Radio-heliographic diagnostics of potential flare productivity of active regions

As deduced from the data with high spatial resolution obtained at radio heliographs of the Siberian Solar Radio Telescope (SSRT, 5.7 GHz) and the Nobeyama radiohelyograph (NoRH, 17 GHz), displacements of radio brightness centers in distribution of the Stokes parameter I relative to that of the parameter V can be registered 1-2 days before an energetic flare. As shown, this phenomenon may be related to the behaviour of quasi-stationary sources over the inversion line of the radial magnetic-field component (neutral-line associated sources (NLS)). These sources have a brightness temperature up to 106 K and a circular polarization up to 90 %. NLS formation is associated with an outflow of a new magnetic flux into the atmosphere of an active region (AR) that is a classical factor of the flare activity. Therefore, the NLS is a predictor of energetic solar flares and can be used as a forecast factor. SSRT high resolution made it possible to establish, as a predictor of AR preflare state, a deviation of the observable distribution of AR microwave radiation polarization from the normal one within the Sun's disk area with an active region. This resulted in modification of Tanaka-Enome criterion as observed at a certain frequency. Using the data from two radio heliographs (SSRT and NoRH) allowed us to suggest more effective for short-term forecast of solar flares, namely, two-frequency criterion of normal longitudinal zones. Preflare features associated with the displacement of brightness centers in I and V, namely, with NLS transformation into spot sources, are fine traces added to forecast according to two-frequency criterion. This is illustrated by example of AR 10930 which produced energetic proton flares on December 6 and 13, 2006.