资源环境科技发展态势分析平台

This study investigates the effects of tropospheric vertical wind shear on gravity waves generated by tropical cyclones using idealized tropical cyclone simulations with different vertical profiles of environmental zonal wind. It is found that without shear, gravity wave momentum fluxes are distributed uniformly over a broad spectral range, with fluxes in opposite directions showing symmetry. Westerly shear in the troposphere leads to asymmetry between eastward and westward momentum fluxes, resulting in net westward fluxes and a resultant westward drag forcing on the background flow in the lower stratosphere. Under westerly shear, the active momentum fluxes extend to shorter horizontal wavelengths, and contract to longer periods and slower phase speeds. In addition, clear local peaks appear at large horizontal wavelengths, long periods, and moderate phase speeds, particularly for westward momentum fluxes.

Plain Language Summary Gravity wave activity is a ubiquitous atmospheric phenomenon, and tropical cyclones (TCs) are a significant source of nonstationary gravity waves in both the tropics and extratropics. Despite increased observational and simulation studies of gravity waves generated by TCs in recent years, our understanding of this issue remains inadequate and unsystematic. The vertical wind shear in the troposphere is one of the important factors that affect TCs. Here we investigate the effect vertical wind shear exerts on gravity waves generated by TCs. We perform idealized numerical simulations of TCs with different vertical profiles of environmental zonal wind, and compare gravity wave momentum fluxes generated by TCs in the lower stratosphere for different simulations. We find that westerly shear modifies wave activity in at least three aspects. First, it leads to asymmetry between eastward and westward momentum fluxes, resulting in net westward fluxes and a resultant westward drag forcing on the background flow. Second, it causes the active momentum fluxes to extend to shorter horizontal wavelengths, and contract to longer periods and slower phase speeds. Third, clear local peaks appear at large horizontal wavelengths, long periods, and moderate phase speeds, particularly for westward momentum fluxes.