Secondary Gravity Waves in the Winter Mesosphere: Results From a High‐Resolution Global Circulation Model

This study analyzes a new high‐resolution general circulation model with regard to secondary gravity waves in the mesosphere during austral winter. The model resolves gravity waves down to horizontal and vertical wavelengths of 165 and 1.5 km, respectively. The resolved mean wave drag agrees well with that from a conventional model with parameterized gravity waves up to the midmesosphere in winter and up to the upper mesosphere in summer. About half of the zonal‐mean vertical flux of westward momentum in the southern winter stratosphere is due to orographic gravity waves. The high intermittency of the primary orographic gravity waves gives rise to secondary waves that result in a substantial eastward drag in the winter mesopause region. This induces an additional eastward maximum of the mean zonal wind at z ∼ 100 km. Radar and lidar measurements at polar latitudes and results from other high‐resolution global models are consistent with this finding. Hence, secondary gravity waves may play a significant role in the general circulation of the winter mesopause region. Plain Language Summary We present a new gravity‐resolving general circulation model that extends into the lower thermosphere. The simulated summer‐to‐winter‐pole circulation in the upper mesosphere is nearly realistic and driven by resolved waves. We find a new phenomenon that results from the generation of secondary gravity waves in the stratosphere and lower mesosphere. The effect is characterized by an eastward gravity drag that causes a secondary eastward wind maximum around the polar winter mesopause. Analysis of the simulated gravity waves shows consistence with other gravity wave resolving models and with observational studies of the austral winter middle atmosphere, including the mesopause region. Key Points Primary and secondary GWs are resolved in the SH during winter using a new high‐resolution GCM from the surface to the lower thermosphere Secondary GWs are created by localized and intermittent body forces from the dissipation of mountain waves near the stratopause Significant eastward drag and an eastward wind peak are created in the polar mesopause region by the dissipation of secondary GWs