Surface-layer scaling for the convection-induced stress regime

The Prandtl, Obukhov, and Monin and Obukhou similarity theories are widely used to describe the structure of turbulence in the atmospheric surface layer. Currently it is understood that in strong convection with no or very weak mean wind the traditional theory breaks down. In particular, the traditional theory implies a single-valued correspondence between local turbulence statistics and local properties of the flow. In very strong convection, this is not true because of large-scale (similar to 10(3) m) coherent structures, embracing the entire convective boundary layer (CBL). These structures produce random gusts that crucially affect surface-layer turbulence and make it dependent on global properties of the flow, such as the CBL depth. In the present paper the limits of validity of the traditional surface-layer similarity theory are determined and a revised theory of fair weather convection in the surface layer is developed by considering the effect of gustiness. It is shown that the theoretical predictions are consistent with field data from the TOGA COARE and SCOPE experiments.