MMS Observations of a Compressed Current Sheet: Importance of the Ambipolar Electric Field

TL;DR

This study uses MMS spacecraft data to analyze a thin magnetotail current sheet, highlighting the role of ambipolar electric fields and associated wave phenomena in magnetic reconnection.

Contribution

It provides new insights into the importance of ambipolar electric fields and localized wave activity in the structure and dynamics of current sheets during reconnection.

Findings

Ambipolar electric field causes significant ExB velocity shear.

Localized lower hybrid waves are driven by the electric field.

Embedded substructures indicate a non-ideal current sheet.

Abstract

Spacecraft data reveals a nonuniform ambipolar electric field transverse to the magnetic field in a thin magnetotail current sheet that leads to intense ExB velocity shear and non-gyrotropic particle distributions. The ExB drift far exceeds the diamagnetic drift and drives lower hybrid waves localized to the magnetic field reversal region, which is ideally suited for the anomalous dissipation necessary for reconnection. It also reveals substructures embedded in the current density, indicating the formation of a non-ideal current sheet.