An analysis of the shocklike electrostatic noise observed during AMPTE solar wind ion releases

Abstract

For the purpose of explaining the shocklike noise detected by the Ion Release Module (IRM) instruments during the Active Magnetospheric Particle Tracer Explorers (AMPTE) solar wind ion releases, we present an analysis of electrostatic waves produced by the interaction of the ion cloud with the solar wind. This analysis considers an arbitrary direction of propagation. It is found that in the absence of cold photoelectrons the maximum growth rate occurs almost perpendicular to the solar wind velocity. The wave growth is much higher than for propagation parallel to the solar wind direction, and is caused by an ion‐ion interaction between the injected ions (Ba+ or Li+) and the solar wind protons. However, in the presence of cold photoelectrons, the growth rate for the ion‐ion interaction is comparable or less than for parallel propagation, which is primarily an ion‐electron interaction. Therefore both types of interactions are probably involved in generating the shock‐like electrostatic noise. The ion‐ion instability is more likely to occur in the later stage of the cloud expansion after the cold photoelectrons have escaped and the ion‐electron instability is more likely, or at least comparable to the ion‐ion instability, in the early stages when the photoelectrons are dominant.