Reconstruction of a flux transfer event based on observations from five THEMIS satellites

Abstract

We investigate a flux transfer event (FTE) observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) near the duskside magnetopause using the reconstruction technique based on solving the Grad‐Shafranov equation; see review by Sonnerup et al. (2006). THEMIS D detected the FTE with the largest core magnetic field. THEMIS B and C observed deep troughs in the magnetic field associated with the FTE. THEMIS A and E sensed only slightly altered magnetic field from their surroundings. Two‐dimensional reconstruction maps of magnetic field and plasma pressure are generated by combining observations from all five THEMIS satellites. These reconstructed maps show distinct differences between a magnetic island and an FTE in terms of vector potential and the derived plasma parameters. The origin of the magnetic field troughs in the crater FTEs can be traced to intrusions of the magnetosheath plasma around the structure in the reconstruction maps. Furthermore, the resulting maps show also cylindrical asymmetry in these parameters between the magnetosheath and magnetospheric sides of the FTE. This asymmetry and the different impact parameters of these satellites with respect to the FTE center together contribute to the different characteristics of the FTE signatures seen by the five THEMIS satellites.