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

Kurzfassung

Resonant wave-particle interactions in the Earth's magnetosphere can lead to the scattering of plasma sheet electrons into the atmospheric loss cone, which can consequently cause the optical phenomenon of diffuse aurora. The Earth's diffuse auroral precipitation poses the main source of energy input into the high-latitude nightside upper atmosphere and therefore provides a strong coupling mechanism between the magnetosphere and the ionosphere. Specifically, electrostatic electron cyclotron harmonic (ECH) waves can effectively precipitate low-energy (100s of eV to 10s of keV) electrons into the upper atmosphere and contribute to the formation of diffuse aurora. 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 of the waves, changing the magnitude of the diffusion coefficients over a large range of pitch angles and energies. This also changes the lifetimes of the electrons near the loss cone.