A Laboratory Study of the Zonal Structure of Western Boundary Currents

Abstract The zonal structure of strongly nonlinear inertial western boundary currents (WBCs) is studied experimentally along a straight “meridional” coast in a 5-m-diameter rotating basin by analyzing the “zonal” profile of the meridional velocity field as a function of transport intensity and other dynamical parameters. The return flow that is generated by the surface wind stress curl in the oceanic interior is forced in the rotating basin by the motion of a piston, in the absence of any surface stress. The laboratory setup consists of two parallel rectangular channels separated by an island and linked by two curved connections: in the first channel, a piston is forced at a constant speed up ranging from 0.5 to 3 cm s−1 over a distance of 2.5 m, producing a virtually unsheared current at the entrance of the second channel. In the latter, a linear reduction of the water depth provides the topographic beta effect that is necessary for the development of the westward intensification. Nearly steady currents ...