LANGMUIR WAVE DECAY AND COLLAPSE IN THE JOVIAN FORESHOCK

Langmuir waves are known to be created upstream of planetary bow shocks by the two-stream instability driven by sunward-streaming particles. In this paper we examine Langmuir waves detected by Ulysses' Unified Radio and Plasma wave experiment (URAP) upstream of Jupiter. Wave envelopes qualitatively consistent with collapsed Langmuir waves are common in the Ulysses dataset, and while a few events have amplitudes exceeding the published theoretical thresholds for tu rbulent Langmuir wave collapse, the majority of events are too weak. Langmuir wave decay via backscattering within preexisting density fluctuations in the solar wind is examined as a mechanism capable of localizing Langmuir waves. Langmuir decay is found to be a viable process which may play a role in preparing plasma conditions for collapse, but cannot alone account for the observed data.