Magnetospheric Multiscale Observations of Electron Vortex Magnetic Hole in the Magnetosheath Turbulent Plasma

TL;DR

This paper reports the first direct observations of an electron vortex magnetic hole in the magnetosheath, revealing a new coherent structure in turbulent space plasma with unique magnetic and electron flow characteristics.

Contribution

It provides the first observational evidence of an electron vortex magnetic hole, confirming predictions from kinetic simulations and expanding understanding of plasma turbulence structures.

Findings

Magnetic depression with density peak and temperature changes

Electron vortex formation indicated by electron flux and velocity variations

Size of magnetic hole approximately 0.23 proton gyroradii

Abstract

We report the observations of an electron vortex magnetic hole corresponding to a new type of coherent structures in the magnetosheath turbulent plasma using the Magnetospheric Multiscale (MMS) mission data. The magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the center of the magnetic hole and a peak in the outer region of the magnetic hole. The estimated size of the magnetic hole is about 0.23 \r{ho}i (~ 30 \r{ho}e) in the circular cross-section perpendicular to its axis, where \r{ho}i and \r{ho}e are respectively the proton and electron gyroradius. There are no clear enhancement seen in high energy electron fluxes, but an enhancement in the perpendicular electron fluxes at ~ 90{\deg} pitch angles inside the magnetic hole is seen, implying that the electron are trapped within it. The variations of the electron velocity components Vem and Ven suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the circular cross-section (in the M-N plane). These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations.