Three-dimensional simulation of energetic outer zone electron dynamics due to wave-particle interaction and azimuthal advection

摘要

We present a three-dimensional code treating the local resonant interaction with various waves and azimuthal advection around the Earth to evaluate storm-time energetic outer zone electron phase space density (PSD) evolution at a constant L shell without radial diffusion. Assuming a model distribution of wave characteristics at L = 4.5, we show that energetic (–MeV) electron PSD can decrease by about three orders over all pitch angles with a visible azimuthal asymmetry during the main phase and enhance by about 30 times of magnitude with a weak azimuthal asymmetry during the recovery phase. The differences between magnetic local time (MLT)-dependent and MLT-averaged simulations are also investigated in detail under cases of different wave characteristics. When a single type of wave is present, the differences between MLT-averaged and MLT-dependent simulations are fairly small. Energetic (–MeV) electron PSD is found to be overestimated by a factor of 2 at larger pitch angles for chorus or hiss alone, and underestimated by a factor of 5-10 near the loss cone for electromagnetic ion cyclotron (EMIC) waves alone under the MLT-averaged approximation. When multiple types of waves are taken into account, there are considerable differences between MLT-averaged and MLT-dependent simulations. MLT-averaged simulations can overestimate the energetic (–MeV) electron PSD by a factor of 5-50 during the main phase and 9-13 during the recovery phase. Additional control experiments show that larger drift speed tends to diminish the azimuthal asymmetry of MLT-dependent simulations as well as the difference between MLT-dependent and MLTaveraged simulations. These numerical results suggest that azimuthal advection can play an important role in the radiation belt electron dynamics, which should be incorporated in future radiation belt models for space weather application.