The Difference Between Isolated Flux Transfer Events and Flux Transfer Event Cascades

摘要

This flux transfer event (FTE) study is based on 984 FTEs originally identified by Wang et al. (2005, https://doi:10.1029/2005JA011150) in Cluster data. Due to Cluster's orbit, the FTE list exclusively contains events detected at the high-latitude dayside magnetopause and low-latitude flanks. The focus of this study is on FTE separation time. The results show that FTEs appearing in cascades are mainly located at the northern dusk and southern dawn magnetopause, while isolated FTEs are equally spread over the region covered by Cluster. This difference may be explained by the different interplanetary magnetic field (IMF) conditions during which the subsets occur. For isolated FTEs, average IMF B_y is close to zero. During such conditions, FTEs are expected to form at arbitrary longitudes along an equatorial merging line. After formation, they propagate northward and southward, causing an equal distribution at higher latitudes. In contrast, FTE cascades typically occur during weakly southward IMF with a negative B_y component. Their asymmetric distribution at higher latitudes is consistent with both the component and the antiparallel merging model for nonzero B_y. In both scenarios, newly formed FTEs are expected to move to the northern dusk and southern dawn regions, as observed. Many FTE cascades appearing during northward IMF are located close to the low-latitude flanks, confirming previous reports. We discovered that such FTEs appear during large IMF values. Another new result is that 16% of all isolated FTEs appear during small IMF cone angles, suggesting that these may form as a result of magnetosheath jets impacting on the magnetopause.