Electric structure of dipolarization fronts associated with interchange instability in the magnetotail

Abstract

AbstractThe electric structure of dipolarization fronts (DFs) is very important to both DF dynamics and particle acceleration. We performed two‐dimensional Hall MHD simulation to study the electric structure of DF produced by interchange instability on the scale of ion inertial length in the flow braking region of near‐Earth tail. The results indicate that the Hall effect makes the structures of plasma density and magnetic field deformed in the dawn‐dusk direction. This deformation is caused by the induced Lorentz force along the tangent plane of DF, which is associated with the outward moving of demagnetized ions driven by the ion‐scale Earthward electric field on DF. In addition, the x component of electric field contributed jointly by Hall and electron pressure gradient terms along with Bz can produce a dawnward E × B drift to the whole “mushroom” structure. Inside the DF, the electric field is mainly produced by Hall term, and the contributions from the convectional and electron pressure gradient electric fields are very small. This indicates that the ion frozen‐in condition of magnetic field is violated inside the DF. Therefore, it is the electric field contributed by Hall term inside the DF that changes the overall MHD “mushroom” pattern. The comparison between the simulation results and the observations of THEMIS satellites demonstrates that the model of Hall MHD simulation can reproduce the plasma and electric field observed at DF.