Modeling ring current proton precipitation by electromagnetic ion cyclotron waves during the May 14-16, 1997, storm

We study mechanisms contributing to proton precipitation from the ring curr ent during the May 14-16, 1997, geomagnetic storm. This storm was caused pa rtly by B-z < 0 fields in the sheath region behind an interplanetary shock and partly by the magnetic cloud driving the shock. The storm was character ized by a maximum Kp=7(-) and a minimum Dst=-115 nT and had a distinctive t wo-phase decay related to the passage of the ejection at the Earth. We mode l the ring current development caused by adiabatic drifts and losses due to charge exchange, Coulomb collisions, wave-particle interactions, and atmos pheric collisions at low altitudes. The nightside magnetospheric inflow is simulated using geosynchronous Los Alamos National Laboratory data, whereas the dayside free outflow corresponds to losses through the dayside magneto pause. We calculate the equatorial growth rate of electromagnetic ion cyclo tron waves with frequencies between the oxygen and helium gyrofrequencies a nd their integrated wave gain as the storm progresses. The regions of maxim um wave amplification compare reasonably well tb satellite observations. A time-dependent global wave model is constructed, and the spatial and tempor al evolution of precipitating proton fluxes during different storm phases i s determined. We find that the global patterns of proton precipitation are very dynamic: located at larger L shells during prestorm conditions, moving to lower L shells as geomagnetic activity increases during storm main phas e, and receding back toward larger L shells with storm recovery. However, t he most intense fluxes are observed along the duskside plasmapause during t he main and early recovery phase of the storm and are caused by plasma wave scattering. This study is relevant to the analysis of the anticipated new data sets from the Imager for Magnetopause-to-Aurora Global Exploration (IM AGE) and Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) mis sions.