Simulation of off-equatorial ring current ion spectra measured by Polar for a moderate storm at solar minimum

We use our kinetic drift-loss model to study ring current dynamics during m oderate geomagnetic activity at the minimum phase of the current solar cycl e, on March 20-22, 1996. Interplanetary conditions monitored by Wind during this period show fluctuations about zero in the (GSM) B-z component, which are due to Alfven waves in a stream-stream interaction region. The corresp onding Dst index shows general activity punctuated by 2 moderate storms (mi n Dst approximate to-50 nT and approximate to-70 nT, respectively) of simil ar to 15 hours duration each. We calculate the off-equatorial ring current proton spectra in the energy range 100 eV to 300 keV and compare them with measurements provided by the HYDRA, TIMAS, and CEPPAD instruments on the Po lar spacecraft at MLT approximate to 2 and MLT approximate to 14. We find r easonable overall agreement. An eastward offset of 3 hours in the Kp-depend ent Volland-Stern convection electric field with gamma=2 is necessary in or der to match modeled with observed dips in the energy spectra. Collisional losses have larger effect on the postnoon spectra and reduce significantly the low-energy proton distribution at low L shells and at higher magnetic l atitudes. These losses reach maximum values for slowly drifting (similar to 2-10 keV) particles. Our study suggests that a more realistic magnetospher ic electric held and additional diffusion processes should be considered to reduce the overestimated width and depth of the dip in the modeled dayside spectra.