Kinetics of Magnetic Hole Behind Dipolarization Front

Abstract

AbstractMagnetic holes (MHs)—depressions in magnetic field strength—have been reported around dipolarization fronts (DFs), but their generation and dynamics remain elusive owing to the limited capacity of previous spacecraft measurements. Taking advantage of magentospheric multiscale mission high‐resolution data, here we present the first observational evidence for MH generation by electron mirror instability behind a DF. The MH is sustained by an electron flow vortex at sub‐proton scale and primarily drifting downward. Instability analysis shows that local condition is unstable to electron mirror instability, suggesting that the MH is electron mirror mode. The MH contains strong field‐aligned currents which may contribute to the magnetosphere‐ionosphere coupling. The MH also hosts oscillatory energy conversion with energy loads dominant (integral of E·J is positive), suggesting that it can be efficient in transferring electromagnetic energy into particle energy. Sub‐ion‐scale dissipation of the magnetic field is coupled with electron‐scale whistlers and Debye‐scale solitary waves, indicating cross‐scale coupling therein.