Effects of magnetic field asymmetry and compressional magnetic perturbations on radial diffusion of radiation belt electrons

The radial diffusion coefficient of particles in a symmetric magnetic field perturbed by fluctuating electric fields is well known to depend on the power spectral density of the electric field at frequencies ω = m ω _d (where m is the azimuthal mode number, ω _d is the particle drift frequency) with an L⁶ factor. In this work we have derived a radial diffusion coefficient for particles in an asymmetric magnetic field. The asymmetric diffusion coefficient depends on electric field power at resonance frequencies ω = (m ± 1) ω _d with L¹² dependence multiplying the power spectral density. Numerical diffusion rates obtained using test-particle simulations in model fields agree well with the analytical diffusion coefficients. Solutions of the radial diffusion equation for the September 1998 storm event are compared to an MHD-particle simulation. Earlier calculations used only electric-field diffusion coefficients, which had to be increased by a factor of 2 to 3 to get the best match with the MHD-particle results. New results will be presented of a radial diffusion calculation with compressional ULF waves added.