Observation, Parameterization and Simulation of Turbulent Mixing in the Gulf of Finland, the Baltic Sea

Three time series of shear microstructure measurements (duration 13, 24 and 14 h respectively) were performed in 3 different wind forcing regimes as well as in 3 different background density stratification and current velocity shear situations at the entrance to the Gulf of Finland, in July 1998. Vertical shear of current velocity was enhanced by near-inertial waves during the first (A1) and third (A3) time series. We compared a Richardson number based parameterization and an estimation using the two equation k-epsilon turbulence closure (General Ocean Turbulence Model, GOTM) with "measured" eddy diffusivities. For two out of the three time series eddy diffusivities calculated via a Richardson number parameterization and via simulation using the k-epsilon model agreed well with the experimental data. However, in the case of relatively high current velocity shear and weak background density stratification (time series A3) both applied methods resulted in a remarkable discrepancy against the measured eddy diffusivity. On the contrary, calculations with a new parameterization scheme, which considers the internal wave kinetic energy fitted well for all three time series. Similarly the modified k-epsilon simulations which considered the internal wave energy level better matched the measured profiles.