Characteristics of Energy-Latitude Dispersed Electron Precipitation Driven by EMIC Waves

Abstract

The resonant interaction of relativistic electrons and electromagnetic ion cyclotron (EMIC) waves significantly contributes to electron depletion in the outer radiation belts, resulting in their precipitation into Earth's atmosphere. While these interactions can effectively cause electron losses, their efficacy is influenced by various equatorial plasma and magnetic field characteristics, which are not always reliably measured in the wave source region. To gain a deeper understanding of the interaction between EMIC waves and electrons, we conduct a statistical analysis of low-altitude observations of dispersed electron precipitation induced by EMIC waves. Combining near-equatorial measurements from THEMIS, we show that the energy-latitude ($L$-shell) dispersion can be attributed to equatorial density and magnetic field gradients within the EMIC source region. By comparing properties of near-equatorial EMIC wave measurements and low-altitude precipitation measurements, we demonstrate that effective electron losses during these dispersion events are intimately associated with plasmasphere density gradients, well equatorward from the plasma sheet inner edge.