GEM: Magnetosphere-Ionosphere Coupling--Theory and Modeling of Small-Scale Auroral Currents and Fields

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The electromagnetic coupling between the ionosphere and the magnetosphere ultimately takes place through small-scale currents and fields. Auroral arcs form on scales smaller than 1 kilometer. This project will investigate the processes by which electromagnetic energy can be transferred to these small scales in the topside auroral ionosphere. It will focus on two of primary processes: (1) linear phase mixing of Alfven waves where there are perpendicular gradients in the Alfven speed, and (2) nonlinear interactions between Alfven waves trapped in the ionospheric Alfven resonator. The research will be carried out by using two and three dimensional simulations of the propagation of Alfven waves using a nonlinear MHD code. The currently existing linear MHD code will be modified to include electron inertial effects along auroral field lines. It will include the effects of the formation of density cavities and the outflow of ions along auroral field lines.