Solar radiation at radio frequencies and its relation to sunspots

Abstract

Experimental studies of solar radiation on a frequency of 200 Mcyc./sec. are described. This radiation has characteristics similar to those of thermal radiation but is always hundreds of times greater than the thermal radiation anticipated from the photosphere and sometimes greater by a factor of 10 4 . The day-to-day intensity variations over a period of 6 months confirm a correlation with simspots. The received intensity of radiation is subject to rapid fluctuations; sudden in­creases, or ‘bursts’, of duration from a fraction of a second to a minute are characteristic. These rapid fluctuations are similar at widely-spaced receiving points, and it is concluded that most of them are extraterrestrial, and presumably solar, in origin. Directional observations, based on the interference phenomenon as the sun rises over the sea, indicate that the radiation originates not uniformly over the sun’s disk but in restricted areas in the immediate vicinity of a sunspot group. Values of received intensity are at times too great to be accounted for in terms of thermal radiation, so that another mechanism producing radiation must exist. Radiation from gross electrical discharges is suggested.