Relativistic electron precipitation by EMIC waves from self‐consistent global simulations

Abstract

We study the effect of electromagnetic ion cyclotron (EMIC) wave scattering on radiation belt electrons during the large geomagnetic storm of 21 October 2001 with minimum Dst = −187 nT. We use our global physics‐based model, which solves the kinetic equation for relativistic electrons and H+, O+, and He+ ions as a function of radial distance in the equatorial plane, magnetic local time, energy, and pitch angle. The model includes time‐dependent convective transport and radial diffusion and all major loss processes and is coupled with a dynamic plasmasphere model. We calculate the excitation of EMIC waves self‐consistently with the evolving plasma populations. Particle interactions with these waves are evaluated according to quasi‐linear theory, using diffusion coefficients for a multicomponent plasma and including not only field‐aligned but also oblique EMIC wave propagation. The pitch angle diffusion coefficients increase from 0° to ∼60° during specific storm conditions. Pitch angle scattering by EMIC waves causes significant loss of radiation belt electrons at E ≥ 1 MeV and precipitation into the atmosphere. However, the relativistic electron flux dropout during the main phase at large L ≥ 5 is due mostly to outward radial diffusion, driven by the flux decrease at geosynchronous orbit. We show first results from global simulations indicating significant relativistic electron precipitation within regions of enhanced EMIC instability, whose location varies with time but is predominantly in the afternoon‐dusk sector. The precipitating electron fluxes are usually collocated with precipitating ion fluxes but occur at variable energy range and magnitude. The minimum resonant energy increases at low L and relativistic electrons at E ≤ 1 MeV do not precipitate at L < 3 during this storm.