Radio Observations of Small Activity Prior to Main Energy Release in Solar Flares

Abstract

Abstract Small activities prior to impulsive bursts or large complex bursts are occasionally observed with an interferometer at 17 GHz. It is demonstrated here that these “pre-flare activities” are not observed merely by chance but related to the subsequent main energy release. From a statistical study of 97 bursts with a peak flux density greater than 10 sfu, we show (1) that 26% of them are preceded by much smaller bursts from the same active regions as the main bursts, and (2) that the time interval between the preceding and main bursts ranges from 10 to 35 min with an average value of 25 min. We describe some typical examples of bursts with pre-flare activities. However it is not clear from the present observations alone what kind of pre-flare conditions they manifest.