The Ionospheric Lunar Tidal Response to the 2020–2021 Sudden Stratospheric Warming Observed by COSMIC-2, ICON and Modeled by SD-WACCMX, TIE-GCM

This study examines how the breakdown of the stratospheric polar vortex influences lunar semidiurnal (M2) tides in F-region electron density using Global Ionospheric Specification (GIS) data from the Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2). During the 2020–2021 Sudden Stratospheric Warming (SSW) event—marked by an exceptionally disrupted polar vortex—we observe up to a 16% enhancement in the M2 lunar tide at low latitudes (equatorial ionization anomaly) around 300 km altitude relative to the mean state. The response of M2 in vertical plasma drifts measured by the ion velocity meter on board the Ionospheric Connection Explorer satellite shows similar variability. Whole-atmosphere model simulations using the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (SD-WACCM-X) reproduce consistent M2 tidal signatures in E-region zonal winds, F-region vertical drifts, and electron density. To quantify the relative contributions of electrodynamics and neutral winds, we analyzed the ion continuity equation using the National Center for Atmospheric Research Thermosphere–Ionosphere–Electrodynamics General Circulation Model with SD-WACCM-X as the lower boundary. Results show M2 tides impact F-region electron densities primarily through vertical plasma drifts, which increase by ∼114% during the SSW, while transport by neutral winds rises by ∼43%. These findings confirm that vertical drifts dominate lunar tide transport, with neutral winds providing a secondary contribution.