A STATISTICAL STUDY OF TRANSIENT EVENTS IN THE OUTER DAYSIDE MAGNETOSPHERE

The AMPTE CCE satellite frequently observed transient (1 less than or equal to tau less than or equal to 8 min) events marked by magnetic fi eld strength increases and bipolar magnetic field signatures peak-to-p eak amplitudes greater than or equal to 4 nT) while in the outer daysi de magnetosphere. We report a survey of 59 prominant events observed f rom August to November 1984. The bipolar signatures and minimum varian ce analysis reveal that most events move poleward and antisunward, exc ept in the immediate vicinity of local noon. Here the motion of the ev ents appears to be better governed by the spiral/orthospiral interplan etary magnetic field (IMF) orientation than magnetic curvature forces associated with IMF B-y. The IMF orientation appears to have little or no influence on event occurrence or orientation. We interpret the eve nts in terms of solar wind/foreshock pressure pulse induced ripples on the magnetopause surface. Our results can be reconciled with those ob tained in previous studies which made use of ISEE 1/2, AMPTE IRM, and AMPTE UKS observations if pressure pulses produce large-amplitude even ts and bursty merging (or reconnection) produces small-amplitude event s.