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The Shadowed Island

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  • 1 Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
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Abstract

The circulation of fluid in a basin containing several topographic barriers is considered. Meridional barriers situated east of another barrier “shadow” the western barrier with respect to Rossby wave propagation. The steady circulation responds by reducing the flow through the gaps in the western barrier. As a consequence, the nature of the recirculation zone described in Pedlosky et al. is strongly affected by the shadowing topography. Generally, the effect of the shadowing topography is to enhance and enlarge the zone of recirculation.

It is shown that the effectiveness of the shadow depends on whether the eastern barrier is a peninsula or internal “island.” In the latter case, the effect of the barrier depends strongly on the relative meridional extents of the two topographic features. In all cases, the peninsula is by far the most effective shadowing barrier in reducing the flow around the western barrier.

Both analytical and laboratory models of the circulation are described. In the former case, the analysis is restricted to linear theory. The laboratory model employs the “sliced cylinder” geometry. Good agreement is found between theory and experiment, although significant alterations are found when the flow becomes strongly nonlinear.

Corresponding author address: Dr. Karl R. Helfrich, Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.

Email: khelfrich@whoi.edu

Abstract

The circulation of fluid in a basin containing several topographic barriers is considered. Meridional barriers situated east of another barrier “shadow” the western barrier with respect to Rossby wave propagation. The steady circulation responds by reducing the flow through the gaps in the western barrier. As a consequence, the nature of the recirculation zone described in Pedlosky et al. is strongly affected by the shadowing topography. Generally, the effect of the shadowing topography is to enhance and enlarge the zone of recirculation.

It is shown that the effectiveness of the shadow depends on whether the eastern barrier is a peninsula or internal “island.” In the latter case, the effect of the barrier depends strongly on the relative meridional extents of the two topographic features. In all cases, the peninsula is by far the most effective shadowing barrier in reducing the flow around the western barrier.

Both analytical and laboratory models of the circulation are described. In the former case, the analysis is restricted to linear theory. The laboratory model employs the “sliced cylinder” geometry. Good agreement is found between theory and experiment, although significant alterations are found when the flow becomes strongly nonlinear.

Corresponding author address: Dr. Karl R. Helfrich, Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.

Email: khelfrich@whoi.edu

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