DECAY OF EQUATORIAL RING CURRENT IONS AND ASSOCIATED AERONOMICAL CONSEQUENCES

The decay of the major ion species which constitute the ring current i s studied by solving the time evolution of their distribution function s during the recovery phase of a moderate geomagnetic storm. In this w ork, only equatorially mirroring particles am considered. Particles ar e assumed to move subject to EXB and gradient drifts. They also experi ence losses along their drift paths. Two loss mechanisms are considere d: charge exchange with neutral hydrogen atoms and Coulomb collisions with thermal plasma in the plasmasphere. Thermal plasma densities am c alculated with a plasmaspheric model employing a time-dependent convec tion electric field model. The drift-loss model successfully reproduce s a number of important and observable features in the distribution fu nction. Charge exchange is found to be the major loss mechanism for th e ring current ions; however the important effects of Coulomb collisio ns on both the ring current and thermal populations are also presented . The model predicts the formation of a low-energy (< 500 eV) ion popu lation as a result of energy degradation caused by Coulomb collisions of the ring current ions with the plasmaspheric electrons; this popula tion may be one source of the low-energy ions observed during active a nd quiet periods in the inner magnetosphere. The energy transferred to plasmaspheric electrons through Coulomb collisions with ring current ions is believed to be the energy source for the electron temperature enhancement and the associated 6300 angstrom (stable auroral red [SAR] arc) emission in the subauroral region. The calculated energy-deposit ion rate is sufficient to produce a subauroral electron temperature en hancement and SAR arc emissions that are consistent with observations of these quantities during moderate magnetic activity levels.