Solar radio-frequency radiation

The paper attempts to survey research on solar radio-frequency radiation, or solar noise, to early 1948. After an introduction concerned with history and units for specification of intensity, the observed characteristics of solar noise in the wavelength range from 1 cm to some metres are described. These include intensity, region of origin on the sun, association with visual phenomena, and polarization; on the basis of these characteristics a classification of types of solar noise is proposed. Known data on solar physics relevant to the generation and propagation of radio waves in the solar atmosphere are outlined, and the mode of origin is discussed. A thermal component is recognized corresponding in intensity to black-body radiation of a temperature that rises from 104 °K at a wavelength of 1 cm to 106 °K at a few metres. This change is believed to be associated with a rise in the region of origin of the radiation from the lower chromosphere to the corona. Non-thermal components, prominent at metre wavelengths, are subject to remarkably rapid variations and reach occasional peak intensities 103 to 106 times the thermal ones. They are believed to originate in some form of electrical disturbance in the solar atmosphere.