Observations at low latitudes of magnetic merging signatures within a flux transfer event during a northward interplanetary magnetic field

Abstract

Flux transfer events (FTE) have been postulated to result from transient magnetic merging. If so, the ion distributions within an event should exhibit features known to result from merging. Observations of an FTE by instruments on the Polar spacecraft revealed classical merging signatures that included: (1) D-shaped, accelerated, magnetosheath ion distributions, (2) a well-defined de Hoffman-Teller frame, (3) local stress balance, and (4) a P-N magnetic field signature. This FTE was observed near the magnetic equator at ∼13 magnetic local time under conditions of a strongly northward interplanetary magnetic field (IMF) (clock angle of <10°). The nature of the ion distributions and the consistency of the measured cutoff speed with that calculated from the measured local magnetic field and the derived de Hoffman-Teller speed show the ion injection to be local. Coupled with the northward IMF, these results lead to the conclusion that component merging in the low-latitude region was responsible for the FTE.