Three-dimensional electron radiation belt simulations using the BAS Radiation Belt Model with new diffusionmodels for chorus, plasmaspheric hiss, and lightning-generated whistlers

摘要

The flux of relativistic electrons in the Earth’s radiation belts is highly variable and can change by orders of magnitude on timescales of a few hours. Understanding the drivers for these changes is important as energetic electrons can damage satellites. We present results from a new code, the British Antarctic Survey (BAS) Radiation Belt model, which solves a 3-D Fokker-Planck equation, following a similar approach to the Versatile Electron Radiation Belt (VERB) code, incorporating the effects of radial diffusion, wave-particle interactions, and collisions. Whistler mode chorus waves, plasmaspheric hiss, and lightning-generated whistlers (LGW) are modeled using new diffusion coefficients, calculated by the Pitch Angle and Energy Diffusion of Ions and Electrons (PADIE) code, with new wave models based on satellite data that have been parameterized by both the AE and Kp indices. The model for plasmaspheric hiss and LGW includes variation in the wave-normal angle distribution of the waves with latitude. Simulations of 100 days from the CRRES mission demonstrate that the inclusion of chorus waves in the model is needed to reproduce the observed increase in MeV flux during disturbed conditions. The model reproduces the variation of the radiation belts best when AE, rather than Kp, is used to determine the diffusion rates. Losses due to plasmaspheric hiss depend critically on the the wave-normal angle distribution; a model where the peak of the wave-normal angle distribution depends on latitude best reproduces the observed decay rates. Higher frequency waves (～ 1–2 kHz) only make a significant contribution to losses for L? < 3 and the highest frequencies (2–5 kHz), representing LGW, have a limited effect on MeV electrons for 2 < L? < 5.5.