Cusp-Region Ion Outflows Observed During January 21, 2005 Storm Period

The FAST spacecraft observed intense ion outflows following the initiation of a geomagnetic storm on January 21, 2005. These outflows occur in conjunction with both magnetosheath electron precipitation and large-scale field-aligned currents. The detailed structure of the outflows appears to better correlated with the electron precipitation; a conclusion consistent with an earlier study of FAST data comparing cusp-region ion outflows to Poynting flux and electron precipitation. On comparing the observed ion fluxes to the soft electron precipitation using scaling laws derived from the earlier study we find the fluxes to be somewhat lower than predicted. This may be a consequence of the FAST observations being at lower altitudes than in the earlier study. At these lower altitudes the ions have not been accelerated to sufficiently high energy to overcome the energy cut-off of the detector. In addition the observed fluxes may be reduced since the spacecraft is moving upwards at ~ 1 km/s. It is also of interest to note that the velocity-dispersed ion precipitation signatures can appear to contradict the convection pattern inferred from the field-aligned current signatures. In particular while the field-aligned currents indicate convection to higher latitudes within the cusp-region, the velocity-dispersed ions can, on occasion, suggest convection to lower latitudes. This may be a manifestation of temporal effects, or it could be caused by complicated reconnection geometry at the magnetopause.