Numerical modeling of multidimensional diffusion in the radiation belts using layer methods

A new code using layer methods is presented to solve radiation belt diffusion equations and is used to explore effects of cross diffusion on electron fluxes. Previous results indicate that numerical problems arise when solving diffusion equations with cross diffusion when using simple finite difference methods. We show that layer methods, which are based on stochastic differential equations, are capable of solving diffusion equations with cross diffusion and are also generalizable to three dimensions. We run our layer code using two chorus wave models and a combined magnetosonic wave and hiss wave model (MH wave model). Both chorus and magnetosonic waves are capable of accelerating electrons to MeV levels in about a day. However, for the chorus wave models, omitting cross diffusion overestimates fluxes at high energies and small pitch angles, while for the MH wave model, ignoring cross diffusion overestimates fluxes at high energies and large pitch angles. These results show that cross diffusion is not ignorable and should be included when calculating radiation belt electron fluxes.