The Dynamics of Barotropically Dominated Rings

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Abstract
Based on observations, the proposition is forwarded that some rings involve important deep flow. The work described herein is directed at understanding the consequences on eddy evolution of such structure. An analysis of the equations of motion is conducted that emphasizes the importance of the lower layer evolution. The thermocline responds in a largely passive fashion. This analysis differs considerably from previous theories, which focus on the evolution of surface-intensified rings. The most important practical differences are that the coupled system can be expected to exhibit propagation in any direction (as opposed to predominantly west, as in reduced gravity theories), and that the propagation rates can be an order of magnitude greater than those of reduced gravity systems. These aspects of the present analysis are in accord with many ring observations. A series of primitive equation numerical experiments are conducted to test these ideas, with the result that the experiments support such “barotropically dominated dynamics” as a useful qualitative and quantitative tool for the study of eddies and rings. The asymptotic analysis also suggests that initial conditions with closed regions of potential vorticity should differ significantly from those with no closed potential vorticity zones. This hypothesis is supported by primitive equation runs; approximately compensated lower-layer experiments (with no closed potential vorticity contours) exhibit qualitatively and quantitatively different behavior than experiments with initially energetic lower layers (which have closed potential vorticity contours).

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