Kinetic simulations of ring current evolution during the Geospace Environment Modeling challenge events

Abstract

We investigate the temporal and spatial evolution of the ring current during two storms selected for study by the Geospace Environment Modeling (GEM) program using our kinetic drift‐loss model coupled with a time‐dependent plasmasphere model. We use geosynchronous data from LANL satellites to model the inflow of plasma from the magnetotail. We compare results from simulations using either Volland‐Stern (VS) or Weimer (W01) model of the convection electric field and investigate the relative effect of magnetospheric convection and radial diffusion on the storm‐time injection and trapping of energetic particles and ring current asymmetry. Model comparisons with in situ Cluster, NOAA, and Polar energetic particle observations show overall better agreement with W01 than with VS model. On the other hand, VS model reproduced better the evolution of the plasmapause as observed by IMAGE. Additional ring current ion injections caused by radial diffusion near Dst minima improved the agreement with observations. Radial diffusion did not affect much ring current buildup during the main phase of the storms and the ring current fluxes remained asymmetric, in good agreement with NOAA data. We calculated the excitation of electromagnetic ion cyclotron (EMIC) waves self‐consistently with the evolving plasma populations, and the resulting precipitating fluxes of resonant protons. These fluxes increased significantly within regions of enhanced plasma wave excitation near the plasmapause or inside plasmaspheric plumes and reduced the total H+ energy by ∼10% during the storm recovery phase. Initial results from self‐consistent magnetic field calculations are presented as well. We found that while the magnitude of the ring current fluxes was reduced when adiabatic drifts in a self‐consistent magnetic field were calculated, their morphology was not affected significantly and the local time of the equatorial flux peaks remained almost unchanged.