To the Nature of Double Polarization Inversion in the Microwave Emission of Flare-productive Active Regions

V. Kotelnikov$^1$, V. Bogod$^1$, L. Yasnov$^2$

$^1$ St.-Petersburg Branch of the Special Astrophysical Observatory, Russian Academy of Sciences, St.-Petersburg 196140, Russia
$^2$St-Petersburg State University, Russia

Here we discuss the nature of the circular polarization double inversion in the microwave emission of flare-productive active regions. This phenomenon was often registered on the pre-flare phase of active regions observations with the RATAN-600 radio telescope in the broad microwave range during the period from 2000 to 2004. We propose two alternative models for the explanation of this phenomenon. In the first model we suggest the existence of magnetic ``hole'' in the active region. In the second model the propagation of radio waves through the layers with zero magnetic fields is proposed.