Modeling of the ionospheric Alfvén resonator in dipolar geometry

A new model for the propagation of ultralow-frequency (ULF) waves in dipolar geometry has been developed. This model features a full height-resolved ionosphere including finite Pedersen, Hall, and parallel conductivities. By using a nonorthogonal coordinate system, this model is capable of calculating the ground magnetic field produced by ULF waves and comparing these fields to those measured in the ionosphere and magnetosphere. This model has been used to investigate the properties of the ionospheric Alfvén resonator (IAR) in a dipolar magnetosphere. Although the IAR mode frequencies are not strongly affected by the finite magnetic zenith angle, the damping of these waves is enhanced by the presence of the height-resolved ionosphere. Pedersen conductivity shields higher frequency ULF waves such as Pc1 from penetrating through the ionosphere, limiting the magnitude of the ground magnetic field, whereas Hall conductivity and finite azimuthal wave number enhance the coupling to the ground. Results for runs in which a wave packet is introduced into the model show that the ground magnetic field is enhanced when the central frequency of the wave packet matches a resonant frequency of the IAR. Including a more realistic height-resolved ionosphere yields a more direct calculation of ionospheric fields, allowing a comparison between ground and ionospheric fields.