Analysis on gust factor of tropical cyclone strong wind over different underlying surfaces

Based on one year gradient wind data and the wind data of a strong typhoon observed by three meteorological towers located on the coast and at the inshore sea, the underlying surfaces of the meteorological towers were classified and the roughness lengths were calculated quantitatively. On the basis of strong wind characteristic representative assessment and sample selection on the wind data of strong typhoon Hagupit, the gust factor variation characteristics of tropical cyclones under different underlying surfaces were analyzed. The observed fact and variation rule were found as follows: 1) The roughness lengths under neutral atmospheric condition which were calculated using logarithmic wind profile fitting based on the observation data can describe the slight change of the underlying surface objectively. 2) The gust factor of strong typhoon wind didn’t have variation trends with wind speed. But the variation amplitude of the gust factor was rather large over rough underlying surface which had pronounced effect on the numerical design of structural engineering. 3) The variation of the gust factor with height satisfied power law or logarithmic law. The power law fitting was more suitable for smooth underlying surface while the logarithmic fitting was better over rough underlying surface. 4) The observation data also suggested that the relationship between gust factor and roughness length can be described by power or linear equation. 5) The gust factor observed in this typhoon case was different from the gust factor recommended by WMO: The gust factor of the offshore wind came from rough underlying surface was higher than the value recommended by WMO while the gust factor of the onshore wind came from smooth underlying surface is less than the WMO recommended value.