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Development of Solar Flares and Features of the Fine Structure of Solar Radio Emission  

Gennady Chernov   Submitted: 2017-11-22 02:59

The reason for the occurrence of different elements of the fine structure of solar radio bursts in the decimeter and centimeter wavelength ranges has been determined based on all available data from terrestrial and satellite observations. In some phenomena, fast pulsations, a zebra structure, fiber bursts, and spikes have been observed almost simultaneously. Two phenomena have been selected to show that the pulsations of radio emission are caused by particles accelerated in the magnetic reconnection region and that the zebra structure is excited in a source, such as a magnetic trap for fast particles. The complex combination of unusual fiber bursts, zebra structure, and spikes in the phenomenon on December 1, 2004, is associated with a single source, a magnetic island formed after a coronal mass ejection.

Authors: G. P. Chernov, V. V. Fomichev, Y. Yan, B. Tan, Ch. Tan, and Q. Fu
Projects: None

Publication Status: Accepted in Geomagnetism and Aeronomy, 2017, N6
Last Modified: 2017-11-22 13:20
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Comparison of alternative zebra-structure models in solar radio emission  

Gennady Chernov   Submitted: 2017-04-11 01:50

Discussion about the nature of zebra-structure (ZS) in the type IV radio bursts continues, despite the ten proposed models. First of all, this is due to the wide variety of stripes in each new phenomenon, when the explanation of all the fine details by any one mechanism becomes impossible. The most widespread explanation is the emission at different levels of double plasma resonance (DPR), sequential on the height surfaces in the magnetic trap, where the upper hybrid frequency (ωUH) becomes equal to the integer of electronic cyclotron harmonics sωBe: ωUH = (ωPe^2 + ωBe^2)1/2 = sωBe (Zheleznyakov, Zlotnik, 1975; Winglee, Dulk, 1986; Kuznetsov & Tsap (2007) ). An important alternative mechanism is the interaction of plasma waves with the whistlers: l + w \Rightarrow t (Chernov, 1976; 2006). Here, we will show the possibility of explaining the main features of the zebra stripes in the model with whistlers, using the example of the phenomenon on August 1, 2010.

Authors: Chernov G.P., Fomichev V.V., Sych R.A.
Projects: None

Publication Status: Solar Radio Science CESRA Highlights. Oral report at the conference: XII Solar System Plasma Conference, February 6?10, 2017, Space Research Institute of RAS. arXiv:1704.02528
Last Modified: 2017-04-11 23:29
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Latest news on zebra pattern  

Gennady Chernov   Submitted: 2015-12-27 12:12

The publications of the last three years concerning the study of the most intriguing fine structure in type IV solar radio bursts ? zebra pattern (ZPs), are surveyed. The main attention is paid to new observations, irrespective of whether a paper includes detailed interpretation of an event or simply reports the beginning of operation of a new tool. The radiation mechanism of a ZP on a double plasma resonance (DPR) remains the most widespread and standard, though ten alternative mechanisms have been offered. However, in a number of works difficulties with the explanation of a complex zebra are noted, especially in combination with fiber bursts and spikes. Therefore, several papers in which description of the radiation mechanism of a ZP on the DPR is improved are considered in more detail. Without positional observations we have a great opportunity to follow the dynamics of flare processes using SDO/AIA images in several EUV lines. In the discussion, the debatable questions regarding the comparison of mechanisms associated with DPR in terms of the model of interaction of plasma waves with whistlers are illuminated.

Authors: Gennady Chernov
Projects:

Publication Status: Submitted to Solar Physics
Last Modified: 2016-03-15 11:26
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Last news on zebra pattern  

Gennady Chernov   Submitted: 2015-12-27 12:12

The publications of the last three years concerning to studying of the most intriguing fine structure in type IV solar radio bursts - zebra pattern (ZP), are surveyed. The main attention is paid to new observations, irrespective of whether a paper does include detailed interpretation of an event or simply reports about the beginning of operation of a new tool. The radiation mechanism of the ZP on a double plasma resonance (DPR) remains the most widespread and standard, though ten alternative mechanisms were offered. However, in a number of works difficulties with the explanation of a complex zebra are noted, especially in a combination with fiber bursts and spikes. Therefore, several papers in which the radiation mechanism of a zebra on the DPR is improved, are considered in more detail. Without positional observations we have a great opportunity to follow the dynamics of flare processes using SDO / AIA images in several EUV lines. In the discussion, the debatable questions with the comparison of mechanism on DPR with the model of interaction of plasma waves with whistlers are illuminated.

Authors: Gennady Chernov
Projects: None

Publication Status: Submitted to Solar Physics
Last Modified: 2015-12-30 12:41
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Flare processes evolution and polarization changes of fine structures of solar radio emission in the April 11, 2013 event  

Gennady Chernov   Submitted: 2015-09-25 12:30

The measurement of positions and sizes of radio sources in the observations of solar radio spectral fine structures in an M6.5 flare on April 11, 2013 were observed simultaneously by several radio instruments at four different observatories: Chinese Solar Broadband Radio Spectrometers 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 include microwave zebra patterns (ZP) fast pulsations, and fibers. 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 on board NASA's satellite Solar Dynamics Observatory (SDO) images. The flare occurred at 06:58 - 07:26 UT in solar active region NOAA 11719 located close to the solar disk center. ZP 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 impulsive phase, a strong narrowband ZP burst occurred with a moderate left-handed circular polarization. Then a series of pulsations and ZPs were observed almost in an unpolarized emission. After 07:00 UT a ZP appeared with a moderate right-handed polarization. In the flare decay phase (at about of 07:25 UT), ZP and fiber bursts become strongly righthand polarized. BMS/Irkutsk spectral observations indicated that the background emission showed left-handed circular polarization (similar to SBRS/Huairou spectra around 3 GHz in). 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 andmagnetic Imager (SDO/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.

Authors: Gennady Chernov, Robert Sych, Baolin Tan, Yihua Yan, Chengming Tan, Qijun Fu, Marian Karlický and Valery Fomichev
Projects: None

Publication Status: Accepted in RAA
Last Modified: 2015-09-26 14:56
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Dynamics of flare processes and variety of the fine structure of solar radio emission over a wide frequency range of 30 - 7000 MHz  

Gennady Chernov   Submitted: 2014-09-03 02:33

Radiobursts exibiting fine structure observe d over two years during the rising phase of Cycle 24 by the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou) in the range 1?7.6 GHz and the spectrograph IZMIRAN in the meter range (25 - 270 MHz) are analyzed. In five events zebra structure, various fiber bursts and fast pulsations were observed. These observations have great importance for testing different theoreti cal models of fine structure formation, as, for example, only for explaining the zebra-structure more than ten mechanisms have been proposed. Events on 15 and 24 February 2011 are of the greatest interest. In the course of the flare on 15 February (which occurred close to the center of disk) zebra structure was observed during three sequential flare brightenings. The polarization changed sign in the third. This behavior of polarization combined with images of the corresponding flare brightenings, obtained in extreme ultraviolet radiation by the Solar Dynamics Observatory (SDO/AIA, 171 Å) provides important clues. The polarization of radio emission in all three cases is related to the ordinary wave mode of radio emission. The zebra structure was present at frequencies 190-220 MHz in the Culgoora spectrum. The event on 24 February 2011 is remarkable , as the zebra structure at frequencies of 2.6- 3.8 GHz was not polarized and it appeared duri ng the magnetic reconnection observed by SDO/AIA 171 Å in this limb flare. In the event on 9 August 2011, for the first time, a superfine millisecond structure was registered simultaneously in the fast pulsations and the stripes of zebra structure. In the event on 1 August 2010 after the zebra structure two families of fibers bursts with an opposite frequency drift were observed. On 19 April 2012 the fibers against the background of type III bursts were observed by IZMIRAN and Nançay spectrographs. In the band of 42 ? 52 MHz a group of nine slowly drifting narrow-band (
Authors: Gennady Chernov , Valery Fomichev, Baolin Tan, Yihua Yan, Chengming Tan, Qijun Fu
Projects: None

Publication Status: Acepted in Solar Physics
Last Modified: 2014-09-03 13:11
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CONCERNING SPIKES IN EMISSION AND ABSORPTION IN MICROWAVE RANGE  

Gennady Chernov   Submitted: 2012-07-03 05:16

In some events weak fast solar bursts (near the quiet Sun level) were observed at the background of numerous spikes in emission and absorption. In such a case the background contains the noise signals of the receiver. In the events 16 September 2005 and 14 April 2002 the solar origin of fast busts was confirmed by simultaneous registration of the bursts in several remote observatories. The background noisy pixels in emission and absorption can be excluded by more high subtracted level of continuum during construction of spectra. The wavelet spectrum, noisy profiles in different polarization channels and the spectrum with greater subtracting zero level of the continuum prove a noisy character of shortest pixels in emission and absorption. Thus, in each case, in order to judge the solar origin of all spikes, it is necessary to determine the level of continuum against the background of which the solar bursts are observed. Several models of microwave spikes are discussed. The ECM emission mechanism runs into serious problems with the interpretation the microwave millisecond spikes: the main obstacles are too high values of the magnetic field strength in the source (w_Pe < w_Be). The probable mechanism is the interaction of plasma Langmuir waves with ion-sound waves (l+s ->t) in a source related with shock fronts in the reconnection region.

Authors: G.P.Chernov, R.A.Sych, G.L.Huang, H.S. Ji, Y.H.Yan, and C.M.Tan
Projects:

Publication Status: Accepted in Research in Astron. Astrophys. http://arxiv.org/submit/505638/process
Last Modified: 2012-07-04 04:29
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COMPLEX RADIO ZEBRA PATTERNS ESCAPING FROM THE SOLAR CORONA AND NEW GENERATION MECHANISMS  

Gennady Chernov   Submitted: 2012-06-28 06:09

Sources of solar radio bursts in meter/decimeter/microwave ranges are located in the solar corona. The study of the radio fine structure is a key to understanding of plasma processes in the solar corona. The most intriguing fine structure is the zebra pattern (ZP) in continuous type-IV radio bursts (the regular harmonics in emission and absorption). A disputable discussion about nature of the ZP in the type IV radio bursts continues more than 40 years. Only in the last 5 years about 10 works devoted to an improvement of the mechanism based on the double plasma resonance (DPR, when upper hybrid frequency is equal to an integer of the cyclotron frequency) were published, and 5 new models were proposed. The explanation to this is connected with the new observations of the uncommon forms of ZP, which it is difficult to interpret as the regular harmonics within the framework of known models. According to all works, which analyze mechanism based on the DPR, we must observe ZP in all continuous bursts. But observations suggest otherwise: ZP appears in the pulsation regime, and in not all bursts. Nevertheless, it is sometimes asserted that mechanism on DPR explains all basic properties of ZP, and it is indicated on the error of many authors in the calculations of the growth rates of plasma waves at the upper hybrid frequency: it is not possible to enlarge calculations for the regions adjacent with the hybrid band, since the dispersion relation - is correct only inside the hybrid band. However, the calculations, which show the significance of this erroneous approach should be conducted for the loss-cone distribution of fast particles in the relativistic approximation. Moreover, in a whole series of works it is noted that the contribution of the term, connected with the harmonic in the hybrid band, considerably exceeds contribution from those harmonics adjacent from above, especially for the slightly non-perpendicular propagation in the relativistic examination. New observations and incompleteness of many known mechanisms stimulate for the new developments. We show some properties of the ZP which cannot explained in the framework of the DPR model: the frequency drift of ZP stripes which changes synchronously with the space drift of the radio sources, the frequency splitting of the ZP stripes, the superfine structure of the stripes in the form of millisecond spike-bursts etc. It is shown that simultaneous excitation of waves at ~30 DPR- levels in the corona is impossible for any realistic profile of the plasma density and magnetic field. All new properties of ZP are considered in the light of both old and new theoretical models. The main properties of the emission and absorption stripes can be explained in a model involving interactions between electrostatic plasma waves and whistlers, taking into account the quasi-linear diffusion of fast particles with the loss-cone distribution on whistlers. We also propose a new advanced model of the ZP. It is shown that in the system the weakly-relativistic mono-velocity beam of protons - the strongly nonisothermic plasma the slow beam mode can possess negative energy and the explosive instability with interaction of slow and rapid beam modes and ionic sound is developed. As a result of the weak spatial dispersion the generation of ionic sound is accompanied by the cascade process of coalescence, and the stabilization of explosive instability occurs. ZP is formed by scattering of fast protons on the ion-acoustic harmonics. The effectiveness of new mechanism in comparison with the previously discussed hypotheses is explained.

Authors: G.P.Chernov
Projects: None

Publication Status: Open Access in NovaPublishers.com
Last Modified: 2012-06-28 13:03
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RECENT RESULTS ON ZEBRA PATTERN IN SOLAR RADIO BURSTS  

Gennady Chernov   Submitted: 2010-02-13 07:11

This review covers the most recent experimental results and theoretical research on zebra pattern (ZP) in solar radio bursts. The basic attention is given to events with new peculiar elements of zebra patterns received some last years. All new properties are considered in light both known earlier, and new theoretical models. Large-scale ZP consisting of small-scale fiber bursts could be explain by simultaneous including of two mechanism when whistler waves "highlight" the levels of double plasma resonance (DPR). A unique fine structure was observed in the event 13 December 2006: spikes in absorption formed darks ZP stripes against the absorptive type III-like bursts. The spikes in absorption can appear in accordance with well known mechanism of absorptive bursts. The additional injection of fast particles filled the loss-cone (breaking the loss-cone distribution), and the generation of continuum was quenched at these moments. The maximum absorptive effect realizes at the DPR levels. The parameters of millisecond spikes are determined by small dimensions of the particle beams and local scale heights in the radio source. Thus, the DPR model helps to understand several aspects of unusual elements of ZP. But the simultaneous existence of several tens of the DPR levels in the corona is impossible for any realistic profile of the plasma density and magnetic field. Three new theories of ZP are examined. The formation of eigenmodes of transparency and opacity during the propagation of radio waves through regular coronal inhomogeneities is the most natural and promising mechanism. Two other models (nonlinear periodic space ? charge waves, and scattering of fast protons on ion-sound harmonics) could be realized in large radio bursts.

Authors: G.P. CHERNOV
Projects: None

Publication Status: Submitted to Research in Astronomy and Astrophysics (RAA)
Last Modified: 2010-02-13 10:11
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Spiky Fine Structure of Type III-like Radio Bursts in Absorption  

Gennady Chernov   Submitted: 2009-12-21 10:22

An uncommon fine structure in the radio spectrum consisting of bursts in absorption was observed with the Chinese Solar Broadband Radiospectrometer (SBRS) in the frequency range of 2.6 - 3.8 GHz during an X3.4/4B flare on 13 December 2006 in active region NOAA 10930 (S05W33). Usual fine structures in emission such as spikes, zebra stripes, and drifting fibers were observed at the peak of every new flare brightening. Within an hour at the decay phase of the event, we observed bursts consisting of spikes in absorption which pulsated periodically in frequency. Their instantaneous frequency bandwidths were found to be in the 75 MHz range. Moreover, in the strongest type III-like bursts in absorption, spikes showed stripes of the zebra-pattern (ZP), which drifted to higher frequencies. All spikes had the duration as short as down to the limit of the instrument resolution of ≈ 8 ms. The TRACE 195 Å images indicate that the magnetic reconnection at this moment occurred in the western edge of the flare loop arcade. Taking into account the presence of the reverse-drifting bursts in emission, in the course of the restoration of the magnetic structures in the corona, the acceleration of the beams of fast particles must have occurred both upward and downward at different heights. The upward beams would have been captured by the magnetic trap, where the loss-cone distribution of fast particles (responsible for the emission of continuum and ZP) were formed. Additional injection of fast particles would have filled the loss-cone later, breaking the loss-cone distribution. Therefore the generation of continuum would have been quenched at these moments, which was evidenced by the formation of bursts in absorption.

Authors: G.P. Chernov, Y.H. Yan, C.M. Tan, B. Chen, Q.J. Fu
Projects: Hinode/XRT,TRACE

Publication Status: Accepted in Solar Physics
Last Modified: 2009-12-21 12:27
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Abstracts by Author
Development of Solar Flares and Features of the Fine Structure of Solar Radio Emission
Comparison of alternative zebra-structure models in solar radio emission
Latest news on zebra pattern
Last news on zebra pattern
Flare processes evolution and polarization changes of fine structures of solar radio emission in the April 11, 2013 event
Dynamics of flare processes and variety of the fine structure of solar radio emission over a wide frequency range of 30 - 7000 MHz
CONCERNING SPIKES IN EMISSION AND ABSORPTION IN MICROWAVE RANGE
COMPLEX RADIO ZEBRA PATTERNS ESCAPING FROM THE SOLAR CORONA AND NEW GENERATION MECHANISMS
RECENT RESULTS ON ZEBRA PATTERN IN SOLAR RADIO BURSTS
Spiky Fine Structure of Type III-like Radio Bursts in Absorption

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