The stability of buoyancy-driven coastal currents |
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| Authors: | RW Griffiths PF Linden |
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| Institution: | Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge CB3 9EW Great Britain |
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| Abstract: | Buoyancy-driven boundary currents were generated in the laboratory by releasing buoyant fluid from a source adjacent to a vertical boundary in a rotating container. The boundary removed the Coriolis force parallel to it, allowing the buoyant fluid to spread in a current along the boundary. Ise of a cylindrical boundary and a line source that released fluid uniformly around the circumference enabled an axisymmetric (zonal) current to be produced. With the continuous release of fluid from the source, the current grew in width and depth until it became unstable to non-axisymmetric disturbances. The wavelength and phase velocities of the disturbances were consistent with a model of baroclinic instability of two-layer flow when frictional dissipation due to Ekman layers is included. However, when the current only occupied a small fraction of the total depth, barotropic processes were also thought to be important, with the growing waves gaining energy from the horizontal shear.In other experiments, gravity currents were produced by a point source adjacent to either a zonal (circular) or a meridional (radial) vertical boundary. The currents were also observed to become unstable to the same upstream breaking waves as those on the continuous zonal current. Finally, some comparisons are made with oceanic coastal currents. |
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