Field‐Aligned Currents Originating From the Chaotic Motion of Electrons in the Tilted Current Sheet: MMS Observations. Issue 9 (10th May 2021)

• Record Type: Journal Article
• Authors: Wang, G. Q.; Zhang, T. L.; Wu, M. Y.; Xiao, S. D.; Wang, G.; Chen, Y. Q.; Sun, J. C.; Volwerk, M.
• Is Part Of: Geophysical research letters. Volume 48:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-10
• Subjects: current sheet -- flapping motion -- field‐aligned current -- neutral sheet -- non‐adiabatic electron; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL088841
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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. Plain Language Summary: Flapping motions are large‐scale movements of the current sheet in the north‐south direction. They can create magnetic pulsations with a period of 40–150 s via field‐aligned currents connecting to the ionosphere along the magnetic field line. The generation mechanism of the field‐aligned current during the flapping is unclear, although the field‐aligned current often appears at the neutral sheet. Here we investigate two flapping motion events using the data obtained from the Magnetospheric Multiscale mission. We find that a strong current density contributed by electrons occurs in the tilted current sheet. The perpendicular current is mainly formed by the combination of the electron drift motions. The high‐resolution data obtained from the Magnetospheric Multiscale mission enable us to reveal that the electron can become chaotic or non‐adiabatic at the neutral sheet, which can scatter the pitch angle distribution. The field‐aligned currents in both events are associated with the non‐adiabatic electron. We also find that the adiabatic electron has almost no contribution to the field‐aligned current. The electron scattering can divert the perpendicular current to field‐aligned. Thus, our results suggest that the non‐adiabatic electron scattering is one possible generation mechanism of the field‐aligned current during the flapping motion. Key Points: A strong current contributed by electrons occurs in the tilted current sheet during the flapping motion Electrons are non‐adiabatic at the neutral sheet, and their pitch angle distributions undergo scattering The field‐aligned current is suggested to be generated by the non‐adiabatic electron at the neutral sheet during the flapping motion