondrejov Observatory on July 3, 1974. The burst probably originated in the complicated magnetic structure of active region McMath 13043 following a proton flare. The method of spectral analysis and signal filtering was used to process the event. The results were discussed from the point of view of statistical likelihood. The observed periods of intensity modulation of the burst are interpreted in the considered model as the periods of generation and acceleration of electron beams in an X-type magnetic configuration, as periods in electron beam injections into the coronal plasma taking into account the finite velocities of propagation of electromagnetic radiations. Title: On the Determination of the Solar Coronal Magnetic Field by Using Type II Burst Observations and Theories Authors: Karlicky, M.; Tlamicha, A. Bibcode: 1979BAICz..30..246K Altcode: No abstract at ADS Title: Collision of Two Shock Waves as a Hypothetical Mechanism of Producing Drifting Radio Bursts in the 400-500 MHz Range Authors: Karlicky, M. Bibcode: 1978BAICz..29..313K Altcode: After the proton flare of July 3, 1974 a hitherto unclassified phenomenon with a diffusion 'banner' and with a considerably decelerating drift within the type II and III burst drifts range was observed in the radio dynamic spectrum between 410 and 470 MHz. The hypothesis is presented that the phenomenon is due to the collision of two shock waves, propagating against one another, during which the flux of electromagnetic radiation is considerably enhanced relative to the sum of the fluxes of the electromagnetic radiation of the individual shock waves. The Newkirk 4-density model of the corona is used to describe the phenomenon, the mechanism of plasmon-plasmon conversion in electromagnetic radiation with a double plasma frequency is considered and, according to the parameters derived from the dynamic spectrum, the velocities, radii of curvature and direction of propagation of the anticipated shock waves are analyzed in a simplified symmetric case. Title: Type III Radio Bursts in a Flaming Structure Authors: Karlicky, M.; Tlamicha, A. Bibcode: 1977BAICz..28..117K Altcode: This paper interprets the burst of July 3, 1974. The slowly drifting fine structure in this type III burst is evidence of the existence of very fast processes in large volumes of the corona. The concept of a rapidly varying magnetohydrodynamically unstable 'blazing' magnetic-field structure is developed. Based on this model, the magnetic-field intensity at specific heights is computed for two times separated by 1.4 sec. Title: Statistical Study of the Time Sequence of CA II Flocculae and Series of Radio Fluxes During Solar Activity Cycle 20 Authors: Karlicky, M. Bibcode: 1977BAICz..28..200K Altcode: Eleven one-year time series and an eleven-year time series of the Ca II plage index and radio fluxes detected at frequencies of 600, 606, 1000, 2000, 2800, 3750, and 9400 MHz are analyzed statistically for the interval from 1964 to 1974 (roughly the period of solar activity cycle 20). Power spectra, cross spectra, autocorrelation curves, and cross correlations are computed for each one-year series, and 'mean' spectra (integrated over 11 years) are obtained and compared with the spectra for each individual year. Slowly varying components of the radio fluxes are examined, and an attempt is made to relate the development of the statistical characteristics of cycle 20 to large-scale manifestations of their development, shifts in active-region longitudes, and maxima as well as minima of solar activity. It is found that the closest statistical relation exists between the Ca II and 1000-MHz series and that solar cycle 20 can be divided into two phases with respect to the cross correlations. The results also indicate that lower-frequency radio sources tend to have longer lifetimes than higher-frequency sources and that the average synodic rotation period of coronal layers increases with height above the photosphere. Title: The Velocities of Type II Solar Radio Bursts Authors: Tlamicha, A.; Karlicky, M. Bibcode: 1976BAICz..27....6T Altcode: This paper is a summary of type II radio bursts identified at Ondrejov between January 1973 and December 1974 in the frequency range of the dynamic spectrum 70-810 MHz. The velocities of shock waves in the individual cases of the type II bursts are given using the fourfold Newkirk model. Some questions associated with type II radio bursts and with the propagation of the shock wave into interplanetary space and into the region of the earth are also discussed. Title: The Trajectories of U-type Solar Radio Bursts Authors: Karlicky, M.; Tlamicha, A. Bibcode: 1976BAICz..27..223K Altcode: This paper presents the computation of the trajectory of the U-type solar radio burst observed on October 18, 1974. It also presents the correction of this trajectory with respect to the finite velocity of radio-wave propagation. An attempt is made at comparing the trajectory arcs of the disturbance with the angular dimensions of a sunspot group. In the special case where the sunspot group is located at the solar limb, the comparison of the size of the corrected trajectory arcs with the size of the sunspot group enables trajectories to be selected by means of the elimination method, to determine the preference of the trajectory for a certain direction and orientation relative to the observer and, thus, to determine the possible actual trajectory.