华南地区台风全局化结构及风场特征实测研究

Field measurement of the global structure and wind field of typhoons in South China

基于探空气球、雷达风廓线仪等设备长期观测数据,对影响华南地区热带气旋的全局化结构及风场特征进行了实测研究。以典型台风为例,考察了系统水平及垂直主结构特征,揭示了台风双眼壁结构、眼壁置换现象以及登陆后结构的轴非对称变化特征。提出了台风气压场水平轴非对称模型和垂直剖线模型,分析了台风气压场两关键参数(最大风速半径及Holland-B)数值分布特征及其与其他参数间的内在关系。采用复合分析技术,对不同来流状况下台风边界层风场特征进行研究,考察了风速剖线低空急流和风向随高度偏转的特征及其随径向距离和来流地貌的变化规律,建立了以低空急流为特征的台风垂直剖线经验模型,为精确化评估高层建筑风荷载提供数据和技术支撑。相关研究成果有助于深化对华南地区热带气旋全局化结构及风场特征的认识,并为合理评估该地区台风风灾害及构筑物台风风效应提供参考。

Based on long-term observation by radiosonde balloons and radar profilers,this article presents a comprehensive in-situ study on the global structure and wind field of tropical cyclones(TCs)that impact South China severely.Typical features of the primary structure of TCs are explored.It is shown that TCs may exhibit concentric-eyewall features and undergo eye-wall replacement before the landfall,and their structural characteristics may vary significantly before and after the landfall.Models for the horizontal and vertical distributions of typhoon pressure field have been established.Quantitative analysis has been conducted on the distribution features of two key parameters for TC pressure fields(i.e.,the radius of maximum wind and Holland-B)and on the relationship among the two parameters and others.Wind characteristics throughout typhoon boundary layers are investigated under different exposure conditions via composite analysis.Features of the low-level-jet and twisted wind as well as their variations with radial distance and exposure condition are highlighted.An empirical model is proposed to quantify the vertical distribution of typhoon horizontal mean wind speed,which can be used to better determine the wind load acting on high-rise buildings.The characteristics of surface wind are found to be influenced severely by terrain/topographic features.It is interesting that the records of gradient wind above two sites with varied terrain features show good agreement,but they start to differ evidently when typhoons got closer to the sites and the difference between the radial distances of the two sites with respect to the TC center became non-negligible.Such differences reflect the storm-relative dependence of TC wind fields,especially in the inner regions of TC.Results presented in this study should be beneficial for further understanding of the global structure and wind field of TCs in South China.They can also provide reference for better assessing the hazards and effects of typhoon wind on civil structures in this region.