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

电离层和磁层之间的电磁耦合最终是通过小规模的电流和场来实现的。极光弧形成的尺度小于1公里。这个项目将研究电磁能量在上层极光电离层的这些小尺度上转移的过程。它将重点研究两个主要过程：(1)Alfven波的线性相位混合，其中Alfven速度存在垂直梯度；(2)被困在电离层Alfven谐振器中的Alfven波之间的非线性相互作用。该研究将通过使用非线性MHD代码对阿尔芬波的传播进行二维和三维模拟来进行。目前现有的线性MHD代码将被修改，以包括沿极光场线的电子惯性效应。它将包括密度空腔的形成和沿极光场线离子流出的影响。

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.