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.