Some Studies on the Fluctuation of Wind Direction near the Ground

[摘要] The fluctuations of lateral wind direction were measured at the U.S. Weather Bureau Observation Test and Development Center in Sterling, Virginia. Four sets of light weight anemometer and wind vane were installed along the observation tower at the heights of 2, 4, 8 and 16 m above the ground. During the observations nine runs were taken and these were then analyzed.Results are as follows : (1) The standard deviation generally decreases both with stability and with height. The value in the neutral condition is about 12 degrees. (2) The variance spectra in nondimensional form is likely to unify the original ones over the wide stability. They can be roughly represented as a " -5/3 power" in higher frequencies (larger than 0.2 ƒz /U, say ; ƒ=frequency, z=height, and U=mean wind speed at z), while they separate in lower ranges according to the stability. Some explanations are given from the standpoint of the similarity theory.Furthermore, from the angle of "selective method ", a filter after Brier (1961) is applied to the data, and the standard deviation and the cross correlation coefficients both with and without lag are calculated for a few processed data of a single run, and thus some tentativeresults are obtained. Among them are the relations of time-lag with height and height difference.

[学科分类] 大气科学