Day-to-Day Variability of the Semidiurnal Tide in the F-Region Ionosphere During the January 2021 SSW From COSMIC-2 and ICON.

The semidiurnal tidal spectrum in the F-region ionosphere obtained from hourly COSMIC-2 Global Ionospheric Specification (GIS) data assimilation is greatly (>50%) enhanced during the January 2021 Sudden Stratospheric Warming (SSW). Moreover, the semidiurnal migrating tidal response in topside electron densities closely follows the day-to-day changes of the 10 hPa, 60°N zonal wind from MERRA-2 during the SSW. The response is similar in the northern and southern crests of the Equatorial Ionization Anomaly (EIA) but persists toward higher magnetic latitudes and the EIA trough. A slight phase shift toward earlier local times is consistent with theoretical expectations of an E-region dynamo driving and agrees with semidiurnal tidal diagnostics of MIGHTI/ICON zonal winds at 105 km. COSMIC-2 GIS are the first data set to resolve the tidal weather of the ionosphere on a day-to-day basis and, therefore, provide a new perspective on space weather variability driven by lower and middle atmosphere dynamics.