Characteristics of Wind plex Terrain Conditions Speed Profiles under Com- in Loess Plateau

To reveal the changing characteristics of wind speed with altitude in under complex terrain conditions in Loess Plateau in Northern Shaanxi,based on the complete data of wind speed profiles of six wind towers in the region in a year,the diurnal,monthly,and seasonal variations of wind shear index of the wind towers as well as the changes of wind shear index with wind speed under complex terrain conditions were studied.The results showed that the wind shear index of each wind tower was positive,showing that wind speed tended to increase with the rising of altitude in most areas of Loess Plateau in Northern Shaanxi; terrain had obvious effects on wind speed profiles. The wind shear index of the wind towers was small during the day and large at night; the differences between day and night in the wind shear index of various wind towers were different;there were obvious seasonal variations in the wind shear index of the wind towers under different terrain conditions. With the increase of wind speed,the wind shear index of each wind tower increased firstly and then decreased,but the peaks of wind shear index of various wind towers appeared in different wind speed ranges. When wind speed varied from 3 to 12 m/s,wind shear index was larger than the comprehensive wind shear index of the wind towers,which is beneficial to the improvement of power generation of a wind power plant. Wind shear index can be used to assess wind resources of a wind power plant.