Relativistic electron precipitation by EMIC waves: importance of nonlinear resonant effects

TL;DR

This study investigates how nonlinear resonant effects of intense EMIC waves influence relativistic electron precipitation in Earth's radiation belts, combining simulations and observations to reveal complex wave-particle interactions.

Contribution

It demonstrates that nonlinear effects can both transport electrons away from the loss cone and still result in electron precipitation through higher pitch-angle scattering.

Findings

Nonlinear EMIC wave effects can prevent electron precipitation by transporting electrons away.

Higher pitch-angle scattering leads to loss cone filling despite nonlinear transport.

Simulations and observations agree on the role of nonlinear resonant effects in electron precipitation.

Abstract

Relativistic electron losses in Earth's radiation belts are usually attributed to electron resonant scattering by electromagnetic waves. One of the most important wave mode for such scattering is the electromagnetic ion cyclotron (EMIC) mode. Within the quasi-linear diffusion framework, the cyclotron resonance of relativistic electrons with EMIC waves results in very fast electron precipitation to the atmosphere. However, wave intensities often exceed the threshold for nonlinear resonant interaction, and such intense EMIC waves have been shown to transport electrons away from the loss cone due to the force bunching effect. In this study we investigate if this transport can block electron precipitation. We combine test particle simulations, low-altitude ELFIN observations of EMIC-driven electron precipitation, and ground-based EMIC observations. Comparing simulations and observations, we show that, despite of the low pitch-angle electrons being transported away from the loss cone, the scattering at higher pitch angles results in the loss cone filling and electron precipitation.