Electron dynamics surrounding the X line in asymmetric magnetic reconnection

Abstract

Electron dynamics surrounding the X line in magnetopause‐type asymmetric reconnection is investigated using a two‐dimensional particle‐in‐cell simulation. We study electron properties of three characteristic regions in the vicinity of the X line. The fluid properties, velocity distribution functions (VDFs), and orbits are studied and cross‐compared. On the magnetospheric side of the X line, the normal electric field enhances the electron meandering motion from the magnetosheath side. The motion leads to a crescent‐shaped component in the electron VDF, in agreement with recent studies. On the magnetosheath side of the X line, the magnetic field line is so stretched in the third dimension that its curvature radius is comparable with typical electron Larmor radius. The electron motion becomes nonadiabatic, and therefore the electron idealness is no longer expected to hold. Around the middle of the outflow regions, the electron nonidealness is coincident with the region of the nonadiabatic motion. Finally, we introduce a finite‐time mixing fraction (FTMF) to evaluate electron mixing. The FTMF marks the magnetospheric side of the X line, where the nonideal energy dissipation occurs.

Reconstruction of the Electron Diffusion Region of Magnetotail Reconnection Seen by the MMS Spacecraft on 11 July 2017

“…We note that the locations of the stagnation point and significant energy conversion are both on the earthward side of the X point in the present event and that for asymmetric reconnection with higher density and lower magnetic field magnitude on the magnetosheath side, the region of significant electron‐frame dissipation is shifted toward the same side (i.e., magnetospheric side) relative to the X point as is the stagnation point (Burch, Torbert, et al, ; Hesse et al, ; Zenitani et al, ). Although the direction of the displacement is different between the present event (along the outflow) and asymmetric reconnection (along the inflow), the displacement of both the stagnation point and the location of significant energy conversion in the same direction may not be a coincidence.…”

Drift turbulence, particle transport, and anomalous dissipation at the reconnecting magnetopause

“…9(b). This indicates that the mixing results not only from finite electron orbit effects, which are limited to ρ e length scales and also occur in 2D [5,22,27]. To demonstrate that this region indeed contains magnetosheath electrons mixed into the magnetosphere inflow, reduced electron velocity distributions in the v − v ⊥ (directions with respect to local magnetic field) are plotted in Fig.9(c…”

Electron Distribution Functions Around a Reconnection X‐Line Resolved by the FOTE Method

“…So far, there have been several studies focusing on this topic in both simulations and observations. For example, in simulations, the crescent-shape electron distributions were found near the X-lines and had been suggested as a signature of the EDR crossing Chen, Hesse, Wang, Bessho, et al, 2016;Egedal et al, 2016;Hesse et al, 2014;Le et al, 2017;Price et al, 2016;Zenitani et al, 2017). Such type of electron distribution was soon observed on the magnetosheath side of a X-line during the magnetopause ©2019.…”

“…For example, in simulations, the crescent-shape electron distributions were found near the X-lines and had been suggested as a signature of the EDR crossing Chen, Hesse, Wang, Bessho, et al, 2016;Egedal et al, 2016;Hesse et al, 2014;Le et al, 2017;Price et al, 2016;Zenitani et al, 2017). For example, in simulations, the crescent-shape electron distributions were found near the X-lines and had been suggested as a signature of the EDR crossing Chen, Hesse, Wang, Bessho, et al, 2016;Egedal et al, 2016;Hesse et al, 2014;Le et al, 2017;Price et al, 2016;Zenitani et al, 2017).…”