Field‐Aligned Anisotropy of Electrons in Magnetic Hole Behind the Dipolarization Front in the Flow Braking Region

Abstract Magnetic holes (MHs) are magnetic structures characterized by a depression of magnetic field strength and have been frequently observed around dipolarization fronts (DFs), which are characterized by the increase in the magnetic field B z . Both MHs and DFs are potential contributors to the formation of electron anisotropy. However, it remains unclear whether the electron anisotropy within MH can form locally when the MH occurs around a DF. In this study, we present an observation of a MH behind the DF in the flow braking region. The enhancement of high‐energy electron flux inside the MH, together with the contraction of the MH, suggests that local Fermi acceleration could contribute to the formation of electron field‐aligned anisotropy inside the MH. Our results show that in the flow braking region, where multiple dynamic processes occur, the electron field‐aligned anisotropy inside the MH behind the DF can be formed locally by Fermi acceleration. This study provides a new perspective for understanding the dynamic process of electrons around the DFs in the magnetotail.