A three-dimensional model of the propagation of alfvén waves through the auroral ionosphere: First results

The propagation of Alfvén waves in the auroral ionosphere is important in the determination of ground signatures of time-varying currents, in the formation of Pc1 compressional waves that can be ducted in the ionospheric waveguide, and in the development of field-aligned currents and parallel electric fields during auroral acceleration processes. This report presents the first results from a three-dimensional model of the linear propagation of these waves. In this model, the ionosphere is treated as a thin slab carrying Pedersen and Hall currents. The jump conditions across this boundary lead to the coupling of shear and compressional MHD modes at the ionosphere and also allow the ground signatures of these waves to be calculated within the context of the model. This model has been used to study this coupling and to illustrate the excitation and propagation of compressional MHD waves within the ionospheric waveguide. A new numerical scheme for the modeling of parallel electric fields is introduced and the excitation of resonance cone structures by narrow impulses is demonstrated.