Source and structure of bursty hot electron enhancements in the tail magnetosheath: Simultaneous two-probe observation by ARTEMIS

Bursty enhancements of hot electrons (≳0.5 keV) with duration of minutes sometimes occur in the tail magnetosheath. In this study we used the unique simultaneous measurements from the two Acceleration Reconnection Turbulence and Electrodynamics of Moon\textquoterights Interaction with the Sun probes to investigate the likely sources, spatial structures, and responsible processes for these hot electron enhancements. The enhancements can be seen at any distance across the magnetosheath, but those closer to the magnetopause are more often accompanied by magnetosheath density and flow magnitudes changing to more magnetosphere-like values. From simultaneous measurements 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, the enhancements and changes in the magnetosheath properties becoming smaller with increasing outward distance from the intrusion. From limited events having specific 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 over 7 RE in the Y direction, and as thin as 1 RE in the Z direction. We propose that Kelvin\textendashHelmholtz perturbations at the magnetopause and subsequent magnetosphere-magnetosheath particle mixing due to reconnection or diffusion can plausibly play an important role in generating the bursty magnetosphere intrusion into the magnetosheath and the hot electron enhancements.