An examination of stable auroral red (SAR) arc emissions over the last solar cycle (Slater and Kleckner, 1989) indicates that the strongest emissions, during the lifetime of a particular SAR arc, often occur in association with the main phase of the magnetic storm. Previous observations of thermal and energetic particle populations at high and low altitudes on SAR arc field lines by Kozyra et al. (1987a) indicate that the energy source for these emissions is the O+ in the ring current. The O+ content of the ring current increases with increasing magnetic activity reaching its maximum percentage contribution near minimum Dst for a particular storm. This variation in the O+ content of the ring current is inconsistent with an early main phase enhancement of SAR arc emissions. To investigate the source of main phase enhancements in SAR arc emissions, a study of the September 19--24, 1984, magnetic storm period during which SAR arc emissions were observed by the ground-based mobile automatic scanning photometer network in both the main and recovery phases is presented. The emissions associated with the main phase (~400 R) were an order of magnitude greater than those associated with the recovery phase (tens of R). Energetic particle measurements from the DE1 and AMPTE spacecraft, on field lines that map to the SAR arc position at low altitude, were examined to determine if differences in the energy sources during these time periods were evident.

In agreement with previous work, ring current O+ supplied the bulk of the electron heating during storm recovery phase as a result of Coulomb collisions of O+ with the plasmaspheric electrons; contributions by ring current H+ were negligible. A new result of the present work is that an enhancement of the 15--25 keV H+ component of the ring current during the main phase of the September 19 magnetic storm was responsible for an approximately one order of magnitude increase in the electron heating rate and SAR arc emissions during the main phase compared to the recovery phase. The increase in the H+ flux occurred in association with a ring current ''nose event'', a front of ions injected into the inner magnetosphere in response to a discontinuous change in the cross-tail electric field. The association between nose events and intensifications of SAR arc emissions in the main phase has not previously been explored but is natural consequence of the injection of significant fluxes of relatively low-energy ring current ions earthward of the plasmapause during early storm time ring current formation. ¿ American Geophysical Union 1993