Abstract:Based on the daily observation data of seven stations in Dalian from 1971 to 2015, the cumulative frequency the diurnal and monthly distributions of low wind speed are analyzed. The trend of annual percentage of low wind speed are also studied. The results show that: (1) The frequency of low wind speed conditions in Dalian is about 20% in the recent 45 years, with the lowest (8%) at Changhai, and the highest (35%) at Pulandian. (2) The frequency of low wind speed has an increasing trend, and there are significant increasing trends at Dalian, Pulandian and Changhai, especially in the past ten years. (3) The frequency of low wind speed conditions has significant diurnal changes, which is high over the night and low during the daytime. (4) From March to July, the frequency of low wind speed is low and from September to February it is higher with the maximum value seen in Dalian in September. (5) Changhai is the station with the longest duration of low wind speed. The 27% low wind-speed condition can last at least 10 h and the 9% low wind speed conditions can last at least 20 h at Changhai Station. Dalian Station is the station with the shortest duration, more than 85% low wind speed condition in Dalian Station can last 4 h or less.