The magnetised plasma of the near-Earth space environment supports ultra-low frequency (ULF ;1-100 mHz), magnetohydrodynamic (MHD) oscillations in predominantly two wave modes. The fast Alfvén mode spreads ULF wave energy isotropically throughout the magnetosphere. For sufficiently large ionospheric conductances the shear Alfvén mode forms field line resonances (FLRs) between the northern and southern ionospheres. These conditions are usually met for daytime ionosphere conductance values. The FLRs are used to remotely sense plasma mass densities in the magnetosphere. The oscillations lose energy in the ionosphere, whose properties determine the boundary conditions, particularly by resonance damping effects. Using a MHD model of the magnetosphere with realistic ionosphere boundary conditions, the variation in resonant frequency with ionosphere conductance is reported. The effects of the ionospheric conductance on the ULF wave fields along the resonant field lines are also shown. The finite Pedersen and Hall conductances dissipate wave energy into the ionosphere and the spatial and temporal distributions of this energy show a distinct poleward propagation.
7th Australian Space Science Conference. Proceedings of the 7th Australian Space Science Conference (Sydney 24-27 September, 2007) p. 98-109