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

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 i (~30 e) in the circular cross-section perpendicular to its axis, where i and 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°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.

Waves in Kinetic‐Scale Magnetic Dips: MMS Observations in the Magnetosheath

“…Kinetic‐scale magnetic dips (KSMDs) are a significant depression of magnetic field strength with a scale size close to or less than a proton gyroradius (ρ i ). These structures have been observed both in the Earth's magnetospheric plasma sheet (e.g., Ge et al, ; Gershman et al, ; Goodrich et al, ; Sun et al, ; Sundberg et al, ; Yao et al, ; Zhima et al, ; Zhang et al, ) and magnetosheath (e.g., Huang, Sahraoui, et al, ; Yao et al, ). In addition to observational investigations, KSMDs have also been extensively studied through theoretical analysis and numerical simulations (e.g., Balikhin et al, ; Haynes et al, ; Ji et al, ; Li et al, ; Roytershteyn et al, ).…”

“…Many of these key processes involve kinetic‐scale physics. With measurements of high‐temporal cadence from the Magnetospheric Multiscale (MMS) mission (Burch et al, 2016), the KSMDs and some possible related structures were reported in the turbulent magnetosheath (Huang, Sahraoui, et al, ; Yao et al, ; Yao, Shi, Guo, et al, ) and are thought to play an important role in dissipating energy (Huang, Sahraoui, et al, ). In addition, from recent two‐ and three‐dimensional particle‐in‐cell simulations, the KSMDs were found in turbulent magnetized plasmas (Haynes et al, ; Roytershteyn et al, ).…”

Intense Electric Fields and Electron‐Scale Substructure Within Magnetotail Flux Ropes as Revealed by the Magnetospheric Multiscale Mission

“…The electron vortex is reminiscent of small‐scale magnetic holes, observed extensively in the plasma sheet (Gershman et al, ; Goodrich, Ergun, & Stawarz, ; Goodrich, Ergun, Wilder, et al, ), magnetosheath (Huang, Du, et al, ; Huang, Sahraoui, et al, ; Yao et al, ), and kinetic simulations (Haynes et al, ). In these structures, electron‐scale current loops generate depletions in | B |, and similar to the structure observed here, J in some cases is linked to electron E × B drifts (Goodrich, Ergun, & Stawarz, ).…”

Measurements of the Vorticity in the Bursty Bulk Flows

“…The spacecraft separation is about 10–20 km, capable of resolving the vorticity of ion‐scale and larger‐scale structures. Such configuration, however, may not measure the vorticity of electron‐scale vortex such as in Huang et al (, ) and Zhong et al ().…”