Thin current sheets in the magnetotail at lunar distances: statistics of ARTEMIS observations

TL;DR

This study statistically analyzes 1261 ARTEMIS satellite crossings of the lunar-distance magnetotail current sheet, revealing its persistent thinness, partial force-free configurations, and the influence of solar wind conditions on its properties.

Contribution

It provides the first comprehensive statistical characterization of the midtail current sheet at lunar distances over an entire solar cycle, highlighting its thinness and magnetic configurations.

Findings

The current sheet remains extremely thin, comparable to the ion gyroradius.

Approximately 25% of current sheets are partially force-free with magnetic shear dominance.

Solar wind activity influences the occurrence and properties of the current sheets.

Abstract

The magnetotail current sheet's spatial configuration and stability control the onset of magnetic reconnection - the driving process for magnetospheric substorms. The near-Earth current sheet has been thoroughly investigated by numerous missions, whereas the midtail current sheet has not been adequately explored. This is especially the case for the long-term variation of its configuration in response to the solar wind. We present a statistical analysis of 1261 magnetotail current sheet crossings by the Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) mission orbiting the moon (X~-60 RE), collected during the entirety of Solar Cycle 24. We demonstrate that the magnetotail current sheet typically remains extremely thin, with a characteristic thickness comparable to the thermal ion gyroradius, even at such large distances from Earth's dipole. We also find that a substantial fraction (~one quarter) of the observed current sheets have a partially force-free magnetic field configuration, with a negligible contribution of the thermal pressure and a significant contribution of the magnetic field shear component to the pressure balance. Further, we quantify the impact of the changing solar wind driving conditions on the properties of the midtail around the lunar orbit. During active solar wind driving conditions, we observe an increase in the occurrence rate of thin current sheets, whereas quiet solar wind driving conditions seem to favor the formation of partially force-free current sheets.