Electron scale nested quadrupole Hall field in Cluster observations of magnetic reconnection

TL;DR

This paper reports the first observational evidence of a nested quadrupole Hall field at electron scales during magnetic reconnection, revealing new electron-scale processes and structures in space plasma physics.

Contribution

It introduces the discovery of a nested quadrupole Hall field in electron current sheets, supported by Cluster observations and electron-magnetohydrodynamic simulations.

Findings

First evidence of nested quadrupole Hall field in space observations

Whistler response causes large-scale quadrupole structure

Simulation confirms mechanism of nested quadrupole formation

Abstract

This Letter presents the first evidence of a new and unique feature of spontaneous reconnection at multiple sites in electron current sheet, viz. nested quadrupole structure of Hall field at electron scales, in Cluster observations. The new nested quadrupole is a consequence of electron scale processes in reconnection. Whistler response of the upstream plasma to the interaction of electron flows from neighboring reconnection sites produces a large scale quadrupole Hall field enclosing the quadrupole fields of the multiple sites, thus forming a nested structure. Electron-magnetohydrodynamic simulations of an electron current sheet yields mechanism of the formation of nested quadrupole.