On the Dipolarization Front and Magnetopause: 3. Evidence of Electron Kelvin–Helmholtz Instability at Dipolarization Front

Abstract Over the past 6 decades, Kelvin–Helmholtz (K–H) vortices, arising from quasi‐viscous flow velocity shear on the flanks of the magnetopause, have been extensively studied and are recognized as a key pathway for solar wind entry into the magnetosphere. Recent research by W. D. Fu et al. (2025a, ( https://doi.org/10.1029/2025ja033633 ), 2025b), ( https://doi.org/10.1029/2025ja033894 ) has shown that the magnetopause and dipolarization front share many similar characteristics, implying that such instabilities could also be triggered on the flanks of dipolarization fronts. Here, we report a DF crossing event observed by the Magnetospheric Multiscale (MMS) mission, during which the spacecraft traversed from the dawnside flank of the front. Electron flow vortices were detected at the boundary, which are confirmed to result from electron K–H instability, developed by velocity shear in the electron flows. Using the FOTE‐V method, we reconstruct the local velocity topology and identify a vortex with a characteristic scale of ∼6 d e , in agreement with theoretical predictions. These results provide direct evidence for electron K–H instability at the DF flanks, unveiling a new layer of complexity in boundary dynamics and offering a powerful window for studying these fundamental instabilities across different scales.