The Electric Field and Its Impact on the Pitch Angle of Trapped Electrons in a Sub-ion-scale Magnetic Hole

Abstract Sub-ion-scale magnetic holes (MHs) are ubiquitous structures in plasmas across a wide range of environments. Despite previous observational and modeling efforts, the three-dimensional (3D) electric field in MHs has yet to be adequately resolved. In this study, utilizing high-resolution measurements of an MH (∼0.08 ρ i × 0.14 ρ i ) from the Magnetospheric Multiscale mission in Earth’s turbulent magnetosheath, we report this 3D electric field and unveil its roles and generation mechanism. A model is established to quantify the impacts of E ∥ on increasing the loss cone of trapped electrons. The electric field is attributed to electron convection and pressure gradient terms of generalized Ohm’s law. The MH, primarily coupling to the electron, is accompanied by electron jets. These electron jets can be interpreted as different segments of an electron vortex. These electron jets combined with nonideal electric fields not only lead to strong energy conversion ( j · ( E + v e × B ) ∼ 40 nW m −3 ) from the electromagnetic field to electrons but also enable energy conversion between different electron motion directions. Our study significantly clarifies the physical image of kinetic-scale MHs.