RECTIFIED FLOW ALONG A VERTICAL COASTLINE

Laboratory experiments are conducted on a physical system in which an oscillatory, along-shore, free stream flow of a homogeneous fluid occu rs in the vicinity of a long coastline with vertical slope; the model sea-floor is horizontal. Particular attention is given to the resultin g rectified (mean) current which is along the coastline with the shore on the right, facing downstream. In the lateral far field region defi ned by y/H >> 0(1), where y is the offshore coordinate and H is the de pth of the fluid, the motion field is approximately independent of the lateral distance from the coast. The vertical structure of the cross- stream motion in this region consists of Ekman layers near the sea-flo or and interior adjustment flows, both periodic in time. In the near f ield, defined by y/H less than or similar to 0(1), the motion is stron gly dependent on the cross-stream coordinate as well as time, and rect ified currents are observed. The mechanism responsible for the rectifi cation is a complex nonlinear coupling between laterally directed adju stment flows driven by the transport in the bottom Ekman layers, and t he free stream motion field. The rectified current is found to be subs tantially wider than the Stewartson layer thickness but much narrower than the Rossby deformation radius. The characteristic width, delta(y) , of the rectified current is shown to scale as delta(y)/H similar to RoRo(t)(-1)E(1/2), where Ro is the Rossby number, Ro(t), is the tempor al Rossby number and E is the Ekman number. Experiments are presented which support this scaling.