A 3B Fiare in a Spotless Region on Oct. 15 in 1980

A.3B flare which occurred in a spotless region on Oct. 15, 1980 is mophologically analysed in some detail. The main results of the analysis are as follows: 1) The flare had no flash phase and the maximum intensity of the flare was about 2.4 times as much as that of the undisturbed region. 2) The flare had the double-ribbon structure with the separation velocity of about 5 km/sec. 3) The filament in connection with the flare was located at the boundary of a large scale magnetic field with opposite polarities. The filament obviously changed just before and after the flare, and finally disappeared. 4) The increment of the corresponding microwave burst was very small and the rise and fall of the burst were very slow. There were the meter-wave bursts of type-Ⅱ, type-Ⅲ and type-Ⅳ to go with the flare. 5) During the flare the x-ray emission of the flare caused a SID of Important 2 but there was no corresponding geomagnetic storm. 6) The flare region exsisted for three solar rotations and the flare occurred in the declining phase of the active region. Basically, all of the results mentioned above are very similar to Dodson's results.There is a brief discussion on the formation of flares which occurred in spotless regions. It is pointed out that the explanation of the splash-down of prominence material encounters difficulties in energy deficit; the intensity of the shock formed by the splash-down of, prominence material will be weakened by the exsisting magnetic field and the magnetic field can not be transformed into radiation energy with the aid of shocks; the mechanism of the formation of flares which occurred in spotless regions may be similar to that of flares which occurred in ordinary spot active regions.