On the Spectrum and Generation Regions of Solar Microbursts in the Decimeter Wave Band

We analyze the nature and physical conditions in the generation regions of decimeter microbursts (MBs), which were discovered with the radiotelescope of the Russian Academy of Sciences (RATAN-600). One of the main peculiarities of MBs is an almost constant upper-frequency limit of about 1.1 GHz, which has not been explained in previously studied generation models. Here it is shown that this spectral peculiarity can be explained by the generation of the upper-hybrid waves at the double plasma resonance (DPR) and a subsequent transformation into low-frequency plasma waves considering free–free and cyclotron absorption. Model calculations show that MBs occur in the active regions where the magnetic-field strength is close to 100 G. MBs are most probably generated in the transition region of the solar atmosphere between main magnetic fields with opposite polarities.