Active region flare rates and 8.6 mm brightness temperatures

The relationship between the flaring rates and 8.6 mm brightness temperatures of active regions has been analyzed. It is found that as the 8.6 mm brightness temperature of an active region increases, a larger proportion of the energy released by the region in the form of flares is contained in progressively larger flares. At all temperatures subflares are the most frequent event. At intermediate and high temperatures about 10% of the events are flares of importance 1 or larger with flares of importance 2 or larger contributing an increasing fraction of these events as the brightness temperature increases. (Auth.)