New Developments in the Comprehensive Inner Magnetosphere‐Ionosphere Model

Abstract

AbstractA Comprehensive Inner Magnetosphere‐Ionosphere (CIMI) model was developed to study the dynamic variations of the radiation belts, ring current, and plasmasphere as well as the couplings between these populations and with the ionosphere. The CIMI model has been used in multiple studies to simulate a number of magnetic storms and reproduce many observable features that involve cross‐region and cross‐energy processes. This model has been continuously validated and improved. In this study, we report on two major recent advancements in CIMI. The first improvement is transforming coordinates in both configuration and velocity space into uniform grids. Numerical schemes, especially those of high order, are generally more stable on such uniform grids. The second advancement is to solve both advection and diffusion in the CIMI equation in a single coordinate system. Previously, the phase space distribution was expressed in terms of the first two adiabatic invariants when solving for particle drift, whereas particle distributions were transformed into energy and pitch angle for calculating wave diffusion. In the new approach in CIMI, particles and distribution functions are identified by their momentum. This change avoids interpolation errors inherent in the mapping of the phase space distribution when switching back and forth between advective and diffusive transport. We describe the detailed implementation of these recent advancements in the CIMI model, and demonstrate how the newly improved model provides better predictions of the ring current and radiation belt dynamics.