Electron-scale reconnecting current sheet formed within the lower hybrid wave-active region of Kelvin-Helmholtz waves

The Kelvin-Helmholtz instability (KHI) excited at the Earth’s magnetopause has been considered responsible for causing efficient mass and energy transfer across the magnetopause. Theoretical, numerical and observational studies have revealed that the evolution of the KHI and the resulting nonlinear vortex flow involve secondary processes. As a unique case of such multi-scale and inter-process couplings, we recently reported observations of the MHD-scale KH waves and embedded smaller-scale phenomena in data from NASA’s Magnetospheric Multiscale (MMS) mission at the dusk- flank magnetopause during southward interplanetary magnetic field (IMF) conditions. Given quantitative consistencies with corresponding fully-kinetic particle-in-cell (PIC) simulations designed for this event, the MMS observations demonstrate the onset of the Lower-Hybrid Drift Instability (LHDI) during the nonlinear phase of the KHI and the subsequent turbulence and mixing of plasmas near the boundary layer.

In this study, we further explored this southward IMF KHI event and found signatures of magnetic reconnection in an electron-scale current sheet observed in the KH vortex-driven LHDI turbulence. This reconnection event was observed under high guide field conditions and features a super-Alfvénic electron outflow, a Hall perturbation of the magnetic field and enhanced energy conversion. Results from a high-resolution PIC simulation designed for this reconnecting current sheet suggest a highly dynamical current sheet evolution, quantitatively consistent with the observations made by MMS.

In addition, results from statistical studies utilizing data from several KH wave/vortex edge crossings throughout this southward IMF KH event show that the formation of electron-scale current sheets due to the interplay of the KHI and LHDI would be a ubiquitous phenomenon at least under the observed conditions of this magnetopause event and thus an important factor in the study of cross-scale energy transfer of the KHI.