Structure of the subsolar magnetopause regions during northward IMF: First results from THEMIS

Abstract

THEMIS observations at the sub-solar magnetopause reveal the structure of the low latitude boundary layer (LLBL) and magnetosheath boundary layer (MSBL) during northward IMF. Unlike previous single spacecraft observations of this region, four of the five THEMIS spacecraft were able to capture the transition of magnetosheath plasma with no electron heating to unidirectional heated electrons followed by bi-directional heated electrons, demonstrating that this electron structure is spatial. Furthermore, the sequence of these transitions shows that the bi-directional heated electrons appear at the outer edge of the weak magnetopause current sheet. Since heated magnetosheath electrons outside the magnetopause current layer are used as an indicator of lobe reconnection in the hemisphere radiating these electrons, reconnection in both lobes is observed before the flux tubes cross the magnetopause. In essence, these observations provide convincing evidence that the LLBL was formed by dual-lobe reconnection. Copyright 2008 by the American Geophysical Union.