Variations and Potential Causes of Surface and Free Atmospheric Wind Velocities in Jilin

Based on the observation data of 50 meteorological stations and 3 radiosounde stations in Jilin Province from 1975 to 2012,the temporal and spatial variations of wind velocities at surface layer(10 m above the ground level) and free atmosphere(0.5~40 km) were analyzed.The annual and seasonal average winds at surface layer were more intense in central and western Jilin Province and weaker in southeast.During the 38 years,the annual mean surface wind velocity decreased at a rate of 0.21 m·s~(-1) ·(10a)~(-1) over Jilin Province,more than that averaged over the whole China and many other areas.The decrease was more intense in strong wind regions and seasons.In general,the wind velocities decreased first and then increased with increasing height.The wind velocities in troposphere and low level stratosphere decreased in summer during the research period while increased more in winter resulting in the increase in the annual mean winds.The variations of surface and free atmospheric wind velocities were greatly influenced by the large scale circulation,and the weakened surface winds were also related to the urbanization and the brought change of the environment around the observation sites.