On the nature of the microwave spike emission in loop structures of an active region

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Space and Atmospheric Physics
1Kryshtal, AN, 2Gerasimenko, SV, 1Voitsekhovska, AD
1Main Astronomical Observatory of the NAS of Ukraine, Kyiv, Ukraine
2Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
Kosm. nauka tehnol. 2010, 16 ;(5):29-37
https://doi.org/10.15407/knit2010.05.029
Publication Language: Russian
Abstract: 
We investigated the stability of the first harmonics of pure electron oblique bernstein modes which are modified by taking into account the influence of pair Coulomb collisions and by the existence of the weak large-scale electric field in a loop. It is assumed that the main characteristics of magnetoactive plasma at the loop footpoint in the part of current circuit of the loop which corresponds to the lower chromosphere of a solar active region can be obtained from the Fontela, Avrett, and Loeser (FAL) semiempirical model for the solar atmosphere. As the main reasons of instability rise and development the following effects are considered: a) the existence of subdreicer electric field with the amplitude which adiabatical-ly grows slow during the flare process activation; b) dissipation of energy due to pair collisions; c) direction of the perturbation propagation, which is not pure perpendicular to the loop magnetic field.
             Our investigation of the instability growth rate showed that the use of the FAL model instead of the models MAVN and VAL used before leads to the decrease of the instability threshold as a function of subdreicer field amplitude. Some emission in the centimetre-millimetre range can arise under the favourable conditions due to the separation of the generated wave into the kinetic Alfven wave and ordinary electromagnetic wave.
Keywords: chromosphere, loop circuit, magnetoactive plasma
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