Ionospheric Signatures of Secondary Waves From Quasi-6-Day Wave and Tide Interactions

A sudden stratospheric waring occurred in the southern hemisphere during September 2019, accompanied by an exceptionally strong quasi-6-day wave (Q6DW). We examine the ionospheric response using global total electron content (TEC) maps, with a focus on the short-period variability (5–48 h). A Fourier analysis of the TEC data reveals ionospheric variations associated with the secondary waves due to the non-linear interaction between the Q6DW and atmospheric tides. The largest signatures among them are related to the ∼29-h standing oscillation, which is attributable to the Q6DW interaction with the migrating diurnal tide, with the maximum amplitude ∼8% of the zonal mean. Also detected are the signatures associated with the westward-propagating ∼13-h oscillation with the zonal wavenumber 1 (∼4%) and westward-propagating ∼11-h oscillation with the zonal wavenumber 3 (∼3%), both of which can be attributed to the Q6DW interaction with the migrating semidiurnal tide. The signatures related to the Q6DW interaction with the migrating terdiurnal tide and some non-migrating tides are also observed. This is the first time that secondary wave signatures of the Q6DW-tidal interaction are identified in ionospheric observations with predicted zonal wavenumbers and periods. The oscillations are symmetric about the magnetic equator with amplitude peaks at ±20° magnetic latitudes, suggesting that the oscillations are generated by the modulation of the equatorial plasma fountain.