Validation of VERB‐3D Simulation Results in Response to the COSPAR ISWAT Challenge

Abstract In response to the first long‐term simulation challenge issued by the COSPAR International Space Weather Action Team (ISWAT) G3‐04 team (“ Internal Charging Effects and the Relevant Space Environment ”), we evaluate the performance of the Versatile Electron Radiation Belt‐3D model by simulating the radiation belt electron dynamics for the entire year of 2017. Model validation is performed by directly comparing simulated differential electron fluxes at 0.9 MeV and 57.27° local pitch angle with observations from the Van Allen Probes. The specific energy and pitch‐angle are selected by the ISWAT team so that modelers don't need to interpolate satellite data for comparison. The simulation results show generally good agreement with observations, although some discrepancies are evident near the plasmapause boundary. To investigate these mismatches, we conduct a series of sensitivity tests by varying key model parameters, including radial diffusion coefficients, hiss wave scattering rates, and magnetopause shadowing loss terms. Model performance is further quantified using several metrics, including normalized difference, median symmetric accuracy, and symmetric signed percentage bias. The results provide valuable insights for future model tuning and highlight the importance of parameter selection in long‐term radiation belt simulations.