Analysis of aerodynamic roughness in the western coast of the Bohai Sea

Based on the observed wind speed,wind direction and temperature data from wind energy tower at Dagang in the western coast of the Bohai Sea from December of 2009 to November of 2010,the aerodynamic roughness Z0 around the wind energy tower was calculated using two methods: a wind-profile and a wind speed standard deviation. The results were analyzed and compared. The applicability of the wind speed standard deviation method and the effect of the inhomogeneous underlying surface on the roughness were discussed. The results show that the average roughnesses on three main wind directions are 0. 1319 m( north),0. 0386 m( south-east) and 0. 0182 m( south-west),respectively. The roughness calculated using the two methods could be similar if a strictly condition control is carried out. On the same direction,the seasonal differences of the roughness calculated by the two methods using 10-30 m meteorological data are not significant,while those using the 50-70 m data are significant. On the same layer,the differences of the roughness between different seasons are significant,which reflects the effect of the seasonal vegetation change on the roughness.