Observations of Electron Vortex at the Dipolarization Front

Abstract

Abstract Dipolarization front (DF), embedded in fast plasma flow, is a sharp structure with the increase of B z in a short time and plays an important role in the energy dissipation and particle accelerations in the magnetotail. However, detailed physics at the small scales is still unclear in the DF due to the limitation of the previous mission. In the present study, an electron‐scale plateau in B z is observed at the DF by Magnetospheric Multiscale (MMS) mission. By analyzing the velocity of the electrons, we find that the electron‐scale plateau is surrounded by a sub‐ion‐scale electron vortex, which is the first observation of electron vortex at the DF as far as we know. The magnetic field generated by the electron vortex cancels parts of the increase of B z and causes the plateau. Strong asymmetric electric field and demagnetization of electrons and ions are observed at the boundary of the electron vortex. These results shed new light on that small‐scale structures can develop within the ion‐scale DF and affect the evolution and kinetic effects at the DF.