|
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
|
 
 
 
 
|
|