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

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 $\sim$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 $r=0.43$–0.63 in agreement with ICON/MIGHTI and COSMIC-2/GIS observations. Improved vertical propagation and in situ wave generation above $\sim$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.