The Impact of Moist Orographic Gravity Wave Drag Parameterization on Summer Circulation and Heavy Rainfall

Abstract

Subgrid-scale orographic gravity wave drag (OGWD) significantly influences atmospheric circulation and weather systems. However, Current OGWD schemes, based on the “dry air” assumption, struggle to meet high-precision simulation demands. This study uses the moist OGWD scheme that incorporates moisture effects in gravity wave surface stress and vertical propagation of waves to simulate the global summer circulation in 2023 and three recent heavy rainfall events in China. In this scheme, moist buoyancy frequency varies with moisture: it decreases with abundant moisture and increases with less moisture, compared to the original scheme. Results show that buoyancy frequency differences alter low-level blocking height and drag, directly affecting gravity wave surface stress. During the vertical propagation of gravity waves, reduced tropospheric buoyancy frequency increases wave amplitudes and reduces Richardson number in moist scheme, which enhances tropospheric wave breaking and reduces waves propagation to the stratosphere. This increases tropospheric OGWD and decreases stratospheric OGWD, improving positive biases of troposphere westerly winds and negative biases of stratosphere easterly winds in Northern Hemisphere (NH) mid-high latitude, as well as the bias in the stratospheric jet near the Antarctic. The moist OGWD scheme also improves simulations of three recent heavy rainfall cases. In the Henan extreme rainfall, moist buoyancy frequency decreases due to abundant water vapor. Increased tropospheric OGWD weaken circulation and moisture transport to western and northern mountainous areas, intensifying rainfall and improving underestimation. The moist OGWD scheme partially addresses the limitations of “dry air” assumption, improving atmospheric circulation and heavy rainfall simulations.