The Kelvin-Helmholtz instability generates vortices and mixing of magnetosheath and magnetosphere plasma populations at the
magnetopause during northward interplanetary magnetic field configurations. A Kelvin-Helmholtz event has been recorded by the four
spacecraft of the Magnetospheric Multiscale (MMS) mission during a magnetopause crossing on the dusk side flank on 8 September
2015. MMS high resolution measurements permit unprecedented detailed analysis of small-scale structures within the vortices.
Magnetic reconnection events were identified and analyzed to understand the associated small- and large-scale topological changes, in
particular using the fine structure of the electron boundary layers. Owing to the existence of a previously formed boundary layer, the
plasma density ratio across the reconnecting current sheets is typically 2. This makes such KH-related reconnection events interesting
for studying quasi-symmetric reconnection (with bifurcated current sheets).