Resonant diffusion of radiation belt electrons by whistler‐mode chorus

Abstract

We present the first relativistic electron pitch‐angle and momentum diffusion rates for scattering by whistler‐mode waves in the low density regieme. Diffusion rates are strongly dependent on the ratio between the electron plasma and gyro‐frequencies ω pe /Ω e . For conditions typical of storm times, diffusion rates at a few MeV increase by more than 3 orders of magnitude as ω pe /Ω e is reduced from 10 to 1.5. Diffusion rates are extremely sensitive to energy and become ineffective above 3 MeV. At energies below 100 keV pitch‐angle diffusion approaches strong diffusion loss to the atmosphere, while loss at higher energies is much weaker. For storm‐time whistler‐mode chorus amplitudes near 100 pT, and ω pe /Ω e ≤ 2.5, acceleration timescales can be less than a day at 1 MeV. This indicates that chorus diffusion could provide an important mechanism for local acceleration during the recovery phase of storms outside the plasmapause.