Abstract:
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.