Impacts of Resolved Gravity Waves on Global‐Scale Wave Variability in the Ionosphere‐Thermosphere: Insights From WACCM‐X, ICON, and COSMIC‐2

Abstract Accurately representing the generation and evolution of global‐scale wave structures in the ionosphere‐thermosphere (IT) system remains a central challenge for whole‐atmosphere models. The IT region exhibits substantial day‐to‐day variability driven by external forcing and internally generated waves. Among the most prominent internal drivers are non‐migrating tides and ultra‐fast Kelvin waves (UFKWs), which modulate electrodynamics and plasma distributions via wave‐driven neutral winds. This study evaluates a high‐resolution configuration of the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere extension (HR‐WACCM‐X) in simulating global‐scale waves during September 2021, a period of enhanced vertical coupling and quiet geomagnetic conditions. Focusing on the eastward diurnal tide with zonal wavenumber 3 (DE3) and the 3‐day UFKW, we show that HR‐WACCM‐X captures more realistic amplitudes, vertical structures, latitudinal extent, and variability than coarse‐resolution runs. The HR simulation reproduces observed DE3 and UFKW signals in equatorial thermospheric winds and associated electron density perturbations, with correlation coefficients of –0.63 in agreement with ICON/MIGHTI and COSMIC‐2/GIS observations. Improved vertical propagation and in situ wave generation above 200 km yield enhanced spectral fidelity and spatial coherence in the thermospheric response. In contrast, coarse‐resolution simulations underestimate amplitudes and miss key spectral features, reflecting limitations from nudging and parameterized gravity wave schemes. These results underscore the importance of resolving small‐scale gravity waves to capture multiscale variability and electrodynamic coupling. The findings support the use of high‐resolution whole‐atmosphere models for advancing understanding of vertical coupling and wave‐driven IT dynamics and provide a benchmark for future observational missions and space weather modeling.