Gravity Wave Influences on MSTID Climatology Over CONUS: WACCM-X Year-Long Simulation and GNSS Long-Term Observation

Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) are prominent wave-like structures in the ionosphere, with complex generation mechanisms involving both atmospheric gravity waves (GWs) and electrodynamic instabilities such as the Perkins instability (PI). This study aims to understand the observed MSTID climatology, especially to clarify the impact of GWs on MSTID excitation and propagation over the continental United States (CONUS). Year-long high-resolution simulations from the latest version of the Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM-X) are compared with GNSS-based MSTID climatology deduced from the extensive Madrigal database. Our results indicate good consistency between the model and data in key features of MSTID climatology, including the diurnal and seasonal patterns of occurrence rate and propagation direction, particularly the dominant daytime southward/southeastward propagation. This highlights the fundamental influence of GWs, as these WACCM-X waves are driven by GW forcing from below. However, some discrepancies exist, especially in the nighttime occurrence rates and propagation directions, which are partially due to limitations in the model's representation of GW sources, background winds, and other non-GW regional factors. These nighttime MSTID climatological features over CONUS are inconsistent with the anticipated PI effects either (e.g., southwestward propagation) implying that the actual generation involves mixed processes where PI effects may not be dominant and GWs can still contribute. These findings advance our understanding of MSTID generation mechanisms and offer valuable insights for improving ionospheric modeling and forecasting.