On Multiple Hall‐Like Electron Currents and Tripolar Guide Magnetic Field Perturbations During Kelvin‐Helmholtz Waves

Abstract

Two magnetopause current sheet crossings with tripolar guide magnetic field signatures were observed by multiple Magnetosphere Multiscale (MMS) spacecraft during Kelvin‐Helmholtz wave activity. The two out‐of‐plane magnetic field depressions of the tripolar guide magnetic field are largely supported by the observed in‐plane electron currents, which are reminiscent of two clockwise Hall current loop systems. A comparison with a three‐dimensional kinetic simulation of Kelvin‐Helmholtz waves and vortex‐induced reconnection suggests that MMS likely encountered the two Hall magnetic field depressions on either side of a magnetic reconnection X‐line. Moreover, MMS observed an out‐of‐plane current reversal and a corresponding in‐plane magnetic field rotation at the center of one of the current sheets, suggesting the presence of two adjacent flux ropes. The region inside one of the ion‐scale flux ropes was characterized by an observed decrease of the total magnetic field, a strong axial current, and significant enhancements of electron density and parallel electron temperature. The flux rope boundary was characterized by currents opposite this axial current, strong in‐plane and converging electric fields, parallel electric fields, and weak electron‐frame Joule dissipation. These return current region observations may reflect a need to support the axial current rather than representing local reconnection signatures in the absence of any exhausts.

Reconstruction of the Electron Diffusion Region of Magnetotail Reconnection Seen by the MMS Spacecraft on 11 July 2017

“…This validates our assumptions that the structure is roughly time‐independent and 2‐D for this particular 1.4‐s interval including the EDR. Note that a similar agreement between the magnetic field variation directly measured and that derived from FPI measurements of the current density was reported for a current sheet embedded in a magnetopause Kelvin‐Helmholtz wave event (Sturner et al, ).…”

Satellite Data‐Based 3‐D Simulation of Kelvin‐Helmholtz Instability and Induced Magnetic Reconnection at the Earth's Magnetopause

“…Signatures of the Hall quadrupole are visible below z = 0, even if quite distorted because of the "guide field" effect (Eastwood et al, 2010) and of the density asymmetry across the current sheet (Pritchett, 2008). A kinetic description would probably reduce the distortion associated with the density asymmetry since particles streaming along reconnected field lines would rapidly smooth out density variations (Sturner et al, 2018). At z ∼ 100, the magnetic fluctuations due to the KH vortex strengthen, suppressing possible quadrupolar signatures (see Figures S3 and S4).…”

Energy Conversion by Parallel Electric Fields During Guide Field Reconnection in Scaled Laboratory and Space Experiments

“…(e.g., for Wilder et al, ). Reconnection events driven by KH waves in the magnetopause flank have been proposed to contain multiple flux ropes which might support such dynamics (Eriksson et al, ; Nakamura et al, ; Sturner et al, ). Recent observations in sub‐ion scale current sheets have also observed very large parallel electric fields E || ∼5 E 0 (Phan et al, ); this presents a second idea that large reconnection rates may be linked to reconnection at small spatial scales.…”