Electron-only Reconnection in Ion-scale Current Sheet at the Magnetopause

TL;DR

This paper reports observations of electron-only magnetic reconnection at the Earth's magnetopause, revealing an extended electron diffusion region within an ion-scale current sheet, challenging existing reconnection models.

Contribution

It provides the first observational evidence of electron-only reconnection in an ion-scale current sheet at the magnetopause, with an unexpectedly long electron diffusion region.

Findings

Extended electron diffusion region observed, longer than theoretical predictions.

Reconnection occurs without ion outflow, indicating electron-only reconnection.

Challenges existing models of magnetic reconnection at ion scales.

Abstract

In the standard model of magnetic reconnection, both ions and electrons couple to the newly reconnected magnetic field lines and are ejected away from the reconnection diffusion region in the form of bidirectional burst ion and electron jets. Recent observations propose a new model: electron only magnetic reconnection without ion coupling in electron scale current sheet. Based on the data from Magnetospheric Multiscale (MMS) Mission, we observe a long extension inner electron diffusion region (EDR) at least 40 di away from the X line at the terrestrial Magnetopause, implying that the extension of EDR is much longer than the prediction of the theory and simulations. This inner EDR is embedded in an ion scale current sheet (the width of 4 di, di is ion inertial length). However, such ongoing magnetic reconnection was not accompanied with burst ion outflow, implying the presence of electron only reconnection in ion scale current sheet. Our observations present new challenge for understanding the model of standard magnetic reconnection and electron only reconnection model in electron scale current sheet.