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The Effect of a Maintained Surface Stress on the Velocity and Density Fields Within a Contained, Rotating, Two-Layer Stratified Fluid

Author(s): William F. Rizk; Peter A. Davies; Yarko Nino; Alan J. S Cuthbertson

Linked Author(s): Peter A. Davies, Yarko Niño, Alan J S Cuthbertson

Keywords: No Keywords

Abstract: Laboratory experiments are described in which the time development of the velocity and density disturbance fields within a shallow, contained, stratified, rotating fluid driven by a maintained surface stress are determined over a wide range of parametric conditions. The flow configuration models that of a large lake, reservoir or semi-enclosed sea subjected to a surface wind stress-a case that has accumulated much field data to show that the background rotation of the Earth exerts a strong dynamical role in the circulation physics of the water body. The experiments demonstrate that one of the main distinguishing features of the flow is the role of the background rotation in destroying the symmetrical behaviour of the fluid response seen in similar experiments with non-rotating counterpart cases. The results confirm that the combination of background rotation and surface forcing generates within the forced layer an interior flow that consists of strong side wall boundary currents with weak interior gyre motions. The motion within the layer that is not in contact with the surface stress is initially relatively quiescent but the interface between the fluids is seen to erode quickly in response to shearinduced vertical mixing. The response of the forced water basin occurs in two phases, namely an initial adjustment phase in which the interfacial isopycnals are stretched (as longitudinal and transverse interface slopes are established) and a second phase in which entrainment processes result in vertical mixing. The tilts of the isopycnals are shown to be those required for the maintenance of geos trophic. Measured entrainment velocities are shown to be parameterised well by the bulk Richardson number of the flow (as for non-rotating counterpart flows) but the entrainment rates show spatial dependence with relatively low values in the interior of the fluid and high values at the edges where the boundary currents are generated.


Year: 2009

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