Impacts of Wind Profile Shear and Curvature on the Parameterized Orographic Gravity Wave Stress in a Middle Atmosphere Resolving General Circulation Model

The cold pole and westerly wind biases associated with an overly strong polar vortex are typical systematic biases in climate models, indicating the insufficient stratospheric wave drag. To investigate the effects of orographic gravity wave drag (OGWD) on the stratospheric atmospheric circulation, two sets of experiments are performed by the middle-atmosphere version of Beijing Climate Center Atmospheric General Circulation Model, employing different OGWD parameterization schemes with and without the second-order Wentzel-Kramers-Brillouin (WKB) corrections to the surface wave momentum flux (SWMF) caused by wind profile shear and curvature. In the simulation with the WKB-corrected OGWD scheme, the cold pole bias is reduced up to 2°C, and the associated westerly wind bias diminishes up to 4 m s⁻¹, particularly during the austral winter. Changes in the SWMF can further affect the vertical transport of orographic gravity waves. The enhanced SWMF in the modified scheme transports more wave momentum flux upward. Consequently, more wave momentum flux is transported into the upper stratosphere, enhancing the wave breaking there. The OGWD-induced meridional circulation is strengthened over Antarctic, contributing to the alleviation of the cold pole and westerly wind biases. In addition, the upward propagation of planetary Rossby waves in the mid-high latitudes of the Southern Hemisphere is enhanced, which contributes to the reduction of the westerly wind biases of the polar vortex as well. Overall, the WKB-corrected scheme is effective to alleviating the delayed breakdown of the polar vortex in Antarctica.