LASP Magnetosphere Seminars

Abstract

Electron precipitation driven by Electromagnetic Ion Cyclotron (EMIC) waves plays a pivotal role in the loss of radiation belt electrons. During the wave-particle interaction, electrons can be pushed into the loss cone and subsequently lost into Earth’s atmosphere (electron precipitation), where they deposit their energy. Electron precipitation affects the atmospheric chemistry, enhancing ionization and leading to the production of more nitrogen and hydrogen oxides, which can destroy ozone. Despite its significance, the properties and impacts of EMIC-driven electron precipitation still require comprehensive characterization and understanding. 

In this talk, I will present observations of EMIC-driven precipitation from LEO satellites and summarize our current knowledge of the spatial extent and energy spectra of the precipitation. I will describe in detail observations from the twin ELFIN CubeSats, which provide precise electron flux measurements at high resolution in both energy and pitch-angle at an altitude of ~450 km. By leveraging observations of nearby proton precipitation (from the POES/MetOp constellation of spacecraft) as a proxy for EMIC wave activity, we identify 144 EMIC-driven precipitation events. Our findings reveal that precipitation is most efficient for ~MeV electrons and is accompanied by weaker low-energy precipitation down to ~100–200 keV. Notably, ELFIN’s high pitch-angle resolution enables us to conduct an unprecedented analysis of the electron pitch-angle distribution at LEO, both inside and outside the loss cone. The statistical analysis indicates a progressive filling of the loss cone with increasing energy, which aligns well with quasilinear predictions of EMIC-electron interactions at ≳250 keV.