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<SUP>∘</SUP>. The highest growth rates for
  these loss-cone angles are obtained for velocity v<SUB>κ</SUB>=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<SUP>∘</SUP>) 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. <BR /> Aims: We simulated two zebras
  to verify their double-plasma resonance (DPR) model. <BR /> 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. <BR /> 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 × 10<SUP>9</SUP>
  cm<SUP>−3</SUP>, 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 P<SUB>n</SUB>=2.01 ±0.03
  (in numbers of zebra stripes) and as P<SUB>f</SUB>=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<SUP>−1</SUP>. 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 ×10<SUP>8</SUP> cm<SUP>−1</SUP>
  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. <BR /> Aims: We analyze
  seven zebra events in order to search for spatial variations in the
  plasma density and magnetic field in zebra-stripe sources. <BR />
  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. <BR /> 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<SUP>-1</SUP>. 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<SUP>-1</SUP>. 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 =L<SUB>bh</SUB>/L<SUB>nh</SUB> (L<SUB>bh</SUB> and
  L<SUB>nh</SUB> 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 (&gt;
  ≈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. <BR
  /> 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. <BR />
  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 = L<SUB>b</SUB>/L<SUB>n</SUB> (L<SUB>n</SUB> and L<SUB>b</SUB>
  are the density and magnetic field scales) is constant in the whole
  zebra source. <BR /> 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) × 10<SUP>10</SUP>
  cm<SUP>-3</SUP> 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|<SUB>t</SUB> = 0.0112-0.0149 and |ΔB/B|<SUB>t</SUB>
  = 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|<SUB>s</SUB> = 0.0047
  and |ΔB/B|<SUB>s</SUB> = 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:
  <BR /> Aims: We study the transverse oscillations of a double-structured
  solar filament. <BR /> 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. <BR
  /> 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. <P />The movie associated to Fig. 3 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201936836/olm">https://www.aanda.org</A>

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<SUP>-1</SUP>,
  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 <SUB>⊥</SUB> 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 <SUB>⊥</SUB> 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:
  <BR /> 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. <BR /> 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. <BR /> 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. <BR />
  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. <BR /> Methods: We used analytical
  methods. <BR /> 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 θ<SUB>c</SUB>≈50<SUP>∘</SUP>. 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 p<SUB>κ</SUB> 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 p<SUB>m</SUB>
  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
  <SUB>1</SUB> 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 × 10<SUP>10</SUP>-16.03 × 10<SUP>10</SUP>
  cm<SUP>-3</SUP>, respectively. Finally, we found that with increasing
  the gyro-harmonic number s <SUB>1</SUB>, 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(k<SUB>z</SUB>)=[1.8 ,2.9 ] (where k<SUB>z</SUB> 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(k<SUB>z</SUB>)≈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:
  <BR /> 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. <BR />
  Methods: To compute the DPR surfaces, we used numerical and analytical
  methods. <BR /> 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 × 10<SUP>14</SUP> K, 6.58 × 10<SUP>13</SUP> K, and
  7.35 × 10<SUP>15</SUP> K, respectively. These brightness temperatures
  are much lower than those derived for the view along the loop axis
  (up to 10<SUP>17</SUP> 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:
  <BR /> 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. <BR /> 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. <BR
  /> 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<SUB>∥</SUB>/T<SUB>⊥</SUB> 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<SUB>∥</SUB>
  &gt; T<SUB>⊥</SUB>. 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 &gt; 1 than for
  those with p &lt; 1. Therefore, distributions with p &gt; 1 can be
  much more easily diagnosed than those with p &lt; 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−<SUP>1</SUP>. 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. <BR /> Aims: In the present paper we
  numerically study the double plasma resonance instability from the
  point of view of the zebra interpretation. <BR /> 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. <BR /> 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 ω<SUB>UH</SUB> and electron-cyclotron
  ω<SUB>ce</SUB> 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 ω<SUB>UH</SUB>/ω<SUB>ce</SUB> 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 ω<SUB>UH</SUB>/ω<SUB>ce</SUB> = 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<SUB>
  α </SUB> 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<SUP>-1</SUP>. The dark loop was visible
  in H<SUB> α </SUB> but disappeared afterward. Furthermore, we found
  that the falling blob interacted with the chromosphere as expressed
  by a sudden change of the H<SUB> α </SUB> 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 ×10<SUP>15</SUP> - 1.3 ×10<SUP>17</SUP>K, and for the lower
  value, it was 4.7 ×10<SUP>13</SUP> - 5.6 ×10<SUP>15</SUP>K. 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}<SUB>{{A</SUB>}}, where L is the size of the
  plasmoid and c <SUB>A</SUB> is the Alfvén speed in the lateral parts
  of the plasmoid. In our model, L/{c}<SUB>{{A</SUB>}} 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}<SUB>{{A</SUB>}}, but here L means the
  length of the loop and c <SUB>A</SUB> 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
  <BR /> 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. <BR />
  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. <BR /> 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:
  <BR /> 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. <BR />
  Methods: Characteristics and parameters of both these radio bursts
  are compared. <BR /> 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. <BR /> 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. <BR /> Methods:
  We numerically integrated the analysed model equations, using Python
  and Wolfram Mathematica. <BR /> 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
  ×10<SUP>4</SUP>K. 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:
  <BR /> 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. <BR /> Methods: We use analytical and numerical
  methods to compute distribution functions of electrons accelerated
  by a shock. <BR /> 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<SUP>-1</SUP> 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:
  <BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP> 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 (f<SUB>x</SUB>),
  the lifetime of each burst is anti-correlated to f<SUB>x</SUB>,
  while the frequency gap is independent of f<SUB>x</SUB>. 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}<SUP>10</SUP>{--}{10}<SUP>11</SUP> cm<SUP>-3</SUP> and
  the temperature is higher than 10<SUP>7</SUP> 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:
  <BR /> Aims: We present a new method for determining the magnetic field
  strength and plasma density in the solar zebra radio sources. <BR />
  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. <BR /> 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
  L<SUB>nb</SUB> = 2L<SUB>b</SUB>/ (2L<SUB>n</SUB> - L<SUB>b</SUB>), where
  L<SUB>n</SUB> and L<SUB>b</SUB> 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 &gt;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. <P />.

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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP>
  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<SUP>-1</SUP>. 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: DaÌ§browski, 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. <BR /> Aims: Within a physically simplified, but exact
  mathematical model, we study the electric currents and corresponding
  electric fields generated by shear flows. <BR /> 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. <BR /> 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<SUP>-1</SUP> 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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> Aims: Power spectra of the frequency variations
  of zebras are computed to estimate the spectra of the plasma density
  variations in radio zebra sources. <BR /> 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. <BR /> 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 ω<SUB>pe</SUB> is much higher than
  the electron-cyclotron frequency ω<SUB>ce</SUB>, 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. <BR
  /> Aims: The polarization-free telescope THEMIS used in multiline 2
  MulTiRaies (MTR) mode allows accurate simultaneous linear polarization
  measurements in various spectral lines. <BR /> 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. <BR /> 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. <P />Appendix A is available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

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
  <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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:
  <BR /> Aims: We aim to answer the question how waves with plasma density
  variations affect the radio continua generated by the plasma emission
  mechanism. <BR /> 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. <BR
  /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <BR
  /> 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
  <BR /> 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. <BR /> 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. <BR /> 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:
  <BR /> 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. <BR /> 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. <BR />
  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
  <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <BR />
  Methods: A 2.5-D electromagnetic particle-in-cell model is used and
  its results analysed. <BR /> 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. <BR
  /> 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:
  <BR /> 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. <BR /> 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. <BR /> 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. <P />Appendix A is available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

Title: On the physical meaning of n-distributions in solar flares
Authors: Karlický, M.; Dzifčáková, E.; Dudík, J.
Bibcode: 2012A&A...537A..36K
Altcode:
  <BR /> Aims: We investigate the physical meaning of the n-distributions
  detected in solar flares. <BR /> 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. <BR /> 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:
  <BR /> Aims: To obtain diagnostics tools for solar flare current sheets,
  we numerically studied impulsively generated magnetoacoustic waves
  in the Harris current sheet. <BR /> 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. <BR /> 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<SUP>-1</SUP> and 1608 MHz s<SUP>-1</SUP>,
  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 <SUB>1</SUB>≈ 0.5 s, FD<SUB>1</SUB>=-
  87 MHz s<SUP>-1</SUP> on average, ii) fiber structures with
  P <SUB>2</SUB>≈1.9 s, and iii) drifting structures with P
  <SUB>3</SUB>≈81.4 s, FD<SUB>2</SUB>=- 8.7, + 98.5, and - 21.8 MHz
  s<SUP>-1</SUP>. 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 <SUB>3</SUB>) and to the frequency drift of individual fibers for
  the short-period tadpoles (P <SUB>2</SUB>). 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<SUP>-1</SUP>, 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 P<SUB>1</SUB>≈ 0.5 s, FD<SUB>1</SUB>=−
  87 MHz s<SUP>−1</SUP> on average, ii) fiber structures
  with P<SUB>2</SUB>≈1.9 s, and iii) drifting structures with
  P<SUB>3</SUB>≈81.4 s, FD<SUB>2</SUB>=− 8.7, + 98.5, and − 21.8 MHz
  s<SUP>−1</SUP>. 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<SUB>3</SUB>) and to the frequency drift of individual fibers for
  the short-period tadpoles (P<SUB>2</SUB>). 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<SUP>−1</SUP>, 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: DaÌ§browski, 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<SUP>−1</SUP> and 1608 MHz s<SUP>−1</SUP>,
  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. <BR /> 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. <BR /> 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. <BR /> 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. <P />Appendix A is available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

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). <BR /> 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. <BR /> 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. <BR /> Results: Our
  analysis of H<SUB>α</SUB> 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. <BR /> 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. <BR /> 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. <BR
  /> 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. <BR /> 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. <BR
  /> 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:
  <BR /> 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. <BR /> 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. <BR /> Results: The global properties of the
  observations are most closely matched for heating functions scaling
  as B_0<SUP>0.7-0.8/L_0^{0.5</SUP>} 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. <BR /> 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-&gt;L'+S
    and L+L'-&gt;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'-&gt;T process. Analytical analysis of two subsequent processes
  L-&gt;L'+S a L+L'-&gt;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<SUP>-1</SUP>). 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 10<SUP>9</SUP>-10<SUP>10</SUP> cm<SUP>-3</SUP> 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:
  <BR /> 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. <BR /> 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. <BR /> 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. <BR /> Aims: We investigate the radiative losses due to the
  bound-bound transitions and bremsstrahlung for nonthermal κ- and
  n-distributions. <BR /> 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. <BR
  /> 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. <P />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 <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A103">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A103</A>

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
  n<SUB>e</SUB>=1016<SUP>m-3</SUP>. The n<SUB>e</SUB>*n<SUB>H</SUB>
  factor is not included in the calculations. <P />(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:
  <BR /> 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. <BR /> 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. <BR /> 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.; DaÌ§browski, 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 &gt;1000 km s<SUP>−1</SUP>. 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
  ν<SUB>n</SUB> is always greater than that for the magnetic field
  ν<SUB>B</SUB> and it is linearly dependent on the spectral index of the
  electrons δ as ν<SUB>n</SUB>≈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 ν<SUB>B</SUB>
  is found to be 0.36±0.04, which is very close to the value of
  ν<SUB>B</SUB>=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:
  <BR /> 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. <BR /> Methods: For numerical simulations, we used
  a 2.5-D particle-in-cell electromagnetic relativistic code. Numerical
  data were analyzed by the wavelet methods. <BR /> 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. <BR />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. <BR
  />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. <BR />Methods: Characteristic periods
  with the tadpole pattern were searched for in the radio flux time
  series by wavelet analysis methods. <BR />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<SUP>-1</SUP>. 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. <BR />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. <BR />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. <BR />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. <BR />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. <BR />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. <BR />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. <BR
  />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. <BR />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. <BR
  />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. <BR />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<SUP>−1</SUP>. 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. <BR />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. <BR
  />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. <BR />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. <BR />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 ⩽ 10<SUP>3</SUP> 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 &lt;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. <BR />Methods: For simulations of the return current
  in the beam-plasma system, a 3D particle-in-cell electromagnetic
  code is used. <BR />Results: In conditions of solar flares with the
  electron beam fluxes of E<SUB>F</SUB> = 9.1 × 10<SUP>9</SUP>-4.55 ×
  10<SUP>10</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>, 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. <BR
  />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. <BR />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<SUP>-1</SUP>, is greater
  than the number with positive frequency drift, which is on average
  +807 ± 675 MHz s<SUP>-1</SUP>. The type III bursts have power-law
  distribution function for their half-power duration H(f_start) = 4.79 ×
  10<SUP>8</SUP>~f_start<SUP>-2.145± 0.015</SUP>, bandwidth B_1(f_start)
  = 1.95 × 10^7~f_start<SUP>-1.697± 0.022</SUP> and B_2(f_start) = 7.07
  × 10^5~f_start<SUP>-1.154± 0.015</SUP>, and frequency drift D(f_start)
  = 0.43~f_start<SUP>1.040± 0.031</SUP>. 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<SUP>-1</SUP> and -46 ±
  42 MHz s<SUP>-1</SUP>, 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<SUP>-1</SUP>) in
  groups with visible group drift (~±50 MHz s<SUP>-1</SUP>) and b)
  less numerous broader band bursts (bandwidth 171 MHz) with higher
  frequency drift (~±1800 MHz s<SUP>-1</SUP>) 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 m<SUB>i</SUB>/m<SUB>e</SUB> = 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 v<SUB>D</SUB>/v_{T<SUB>e</SUB>}≥ 1
  (where v<SUB>D</SUB> and v_{T<SUB>e</SUB>} 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
  (η<SUB>anom</SUB>/η<SUB>C</SUB>∼7×10<SUP>5</SUP>, where
  η<SUB>C</SUB> 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&lt;v<SUB>i</SUB> 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. <BR />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. <BR />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. <BR />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. <BR />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 &gt; 60 s are rather
  rare. The periods &lt; 40 s occur more frequently at frequencies below
  2000 MHz than at frequencies above 2000 MHz. Occurrence of the periods
  &gt; 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°. <BR />Methods: A two-dimensional, electromagnetic,
  relativistic particle-in-cell (PIC) code is used. <BR />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. <BR />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. <BR />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<SUP>-1</SUP> 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. <BR />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 × 10<SUP>11</SUP> and 1 × 10<SUP>12</SUP>
  erg cm<SUP>-2</SUP> s<SUP>-1</SUP>. 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. <BR />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. <BR />Methods: We have imaged a high brightness
  temperature (∼ 10<SUP>9</SUP> 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 &amp;
  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. <BR
  />Results: We find that the power input to the nonthermal electrons
  is in the range 3× 10<SUP>25</SUP>-10<SUP>26</SUP> 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<SUP>-9</SUP> to 2.38 × 10<SUP>-8</SUP>.

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 R<SUB>solar</SUB> 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 R<SUB>solar</SUB> 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. <BR
  />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. <BR />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<SUP>−1</SUP>) 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.<BR /> 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.<BR /> 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.<BR />

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. <BR /><BR /> 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. <BR
  /><BR /> 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. <BR /><BR /> 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.<BR /> 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.<BR /> 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.<BR /> 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 10<SUP>3</SUP> km) and large-scale (a few
  10<SUP>5</SUP> 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) &lt;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 10<SUP>4</SUP> 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<SUP>−1</SUP>, whereas
  at 1 MK it amounts to 5 km s<SUP>−1</SUP>; (b) Shrinking becomes
  slower as the flare decays - ten hours after the impulsive phase,
  the shrinkage velocity at 5 MK becomes 5 km s<SUP>−1</SUP>; (c) The
  cooling rate decreases as the flare decays - in the 5 MK range it is
  1 MK min<SUP>−1</SUP> in the first hour of the loop-system growth,
  whereas ten hours later it decreases to 0.2 MK min<SUP>−1</SUP>;
  (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<SUP>−2</SUP> in the T &lt; 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 &lt; 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.<BR /> 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.<BR /> 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.<BR />

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.<BR /> 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.<BR /> 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.<BR />
  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<SUP>-1</SUP> in the RHESSI 10-15 keV energy band to 45 km
  s<SUP>-1</SUP> 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<SUP>-1</SUP>. 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 10<SUP>10</SUP>
  cm<SUP>-3</SUP>. 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) × 10<SUP>11</SUP>
  cm<SUP>-3</SUP>.<BR /> 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 <SUP>4</SUP> 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 (γ<SUB>1</SUB> = 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. <P />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 =B<SUB>max</SUB>/B<SUB>init</SUB>. The
  computations, made for R=10 and R=100 with isotropically injected 5-28.4
  keV electrons and a background plasma density of about n<SUB>e</SUB> =
  10<SUP>10</SUP> cm<SUP>-3</SUP>, 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 -&gt;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<SUP>-1</SUP>) 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<SUP>-1</SUP>). The X-ray source of the May
  17, 2002 was much softer (&lt;40 keV) than those in April 4, 2002 and
  August 30, 2002 (&gt;100 keV). Velocities of the X-ray sources in the
  image plane were estimated as 12 km s<SUP>-1</SUP> for April 4, 2002
  and 10 km s<SUP>-1</SUP> 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
  F<SUB>E</SUB> = 10<SUP>12</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>
  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 &lt;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
  &lt;3-10<SUP>deg</SUP>. 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 f<SUB>uh</SUB>=Nf<SUB>ce</SUB>, 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 (&lt;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 ( &lt; 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,
  ω<SUB>UH</SUB>=(ω<SUB>pe</SUB><SUP>2</SUP>+ω<SUB>Be</SUB><SUP>2</SUP>)<SUP>1/2</SUP>=s
  ω<SUB>Be</SUB> (ω<SUB>UH</SUB>, ω<SUB>pe</SUB>, and ω<SUB>Be</SUB>
  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
  ≍2×10<SUP>4</SUP> 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 (&gt;10<SUP>16</SUP> m<SUP>-3</SUP>), large
  source dimensions (&gt;10<SUP>15</SUP> m<SUP>2</SUP>), and very low
  temperatures (&lt;10<SUP>6</SUP> 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 (&lt;10<SUP>6</SUP>K) plasma necessary for the high mm-flux
  or the spectral slope would be always negative for ν &gt; 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/f<SUP>1.66±0.16</SUP> 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
  (~10<SUP>12</SUP>cm<SUP>-3</SUP>). 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<SUP>-1</SUP> in the first 15 minutes of the eruption and about
  of 66 km s<SUP>-1</SUP> 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)×10<SUP>10</SUP> cm<SUP>-3</SUP> and
  40-230 G, respectively. Assuming then the flare temperature as about of
  10<SUP>7</SUP>K, 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 (~10<SUP>12</SUP> cm<SUP>-3</SUP>)
  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 R<SUB>solar</SUB>. 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 R<SUB>solar</SUB> 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<SUP>-4</SUP> - 10<SUP>-3</SUP>T, the
  total electric current in the helical structure was estimated as J =
  4.8×(10<SUP>9</SUP> - 10<SUP>10</SUP>)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
  3.7×10<SUP>10</SUP> 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 90<SUP>deg</SUP> 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 10<SUP>12</SUP> and 4.8 x 10<SUP>12</SUP>
  ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>, 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 &lt; 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 1.6×10<SUP>32</SUP> 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<SUP>−1</SUP>), expansion (30-44 km s<SUP>−1</SUP>), axial
  (3-19 km s<SUP>−1</SUP>), and global (66-160 km s<SUP>−1</SUP>)
  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 &gt;=1 MeV nucleon<SUP>-1</SUP> 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
  &amp; 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
  R<SUB>solar</SUB>). 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<SUP>+</SUP>,e<SUP>-</SUP>) 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 =~ 0.02E<SUB>p0</SUB> result during the propagation of a neutral
  beam of initial proton energy E<SUB>p0</SUB>. 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&lt; 200 keV). However, we still must examine if low energy electrons
  (E&lt; 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
  1.2×10<SUP>12</SUP>A.

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<SUB>⊙</SUB> from sun
  center); the Nançay Decameter Array operating between 75 and 25 MHz
  (distance range about 1.4-2 R<SUB>⊙</SUB>) 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<SUB>⊙</SUB> 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<SUB>⊙</SUB>-2 R<SUB>⊙</SUB> 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 (&lt;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 10<SUP>9</SUP> erg
  cm<SUP>-2</SUP>/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 ≍
  10<SUP>4</SUP>K 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 (D<SUB>e</SUB>), 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 − D<SUB>e</SUB>) 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 P<SUB>g</SUB>
  reaches 1 dyn cm<SUP>−2</SUP> and should be clearly visible for
  P<SUB>g</SUB>≳ 3 dyn cm<SUP>−2</SUP>, independently of the
  loop diameter. This situation corresponds to the electron density
  of the order 10<SUP>12</SUP> cm<SUP>−3</SUP>. The contrast of
  flare-loops (in projection on the disc) at Hα line center is mainly
  the function of P<SUB>g</SUB>, 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<SUP>-2</SUP>T and 10<SUP>-4</SUP>T
  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 (M<SUB>A</SUB> ≥ 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 n<SUB>e</SUB> = 4.4 × 10<SUP>15</SUP>
  m<SUP>−3</SUP>. 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.

