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

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.