Quantifying event-specific radial diffusion coefficients of radiation belt electrons with the PPMLR-MHD simulation

Using the global Lagrangian version of the piecewise parabolic method-magnetohydrodynamic (PPMLR-MHD) model, we simulate two consecutive storms in December 2015, a moderate storm on 14-15 December and a strong storm on 19-22 December, and calculate the radial diffusion coefficients (D-LL) from the simulated ultralow frequency waves. We find that even though the strong storm leads to more enhanced B-z and E power than the moderate storm, the two storms share in common a lot of features on the azimuthal mode structure and power spectrum of ultralow frequency waves.

For both storms, the total B-z and E power is better correlated with the solar wind dynamic pressure in the storm initial phase and more correlated with AE index in the recovery phase. B-z wave power is shown to be mostly distributed in low mode numbers, while E power spreads over a wider range of modes. Furthermore, the B-z and E power spectral densities are found to be higher at higher L regions, with a stronger L dependence in the B-z spectra.