An s coordinate density evolving model of the northwest European continental shelf -: 1, Model description and density structure

The Proudman Oceanographic Laboratory Three-Dimensional Baroclinic B grid model (POL3DB) has been developed to incorporate features suitable for the modeling of baroclinic processes on the shelf, at the shelf slope, and in ocean regions to allow long-term coupled ocean-shelf simulations. We test the model on the northwest European continental shelf in the period November 1988 to October 1989 against satellite sea surface temperature measurements, against CTD sections both on and off the shelf, and (in summary) against the whole of the North Sea Project CTD data set. The model accurately reproduces the seasonal cycle in the shelf-wide spatial temperature structure seen in the observations. Spatial correlations range from r=0.92 in December to 0.79 in July, and the overall rms errors range from 0.8 degreesC in April to 1.6 degreesC in July. We demonstrate that the increase in the errors during the summer is due to uncertainties in modeling the vertical temperature structure. Compared with a climatology, the large-scale sea surface salinity structure is also well modeled (r = 0.80), but there is a tendency for the model to overestimate the salinity in the Norwegian Trench and underestimate it in the Kattegat. The s coordinates (a modified sigma-coordinate system) allow the formation of a seasonal mixed layer across the shelf break and into the northeast Atlantic with a modest vertical resolution. The accuracy to which this deep water region is modeled is limited by the initial and boundary conditions and by the extent of the model domain.