Dependence of ECH wave-induced scattering rates on the electron distribution

Abstract

Through resonant wave-particle interactions with electrostatic electron cyclotron harmonic (ECH) waves, low-energy (100s of eV to 10s of keV) plasma sheet electrons can be scattered into the atmospheric loss cone and contribute to diffuse auroral precipitation. This process consequently influences the evolution of the electron phase space density, but is currently not included in numerical codes simulating the radiation belt dynamics. In order to describe the ECH wave-induced electron scattering process, bounce-averaged quasi-linear diffusion coefficients need to be calculated. As ECH waves are thought to be generated by the loss cone instability of the ambient hot electron distribution, the numerical calculation of ECH wave-induced scattering rates requires the specification of the wave propagation characteristics, the background magnetic field and plasma density as well as properties of the hot plasma sheet electrons responsible for the wave excitation. In this study, we analyze the dependence of the bounce-averaged quasi-linear scattering rates by ECH waves on the temperature of the hot electron components in the electron distribution. By assuming the background plasma parameters based on previous observations, scattering rates are computed for hot electron temperatures varying from hundreds of eV to several keV, which is consistent with observations as well. A wave power spectral profile based on statistical wave properties is assumed and used to calculate weighted diffusion coefficients. We find that the hot electron temperature influences the growth rate and wave normal angle distribution of the waves, changing the pitch angle diffusion coefficients and lifetimes of the electrons near the loss cone.