Laboratory Study of the General Ocean Circulation

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A thermally driven circulation in a rotating (anti-clockwise) cylindrical basin of constant depth was studied experimentally. The thermal forcing was achieved by cooling a 'northern " portion of the basin's sidewall. In some experiments the working basin was connected to an 'open ocean' through shallow passages.Important new findings are1. An anti-cyclonic circulation with an intense 'western' boundary current is produced in the upper layer by the deep sinking along the 'northern' boundary. So long as the upper fluid surface is free, the surface 'western' boundary current is much stronger and wider than the underlying cold counter current from the sinking region, having a net northward transport. This may be the first western intensification that has been caused without the, beta-effect and wind stresses.2. If there is a shallow passage on the "western" side of the basin, an appreciable inflow occurs through the passage due to the "northern" sinking.3. Vertical structure of buoyancy-driven motions critically depends on the bottom boundary condition. If the bottom is free-slip (this was achieved by using starch emulsion), any convective motions become an internal mode without net horizontal transport. If the bottom is non-slip, however, convective motions generally have a dominant barotropic component.