Vorticity analysis of transient shallow water eddy fields at the river plume front of the River Elbe in the German Bight

The mesoscale variability of the circulation of the German Bight is investigated for selected wind forcing situations with an eddy resolving model. A vorticity equation is derived which considers explicitly both mass distribution and tides. Different shallow water eddy regimes are identified in the German Bight. Using the vorticity equation, the statistical steady state eddy fields are analyzed with respect to the production mechanisms of the gyres and shallow water eddies. The large German Bight gyre is affected by the joint effect of baroclinicity and topography. It is demonstrated that all shallow water eddies which appear at the East-Friesian coast are affected by the interaction between wind stress and the gradient of bottom topography. Small shallow water eddies at the North-Friesian coast formed from the baroclinic forcing, the vortex squeezing and the interaction between wind stress and the gradient of bottom topography. The results further suggest that the contribution of advection or of tidal stress to the vorticity production is of minor relevance. (C) 1998 Elsevier Science B.V.