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Quasi-periodic processes in the flare loop generated by sudden temperature enhancements at loop footpoints  

Marian Karlický   Submitted: 2016-11-18 01:17

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. 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. 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.

Authors: Karlický, M., Jelinek, P.
Projects: None

Publication Status: Published in A&A, 2016, 590, A4
Last Modified: 2016-11-21 12:34
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Flares on A-type Stars: Evidence for Heating of Solar Corona by Nanoflares?  

Marian Karlický   Submitted: 2016-11-14 02:42

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.

Authors: Švanda, M., Karlický, M.
Projects: None

Publication Status: Published in ApJ 831, 9S (2016)
Last Modified: 2016-11-16 12:17
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Oscillation Maps in the Broadband Radio Spectrum of the 1 August 2010 Event  

Marian Karlický   Submitted: 2016-11-14 00:35

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 the periods of 181, 69, and 40 seconds were detected in UV observations. Using the wavelet technique we construct a new type of map of oscillations for selected periods in the whole domain of the radio spectrum. While the oscillation with the period of 181 seconds was recognized in the whole 25-2000 MHz radio spectrum, oscillations with periods of 69 and 40 seconds were confirmed only 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, the oscillation with the 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, in the 2000-500 MHz frequency range the phase of the 181-second oscillation drifts towards lower frequencies. On the other hand, at frequencies 25-500 MHz we found that the phase is nearly synchronous. 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 upwards through the solar corona and generate the 25-500 MHz radio emission with the 181-second period. Due to high beam velocity (~c/3, where c is the light speed) the 25-500 MHz radio emission, corresponding to a large interval of heights in the solar corona, is nearly synchronous.

Authors: Karlický, M., Rybak, J.
Projects: None

Publication Status: Solar Physics (accepted)
Last Modified: 2016-11-16 12:17
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Thermal fronts in solar flares  

Marian Karlický   Submitted: 2015-12-07 06:50

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.

Authors: Karlický, M.
Projects: None

Publication Status: ApJ 814, id. 153, 7 pp. (2015)
Last Modified: 2015-12-08 12:11
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Fragmentation of electric currents in the solar corona by plasma flows  

Marian Karlický   Submitted: 2013-10-03 23:37

Aims: We consider a magnetic configuration consisting of an arcade structure and a detached plasmoid, resulting from a magnetic reconnection process, as is typically found in connection with solar flares. We study spontaneous current fragmentation caused by shear and vortex plasma flows. Methods: An exact analytical transformation method was applied to calculate self-consistent solutions of the nonlinear stationary magnetohydrodynamic equations. The assumption of incompressible field-aligned flows implies that both the Alfvén Mach number and the mass density are constant on field lines. We first calculated nonlinear magnetohydrostatic equilibria with the help of the Liouville method, emulating the scenario of a solar eruptive flare configuration with plasmoids (magnetic ropes or current-carrying loops in 3D) and flare arcade. Then a Mach number profile was constructed that describes the upflow along the open magnetic field lines and implements a vortex flow inside the plasmoid. This Mach number profile was used to map the magnetohydrostatic equilibrium to the stationary one. Results: We find that current fragmentation takes place at different locations within our configuration. Steep gradients of the Alfvén Mach number are required, implying the strong influence of shear flows on current amplification and filamentation of the magnetohydrostatic current sheets. Crescent- or ring-like structures appear along the outer separatrix, butterfly structures between the upper and lower plasmoids, and strong current peaks close the lower boundary (photosphere). Furthermore, impressing an intrinsic small-scale structure on the upper plasmoid results in strong fragmentation of the plasmoid. Hence fragmentation of current sheets and plasmoids is an inherent property of magnetohydrodynamic theory. Conclusions: Transformations from magnetohydrostatic into magnetohydrodynamic steady-states deliver fine-structures needed for plasma heating and acceleration of particles and bulk plasma flows in dissipative events that are typically connected to magnetic reconnection processes in flares and coronal mass ejections.

Authors: Nickeler, D. H., Karlický, M., Wiegelmann, T., Kraus, M.
Projects: None

Publication Status: Published in Astronomy & Astrophysics, Volume 556, id.A61, 12 pp.
Last Modified: 2013-10-05 20:19
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Flare line impact polarization. Na D2 589 nm line polarization in the 2001 June 15 flare  

Marian Karlický   Submitted: 2013-10-03 23:32

Context. The impact polarization of optical chromospheric lines in solar flares is still being debated. For this reason, additional observations and improved flare atmosphere models are needed still. Aims: The polarization-free telescope THEMIS used in multiline 2 MulTiRaies (MTR) mode allows accurate simultaneous linear polarization measurements in various spectral lines. Methods: In the 2001 June 15 flare, Hα, Hβ, and Mg D2 lines linear impact polarization was reported as present in THEMIS 2 MTR observations. In this paper, THEMIS data analysis was extended to the Na D2 line. Sets of I ? U and I ? Q flare Stokes S 2D-spectra were corrected from dark-current, spectral-line curvature and from transmission differences. Then, we derived the linear polarization degree P and polarization orientation angle α 2D-spectra. No change in relative positioning could be found that would reduce the Stokes parameters U and Q values. No V and I crosstalks could explain our results either. Results: The Na D2 line is linearly polarized with a polarization degree exceeding 5% at some locations. The polarization was found to be radial at outer ribbons edges, and tangential at their inner edges. This orientation change may be due to differences in electron distribution functions on the opposite borders of flare chromospheric ribbons. Electron beams propagating along magnetic field lines, together with return currents, could explain both radial and tangential polarization. At the inner ribbon edges, intensity profile-width enlargements and blueshifts in polarization profiles are observed. This suggests chromospheric evaporation.

Authors: Henoux, J.C., Karlický, M.
Projects: None

Publication Status: Published in Astronomy & Astrophysics, Volume 556, id.A95, 8 pp
Last Modified: 2013-10-05 20:19
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Radio continua modulated by waves: Zebra patterns in solar and pulsar radio spectra?  

Marian Karlický   Submitted: 2013-04-09 02:03

We aim to answer the question how waves with plasma density variations affect the radio continua generated by the plasma emission mechanism. 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. 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.

Authors: M. Karlický
Projects: None

Publication Status: published in Astronomy & Astrophysics, Volume 552, id.A90, 6 pp
Last Modified: 2013-04-09 16:47
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Fragmentation during merging of plasmoids in the magnetic field reconnection  

Marian Karlický   Submitted: 2012-05-09 06:33

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. 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. A 2.5-D electromagnetic Particle-In-Cell model is used and its results analysed. 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 beta parameter during these processes. Thus, sheared high-beta plasma flows produce this additional fragmentation. 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.

Authors: M. Karlický, M. Barta, D. Nickeler
Projects: None

Publication Status: published in Astronomy & Astrophysics, Volume 541, id.A86
Last Modified: 2012-05-09 12:08
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THE n-DISTRIBUTION OF ELECTRONS AND DOUBLE LAYERS IN THE ELECTRON BEAM-RETURN SYSTEM OF SOLAR FLARES  

Marian Karlický   Submitted: 2012-04-16 07:01

We investigate processes in the electron beam-return current system in the impulsive phase of solar flares. We want to answer a question about a 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 3-D 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 to that of the n-distribution. Thus, a detection of the n-distributions, where a form of the high-energy part of the distribution is the most important, can indicate a presence of strong double layers in solar flares. A similarity of 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, support this idea.

Authors: Marian Karlický
Projects: None

Publication Status: Published in ApJ 750...49K (2012)
Last Modified: 2012-04-16 09:50
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On the physical meaning of n-distributions in solar flares  

Marian Karlický   Submitted: 2011-12-29 00:28


Aims: We investigate the physical meaning of the n-distributions detected in solar flares.
Methods: We consider a Maxwellian velocity distribution with a velocity drift. This distribution is analytically integrated to obtain the energy distribution, and its stability is investigated numerically using a fully electromagnetic particle-in-cell code.
Results: It is shown that the derived moving Maxwellian energy distribution is very similar to the n-distribution, especially in their high-energy parts. Both these distributions are mutually fitted and a relation between their parameters found. Contrary to the n-distribution, the moving Maxwellian distribution has a simple physical meaning, e.g., the electron component of the return current in the beam-plasma system. However, for high drift velocities of such a component, the moving Maxwellian distribution is unstable. Therefore to keep the form of this distribution similar to the n-distribution, some stabilization processes are necessary. If so, then the high intensities of the Si xiid 5.56 Å and 5.82 Å satellite lines and their evolution in solar flares can be explained by moving Maxwellian distributions instead of the n-distributions. Thus, our previous results connected with the n-distributions can be understood in a new, physically profound way.

Authors: M. Karlický, E. Dzifcakova, J. Dudik
Projects:

Publication Status: publushed in 2012, A&A 537, id. A36
Last Modified: 2011-12-29 14:02
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Successive merging of plasmoids and fragmentation in a flare current sheet and their X-ray and radio signatures  

Marian Karlický   Submitted: 2011-05-18 23:47

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: Marian Karlický and Miroslav Barta
Projects: None

Publication Status: Published in 2011, ApJ 733: 107
Last Modified: 2011-05-19 07:29
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Radio spectra generated during coalescence processes of plasmoids in a flare current sheet  

Marian Karlický   Submitted: 2010-05-10 23:56

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. For numerical simulations, we used a 2.5-D particle-in-cell electromagnetic relativistic code. Numerical data we analyzed by the wavelet methods. 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.

Authors: M. Karlický, M. Barta, J. Rybak
Projects: None

Publication Status: Published in Astronomy and Astrophysics, Volume 514, id.A28 (2010)
Last Modified: 2010-05-11 07:11
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Cyclic magnetic field reconnection  

Marian Karlický   Submitted: 2009-01-28 00:46

Using a 2.5-D electromagnetic particle-in-cell model, we study the magnetic field reconnection around the rotating plasma embedded in the magnetic field. Considering a driving of the plasma rotation 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. It could also be considered in a heating of laboratory plasmas.

Authors: Marian Karlický
Projects:

Publication Status: Published in ApJ 692, L72-L75, 2009
Last Modified: 2009-01-28 13:30
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Electron beam-plasma interaction and return-current formation  

Marian Karlický   Submitted: 2009-01-28 00:37

Using a 3-D 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 into 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. On the other hand, in the models with a sufficiently strong magnetic field or those with shorter sizes of the numerical box (effectively the 1-D case), the Weibel instability was reduced, and the electron distribution function evolved mainly in the beam-propagation direction and the return-current was given by a shift of some bulk electrons and an extended tail.

Authors: Marian Karlický
Projects:

Publication Status: Published in ApJ 690, 189-197, 2009
Last Modified: 2009-01-28 13:30
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Particle-in-cell simulations of return current in solar flares  

Marian Karlický   Submitted: 2008-09-28 23:49

We numerically study a formation of the return current generated in solar flares. For simulations of the return current in the beam-plasma system, a 3-D particle-in-cell electromagnetic code is used. In conditions of solar flares with the electron beam fluxes of E_F = 9.1 x 109 - 4.55 x 1010 ergs s^-1 cm^-2, the beam-plasma interaction with the return current is studied. We found that the electron beam relaxes to the plateau distribution function as known from electrostatic simulations. Simultaneously, due to electromagnetic effects and the Buneman instability of the prescribed Maxwell-shifted return current, the electron distribution function evolves to a new stationary state with a new form of the return current. In this final state the return current is formed not only by electrons in the bulk of the electron distribution function, but also by electrons in the extended tail. We use the results of simulations to estimate the critical beam fluxes for the processes under study in the low corona, the transition region and the upper chromosphere.

Authors: Karlický, M., Nickeler, D.H., Barta, M.
Projects: None

Publication Status: published in A&A 486, 325-329 (2008)
Last Modified: 2008-09-29 11:14
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Subject will be restored when possible  

Marian Karlický   Submitted: 2008-02-18 07:36

We study an acceleration of electrons and positrons in the relativistic magnetic field reconnection using a 2.5-D particle-in-cell electromagnetic relativistic code. We consider the 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 the 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 the electron-proton plasma with the proton-electron mass ratio m_i/m_e = 16 is made.

Authors: Marian Karlický
Projects: RHESSI

Publication Status: Published in The Astrophysical Journal 674, 1211-1216, 2008
Last Modified: 2008-02-18 10:04
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Separation of Accelerated Electrons and Positrons in the Relativistic Reconnection  

Marian Karlický   Submitted: 2008-02-18 07:35

We study an acceleration of electrons and positrons in the relativistic magnetic field reconnection using a 2.5-D particle-in-cell electromagnetic relativistic code. We consider the 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 the 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 the electron-proton plasma with the proton-electron mass ratio m_i/m_e = 16 is made.

Authors: Marian Karlický
Projects: RHESSI

Publication Status: Published in The Astrophysical Journal 674, 1211-1216
Last Modified: 2008-02-18 07:35
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Drifting pulsating structures generated during tearing and coalescence processes in a flare current sheet  

Marian Karlický   Submitted: 2007-03-06 00:01

Aims: Based on particle-in-cell simulations, drifting pulsating structures are interpreted as the radio emission generated during tearing and coalescence processes in the current sheet of a flare. Methods: A 2.5-D 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 2-D Fourier transform. Results: It is found that electrons are accelerated most efficiently in the region near the x-point of the magnetic field structure in the phase at the end of tearing process and at the beginning of plasmoid coalescence. The most energetic electrons are distributed mainly along the x-lines of the magnetic field structure. During these processes, Langmuir waves are generated, along with the electromagnetic (radio) ones. It looks as these electromagnetic waves can be observed mainly on the second harmonics of the plasma frequencies corresponding to the plasma densities in the external parts of the plasmoids.

Authors: M. Karlický and M. Barta
Projects: None

Publication Status: Astronomy and Astrophysics 464, 735-740 (2007)
Last Modified: 2007-03-06 13:53
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Acceleration and heating processes in a collapsing magnetic trap  

Marian Karlický   Submitted: 2004-05-14 08:09

We study the acceleration processes in a collapsing magnetic trap formed in the cusp structure of the flare model, using a test-particle numerical method. Coulomb collisions and scattering are included. It was found that if the trap collapse is sufficiently fast and the energies of the injected electrons are sufficiently high, thus overcoming the collisional losses, electrons can be accelerated in this secondary acceleration process to very high energies depending on the initial magnetic trap ratio R = Bmax/Bmin. 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_e=1010 cm-3, show that the high-energy electrons are accumulated in the central part of the collapsing magnetic trap where their velocities are nearly perpendicular to the magnetic field. This effect gives us a new possibility to explain the formation of loop-top sources observed in hard X-ray and radio emission. A further interesting aspect is that these electrons later on escape from this collapsing trap because its trap ratio decreases to R ~ 1. The time evolution of the energy of the trapped electrons and their energy flux at the end points of the trap (footpoints) are computed for cases without and with collisions. The effect of collisions on the energy spectrum of the accelerated electrons is also shown. The X-ray spectra along the collapsing trap are evaluated. Finally, we suggest a test of this model considering radio waves in the decimetric frequency range.

Authors: Karlický, M., Kosugi, T.
Projects: None

Publication Status: Published in A&A 419, 1159-1168 (2004)
Last Modified: 2004-05-14 08:09
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Series of high-frequency slowly drifting structures mapping the flare magnetic reconnection  

Marian Karlický   Submitted: 2004-05-14 07:42

Rare series of the slowly drifting structures observed during two 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.

Authors: Karlický, M.
Projects: None

Publication Status: Published in A&A 417, 325-332
Last Modified: 2004-05-14 07:42
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Abstracts by Author
Quasi-periodic processes in the flare loop generated by sudden temperature enhancements at loop footpoints
Flares on A-type Stars: Evidence for Heating of Solar Corona by Nanoflares?
Oscillation Maps in the Broadband Radio Spectrum of the 1 August 2010 Event
Thermal fronts in solar flares
Fragmentation of electric currents in the solar corona by plasma flows
Flare line impact polarization. Na D2 589 nm line polarization in the 2001 June 15 flare
Radio continua modulated by waves: Zebra patterns in solar and pulsar radio spectra?
Fragmentation during merging of plasmoids in the magnetic field reconnection
THE n-DISTRIBUTION OF ELECTRONS AND DOUBLE LAYERS IN THE ELECTRON BEAM--RETURN SYSTEM OF SOLAR FLARES
On the physical meaning of n-distributions in solar flares
Successive merging of plasmoids and fragmentation in a flare current sheet and their X-ray and radio signatures
Radio spectra generated during coalescence processes of plasmoids in a flare current sheet
Cyclic magnetic field reconnection
Electron beam-plasma interaction and return-current formation
Particle-in-cell simulations of return current in solar flares
Subject will be restored when possible
Separation of Accelerated Electrons and Positrons in the Relativistic Reconnection
Drifting pulsating structures generated during tearing and coalescence processes in a flare current sheet
Acceleration and heating processes in a collapsing magnetic trap
Series of high-frequency slowly drifting structures mapping the flare magnetic reconnection
High-frequency slowly drifting structures in solar flares
Impact H-alpha line polarization and return current
The EIT coil-like structure in the March 20, 2000 eruptive prominence
Impact H-alpha line polarization and return current
Radio bursts with rapid frequency variations - lace bursts

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