Gust characteristics of near-ground typhoon winds

Abstract

Based on 14 sets of records observed by 4 meteorological stations during 10 typhoons, a comprehensive investigation of gust characteristics, which are usually quantitatively expressed as the turbulence intensity and gust factor, for the near-ground typhoon winds was conducted. The direction- and mean-wind-speed-dependent features of these two gust parameters are analyzed at different heights. It is found that, in general, mean wind speed has little effect on gust parameters for off-sea winds coupled with a small number of over-land winds over 15 km of upstream fetch. Statistical characteristics, including the first four-order moments together with the probability distribution, are examined and turbulence intensity and gust factor profiles are compared with those given in various codes and standards for open-sea and flat-area conditions. The estimation of peak factor based on observations and a Gaussian distribution-based model is also presented, and they show generally good accordance for the level of mean values. The relationship between turbulence intensity and gust factor is also studied and compared with several pioneer results. Two typical upstream conditions, off-sea and over-land winds are separately analyzed, and they show an opposite tendency, i.e., the off-sea gust factor at 10 m is 8% higher than the over-land value while other heights show little difference. We attempt a rapid estimation of gust factor using the model coupled with the MODIS land-use roughness length data and compare the results with observations. Finally, some uncertainties that would induce scatter of gust characteristics and imperfections of the theoretical model are identified and discussed.