Electron Precipitation Observed by ELFIN Using Proton Precipitation as a Proxy for Electromagnetic Ion Cyclotron (EMIC) Waves

TL;DR

This study uses ELFIN CubeSats and POES satellites to analyze EMIC wave-driven electron and proton precipitation in Earth's radiation belts, revealing localized spatial scales, energy-dependent behaviors, and partial agreement with theoretical models.

Contribution

It introduces high-resolution observations of EMIC-driven electron precipitation and uses proton precipitation as a proxy for EMIC wave activity, providing new insights into wave-particle interactions.

Findings

Electron precipitation occurs on localized radial scales of 0.3 L.

Precipitation is stronger at MeV energies and weaker at 100-200 keV.

Loss cone distributions at >250 keV match quasilinear predictions, but low-energy data suggest additional mechanisms.

Abstract

Electromagnetic Ion Cyclotron (EMIC) waves can drive radiation belt depletion and Low-Earth Orbit (LEO) satellites can detect the resulting electron and proton precipitation. The ELFIN (Electron Losses and Fields InvestigatioN) CubeSats provide an excellent opportunity to study the properties of EMIC-driven electron precipitation with much higher energy and pitch-angle resolution than previously allowed. We collect EMIC-driven electron precipitation events from ELFIN observations and use POES (Polar Orbiting Environmental Satellites) to search for 10s-100s keV proton precipitation nearby as a proxy of EMIC wave activity. Electron precipitation mainly occurs on localized radial scales (0.3 L), over 15-24 MLT and 5-8 L shells, stronger at MeV energies and weaker down to 100-200 keV. Additionally, the observed loss cone pitch-angle distribution agrees with quasilinear predictions at >250 keV (more filled loss cone with increasing energy), while additional mechanisms are needed to explain the observed low-energy precipitation.