Characteristics of Wind Direction Change in China During Recent 50 Years

With the development of wind power industries, much attention is paid to the issues of the wind power's sustainable utilization against the global warming background. The stability of wind directions is very important to the effective availability of wind energy resources. The stability of the prevailing wind directions is not only able to enhance the availability rate of the wind energy, but also the life of wind turbogenerators can be prolonged. Therefore, the characteristics of the wind direction changes for the last 50 years in China are focused on. Based on the observation data sets of both wind speed and wind direction in the baseline and standard stations of China of four times per day, the wind data of 488 stations during 1956--2005 are chosen, the changes of wind directions in China for the last 50 years are analyzed. 16 wind directions are used. The statistic methods are employed to analyze the characteristics of the seasonal and annual wind directions, maximum wind directions and prevailing wind directions at each station in 12 sub-regions in China.It is found that the frequencies of the annual prevailing wind directions have decreasing trends, especially in North China, northwestern and southwestern China. There are slightly increasing trends in a few areas in West China. The wind speeds corresponding to the annual prevailing wind directions in most regions of China decrease much more obviously than the decreasing trends of the annual mean wind speeds. It indicates that the reducing annual mean wind speeds are mainly caused by the decreasing annual prevailing wind speeds. Both northerly wind (winter) and southerly (summer) prevailing winds in China decrease significantly. The reducing prevailing wind in China is lead to by the decreasing Asian winter and summer monsoon.