Atmospheric Losses of Radiation Belt Electrons

Abstract

A numerical model of the low-altitude energetic electron radiation belt, including the effects of pitch angle diffusion into the atmosphere and azimuthal drift, predicts lifetimes and longitude-dependent loss rates as a function of electron energy and diffusion coefficient. It is constrained by high-altitude (∼20,000 km) satellite measurements of the energy spectra and pitch angle distributions and then fit to low-altitude (∼600 km) data that are sensitive to the longitude dependence of the electron losses. The fits provide estimates of the parameterized diffusion coefficient. The results show that the simple drift-diffusion model can account for the main features of the low-altitude radiation belt inside the plasmasphere during periods of steady decay. The rate of pitch angle diffusion is usually stronger on the dayside than on the nightside, frequently by a factor ∼10. The average derived lifetimes for loss into the atmosphere of ∼10 days are comparable to the observed trapped electron decay rates. Considerable variability in the loss rates is positively correlated with geomagnetic activity. The results are generally consistent with electron scattering by plasmaspheric hiss as the primary mechanism for pitch angle diffusion.