Bursts of Solar Radiation at Metre Wavelengths

Abstract

The variable components of solar radiation observed on frequencies of 85, 65, 60, and 19 Mc/s. over a period of nine months have been studied. It is shown that two types of variable high-intensity radiation can be distinguished. One of these, referred to as the " enhanced level ", is circularly polarized. The other, a particular type of short duration increase, is not circularly polarized and such an increase is called an " unpolarized burst ". These bursts tend to occur nearly simultaneously over a range of frequencies. They decay exponentially and double-humped bursts are common. Their characteristics are shown to conform broadly with the hypothesis that the bursts originate in localized transitory disturbances in the high corona which radiate over a wide frequency range. The decay constant is correctly predicted on the assumption that it is the decay constant of the excited medium in the region of origin, and the double peaks on the assumption that the second peak is an " echo " of the disturbance after reflection at the appropriate lower level in the corona. The occurrence of time delays between the arrival of " corresponding " unpolarized bursts on different frequencies is confirmed, the higher frequency commonly arriving earlier, with delays of about 0.7 second between 85 and 60 Mc/s. and 9 seconds between 60 and 19 Mc/s. There is a good correlation between major radio ' fade-outs " and large bursts on these frequencies.