Properties of the current sheets in the Earth’s magnetotail electron diffusion regions

Theoretical and numerical simulation studies suggest that, during symmetric magnetic reconnection, the current sheet evolves from a single-peaked Harris-type structure to a double-peaked bifurcated configuration. However, due to limitations in satellite measurement resolution, this evolution has not yet been observationally confirmed. Benefiting from the high-resolution observations of the Magnetospheric Multiscale (MMS) mission, more than ten electron diffusion region (EDR) events have been reported in the Earth’s magnetotail in recent years. In this study, we apply the Harris current sheet model to perform a systematic analysis of 13 magnetotail EDR events reported by Wang et al^[1]. The results show that nine events are well described by a Harris-type current sheet, with relatively thin thicknesses down to 0.67 electron inertial lengths. Moreover, as the current sheet becomes thinner, the electron outflow velocity increases significantly, reaching up to 0.45 electron Alfvén speeds, indicating that the MMS1 crossing locations in each EDR are progressively farther from the X point. The remaining four events exhibit clear bifurcated current sheet features, with double-peaked current density profiles and significantly thicker current sheets, reaching up to ~20 electron inertial lengths, corresponding to locations farther away from the reconnection X point and associated with lower electron outflow speeds. This study statistically determines the relative spatial distribution of 13 electron diffusion region events with respect to the reconnection X point, which helps to improve our understanding of electron kinetic processes within EDR.