Ensemble modeling of long-term radiation belt dynamics: accounting for variability in radial diffusion

This study presents ensemble modeling of outer radiation belt dynamics observed by Van Allen Probes throughout 2017 using DREAM3D simulations. We utilize a recently developed empirical radial diffusion coefficient ( D L L ) model with statistical distributions, employing two outer boundary (OB) conditions: Van Allen Probes data at L * = 5.5 and GOES data at L * = 6 , for two magnetic moments μ = 512 k e V / G and μ = 1237 k e V / G . The results demonstrate that OB location critically influences model performance. A model using Van Allen Probes OB at L * = 5.5 better reproduces observations, particularly for high μ electrons. In this scenario, radial diffusion alone can largely explain the dynamics because the OB is located near the phase space density (PSD) peak region. Stronger D L L outside the plasmasphere effectively captures inward/outward radial diffusion to/from the OB, while an intermediate D L L around the 30th percentile best matches electron PSD inside the plasmasphere. With GOES OB at L * = 6 , not only does strong D L L remain crucial for achieving good performance, but chorus heating also becomes critical. Model performance inside the plasmasphere is the best for the intermediate D L L but consistently worse than that outside the plasmasphere, suggesting a need for improved D L L and loss inputs in the plasmasphere.