EFFECT OF ELECTRON-BEAMS DURING SOLAR-FLARES

Electron bombardment of the solar atmosphere has two effects: one is to enhance hydrogen recombination emission, the other is to increase the opacity via an increase of H- population. The first effect is the most important in the upper part of the atmosphere and the second in the lower part. We predict that, when enhanced absorption dominates in the part of the atmosphere where radiation originates, there will be a decrease in the white-light emission, leading to a 'negative flare', or what we call a 'Black-Light Flare'. This phenomenon occurs only for a short duration, not more than approximately 20 s. 'Black-Light Flares' have already been observed in the case of flare stars and we suggest here that they could also be present on the Sun, just prior to a White-Light Flare.