Thermal stability effects on the structure of the velocity field above an air‐water interface

Abstract

Mean velocity and turbulence measurements are described for turbulent flows above laboratory water waves, under various wind and thermal stratification conditions. Experimental results, when presented in the framework of Monin‐Obukhov similarity theory, support local scaling based on evaluation of stratification effects at the same nondimensional distance (z+ = zu*/ν) (definitions of the various symbols follow in section 2) from the mean water surface. Such scaling allows an extension of application of the above theory to the outer region of the boundary layer. Throughout the fully turbulent region, ratios of mean velocity gradients, eddy viscosities, and turbulence intensities under nonneutral and neutral conditions correlate well with the parameter z/Λ (Λ being a local Obukhov length) and show good agreement with established field correlations. The influence of stratification on the wind‐stress coefficient can be estimated from an empirical relationship in terms of its value under neutral conditions and a bulk Richardson number.