The Scattering of Radio Waves in the Solar Corona

Abstract

Observations of the radio emission from the Crab nebula during June, when it passes within a small angular distance of the Sun, have shown that the radiation suffers considerable scattering during its passage through the solar corona. In this paper an account is given of measurements carried out each year over the period 1952–1958. The following new results have been obtained: (i) measurements at a wave-length of 7.9 m have suggested the presence of refraction effects, in addition to scattering, which may provide information about the mean electron density in the corona; (ii) extension of the measurements to the shorter wave-length of 1.9 m has enabled the large scattering at the distance of closest approach to be determined more accurately; (iii) a pronounced sunspot-cycle variation has been observed in regions of the corona at a distance of $$8{R}_{\odot};$$ and (iv) the scattering has been shown to exhibit anisotropy. This result strengthens the earlier conclusion that the scattering is caused by filamentary irregularities aligned in a magnetic field and suggests that the direction of the field is approximately radial at distances of $$15-20{R}_{\odot}.$$