A statistical study of the magnetic signatures of FTEs near the dayside magnetopause

During magnetopause crossings, the AMPTE CCE satellite frequently observed flux transfer events (FTEs) characterized by fluctuations in the magnetic field strength ( B ) and bipolar signatures in the field component ( B _N ) normal to the nominal magnetopause. In this study, we survey 110 events observed from October to December 1984 and during January 1986. Nearly all events exhibited increases in B , and although the majority of events exhibited a symmetric bipolar signature in B _N , a significant number (31 of 110) had asymmetric bipolar signatures in which the trailing pulse was dominant. Most of the asymmetric events were observed near the magnetic equator. This is consistent with an explanation in which FTEs form via merging along a single subsolar X line with strongly asymmetric signatures but that these signatures evolve into the familiar symmetric bipolar form with distance from the merging line.