Programme by Session

The Van Allen radiation belts dynamically vary across timescales ranging from minutes to hours and thus pose significant challenges to modelling efforts. Here, we describe an Integrated Van Allen Radiation belt model which is implemented within the Global-MHD simulation code, Gorgon. Within the radiation belt model, energetic ions and electrons are represented as test-particles due to their negligible contribution to the overall magnetospheric current systems. Relativistic Lorentz and Guiding Centre integrators are implemented to trace particle’s gyro, bounce, and drift-motion using fields from the MHD grid, and particle phase-space weightings are used to represent realistic radiation belt distributions. Two levels of parallelisation are presented. The first method utilises a Particle-in-Cell algorithm to push particles within the simulated magnetosphere whereas the second method is further optimised to balance the computational load across all processes. The model is tested for the scenario of a strong fast-forward interplanetary shock rapidly compressing the magnetosphere and driving the sub-solar magnetopause from >10 Re to 6 R_e. The two different model implementations are shown to excel at capturing different aspects of the resultant radiation belt evolution. The load-balanced method efficiently reproduces shock-induced adiabatic acceleration across particle-drift timescales, whereas the PIC method is able to accurately resolve complex magnetopause particle dynamics such as drift-orbit-bifurcations. The Integrated Van Allen Radiation belt model is thus shown capable of simulating radiation belt behaviour whilst running in parallel with a global MHD simulation model of the type commonly used for space weather forecasting.