Quantifying the influence of the magnetic field on the radiation belts during storm-recovery

Abstract:

We analyze the effects of the magnetic field geometry on the electron fluxes in the radiation belts during storm-recovery. The two main processes that are at stake in this context are the transport and loss of electrons due to radial diffusion and pitch angle scattering. Here the latter effect is approximated by a loss term, which is combined with radial transport to give a reduced Fokker-Planck equation that governs the evolution of the phase-averaged distribution function at fixed adiabatic invariants (μ,K,L*). In the present study, the resolution of the reduced Fokker-Planck equation is numerically performed with two different magnetic field models, first, with the academic dipole field, and second, with the combination of the IGRF (internal) and T89 (external) magnetic field models. Comparing the fluxes resulting from both simulations, for several energies from 100 keV to several MeV and for different equatorial pitch angles, enables us to emphasize the effects inherent to the azimuthal asymmetries of the magnetic field. Correlations between the shape of the magnetic field lines and the flux intensities in the outer belt are discussed. Statistical comparisons with satellites' measurements are made to evaluate the accuracy of both models.