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Abstract:
Owing to the progress that has been made in the last decades, it is now well established that lower atmospheric forcing plays a vital role in the day-to-day variability of the ionosphere. In this regard, previous studies linking ionospheric variability to SSWs have been significant. The changes to atmospheric circulation associated with SSW events modulate the spectrum of vertically upward propagating atmospheric waves, which then drive changes in the ionosphere through the E-region dynamo. During SSWs, enhancements in semidiurnal solar and lunar tides have been observed at ionospheric altitudes. While there is now a relatively good understanding of the ionospheric tidal variability during SSWs, which are associated with an anomalously weak stratospheric polar vortex (SPV), not much is known about the ionospheric tidal variability during times of anomalously strong SPV. In this work, we explore the impact of strong SPV on solar and lunar semidiurnal tides during Northern Hemisphere (NH) winters using ground-based magnetic field observations of the equatorial electrojet (EEJ). We analyze 34 NH winters between 1980 and 2020 and find that when the SPV is strong, EEJ semidiurnal solar and lunar tides decline, but the intensity of decline is weaker in comparison to the enhancements during weak SPV events. These results provide observational evidence that along with weak SPVs in the NH, strong SPVs also have pronounced effects on the equatorial ionosphere.
