Measurement and simulation of viscous dissipation in the wave affected surface layer

In this study we compare turbulence parameters from field observations and model simulations specifically under the influence of weak to moderate wind forcing and breaking short waves. The experiment was performed during 12 days under very weak stratification at a fetch-limited lake in Switzerland. The near surface observations were obtained by using a quasi-free rising profiler which measured small scale shear and temperature fluctuations. We used a two-equation k-epsilon. turbulence model with an algebraic second-moment Closure scheme. The one-dimensional numerical model was extended to consider breaking waves by a shear-dependent parameterisation. The agreement of observed and simulated turbulence quantities is very promising. Especially well simulated is the enhanced turbulence level in the wave-affected-surface-layer (WASL) of a few din thickness. The logarithmic slope of the turbulent dissipation rate in this WASL was found to vary between -2.1 and -1.7. Below the WASL the classic law-of-the-wall was well reproduced by the data and the model.