VERTICAL PROFILES OF MEAN WIND IN THE SURFACE LAYERS OF THE ATMOSPHERE

摘要

A set of sensitive recording cup anemometers was installed in 1941 over an open grassland site at Proton, Wiltshire, adjacent to equipment for recording vertical temperature gradient. The wind-profile observations obtained there up to 1945, together with some data for other surfaces including the sea, have been analyzed with particular attention to the effects of roughness of the surface and of thermal stratification.nThe well known logarithmic relationship of Prandtl is shown to be a very adequate representation of the wind profiles under neutral conditions. For other conditions of stability the form of the wind profiles and the gustiness of the wind is found to be satisfactorily related to the Richardson number except under very stable conditions. The effect of thermal stratification on the wind profile is small near the surface but increases markedly with height, in keeping with the fact that the Richardson number is very close to zero at the surface and increases numerically almost linearly with height. A generalized wind-profile relationship is proposed which enables the eddy viscosity to be evaluated, and this is compared with some previous formulations. Observations bearing on the critical value of the Richardson number for the onset of turbulence are discussed in relation to the laboratory results of Reinhardt.