Electron Lifetimes and Diffusion Rates Inferred From ELFIN Measurements at Low Altitude: First Results

摘要

In the radiation belts, energetic and relativistic electron precipitation into the atmosphere is expected to be mainly controlled over the long term by quasilinear pitch-angle scattering by whistler-mode and electromagnetic ion cyclotron waves. Accordingly, statistical electron lifetimes have been derived from quasilinear diffusion theory on the basis of multi-year wave statistics. However, the full consistency of such statistical quasilinear models of electron lifetimes with both measured electron lifetimes, spectra of trapped and precipitated electron fluxes, and wave-driven diffusion rates inferred from electron flux measurements, has not yet been verified in detail. In the present study, we use data from Electron Loss and Fields Investigation (ELFIN) mission CubeSats, launched in September 2018 in low Earth orbit, to carry out such comparisons between quasi-linear diffusion theory and observed electron flux variations. We show that statistical theoretical lifetime models are in reasonable agreement with electron pitchangle diffusion rates inferred from the precipitated to trapped 100 keV electron flux ratio measured by ELFIN after correction for atmospheric backscatter, as well as with timescales of trapped electron flux decay independently measured over several days by ELFIN. The present results demonstrate for the first time a broad consistency between timescales of trapped electron flux decay, the pitch-angle distribution of precipitated electrons, and quasilinear models of wave-driven electron loss, showing the reliability of such statistical electron lifetime models parameterized by geomagnetic activity for evaluating electron precipitation into the atmosphere during not too disturbed periods.