Polar/Cammice Investigation of Storm Time Ring Current Asymmetry

Recent results from CRRES and ring current models indicate that the ring current is asymmetric during the main phase of magnetic storms and becomes symmetric during the recovery phase. It is expected that the asymmetry of the ring current is energy dependent and related to the strength of the electric field. The current Polar/CAMMICE data is taken by an instrument nearly identical to that used for the CRRES study. However, Polar has been monitoring magnetic storms since spring 1996 to the present and provides a larger number of events for study. Polar is in an eighteen hour orbit, covers all local times every six months and has observed numerous ring current enhancements. For example, a moderate magnetic storm on October 10, 1997 produced a strong (orders of magnitude) noon-midnight asymmetry in the in the 3 and 5 MeV/G H⁺ ion fluxes at L values of 3 to 4 with the lower flux observed near noon. Several hours into the recovery the noon-midnight asymmetry was less than a factor of two. A similar result was observed during the January 10, 1997 event when Polar was traversing the dawn-dusk plane and the peak H⁺ fluxes at constant μ (3 and 5 MeV/G) were observed on the dusk side for L values of 3 to 4. At higher L values and larger μ values the fluxes were fairly symmetric. This is in qualitative agreement with recent ring current modeling results. These and other storm time ring current asymmetry observations by Polar/CAMMICE will be discussed and summarized.