Propagation of Alfvén waves through the ionosphere

Waves in the 1 Hz frequency band are commonly observed at all local times by both ground observations of magnetic fields as well as satellite observations of electric and magnetic fields. Such waves may be externally generated in the outer magnetosphere, such as Pc1 oscillations that are generally thought to be generated by ion cyclotron instabilities in or near the cusp region of the magnetopause, or may be self-consistently generated in the ionospheric resonant cavity. Modeling the ground signatures of such waves is complicated by the fact that at these frequencies, the electromagnetic skin depth is comparable to the ionospheric thickness and so the vertical structure of the ionosphere must be resolved. In addition, the Hall conductivity in the ionosphere couples shear Alfvén waves to compressional (fast) mode waves that can propagate across field lines in the ionosphere. A model has been developed which can describe these interactions, and which can determine the ground signatures of Pc1 oscillations not only on the field line on which they are generated but also as they propagate horizontally through the ionospheric waveguide. First results from this model are presented.