AURORAL AND GEOMAGNETIC EVENTS AT CUSP MANTLE LATITUDES IN THE PRENOON SECTOR DURING POSITIVE IMF B-Y CONDITIONS - SIGNATURES OF PULSED MAGNETOPAUSE RECONNECTION/

A characteristic sequence of poleward moving auroral events and the as sociated ground magnetic deflections in the vicinity of cusp-type prec ipitation in the convection throat are studied. The occurrence, struct ure, and motion pattern of these events are found to be strongly regul ated by the IMF B-z and B-y components. The present cases are observed in the prenoon sector during positive IMF B-y and negative B-z condit ions. New, improved results on the dynamical structure of the magnetos phere-ionosphere current system of these events are obtained. The curr ent system consists of a central filament or sheet-like field-aligned current (FAC), located on newly opened field lines with oppositely dir ected return currents on the poleward and equatorward sides. The groun d magnetic deflections can be explained by ionospheric Hall currents g enerated by this FAC system and the associated pattern of ionospheric electric fields. The propagation speed of the events (auroral and magn etic signatures) are found to be comparable with the simultaneously ob served antisunward convection speeds (1-2 km/s); that is, they are rel ated to the tailward convection of newly opened magnetic flux. A quali tatively similar current system with opposite current polarity has rec ently been proposed for the corresponding auroral and magnetic signatu res observed during negative IMF B-y conditions. The events are found to be consistent with an interpretation in terms of pulsed magnetopaus e reconnection, that is, flux transfer events.