Systematic Evaluation of the Relationship Between Chorus Waves and Electron Pitch Angle Distributions Using Van Allen Probes Observations: Potential Evidence for Nonlinear Interactions

Abstract:

Whistler mode chorus waves are electromagnetic emissions, which can cause energetic electron acceleration and pitch angle scattering in the Earth’s outer radiation belt. Although such effects are predominantly modeled by quasi-linear theory in many studies, some observations revealed the nonlinear interaction signatures, such as the rapid formation of the electron butterfly pitch angle distribution. In this study, we evaluate the relationship between chorus waves and energetic electron pitch angle distribution using high resolution data from Van Allen Probes, and identified multiple events showing strong correlations between bursts of chorus waves and bursts of electron fluxes. Interestingly, we find some events showing the butterfly pitch angle distribution for tens of keV electrons with a high correlation with chorus waves. By analyzing multiple events, we also evaluate favorable conditions leading to strong correlations between chorus waves and electron distributions, including wave properties, L-shell, MLT, latitude, etc. Our findings are critical for understanding the nonlinear interactions between chorus waves and energetic electrons in the outer radiation belt.