Vertical structure in the marine atmospheric boundary layer and its implication for the inertial dissipation method

The structure of the marine atmospheric boundary layer and the validity of Monin-Obukhov similarity theory over the sea have been investigated using long term measurements. Three levels of turbulence measurements (at 10 m, 18 m and 26 m) at Ostergarnsholm in the middle of the Baltic Sea have been analysed. The results show that turbulent parameters have a strong dependence on the actual height due to wave influence. The wind profile and thus the normalised wind gradient are very sensitive to wave state. The lower part of the boundary layer can be divided into three height layers, a wave influenced layer close to the surface, a transition layer and an undisturbed 'ordinary' surface layer; the depth of the layers is determined by the wave state. This height structure can, however, not be found for the normalised dissipation, which is only a function of the stability, except during pronounced swell where the actual height also has to be accounted for. The results have implications for the height variation of the turbulent kinetic energy (TKE) budget. Thus, the imbalance between production and dissipation will also vary with height according to the variation of wave state. This, in turn, will of course have strong implications for the inertial dissipation method, in which a parameterisation of the TKE budget is used.