Relativistic electron scattering by electromagnetic ion cyclotron waves: the hot plasma Model

Resonant scattering by electromagnetic ion cyclotron (EMIC) waves is one of the most effective mechanisms of relativistic electron losses in the inner magnetosphere. For the majority of observed waves, such scattering is well described by the quasi-linear diffusion theory. Low-altitude spacecraft measurements, however, often show that the energy range of precipitating electrons is wider than theoretical predictions based on the cold plasma dispersion of EMIC waves. We develop a hot plasma model based on the observed ion distribution functions and investigate the hot plasma effects on EMIC wave dispersion for a wide frequency range. The results obtained from the analytical hot plasma model agree very well with the numerical solution of the exact dispersion relation of EMIC waves for a wide range of plasma parameters. We also show the implementation of this model for diffusion rate evaluation. Combining near-equatorial spacecraft measurements and wave dispersion model, we show that hot ion effects tend to increase the minimum resonant energy for the frequency range around wave intensity maxima, but can decrease the minimum resonant energy for the higher-frequency part of wave spectra.

This study highlights the importance of hot plasma effects on the relativistic electron scattering and provides a hot plasma model applicable to a wide range of plasma parameters for realistic quasi-linear diffusion rate calculations.