Nonlinear Landau resonant interaction between whistler waves and electrons: Excitation of electron acoustic waves

TL;DR

This study uses particle-in-cell simulations to reveal how whistler waves excite electron acoustic waves through nonlinear Landau resonance, advancing understanding of wave interactions in Earth's magnetosphere.

Contribution

It uncovers the excitation mechanism of EAWs via nonlinear Landau resonance with whistler waves, providing a critical condition for EAW excitation validated by simulations.

Findings

EAWs are excited by localized electron beams trapped by whistler waves.

A critical condition for EAW excitation based on growth and phase mixing rates.

Results aid interpretation of observations and energy transfer in near-Earth space.

Abstract

Electron acoustic waves (EAWs), as well as electron-acoustic solitary structures, play a crucial role in thermalization and acceleration of electron populations in Earth's magnetosphere. These waves are often observed in association with whistler-mode waves, but the detailed mechanism of EAW and whistler wave coupling is not yet revealed. We investigate the excitation mechanism of EAWs and their potential relation to whistler waves using particle-in-cell simulations. Whistler waves are first excited by electrons with a temperature anisotropy perpendicular to the background magnetic field. Electrons trapped by these whistler waves through nonlinear Landau resonance form localized field-aligned beams, which subsequently excite EAWs. By comparing the growth rate of EAWs and the phase mixing rate of trapped electron beams, we obtain the critical condition for EAW excitation, which is consistent with our simulation results across a wide region in parameter space. These results are expected to be useful in the interpretation of concurrent observations of whistler-mode waves and nonlinear solitary structures, and may also have important implications for investigation of cross-scale energy transfer in the near-Earth space environment.