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

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 d irection 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 coul d not be examined previously can be considered. Currents induced by an alon g channel wind, show a depth mean flow in the wind direction in shallow wat er with a weak return flow at depth in the deeper regions. Under these cond itions there is little exchange with the Clyde Sea, with the majority of th e flow occurring in the North Channel due to topographic constraints. In th e 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. F lows 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 t he region due to local winds and far-field inflows can be computed by linea rly combining solutions due to orthogonal wind forcing (namely winds at rig ht angles to each other, taken here as the along and across-channel winds) and open boundary input. Consequently, the response of the North Channel an d Clyde Sea regions under homogeneous conditions to local and far-field win d forcing can be understood as a linear combination of the solutions presen ted here. (C) 2000 Elsevier Science Ltd. All rights reserved.