Nonlinear wave-particle interactions: Satellite observations and PIC simulations

Using high-resolution waveforms measured by the Van Allen Probes and MMS satellites, we report a novel observation both in the radiation belt and dayside reconnection regions. Namely, we show that whistler mode emissions modulate electrostatic Langmuir wave bursts. In the Earth's outer radiation belt, the modulation occurs in two different timescales: the rising-tone timescale, and the whistler waves phase period timescale. In those modulation events, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E_parallel component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the whistler-modes waves. We conclude that the whistler-mode waves accelerate the suprathermal electrons via Landau resonance and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. We successfully simulated this microscale process using 1-D particle-in-cell simulations.

References:

1. Li et al., (2017), Chorus modulation of Langmuir waves in the radiation belts, Geophysical Research Letters, https://doi.org/10.1002/2017GL0758773. 

2. Li et al., (2018), Electrostatic Langmuir Wave Bursts Driven by Whistler Mode Waves at Dayside Reconnection Regions, Geophysical Research Letters,  https://doi.org/10.1029/2018GL078287

3. An, Li et al., (2019). Unified view of nonlinear wave structures associated with whistler-mode chorus, Phys. Rev. Lett. https://doi.org/10.1103/PhysRevLett.122.045101