The Diabatic Deacon Cell*

Speer, Kevin; Rintoul, Stephen R.; Sloyan, Bernadette M.

doi:10.1175/1520-0485(2000)030<3212:tddc>2.0.co;2

Cited by 336 publications

(319 citation statements)

References 29 publications

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“…The formal asymptotic expansion, however, clarifies this issue by unambiguously separating the effects of mechanical and thermodynamic forcing (grouped together in MR). The new framework explicitly connects and reconciles the diabatic views of the Southern ocean (e.g., Speer, 2000), which emphasize the role of water mass transformation, and purely adiabatic models (e.g., Johnson and Bryden, 1989). The finite air-sea fluxes and small-scale mixing are clearly essential for closing the buoyancy budget of the upper cell of the meridional overturning circulation in the Southern Ocean.…”

Section: Discussionmentioning

confidence: 70%

“…However, specific mechanisms of interaction between the wind forcing, air-sea fluxes and eddy transport in the interior, and their respective roles in controlling the patterns of buoyancy and residual circulation, are still poorly understood (Bryden and Cunningham, 2003). For instance, upwelling of the upper circumpolar deep water and equatorward flow at the surface apparently requires buoyancy gain; Speer et al (2000) examined the air-sea fluxes and concluded that the air-sea fluxes are compatible with the mass transports in the Southern Ocean. However the question remains (e.g., Hallberg and Gnanadesikan, 2001) whether the surface buoyancy fluxes and/or small-scale mixing processes play largely passive roles in maintaining the overturning circulation of the ACC, or whether they can actively participate in setting up its density structure.…”

Section: Introductionmentioning

confidence: 99%

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Analytical solutions for the ACC and its overturning circulation

Radko¹

2005

J Mar Res

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An explicit analytical model of the Antarctic Circumpolar Current (ACC) is presented in which the key feature is the balance between the Eulerian circulation acting to overturn the isopycnals and geostrophic eddies which tend to flatten them. Solutions for the stratification and overturning circulation are obtained by expanding the governing residual mean equations of motion in a small parameter (ε) which measures the relative strength of the surface buoyancy flux and mechanical forcing by winds. Our balanced asymptotic model extends and reconciles the earlier views on the dynamics of the (streamwise-averaged) ACC by demonstrating that the zero order balance between the eddy-induced circulation and the mean flow determines gross features of the buoyancy distribution in the interior of the ACC. The diabatic buoyancy fluxes are essential in driving the secondary (residual) circulation which is, however, largely steered along the pathways set by the dominant adiabatic balance. Model assumptions are supported by a close agreement of the analytical solutions and fully nonlinear numerical calculations.

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Section: Discussionmentioning

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Analytical solutions for the ACC and its overturning circulation

Radko¹

2005

J Mar Res

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“…The dynamics of the Southern Ocean meridional overturning cell has been widely documented elsewhere (Döös and Webb, 1994;Marshall, 1997;Speer et al, 2000;Rintoul et al, 2001;Olbers et al, 2004;Drijfhout, 2005). In this section, we present diagnostics of the potential vorticity fluxes at just two depths, 201 m and 1150 m, in order to demonstrate that integrating the fluxes leads to a great conceptual simplification and to demonstrate how these fluxes can be used to quantify the cancellation between the Eulerian-mean and eddy-induced overturning cells that results in subtropical overturning cells.…”

Section: Southern Oceanmentioning

confidence: 99%

“…In the absence of buoyancy forcing the streamwise Eulerian-mean and eddy-induced overturning circulations cancel, corresponding to non-acceleration conditions (Eliassen and Palm, 1961;Plumb, 1990). More generally, the equilibrium residual circulation is controlled by buoyancy forcing (Marshall, 1997;Speer et al, 2000;Gallego et al, 2004), with quasiadiabatic upwelling of North Atlantic Deep Water and subduction of Antarctic Intermediate and Bottom waters. This residual overturning circulation has been termed the "diabatic Deacon cell" by Speer et al (2000) and includes the what is traditionally called the thermohaline circulation.…”

Section: Introductionmentioning

confidence: 99%

“…This upwelling and compensating downwelling to the north of the ACC steepens the isopycnals, leading to a zonal transport through thermal-wind balance. This process is ultimately arrested either when slumping of the isopycnals by baroclinic instability and/or surface buoyancy forcing (or friction) is able to compensate for the steepening of the isopycnals by the Deacon cell (Johnson and Bryden, 1989;Speer et al, 2000). Thus there is strong coupling between the strength of the overturning cell and the recirculating geostrophic flow.…”

Section: Introductionmentioning

confidence: 99%

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Overturning cells in the Southern Ocean and subtropical gyres

Polton

Marshall

2007

Ocean Sci.

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Abstract. The circulation of the subtropical gyres can be decomposed into a horizontal recirculation along contours of constant Bernoulli potential and an overturning circulation across these contours. While the geometry and topology of Bernoulli contours is more complicated in the subtropical gyres than in the Southern Ocean, these subtropical overturning circulations are very much analogous to the overturning cell found in the Southern Ocean. This analogy is formalised through an exact integral constraint, including the rectified effects of transient eddies. The constraint can be interpreted either in terms of vertical fluxes of potential vorticity, or equivalently as an integral buoyancy budget for an imaginary fluid parcel recirculating around a closed Bernoulli contour. Under conditions of vanishing buoyancy and mechanical forcing, the constraint reduces to a generalised nonacceleration condition, under which the Eulerian-mean and eddy-induced overturning circulations exactly compensate. The terms in the integral constraint are diagnosed in an eddypermitting ocean model in both the North Pacific subtropical gyre and the Southern Ocean. The extent to which the Eulerian-mean and eddy-induced overturning circulations compensate is discussed in each case.

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Temporal variability of transformation, formation, and subduction rates of upper Southern Ocean waters

Kwon

2013

J. Geophys. Res. Oceans

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[1] Kinematic and thermodynamic approaches are employed to diagnose the timedependent transformation, formation, and subduction rates of upper Southern Ocean waters in a multidecadal simulation within an eddy-permitting coupled climate model. In the Subantarctic Mode Water (SAMW) density class, a convergence of diapycnal volume fluxes leads to the formation and inflation of mixed layer waters during winter. A portion of this water is detrained into the pycnocline during early spring, when surface heating restratifies the deep winter mixed layer. The annually averaged subduction rate of SAMW shows pronounced interannual variability, partly controlled by the temporal tendency of the winter mixed layer depth from one year to the next. No significant correlation between the Southern Annular Mode (SAM) and the isopycnally integrated SAMW subduction rate is apparent. However, Ekman downwelling/upwelling intensities modulated by the SAM influence interannual variations in the subduction rates of water masses lighter and heavier than SAMW with an opposing sign: during positive phases of the SAM, more pycnocline waters are entrained into the mixed layer and transformed into lighter densities within the Antarctic Intermediate Water density class, whereas more mixed layer waters are subducted into the pycnocline within the Subtropical Mode Water density class. Such distinct responses of upper Southern Ocean water masses to the SAM are qualitatively consistent with observational constraints. Based on a comparison between offline kinematic and thermodynamic diagnostics, we infer that diapycnal mixing within the mixed layer may contribute up to 50% of the formation rate of SAMW on interannual timescales.

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The Diabatic Deacon Cell*

Cited by 336 publications

References 29 publications

Analytical solutions for the ACC and its overturning circulation

Analytical solutions for the ACC and its overturning circulation

Overturning cells in the Southern Ocean and subtropical gyres

Temporal variability of transformation, formation, and subduction rates of upper Southern Ocean waters

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