Radio-heliographic diagnostics of the potential flare productivity of active regions

As deduced from the data with high spatial resolution obtained at the radio heliographs of the Siberian Solar Radio Telescope (SSRT, 5.7 GHz) and the Nobeyama radio heliograph (NoRH, 17 GHz), radio brightness centers in the distribution of the Stokes parameter I are shifted relative to the distribution of the parameter V 1–2 days before an intense flare. It has been shown that this phenomenon can be related to the behavior of quasi-stationary sources over the inversion line of the radial component of the magnetic field (neutral-line associated sources (NLSs)). These sources have a brightness temperature up to 106 K and a circular polarization up to 90%. The origination of NLSs is associated with the outflow of a new magnetic flux into the atmosphere of an active region that is a classical factor of the flare activity. Therefore, an NLS is a precursor of power solar flares and can be used as a forecast factor. Owing to the high resolution of the SSRT, the deviation of the observed polarization distribution of microwave radiation of the active region from the normal one within the solar disk zone containing the active region can be used as a precursor of the preflare state of the active region. As a result, the single-frequency Tanaka-Enome criterion is modified. The use of the data from two radio heliographs (SSRT and NoRH) allows us to propose a two-frequency criterion of normal longitudinal zones that is more efficient for short-term forecasting of solar flares. Preflare features associated with the displacement of brightness centers in I and V , which is manifested as the transformation of NLSs into spot sources, are fine attributes added to forecast according to the two-frequency criterion. This is illustrated by an example of active region 10930, which produced power proton flares on December 6 and 13, 2006.