Water exchange of the Stockholm archipelago
Abstract
The Stockholm archipelago spans roughly a semicircular area with a radius of approximately 60 km, traditionally partitioned into three parts: the inner, the middle and the outer archipelago. The two innermost parts are characterized by a set of comparatively larger basins, interconnected by a limited number of straits. A discrete basin (DB-) model is obtained by partitioning the area into a set of presently 57 sub-basins according to 101 delimiting straits that may be silled or not. The resulting model configuration thus encompasses a set of hydraulically coupled 1-dimensional (1D) basins that are only resolved vertically with layers of arbitrary thickness. The advantage of this approach over employing a 3D-model of the entire area is the possibility for enhanced vertical resolution and improved strait exchange formulations, making it possible to distinguish between controlled/non-controlled and rotational/non-rotational regimes. For ecological time-scales of about one day, this approach outweighs the disadvantage of neglected horizontal gradients within the basins. In the inner archipelago the dominating exchange process is estuarine circulation, induced by a marked freshwater discharge and the vertical mixing. In the outer and middle archipelagos the density fluctuations due to Ekman pumping along the Baltic boundary interface produce another type of baroclinic process that clearly dominates. Measurements to adequately resolve these density variations do not exist. Missing forcing data are provided by linking the middle archipelago’s boundary straits to a 3D-model of the Baltic with a grid resolution of 0.5 nautical miles (n.m.). This fine resolution model (FR-domain) is in turn driven by the atmospheric forcing and the density variation at the rectangular boundary of the FR-domain which acceptably resolves both the interfacial straits and the outer archipelago's complex hypsography. Massive computing resources would be demanded if the FR-domain were extended to comprise the entire Baltic. The FR-domain is thus interfaced with an existing coarse resolution model of the entire Baltic (CR-domain) with a grid size of 5 n.m., the open boundary of which is located in the Kattegat. This 3-fold model setup is being run for ten years (starting 1990) to obtain sufficient data for a thorough validation versus S-&T-measurements, comparatively sparse in time and space.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....14213E