Simultaneous measurements of the magnetopause and flux transfer events at widely separated sites by AMPTE UKS and ISEE 1 and 2

Abstract

On September 19, 1984, the ISEE 1 and 2 and AMPTE UKS and IRM spacecraft pairs crossed the dayside magnetopause at nearly the same universal time and magnetic local time but at much different latitudes. This fortuitous occurrence allows the magnetopause and flux transfer events (FTEs) to be studied at two widely separated sites simultaneously. FTEs are observed at both locations, those at UKS having standard normal component signatures, while those at ISEE have reverse signatures. The FTEs at UKS, closer to the equator, appear to have less helicity, or “twistedness” than those at ISEE far to the south. By identifying FTEs using the stringent Rijnbeek criterion for the bipolar Bn signature one might conclude that FTEs are not necessarily detected simultaneously at UKS and ISEE. However, careful analysis of the field strength behavior at ISEE does reveal evidence that FTEs are indeed observed at both sites simultaneously. While within the magnetosphere, AMPTE and ISEE both observe a coherent field rarefaction coupled with a tilt; we speculate that the signature is associated with time‐dependent dayside magnetopause reconnection.