Solar Radio-Frequency Emission from Localized Regions at Very High Temperatures

Solar radio-frequency radiation is analysed into three components ; a basic steady component B, a slowly varying component S, and various forms of more or less rapid fluctuations called the X component. The spectra of all three components are drawn between 600 and 24,000 Mc/s., and suggested extensions to lower frequencies are discussed. The properties of the S component are described in some detail ; these include correlation with sunspot data, polarization, and the location of the sources of origin. Evidence is presented in favour of generation by thermal processes. It is suggested that the S component is due to thermal emission from localized regions at temperatures of about 107 �K., often in the vicinity of sunspots. The radiation from a model hot region is examined in detail and the emission spectrum and polarization characteristics are derived. The results are found to compare reasonably with observation. Thermionic emission of electrons and protons would probably occur from the hot regions. These particles would travel to the Earth with average velocities of a few hundred kilometres per second and may be identical with the slow corpuscular radiation whose presence is deduced from terrestrial magnetic data.