Field-Aligned Currents Originating From the Chaotic Motion of Electrons in the Tilted Current Sheet: MMS Observations

Field-aligned currents often appear at the neutral sheet in the tilted current sheet, however, their origins are still unclear. Here we investigate two flapping motion events using the Magnetospheric Multiscale mission data. Strong current densities mainly contributed by electrons appear near the neutral sheet in the severely titled current sheet in both events. The perpendicular current can be explained by the electron drift motions, among which the diamagnetic drift is the main contributor. We find that electrons can be non-adiabatic at the neutral sheet, which is able to scatter their pitch angle distribution. The field-aligned current is associated with non-adiabatic electrons in the energy range of ∼0.2–3 keV, which curvature parameter κ is in the range of 0.9–3. By contrast, adiabatic electrons have almost no contribution to the field-aligned current. We suggest that non-adiabatic electrons are the key factor in generating field-aligned currents at the neutral sheet.