Intense cross-tail field-aligned currents in the plasma sheet at lunar distances

TL;DR

This study reveals a new system of intense field-aligned currents at lunar distances in Earth's magnetotail, which helps balance plasma pressure and magnetic forces, based on ARTEMIS satellite observations.

Contribution

It identifies and characterizes a previously unreported field-aligned current system at lunar distances in Earth's magnetotail, expanding understanding of tail current dynamics.

Findings

Significant field-aligned currents (1-10 nA/m²) flow along magnetic field lines near the neutral sheet.

Magnetic field component across the tail peaks at the equator, contributing to pressure balance.

Approximately half of the observed current sheet crossings show this magnetic field component's importance.

Abstract

Field-aligned currents in the Earth's magnetotail are traditionally associated with transient plasma flows and strong plasma pressure gradients in the near-Earth side. In this paper we demonstrate a new field-aligned current system present at the lunar orbit tail. Using magnetotail current sheet observations by two ARTEMIS probes at $\sim60 R_E$, we analyze statistically the current sheet structure and current density distribution closest to the neutral sheet. For about half of our 130 current sheet crossings, the equatorial magnetic field component across-the tail (along the main, cross-tail current) contributes significantly to the vertical pressure balance. This magnetic field component peaks at the equator, near the cross-tail current maximum. For those cases, a significant part of the tail current, having an intensity in the range 1-10nA/m$^2$, flows along the magnetic field lines (it is both field-aligned and cross-tail). We suggest that this current system develops in order to compensate the thermal pressure by particles that on its own is insufficient to fend off the lobe magnetic pressure.