The Semidiurnal Tidal Response of the Low Latitude Ionosphere to Northern Hemisphere Polar Vortex Strength (2020-2023) From COSMIC-2 Global Ionospheric Specification

This paper investigates the day-to-day global tidal variability in the ionosphere/thermosphere system due to fluctuations in the strength of the northern hemisphere stratospheric polar vortex. Using COSMIC-2 (Constellation Observing System for Meteorology, Ionosphere, and Climate-2) Global Ionospheric Specification data, ionospheric tides are derived, with the Northern Annular Mode (NAM) index indicating polar vortex variability. The semidiurnal migrating solar tide shows the largest response, with relative electron density in the F-region significantly higher (similar to ${\sim} $ 60%) under a weak vortex and lower (similar to ${\sim} $ 20%) under a strong vortex, correlated at -0.58 with the NAM index. The study compares solar/geomagnetic forcing and vortex impacts using SD-WACCM-X (Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension) model runs. Findings suggest tidal modulation of the E-region dynamo as the coupling mechanism. Our study can potentially improve ionospheric space weather predictability because the NAM index can be known a few days in advance.