Observation of a Knotted Electron Diffusion Region in Earth's Magnetotail Reconnection

TL;DR

This paper reports the first observation of a non-coplanar, knotted electron diffusion region in Earth's magnetotail, revealing complex 3D structures and multiscale coupling during magnetic reconnection.

Contribution

It provides direct MMS observations of a 3D knotted EDR, challenging the traditional 2D reconnection models and highlighting the importance of 3D effects.

Findings

Reconnection plane of the knotted EDR deviates by ~38° from the ion diffusion region

Guide field shows a 38° directional shift and doubled amplitude in the EDR

Hall magnetic field is bipolar in the EDR and quadrupolar in the IDR

Abstract

Magnetic reconnection is a fundamental plasma process that alters the magnetic field topology and releases magnetic energy. Most numerical simulations and spacecraft observations assume a two-dimensional diffusion region, with the electron diffusion region (EDR) embedded in the same plane as the ion diffusion region (IDR) and a uniform guide field throughout. Using observations from Magnetospheric Multiscale (MMS) mission, we report a non-coplanar, knotted EDR in Earth's magnetotail current sheet. The reconnection plane of the knotted EDR deviates by approximately 38{\deg} from that of the IDR, with the guide field exhibiting both a 38{\deg} directional shift and a twofold increase in amplitude. Moreover, the Hall magnetic field is bipolar in the EDR but quadrupolar in the IDR, indicating different Hall current structures at electron and ion scales. These observations highlight the importance of three-dimensional effects and illustrate the complexity of multiscale coupling between the EDR and IDR during reconnection studies.1