MMS Observations of Oscillating Energy Conversion and Electron Vorticity in an Electron‐Scale Layer Within a Southward Magnetopause Reconnection Exhaust

The MMS satellites traversed a similar to 6 di-wide and similar to 500 km/s southward reconnection exhaust at the dayside magnetopause on 6 December 2015 and similar to 29 di from the associated X-line region. A narrow similar to 0.26-0.34 di layer of enhanced +/- 3.5 nW/m3 oscillating energy conversion perpendicular to the magnetic field resides in this exhaust. It contained two regions of diverging in-plane electric fields in general agreement with two clockwise electron flow vortices and a proposed increase of the electron vorticity del x Ve. The layer developed sunward of a unipolar Hall magnetic field for a duskward BM/BL similar to 0.9 guide field. Each electron flow vortex supported a local triangle BM similar to 10 nT strengthening of this Hall field. The presence of this electron-scale layer in a southward exhaust for a duskward guide field is consistent with a two-dimensional simulation of a similar structure that evolved from an X-line into a northward exhaust for a similar strength dawnward guide field. Magnetic reconnection is a critical process that drives large-scale plasma convection in the Earth's magnetosphere. In this letter, we report new direct MMS observations for the presence of two electron flow vortices within a sub-ion scale energy conversion channel that resides in a dayside magnetopause reconnection exhaust. Each of the two electron-scale flow vortices is shown to contribute a significant fraction toward the large-scale Hall magnetic field. Electron-scale 0.3 di layer of oscillating energy conversion and electron vorticity detected in 6 di wide reconnection jet 30 di from EDR Two regions of in-plane diverging electric field in energy conversion layer consistent with two measured clockwise electron flow vortices Out-of-plane magnetic field increased similar to 10 nT from each passing electron vortex immediately sunward of 50 nT unipolar Hall magnetic field