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

We compared the performance of DREAM3D simulations in reproducing the long-term radiation belt dynamics observed by Van Allen Probes over the entire year of 2017 with various boundary conditions (BCs) and model inputs. Specifically, we investigated the effects of three different outer boundary conditions, two different low-energy boundary conditions for seed electrons, four different radial diffusion (RD) coefficients (DLL), four hiss wave models, and two chorus wave models from the literature. Using the outer boundary condition driven by GOES data, our benchmark simulation generally well reproduces the observed radiation belt dynamics inside L* = 6, with a better model performance at lower mu than higher mu, where mu is the first adiabatic invariant. By varying the boundary conditions and inputs, we find that: (a) The data-driven outer boundary condition is critical to the model performance, while adding in the data-driven seed population doesn't further improve the performance. (b) The model shows comparable performance with DLL from Brautigam and Albert (2000, ), Ozeke et al. (2014, ), and Liu et al. (2016, ), while with DLL from Ali et al. (2016, ) the model shows less RD compared to data. (c) The model performance is similar with data-based hiss models, but the results show faster loss is still needed inside the plasmasphere. (d) The model performs similarly with the two different chorus models, but better capturing the electron enhancement at higher mu using the Wang et al. (2019, ) model due to its stronger wave power, since local heating for higher energy electrons is under-reproduced in the current model. Relativistic electrons in the outer radiation belt are very dynamic involving various acceleration and loss processes under the influence of radial diffusion (RD), hiss, and chorus waves. The physical processes are regarded as diffusive in behavior. The DREAM3D code solves the Fokker-Plank equation to investigate the radiation belt dynamics in the aspect of the diffusive dynamics of electrons. A variety of empirical models and boundary conditions have been developed and included in the simulations in the literature. In this study, we compare the DREAM3D performance in reproducing the observed radiation belt dynamics with various empirical models of the RD coefficients, hiss and chorus wave, and boundary conditions. In conclusion, we find the data-driven outer boundary condition is very important to reproduce the observed radiation belt variations. For the RD coefficients, all DLL exhibit comparable performances while DLL from Ali et al. (2016, ) shows slower RD due to its smaller magnitude. All the hiss wave models lead to effective loss inside the plasmasphere, but stronger losses are needed. For the chorus wave models, the two models are comparable with a small difference in model performance due to the different levels of wave power. This work compares the performance of long-term radiation belt simulations using various inputs and boundary conditions Using GOES outer boundary condition, the benchmark simulations reproduce the radiation belt dynamics inside L* = 6 observed by Van Allen Probes The data-driven OB condition is critical to the model performance, and stronger loss inside the plasmasphere could improve the performance