A Simplified General Circulation Model for a Baroclinic Ocean with Topography. Part I: Theory, Waves, and Wind-Driven Circulations

Dirk Olbers Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

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Carsten Eden Department of Oceanography, Dalhousie University, Halifax, Canada

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Abstract

A new type of ocean general circulation model with simplified physics is described and tested for various simple wind-driven circulation problems. The model consists of the vorticity balance of the depth-averaged flow and a hierarchy of equations for “vertical moments” of density and baroclinic velocity. The first vertical density moment is the (vertically integrated) potential energy, which is used to describe the predominant link between the barotropic and the baroclinic oceanic flow in the presence of sloping topography. Tendency equations for the vertical moments of density and baroclinic velocity and an appropriate truncation of the coupled hierarchy of moments are derived that, together with the barotropic vorticity balance, yield a closed set of equations describing the barotropic–baroclinic interaction (BARBI) model of the oceanic circulation. Idealized companion experiments with a numerical implementation of the BARBI model and a primitive equation model indicate that wave propagation properties and baroclinic adjustments are correctly represented in BARBI in midlatitudes as well as in equatorial latitudes. Furthermore, a set of experiments with a realistic application to the Atlantic/Southern Ocean system reproduces important aspects that have been previously reported by studies of gyre circulations and circumpolar currents using full primitive equation models.

Current affiliation: Institut für Meereskunde, Kiel, Germany

Corresponding author address: Carsten Eden, Institut für Meereskunde, FB I, Theorie und Modellierung, Düsternbrooker Weg 20, 24105 Kiel, Germany. Email: ceden@ifm.uni-kiel.de

Abstract

A new type of ocean general circulation model with simplified physics is described and tested for various simple wind-driven circulation problems. The model consists of the vorticity balance of the depth-averaged flow and a hierarchy of equations for “vertical moments” of density and baroclinic velocity. The first vertical density moment is the (vertically integrated) potential energy, which is used to describe the predominant link between the barotropic and the baroclinic oceanic flow in the presence of sloping topography. Tendency equations for the vertical moments of density and baroclinic velocity and an appropriate truncation of the coupled hierarchy of moments are derived that, together with the barotropic vorticity balance, yield a closed set of equations describing the barotropic–baroclinic interaction (BARBI) model of the oceanic circulation. Idealized companion experiments with a numerical implementation of the BARBI model and a primitive equation model indicate that wave propagation properties and baroclinic adjustments are correctly represented in BARBI in midlatitudes as well as in equatorial latitudes. Furthermore, a set of experiments with a realistic application to the Atlantic/Southern Ocean system reproduces important aspects that have been previously reported by studies of gyre circulations and circumpolar currents using full primitive equation models.

Current affiliation: Institut für Meereskunde, Kiel, Germany

Corresponding author address: Carsten Eden, Institut für Meereskunde, FB I, Theorie und Modellierung, Düsternbrooker Weg 20, 24105 Kiel, Germany. Email: ceden@ifm.uni-kiel.de

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