Comparative study on characteristics of typhoon gusts in the coastal and offshore areas of the South China Sea

Typhoon gusts are hazardous to buildings and structures in both coastal and offshore areas, but the gust characteristics in the two areas could be quite different. In this study, the observational data from two meteorological stations, one at Shenzhen (coastal) and the other in the offshore area of the South China Sea are used to analyze the typhoon gust-related variables and to find the theoretical distribution model that best describes them. The results show that in both coastal and offshore areas, the probability density distributions of all gust-related variables are non-Gaussian. When fitting the curve of the statistical data, the Gengamma model performs the best, followed by the Lognormal model, and the generalized extreme value (GEV) distribution model. Specifically, the gust factor and turbulence intensity are generally Gengamma- and GEV- distributed, respectively. The distributions exhibit certain differences in different gust variables in coastal and offshore areas. The theoretical probabilistic models perform better in the offshore area than in the coastal area. The gust factor increases linearly with the turbulence intensity, while previous empirical models tend to overestimate it. The gust factor and turbulence intensity are significantly higher in the offshore area than in the coastal area. Slower turbulent dissipation is found in the offshore area during typhoon process. A strong positive correlation is shown between the gust amplitude and the turbulent flux. In both coastal and offshore areas, the larger the gust amplitude is, the more the turbulent flux is transmitted.