On the Role of Topography in the Ocean Circulation: Diffusive and Inertial Effects

Paola Cessi MIT-WHOI Joint Program in Physical Oceanography, Massachusetts Institute of Technology, Cambridge, Massachusetts

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Abstract

In an earlier paper it was shown that the presence of bottom topography can substantially alter the Sverdrup prediction for the large-scale wind driven flow. In their model the abyssal water is set in motion by the eddy field, parameterized as lateral diffusion of potential vorticity. If the topography has a structure in the east-west direction, then the solution found in the inviscid limit by Cessi and Pedlosky predicts the occurrence of strong jets in the interior of the model ocean. In this note I used a numerical model to test whether the jets predicted by the analytic solutions survive when inertia and diffusion are included explicitly.

In the inviscid limit, according to the structure of the topography these internal jets can occur in both vertically homogeneous and stratified models. Specifically, if the topographic slope changes sign, then one kind of jets is observed both in baroclinic and barotropic models. In the present work it is shown that this phenomenon is observed with moderate amounts of diffusion and is not disturbed by the occurrence of recirculating inertial gyres within the basin.

If the topographic slope is constant, then another kind of internal jets is theoretically predicted in the inviscid limit, and it occurs in stratified models only. Numerical calculations did not exhibit this kind of internal jets in the presence of inertia and weak diffusion, and the reasons for this failure are rationalized.

Abstract

In an earlier paper it was shown that the presence of bottom topography can substantially alter the Sverdrup prediction for the large-scale wind driven flow. In their model the abyssal water is set in motion by the eddy field, parameterized as lateral diffusion of potential vorticity. If the topography has a structure in the east-west direction, then the solution found in the inviscid limit by Cessi and Pedlosky predicts the occurrence of strong jets in the interior of the model ocean. In this note I used a numerical model to test whether the jets predicted by the analytic solutions survive when inertia and diffusion are included explicitly.

In the inviscid limit, according to the structure of the topography these internal jets can occur in both vertically homogeneous and stratified models. Specifically, if the topographic slope changes sign, then one kind of jets is observed both in baroclinic and barotropic models. In the present work it is shown that this phenomenon is observed with moderate amounts of diffusion and is not disturbed by the occurrence of recirculating inertial gyres within the basin.

If the topographic slope is constant, then another kind of internal jets is theoretically predicted in the inviscid limit, and it occurs in stratified models only. Numerical calculations did not exhibit this kind of internal jets in the presence of inertia and weak diffusion, and the reasons for this failure are rationalized.

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