Some Turbulence Characteristics in Stable Atmospheric Boundary Layer Flow

Abstract

Atmospheric boundary layer measurements during stable and near neutral condition from seven sites in different kinds of terrain have been analyzed in order to find relationships among turbulence parameters. The shape of the spectral and cospectral distributions turned out to be well represented by the universal expressions found for ideal sites. For near neutral conditions in the surface layer σw/u* increases and σu/u* decreases with height. These results agree with previous result found in the literature for both atmospheric and some wind tunnel data. The ratio σw/σu first increases and then decreases as stability increases in the surface layer. This can be interpreted as a combined effect of stability and the presence of the ground. In a stable layer well above the ground σw/σu decreases monotonically with stability, in accordance with laboratory measurements and numerical simulations of free shear flow. The ratio w?/u? was also investigated. For near neutral conditions the ratio scatters around 0.2 with no apparent variation with height or roughness. The stability dependence of this quantity is very similar to that of the ratio of the vertical to the horizontal standard deviation in the surface layer which first increases and then decreases with increasing stability. Its neutral value in a free shear flow layer is 0.8, decreasing rapidly with stability, in agreement with laboratory data.