Hot Plasma Effects on Electron Resonant Scattering by Electromagnetic Ion Cyclotron Waves

Resonant scattering by electromagnetic ion cyclotron (EMIC) waves is one of the most effective mechanisms of relativistic electron losses in Earth’s inner magnetosphere. 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. To explain this discrepancy, we examine the diffusion rates of EMIC waves by including hot plasma effects in their dispersion relation. Using the observed ion distribution functions, we investigate the hot plasma effects on the EMIC wave dispersion for a wide frequency range. We develop analytical equations for hot plasma effects on EMIC dispersion, and apply this model to diffusion rate evaluations. 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. Plain Language Summary Quantification of dynamics of relativistic electron fluxes in the Earth’s radiation belts is one of the main problems of space plasma physics. Resonance of such relativistic electrons with electromagnetic ion cyclotron (EMIC) waves is considered to provide a very effective electron scattering into the Earth’s atmosphere. Energies of electrons resonating with EMIC waves for typical wave characteristics and background plasma conditions rarely fall below 1 MeV, and most of the observed EMIC waves are believed to scatter and precipitate ultra‐relativistic electrons. Conjugate observations from near‐equatorial and low‐altitude spacecraft, however, often show near‐equatorial EMIC waves correlated with precipitation of sub‐MeV electrons below the minimum resonant energy. Such a decrease in resonant energy can be attributed to hot ion contribution to EMIC wave properties. This paper provides a generic hot plasma model which agrees well with the exact numerical solution and highlights the importance of hot plasma effects on the relativistic electron scattering by EMIC waves for a wide range of plasma parameters. Key Points Hot plasma effects are analyzed and parameterized using analytical equations for observed electromagnetic ion cyclotron (EMIC) waves Hot plasma parametric model agrees very well with numerical results and can be implemented to evaluate diffusion coefficients more precisely Hot plasma effects may decrease the minimum resonant energy of electrons for high