Wavenumber broadening of the quasi 2 day planetary wave in the ionosphere

Using the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model, we investigate the observed zonal wavenumber broadening phenomena in the ionospheric quasi 2 day oscillation (QTDO) that is associated with westward zonal wavenumber 3 (W3) quasi 2 day wave (QTDW) perturbations in the mesosphere and lower thermosphere (MLT). We aim to explain why the observed longitudinal structures of the QTDOs in the ionosphere are different from those of the QTDWs in the MLT. We find that large QTDOs in the ionosphere with zonal wavenumbers other than W3 occur in the model run with the true magnetic field, but not in the model run with an aligned dipole field. These numerical experiments suggest that the occurrence of the additional zonal wavenumbers in ionospheric QTDOs is related to the longitudinal variations of the Earth's magnetic field configuration, strength, and dip angle, which have distinct stationary zonal wavenumbers. We also find that when the specified W3 QTDW winds drive ionospheric plasma motion in the magnetic field, the resultant QTDOs in ionospheric parameters, such as the dynamo electric field, ion vertical drifts, plasma densities, and total electron content, have more complicated longitudinal variations than simply W3, corresponding to a zonal wavenumber broadening effect. Additionally, we find that the wavenumber broadening effect in the ionosphere can be fed back onto the neutrals through ion drag, to produce small QTDW winds with new wavenumbers in the thermosphere.