Auroral radiation ray distribution in the light of Viking observations of AKR

Abstract

The observations of the Viking satellite have shown that the AKR sources are narrow structures with sharp density edges, filled with hot tenuous plasma, into which the wave fields are trapped over some distance before escaping into free space. We examine the consequences of these features for the free propagation of the waves and for the distribution of their energy through space. The length of the trapping is estimated in a realistic situation corresponding to orbit 237 of Viking. The AKR energy is found to be confined inside an emission cone. It is shown that 60% of the wave energy concentrates at the thin edges of the cone, corresponding to an angular range of wave vectors oriented slightly downward. It is shown that in realistic situations met by Viking, the effect of a broad auroral cavity is to stretch significantly the pattern in longitude.