Atmospheric and Ionospheric Responses to Orographic Gravity Waves Prior to the December 2022 Cold Air Outbreak

Mountain waves are known sources of fluctuations in the upper atmosphere. However, their effects over the Continental United States (CONUS) are considered modest as compared to hot spots such as the Southern Andes. Here, we present an observation-guided case study examining the dynamics of gravity waves (GWs) and their impacts on the ionosphere over the CONUS prior to the cold air outbreak in December 2022, which resulted from a significant distortion of the tropospheric polar vortex. The investigation relies on MERRA-2 and ERA5 reanalysis data sets for the climatological contextualization, analysis of GWs based on National Aeronautics and Space Administration Aqua satellite's Atmospheric Infrared Sounder, 557.7 and 630.0 nm airglow emission observations, and the measurements of ionospheric disturbances retrieved from Global Navigation Satellite System signal-based total electron content (TEC) and Super Dual Auroral Radar Network observations. We demonstrate that the tropospheric polar jet stream shifted toward the Rocky Mountains, generated large amplitude GWs (up to 11 K of brightness temperature), which, aided by winter-time winds over mid-latitudes, could propagate to mesospheric heights. The breaking of GWs plausibly led to the generation of a plethora of secondary acoustic and GWs that eventually emerged as the sources of extensive ionospheric fluctuations of ∼3–30 min periods and up to 0.7 TECu, observed across the entire CONUS for several days. This case offers a valuable demonstration of the interplay between tropospheric circulation and the ionosphere over CONUS, pointing to the need for a better understanding of wave-driven deep-atmosphere coupled dynamics.