Gerasimenko S. The influence of spatial inhomogeneity and external electric field on the generation of wave in Sun's active regions

In the framework of linear approximation of the perturbation theory the conditions have been considered for the onset and development of the low-frequency wave instabilities for the plasmas in the external magnetic field as well as in the weak quasistatic electric field, both being parallel. It is assumed that the pair Coulomb collisions are described by the integral of Bhatnagar-Gross-Krook. For the case of long-wave perturbations which propagate almost perpendicular to the external magnetic field, it has been shown that under some additional physical conditions, the dispersion relation is the polynomial of the fourth order with respect to the reduced frequency. Numerical simulation on the basis of the obtained formulas has been performed for the values of main plasma parameters (density, temperature, magnetic field amplitude) which are typical for the flare atmosphere in the solar active regions. It turns out that instability of the one of mentioned roots has clearly expressed threshold character,i.e. it arises at the certain value of slowly increasing amplitude of the weak electric field. This fact can be used for the short-time prediction of solar flare in the arch structures.