Formation Mechanism for the Bursts of Electron Butterfly Distributions

Abstract:

Energetic electron dynamics is highly affected by plasma waves through quasilinear and/or nonlinear interactions in the Earth’s inner magnetosphere. In this study, we provide physical explanations for a previously reported intriguing event from the Van Allen Probes observations, where bursts of electron butterfly distributions exhibit remarkable correlations with chorus waves. Both test particle and quasilinear simulations are used to reveal the formation mechanism for the bursts of electron butterfly distribution. The test particle simulation results indicate that nonlinear phase trapping due to chorus waves is the key process to form the electron butterfly distribution within ~30 s, and reproduce the observed features well. However, quasilinear simulation results show that although the diffusion process alone also contributes to form the butterfly distribution, the timescale is slower and the corresponding pitch angle is shifted compared to the observation. Our study provides remarkable evidence of nonlinear interaction process between energetic electrons and chorus waves.