The Mechanism Responsible for 'Shadow' Type III Solar Radio Bursts. II. Absorption due to Ion Sound Turbulence

Abstract

The hypothesis is explored that ion sound turbulence generated by the exciting agency for type III bursts is responsible for shadow type III events. The possible absorption mechanisms are listed: the most favourable are the coalescence of transverse waves and ion sound waves into Langmuir waves or the decay of transverse waves into Langmuir waves and ion sound waves. These mechanisms can operate only if the background source emits at the fundamental plasma frequency and the absorbing region is directly above it (;$ 3 x 104 km). It is found that the event discussed by Kai (1973) can be explained in terms of such absorption with reasonable parameters, e.g. with an energy density in ion sound turbulence W' ~ 10-12 ergcm- 3 at frequencies co' ~ O·3cop! (where cop! is the ion plasma frequency).