Satellite Observations of Separator Line Geometry of Three-Dimensional Magnetic Reconnection

TL;DR

This paper reports the first direct in situ observation of a 3D magnetic reconnection separator line in Earth's magnetotail, revealing detailed geometry and plasma dynamics crucial for understanding space plasma processes.

Contribution

It provides the first direct observational evidence of a 3D reconnection separator line connecting magnetic nulls in Earth's magnetotail.

Findings

Identified a null-null line connecting magnetic nulls in Earth's magnetotail.

Measured the separation between nulls as approximately 0.7 times the ion inertial length.

Detected a lower hybrid wave with wavelength approximately equal to the electron inertial length.

Abstract

Detection of a separator line that connects magnetic nulls and the determination of the dynamics and plasma environment of such a structure can improve our understanding of the three-dimensional (3D) magnetic reconnection process. However, this type of field and particle configuration has not been directly observed in space plasmas. Here we report the identification of a pair of nulls, the null-null line that connects them, and associated fans and spines in the magnetotail of Earth using data from the four Cluster spacecraft. With di and de designating the ion and electron inertial lengths, respectively, the separation between the nulls is found to be ~0.7di and an associated oscillation is identified as a lower hybrid wave with wavelength ~ de. This in situ evidence of the full 3D reconnection geometry and associated dynamics provides an important step toward to establishing an observational framework of 3D reconnection.