Simulating Long-Term Dynamics of Radiation Belt Electrons Using DREAM3D Model

Long-term radiation belt dynamics in 2017 are studied in this work by conducting DREAM3D simulations and investigating the effects of various model inputs of outer boundary conditions, radial diffusion coefficients, and wave models. The outer boundary condition of our simulation is first set up at L*=6 and calculated using the GOES phase space density (PSD) data. Empirical models of the radial diffusion coefficients, DLL, have been implemented in the simulations, as well as pitch angle and energy diffusion (and cross diffusion) from hiss and chorus waves. We found that the model results strongly depend on the outer boundary conditions, hiss waves reduce electron PSD inside the plasmasphere, and chorus waves enhances the PSD overall. When we moved the outer boundary condition to L*=5.5 using the Van Allen Probes (VAP) data, the model performance is slightly better near the outer boundary but not improving significantly overall. We also compared the model performance with and without the data-driven minimum energy (Emin) boundary condition at E=100 keV derived from the VAP data. Using the data-driven Emin boundary condition increases the electron PSD by enhanced chorus heating; but interestingly we find that using both data-driven outer boundary and Emin boundary conditions reduce the model performance by overestimation of electron PSD. For the radial diffusion coefficients, we have tested four empirical models of DLL and find that DLL from Ali et al. (2016) shows very limited radial diffusion due to the small DLL values compared to others. The -dependent DLL from Liu et al. (2016) is comparable to the other DLL at high values but much larger at lower , which enables faster transport of lower-energy seed electrons from the outer boundary and thus more efficient chorus heating and higher electron PSD at the energy level of a few MeV. For the various hiss wave models implemented, all of them show reduction of electron PSD inside the plasmasphere, but the simplistic electron lifetime model from Shprits et al. (2006) shows the best performance compared to others, implying that faster reduction of electron PSD inside the plasmasphere is needed. For chorus wave models, the model from Wang et al. (2019) shows slightly better performance than using the wave model based on CRRES data.