The response of the North Channel of the Irish Sea and Clyde Sea to wind forcing

Abstract

A three-dimensional non-linear model of the North Channel of the Irish Sea and the adjacent Clyde Sea is used to examine the influence of local wind direction and flow (assumed to be generated by winds over the shelf) through the region, upon currents and transports within the area. The model has a significantly higher resolution (of order 1 km) than previous models of the region and consequently detailed spatial variations of the flow which could not be examined previously can be considered. Currents induced by an along channel wind, show a depth mean flow in the wind direction in shallow water with a weak return flow at depth in the deeper regions. Under these conditions there is little exchange with the Clyde Sea, with the majority of the flow occurring in the North Channel due to topographic constraints. In the case of an across channel wind, there is significant exchange between the North Channel and the Clyde Sea. This suggests that wind-induced flushing of the Clyde Sea, will be produced mainly by across-channel wind forcing. Flows produced by forcing an inflow through the open boundaries of the model are topographically steered along the axis of the North Channel and there is little exchange with the Clyde Sea. Calculations show that currents in the region due to local winds and far-field inflows can be computed by linearly combining solutions due to orthogonal wind forcing (namely winds at right angles to each other, taken here as the along and across-channel winds) and open boundary input. Consequently, the response of the North Channel and Clyde Sea regions under homogeneous conditions to local and far-field wind forcing can be understood as a linear combination of the solutions presented here.