The marine atmospheric boundary layer during neutral stratification

Extended periods with neutral stratification are more frequently observed over sea than over land (higher wind speed and larger heat capacity in the water). During those conditions the detached eddy model (Hunt and Carlotti, 2001) proved successful in explaining the dynamic structure of the neutral atmospheric surface layer both in the Baltic Sea and Lake Ontario. In particular the efficiency of the turbulent exchange of sensible and latent heat is observed to be of smaller scale but strongly enhanced compared to the standard model . However, measurements taken in the open Ocean (the Pacific) with almost the same meteorological conditions (high wind speed, neutral stratification) large scale turbulence structures dominate in the boundary layer. The difference between the sites is the wave state. In the open ocean swell (long waves) dominate the wave field also at high wind speed but in semi-enclosed seas as the Baltic Sea the swell very rapidly disappears and young waves dominate. Swell waves will create a circulation in the entire boundary layer which will prevent wind speed gradients to form higher up , which is a pre-requisite for ‘detached eddies' to form and thus scalar fluxes at the surface will be reduced.

Hunt and Carlotti, 2001: Statistical structure at the wall of the high Reynolds Number turbulent boundary layer. Flow Turbul. Combust., 66, 453-475.