Radio-Frequency Radiation from the Quiet Sun

Abstract

The equation of transfer of radiation is used in a ray treatment of radio-frequency radiation from the solar atmosphere in the absence of solar activity. The chromosphere and the corona are represented as regions of uniform temperature. However, a range of temperatures is considered in order to allow for uncertainties in the temperature distribution in the solar atmosphere. The intensity distribution across the solar disk is shown to depend significantly on the coronal temperature. Both limb-brightening and limb-darkening can occur but are appreciable only when the corona is optically thin, yet not transparent. A measure of the size of the radio-frequency disk is obtained in terms of the size of the optical disk. The apparent temperature (an equivalent measure of the flux density at the earth) is found to reach a maximum as a function of frequency for each coronal temperature and as a function of coronal temperature for each frequency. Within the limits of experimental error all observed apparent temperatures fall within the range of theoretical values corresponding to chromospheric temperatures from 10⁴ to 3 X 10⁴ °K. and coronal temperatures from 2.5 X 10⁵ to 3 X 10⁶ °K. The effects of a possible general magnetic field of the sun are estimated in selected cases and found to be small in relation to those due to the uncertainties in the temperature of the solar atmosphere.