Abstract: On the importance of internal waves for vertical mixing in the Gulf of Finland

 

 

Authors: A. Stips, R. Manasrah

A. Stips¹ and M.-J. Lilover ²

¹ European Commission – Joint Research Centre

Via E. Fermi, 2749 (TP272)

I-21027 Ispra (VA), Italy

² Marine Systems Institute at Tallinn University of Technology

Akadeemia tee 21, 12618 Tallinn, Estonia

Abstract

We applied different well known parameterization schemes of eddy diffusivity and k-ε simulations to three measured time series of shear microstructure data. These short time series have been 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 the third (A3) time series, the background stratification weakened continuously from A1 toward A3.  We compared eddy diffusivities based on the Richardson number parameterization and eddy diffusivities simulated using the two equation k-ε turbulence closure (General Ocean Turbulence Model, GOTM) with the “measured” ones. For two out of the three time series the eddy diffusivities calculated via the Richardson number parameterization and via the k-ε model simulation agreed well with the experimental data. However, summing up the discrepancy of all three time series both methods resulted in a remarkable and consistent bias against the measured eddy diffusivity. Introducing a new parameterization scheme, which considers the internal wave kinetic energy we achieved an improved fit for all three time series. Similarly the modified k-ε simulations which considered the internal wave energy level matched better the measured profiles.