THE ROLE OF RING CURRENT NOSE EVENTS IN PRODUCING STABLE AURORAL RED ARC INTENSIFICATIONS DURING THE MAIN PHASE - OBSERVATIONS DURING THE SEPTEMBER 19-24, 1984, EQUINOX TRANSITION STUDY

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 obser vations of thermal and energetic particle populations at high and low altitudes on SAR arc field lines by Kozyra et al. (1987a) indicate tha t 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 Ds t for a particular storm. This variation in the O+ content of the ring current is inconsistent with an early main phase enhancement of SAR a rc emissions. To investigate the source of main phase enhancements in SAR arc emissions, a study of the September 19-24, 1984, magnetic stor m period during which SAR arc emissions were observed by the ground-ba sed mobile automatic scanning photometer network in both the main and recovery phases is presented. The emissions associated with the main p hase (approximately 400 R) were an order of magnitude greater than tho se associated with the recovery phase (tens of R). Energetic particle measurements from the DE 1 and AMPTE spacecraft, on field lines that m ap to the SAR arc position at low altitude, were examined to determine if differences in the energy sources during these time periods were e vident. In agreement with previous work, ring current O+ supplied the bulk of the electron heating during storm recovery phase as a result o f Coulomb collisions of O+ with the plasmaspheric electrons; contribut ions by ring current H+ were negligible. A new result of the present w ork is that an enhancement of the 15-25 keV H+ component of the ring c urrent during the main phase of the September 19 magnetic storm was re sponsible for an approximately one order of magnitude increase in the electron heating rate and SAR arc emissions during the main phase comp ared to the recovery phase. The increase in the H+ flux occurred in as sociation 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 an d intensifications of SAR arc emissions in the main phase has not prev iously been explored but is a natural consequence of the injection of significant fluxes of relatively low-energy ring current ions earthwar d of the plasmapause during early storm time ring current formation.