Source and Structure of Bursty Hot Electron Enhancements in the Tail Magnetosheath: Simultaneous Two-Probe Observation By Artemis

Friday, 19 December 2014: 9:15 AM
Chih-Ping Wang1, Xiaoyan Xing1, Larry R Lyons2 and Vassilis Angelopoulos1, (1)University of California Los Angeles, Los Angeles, CA, United States, (2)UCLA, Los Angeles, CA, United States
Bursty enhancements of hot electrons (~0.5 to 5 keV) with duration of minutes often occur in the tail magnetosheath. Determining the sources and energization of these hot electrons is important to understanding the coupling of the mangetosheath with the bowshock or magnetosphere. In this study we used the unique simultaneous measurements from the two ARTEMIS probes to investigate the likely source locations, spatial structures, and responsible processes for these hot electron enhancements. The enhancements can be seen at any distances across the magnetosheath, but those closer to the magnetopause more often have magnetosheath density and flow magnitudes decreased to more magnetosphere-like values. From simultaneous measurements of these enhancements with the two probes being on either side of magnetopause or both in the magnetosheath, it is evident that these hot electrons come from the magnetosphere near the current sheet without further energization, and that the enhancements are a result of bursty lateral magnetosphere intrusion into the magnetosheath, with weaker enhancements and smaller changes in the magnetosheath properties further outward from the intrusion. Using simultaneous observations having different separation distances and alignments between the probes, we estimated that a single isolated enhancement can have a thin and elongated structure as narrow as 2 RE wide in the X direction, as long as more than 7 RE in the Y direction, and as thin as 1 RE in the Z direction. From observed correlations between the enhancements seen on the magnetosheath side and magnetosheath intrusion seen on the magnetosphere side, we propose that Kelvin-Helmholtz perturbations at the magnetopause and subsequent magnetosphere-magnetosheath particle mixing due to reconnection or diffusion can plausibly explain the bursty magnetosphere intrusion deep into the magnetosheath and the different decreases of magnetosheath density and flow associated with the hot electron enhancements.