Simultaneous observations of flux transfer events by THEMIS, Cluster, Double Star, and SuperDARN: Acceleration of FTEs

Abstract

We present simultaneous observations of flux transfer events (FTEs) made by the THEMIS and Cluster spacecraft on 3 May 2007, along with supporting observations of fast flows in the dayside ionosphere observed by the SuperDARN radar network. The THEMIS spacecraft were in a string-of-pearls formation approximately 20,000 km long and crossed the postnoon magnetopause at low latitudes between 1200 UT (TH-C) and 1430 UT (TH-E). The Cluster spacecraft were situated in the magnetosheath at high latitudes in the Southern Hemisphere, approaching the magnetopause which was crossed at about 1600 UT. THEMIS observed "standard" polarity FTE signatures between 1100 and 1500 UT, while Cluster observed "reverse" polarity signatures at the same time. The two sets of signatures are consistent with being generated at the same small region of a subsolar reconnection line. Between 1100 and 1230 UT, the Double Star TC-1 satellite was near the magnetopause closer to local noon but still ∼7 RE from the subsolar point. TC-1 only observed a single FTE, suggesting that the variability of the reconnection rate differed between these two locations on the X line. Fast poleward ionospheric flows were observed in the noon and prenoon sector, at similar magnetic local times to the footprints of both Cluster and THEMIS, after 1200 UT. The long string formation of the THEMIS constellation allows the motion of the FTE structures to be tracked, and the acceleration is found to be small but consistent with a model prediction. Copyright 2009 by the American Geophysical Union.