On the short-scale spatial variability of electron inflows in electron-only magnetic reconnection in the turbulent magnetosheath observed by MMS

We investigate the detailed properties of electron inflow in an electron-only reconnection event observed by the four Magnetospheric Multiscale (MMS) spacecraft in the Earth’s turbulent magnetosheath downstream of the quasiparallel bow shock. The lack of ion coupling was attributed to the small scale sizes of the current sheets, and the observed bi-directional super Alfvénic electron jets indicate that the MMS spacecraft crossed the reconnecting current sheet on both sides of an active X-line. Remarkably, the MMS spacecraft observed the presence of large asymmetries in the two electron inflows, with the inflows (normal to the current sheet) on the two sides of the reconnecting current layer differing by as much as a factor of 4. Furthermore, even though the four MMS spacecraft were separated by less than 7 electron skin depths, the degree of inflow asymmetry was significantly different at the different spacecraft. The asymmetry in the inflow speeds was larger with increasing distances downstream from the reconnection site, and the asymmetry was opposite on the two sides of the X-line. We compare MMS observations with 2D-kinetic PIC simulation and find that the asymmetry in the inflow speeds stems from the in plane currents generated via a combination of reconnection mediated inflows and the parallel flows along the magnetic separatrices in the presence of a large guide field.