About the observed brightness distribution of solar radio bursts on decameter wavelengths and a possible effect from the ionosphere

Abstract

Chen and Shawhan (1978) observed the brightness distribution of solar radio bursts at 26 MHz and fitted it to a double gaussian model. The small angle and large angle components were labelled ‘core’ and ‘halo’. As an alternative to the scattering theory by coronal inhomogeneities, the authors introduced an interpretation of these components as the primary source and its reflected image on lower layers of the corona. We stress the difficulties with this interpretation because the corona is indeed very far from being spherically symmetric; the observed source structure may be due to a coronal scattering process involving both weak and strong inhomogeneities. But first of all we point out a relation between the halo dimensions and the local time which casts some doubt on the solar origin of the halo; we argue that it might result at least partially from instrumental or more probably from ionospheric effects.