Phase coupling in Langmuir wave packets: Possible evidence of three-wave interactions in the upstream solar wind
Some theories of the generation of 2ωpe radiation, in the upstream solar wind, invoke the notion of nonlinear wave-wave interactions. We present observations, from the WIND spacecraft, of an event in the upstream solar wind with first and second harmonic emissions. The bicoherence spectrum of this event shows coherence amongst components that suggest three-wave interactions of the type described in (Cairns and Melrose, 1985). We discuss this result and its theoretical context.