Chorus waves modulate Langmuir waves: Van Allen Probe observations

The excitation of the rising-tone chorus waves is subject to nonlinear wave particle interactions. While the particle measurements have limited temporal resolution, the high temporal measurements of the electric and magnetic waveforms provide many microscopic information about the nonlinear process. Using the waveform measurements from Van Allen Probes, we report an event in which the rising-tone whistler mode chorus have multiple harmonics, and each rising-tone burst is correlating to a Langmuir wave emission. What's more, the Langmuir waves are modulated in each chorus phase circle. The parallel electric component of the whistler mode waves is highly distorted, indicating electron trapping at each phase circle. Those trapped electrons can generate Langmuir waves locally, which consequently propagate at the phase speed of whistler mode waves. The interactions between chorus waves and high frequency electrostatic waves provide new insight into the nonlinear excitation of chorus waves.