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

Ground-based solar observations are analyzed for three of the flares discussed in the accompanying Solar Maximum Mission reports. The principal conclusions are that Hα 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 (approx.200 times) of flare plasma was present for the flare main phase. Evidence is presented for the escape 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