An analysis of the characteristics of strong winds in the surface layer over a complex terrain

Based on the gradient wind data and three dimensional ultrasonic wind data observed in the surface layer over a complex terrain in southwestern Guizhou Province, strong wind samples with local climatic characteristics were selected. By using the statistical and spectral analyses, the mean and pulsation characteristics of strong winds in the local complex terrain surface layer were analyzed. Under the impact of the local terrain (a northwest southeast oriented deep gorge) the dominant wind direction and the direction of maximum wind speed are almost completely along the gorge. Even in the neutral atmospheric condition, the vertical wind profile is still totally inconsistent with the exponential distribution. The wind angle of attack is much larger than the recommended normal value, and due to the topographic effect, the difference between the attack angles of strong winds in different directions reaches up to 20°. Meanwhile, the main features of the pulsation wind field under strong wind conditions are: the turbulence intensity of strong winds in different directions are not the same; there is a significant difference between the ratio of turbulence intensity in the three dimensional directions and that given by the existing design specifications. Especially, the vertical turbulence intensity is significantly larger than the normal value, and the turbulence integral scale is much lager, i.e., 20％—60％ larger in the longitudinal direction, or even three times larger in the transversal direction, and one order of magnitude larger in the vertical than that over a flat terrain. Within the frequency domain to which the bridge structure is sensitive, the turbulence spectrum densities in respective directions are significantly different, among which the maximum difference for different wind directions can be as large as eight times in the longitudinal, and six time in the transversal and the vertical directions, respectively. However, the turbulence spectrum densities in all directions are 1-2 orders of magnitude smaller than those in a typhooncentre.