A storm-time ring current model (STRIM)

The ring current, one of the most important current systems around the Earth, intensifies during geomagnetic storms and is believed to be the main reason for large-scale magnetic field perturbations in the geospace environment. Understanding how the ring current builds up and evolves during geomagnetic storms is of great importance not only for advancing the knowledge of the Sun-Earth system but also for improving the modeling capability of predicting hazardous space weather events. In this study, we establish a kinetic ring current model, named STRIM, based on the bounce-averaged Fokker-Planck equation. The STRIM comprehensively embraces key physical processes in association with ring current dynamics, such as plasma source injections from the nightside plasmasheet and transport around the Earth, charge-exchange with neutral hydrogens, Coulomb collisions with thermal plasma, diffusive wave-particle interactions, field line curvature scattering, as well as precipitation loss down to the upper atmosphere. The electric fields needed for particle motion can be optionally taken from empirical models or self-consistently calculated, while the magnetic field configuration is obtained from the Tsyganenko 2005 model plus the IGRF internal model. Simulation results are verified against published literatures and validated with in-situ satellite or ground-based observations and are found to have the same high-level capability and fidelity as other well-known published models. We also discuss future tasks of fostering the model’s performance, such as advancing it to be bounce-resolved, to include N/S asymmetry in precipitation, or to implement a flexible outer boundary.