A NUMERICAL STUDY OF THE WATER EXCHANGE THROUGH THE DANISH STRAITS

The free surface version of the GFDL model is used to study inflow and outflow through the Danish Straits, which connect the Baltic with the North Sea. Three problems are addressed: (i) the piling up of inflowi ng water in the Arkona basin; (ii) the transport ratios between Belt a nd Sound; (iii) the dominance of hydraulic or geostrophic control. Mod el results show that a cyclonic eddy (dome) is formed by the inflowing saline water that prevents this water from passing rapidly into the B ornholm basin. This eddy is enforced with increasing inflow due to a s ea level difference between Kattegat and western Baltic. If density gr adients along the straits are weak and the flow is dominantly driven b y sea level differences between Kattegat and Baltic, the well-known ra tio of 70%:30% for the transports through Belt and Sound are confirmed . Strong density gradients can change this ratio considerably, especia lly in the outflow case, when the light water of the Baltic flows agai nst the heavier water of the Kattegat. Under variable wind conditions, no fixed ratio is found. The now in the Straits is geostrophically co ntrolled; however, the strong baroclinic density field does not allow us to derive the transport simply from sea level inclination.