TURBULENCE CHARACTERISTICS IN AN URBAN ATMOSPHERE OF COMPLEX TERRAIN

An observational experiment carried out in Lanzhou, an urban area of complex terrain, reveals that the influence of the surface on the structure of vertical wind component is rather weak; however, it is comparatively effective on the horizontal, particularly, the lateral wind component. Compared with the results of some urban areas in homogeneous terrain, the turbulence intensity of the lateral wind component in the urban surface layer of Lanzhou is about 20% larger, which is mainly the contribution of eddies with scale greater than a few hundred meters. Due to several factors, the variation of atmospheric stability in this city is small, particularly in the winter, with near neutral stratification for more than half of the time. This is quite different from the results estimated by the conventional Pasquill-Turner scheme, which has been widely used in air pollution assessment in Lanzhou in recent years.