Simulation of ULF Wave Modulated Electron Precipitation During the 17 March 2015 Storm

Abstract

Ultra Low Frequency (ULF) waves play an important role in radiation belt dynamics, modulation of higher frequency wave modes and energetic particle precipitation. We investigate the effects of ULF waves on electron precipitation using a global magnetohydrodynamic (MHD) model and a test particle code. ULF waves are simulated using the Lyon-Fedder-Mobarry (LFM) global MHD model coupled to the Rice Convection Model with solar wind parameters provided as upstream boundary conditions. The MHD fields are used to trace electron trajectories as test particles in the Dartmouth rbelt3d model (Kress et al., 2007, https://doi.org/10.1029/2006JA012218). We simulate the 17 March 2015 storm, the largest geomagnetic storm of Solar Cycle 24 with a Dst of −223 nT, to examine electron precipitation associated with recurring ULF oscillations. The simulation results show that the initial bipolar electric field oscillation observed by Van Allen Probes causes energy dependent electron acceleration and inward radial transport, while the loss cone size increases on the dayside due to magnetopause compression causing precipitation loss across all energies. The subsequent ULF oscillations are more effective in producing precipitation for higher energy electrons that are drift phase bunched due to the initial electric field impulse, with loss continuing to occur on the dusk side where electrons drift in phase with anti-sunward propagating ULF waves.