Application of a three-dimensional numerical model to the idealized conditions of the bosphorus strait.

Sözer, Adil
The Bosphorus Strait is a narrow and shallow channel between the Sea of Marmara and the Black Sea which plays an important role in the Turkish Straits System connecting the Black Sea and the Mediterranean Sea. The exchange flow through the Bosphorus Strait is principally determined by geometry and stratification, and exhibits a complex nonlinear response to forcing by the net water budget, pressure and wind setup effects in adjacent basins. This study aims for a better understanding of the behaviour of the Bospho rus Strait flow, based on a three-dimensional model of its idealized dynam ics. The response of the Strait is investigated with respect to open boundary conditions corresponding to idealized geometrical and hydrographical condi tions. Although the rigid-lid assumption would be appropriate for long-term dynamics, a model with free-surface was used to predict short-term changes and relate them to sea-level variability in the Strait and the adjacent basins. The free-surface, primitive equation model, SCRUM, was used for numerical simulations. The model has terrain-following coordinates, optional mixing iiiparametrizations, and various choices for the bottom, solid or open boundary conditions. Many simulations were performed including the testing of boundary con ditions, experiments with different types of horizontal and vertical mixing and diffusion parametrizations, advection schemes and tests of geometrical effects as well as grid type and the resolution. These results were compared with two-layer analytical solutions of exchange flows and the observations in the Bosphorus. These simulations showed the three-dimensional model to be applicable to the special case of strait exchange flows. The selection of the open boundary conditions is a non-trivial first step for successful application of the model. The results obtained from the tests with idealized cases corresponding to the Bosphorus Strait indicate the need for judicious choices of open boundary conditions, which depend on the flow direction. The results obtained with these choices and even the case with pure radiation boundary conditions started from 'lock-exchange' initial condition, support the existence of max imal exchange type of controlled flows, exemplified by observations in the Bosphorus. With guidance of the results obtained from applications to idealized cases, the model was succesfully implemented to the actual geometrical and to pographical conditions of the Bosphorus Strait, although conclusive results could not yet be obtained. A very encouraging point has been reached for further investigations which are needed on tuning of the model parameters to obtain realistic results consistent with observations in the Bosphorus Strait.
Citation Formats
A. Sözer, “Application of a three-dimensional numerical model to the idealized conditions of the bosphorus strait.,” Middle East Technical University, 2002.