Analysis on the auroral electrojet by numerical simulation

Abstract:

We developed a simplified three dimensional Hall-MHD simulation to understand the magnetosphere-ionosphere coupling in the polar region during the auroral substorm. The governing equations were derived from the law of conservation of momentum of ions and electrons, the equation of continuity of plasma, the law of Ohm, the law of Ampere, and the law of Faraday. The Hall effect is included because it retains the Hall term in the governing equations. The advection in the governing equations were solved by using the implicit scheme and the Lax-Wendroff scheme and the Superbee limiter function. We imposed a flow shear on the topside boundary to excite Alfven wave. Two cases are tested. In the first case, we assumed uniform ionospheric plasma density. It was confirmed that the Alfven wave propagated downward and the FACs were closed by the Pedersen current in the lower ionosphere. In the second case, a high-density channel is imposed in the east-west direction. The secondary electric field is confirmed to appear due to the blockage of the Hall current (polarization), which intensifies the ionospheric current. This is similar to the auroral electrojet. We show 3D current system associated with the auroral electrojet.