Ring current heating of the thermal electrons at solar maximum

To quantify the energy input to the thermal electrons due to Coulomb collis ional degradation of hot ions in the inner magnetosphere, the heating rate is calculated from the results of a time-dependent kinetic ring current mod el. The large June 4-7, 1991, storm during the last solar maximum, when the hot O+ content is maximal, is chosen for this study. Modeled electron heat fluxes into the topside ionosphere reach 10(11) eV cm(-2) s(-1) on the dus k side, a large value that will certainly have an impact on the density, te mperature, and composition of the upper ionosphere and thermosphere. Compar able maximum values of heat inputs to the inner magnetospheric thermal plas ma are expected to arise again during storms of the present solar maximum. The calculated heating rates from the ring current simulations are compared directly with detailed ionospheric modeling results for the Millstone Hill field line (L = 3). It is seen that heating from the ring current is more than adequate to account for the nightside topside heat input necessary to obtain the observed electron temperatures during this storm, even taking in to account the limitations of the comparison. The reason for this is the ab undance of O+ in the ring current at energies of a few tens of keV deep in the inner magnetosphere.