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Abstract

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 hours). 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‐hour 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‐hour oscillation with the zonal wavenumber 1 ( ∼4%) and westward‐propagating ∼11‐hour 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.