基于高塔观测的登陆台风边界层风切变指数拟合

Fitting of Wind Shear Index in the Boundary Layer of Landfalling Typhoons Based on High Tower Observation

利用深圳气象梯度观测塔观测数据,以2017年以来进入深圳150 km范围的7个台风个例为研究对象,基于幂指数律拟合讨论台风边界层风切变指数的变化规律。结果表明:幂指数能较好地拟合台风影响下350 m高度以下风廓线,随着拟合高度范围增加,风切变指数增大,拟合精度基本维持;用深圳气象梯度观测塔等差层数据拟合台风风速效果好于全层次数据和等比层数据拟合;7个台风影响期间拟合风切变指数平均值为0.268,明显高于以往研究(0.1~0.177),主要原因是拟合的高度范围较以往研究明显增大,此外还与强风样本较少以及下垫面更粗糙有关。利用幂函数拟合台风不同风速段最大风切变指数,可在台风过程中预估不同高度极端大风风险。研究还表明:台风眼经过铁塔前后风切变指数明显升高,在抗风设计以及台风防御过程中应充分考虑这一变化。

The characteristics of wind speed variations with height in the boundary layer(especially in the nearground 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 a 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 a 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,a 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.