应用气象学报 (Mar 2022)
Fitting of Wind Shear Index in the Boundary Layer of Landfalling Typhoons Based on High Tower Observation
Abstract
The characteristics of wind speed variations with height in the boundary layer (especially in the near-ground layer) are crucial for the design of wind resistance coefficients of high buildings. The coast of South China is frequently impacted by typhoons, but the study of wind variation characteristics above 100 m within the typhoon boundary layer is insufficient due to the lack of direct observations. The 356 m Meteorological Gradient Observation Tower of Shenzhen can make up for data shortage, and 7 typhoons that affected Shenzhen since 2017(Typhoons Merbok, Roke, Hato, Pakhar, Mangkhut, Higos, and Lupit) are analyzed to study the variation of wind shear index based on the power exponential law. It shows the power index can well fit the wind profile below 350 m under the influence of typhoons, the wind shear index α increases with height, and the fitting accuracy is basically stable. The wind profile of the typhoon boundary layer is fitted with the wind speed data from the tower, the fitting accuracy differs for different combinations of levels, and the equal difference scheme leads to the best fitting results. For 7 typhoon cases, the mean value of 350 m wind shear index α during the impact period is 0.268, which is significantly higher than that of 0.1-0.177. The main cause is that the fitted height range is significantly larger than that of previous studies, and it is also related to the smaller sample of strong winds and rougher underlying surface. The maximum wind shear indices of different wind speed sections of the typhoons can be well fitted with power functions, which can predict the risk of extreme winds at different heights.The wind shear index before and after landing of Typhoon Roke is also analyzed. It shows that after the typhoon eye passes, α increases sharply, because the wind speed above 100 m may have increased significantly before the surface wind re-increase. Therefore, this result should be specially considered in the design of engineering wind resistance and typhoon prevention.
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