Optical and radio observations of the 1980 March 29, April 30, and June 7 flares

Abstract

Ground-based solar observations are analyzed for three of the flares discussed in the accompanying Solar Maximum Mission reports. The principal conclusions are that H-alpha begins to brighten several minutes before the impulsive, hard X-ray bursts, that the preflare heating and impulsive phases of the three flares occurred in loop-shaped structures of about 3500 km semidiameter, and that after the impulsive phase a much larger volume (about 200 times) of flare plasma was present for the flare main phase. Evidence is presented for the escape of 100-500 keV electrons into the larger volume and into the corona during the impulsive phase. For the April 30 flare, the inferred origin of the hard X-ray burst is near the feet of the magnetic loops.