A Continuously Stratified Thermocline Model Incorporating a Mixed Layer of Variable Thickness and Density

Marshall, John; Nurser, A. J. George

doi:10.1175/1520-0485(1991)021<1780:acstmi>2.0.co;2

Cited by 13 publications

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“…To better isolate the waters that are permanently subducted, the bottom boundary can be fixed at the maximum mixed‐layer depth over the year where the fixed boundary is denoted H ( x , y ) = max( h [ x , y , t ]) [e.g., Marshall and Nurser , 1991; Marshall et al , 1999]. can be rewritten with the fixed lower boundary: where the water mass subduction rate now has a subscript “ H ” and the second integral of the right‐hand side is the corresponding eddy subduction rate.…”

Section: Subduction and Transformation In An Open‐ocean Domainmentioning

confidence: 99%

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Does eddy subduction matter in the northeast Atlantic Ocean?

Gebbie

2007

J. Geophys. Res.

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Mesoscale eddies are an important contributor to subduction in the Gulf Stream region and the Antarctic Circumpolar Current, but is eddy subduction also important in the relatively quiescent interior of the world's subtropical gyres? Observations from the Subduction Experiment of the northeast Atlantic do not have the spatial resolution necessary to calculate eddy subduction and answer this question. Regional numerical models can diagnose subduction, but their representativeness is unknown. Furthermore, water mass budgets in an open‐ocean domain show that the simulated properties of subducted water directly depend upon uncertain open‐boundary conditions and surface fluxes. To remedy these problems, a state estimate of the ocean circulation is formed by constraining an eddy‐permitting general circulation model to observations by adjusting the model parameters within their uncertainty. The resulting estimate is self‐consistent with the equations of motion and has the necessary resolution for diagnosing subduction. In the northeast Atlantic during 1991–1993, the time‐variable circulation contributes less than 1 Sv of net subduction, while the total subduction is 4 Sv. Eddy volume fluxes of 40 m/yr in the North Equatorial Current and the Azores Current, however, are significant and rival the subduction by Ekman pumping locally. Furthermore, a state estimate at 1/6° resolution has 2–3 Sv more subduction in the density bands centered around σ = 24.0 kg/m3 and σ = 26.0 kg/m3 than a 2° state estimate. This result implies that the inability to accurately simulate mesoscale phenomena and surface fluxes in climate models would lead to an accumulation of errors in water mass properties over 10–20 years, even in the interior of the subtropical gyre.

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Section: Subduction and Transformation In An Open‐ocean Domainmentioning

confidence: 99%

“…GEBBIE: EDDY SUBDUCTION and Nurser, 1991;Marshall et al, 1999]. Equation (3) can be rewritten with the fixed lower boundary:…”

Section: Kinematic Definition Of Subductionmentioning

confidence: 99%

Does eddy subduction matter in the northeast Atlantic Ocean?

Gebbie

2007

J. Geophys. Res.

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“…This corresponds to the observations of the sharp frontal interfaces in the COARE EQ-3 cruise showing the spatial anisotropy relative to the wind direction. Dewar (1991Dewar ( , 1992, Marshall and Nurser (1991), and Nurser (1995) developed a so-called shock front model. A shock front may form where the convergence is a consequence of some property gradient.…”

Section: A Comparison Of Model and Experimental Datamentioning

confidence: 99%

Sharp Frontal Interfaces in the Near-Surface Layer of the Ocean in the Western Equatorial Pacific Warm Pool

Soloviev¹,

Lukas²

1997

J. Phys. Oceanogr.

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During the TOGA COARE rich horizontal temperature and salinity variability of the near-surface layer of the ocean in the western Pacific warm pool was observed. High-resolution measurements were made by probes mounted on the bow of the vessel in an undisturbed region at ϳ1.7-m depth during four COARE cruises of the R/V Moana Wave. The authors observed several tens of cases of periodic sharp frontal interfaces of width 1-100 m and separation 0.2-60 km. The sharp frontal interfaces were often found in frontal regions and on the periphery of freshwater puddles. Maneuvers of the ship were conducted to determine the spatial orientation of a sharp frontal interface. The interfaces revealed anisotropy with respect to the wind direction. They were most sharp when the wind stress had a component along the buoyant spreading of the front. A possible origin of the sharp frontal interfaces is discussed. These interfaces may develop by nonlinear evolution of long-wave disturbances on the near-surface pycnocline that is often observed in the warm pool area. A shallow-water model may describe some features of the observations. A dimensionless number of the Reynolds type is a criterion of transition from wave train solution to dissipative shock-wave structure. The model predicts spatial anisotropy depending on the relative angle between the wind stress and horizontal density gradient.

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“…However, these theories remain incomplete due to exclusion of explicit western and eastern boundary regimes as well as overly simplified mixed layer representations. In particular, the importance of including an explicit representation of the surface mixed layer has been successfully argued (Marshall and Nurser 1991;Williams 1991;Pedlosky and Robbins 1991). Indeed, active mixed layer dynamics and thermodynamics play an important role in intensifying subduction in that they allow lateral subduction, caused by spatial variations in the mixed layer depth, to sweep water around the subtropical gyre with much of this water simply returning poleward in the western boundary current when the subtropics are studied in isolation.…”

Section: Introductionmentioning

confidence: 99%

A Numerical Simulation of the Mean Water Pathways in the Subtropical and Tropical Pacific Ocean

Rothstein¹,

Zhang²,

Busalacchi³

et al. 1998

J. Phys. Oceanogr.

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A reduced-gravity, primitive-equation, upper-ocean general circulation model is used to study the mean water pathways in the North Pacific subtropical and tropical ocean. The model features an explicit physical representation of the surface mixed layer, realistic basin geometry, observed wind and heat flux forcing, and a horizontal grid-stretching technique and a vertical sigma coordinate to obtain a realistic simulation of the subtropical/ tropical circulation. Velocity fields, and isopycnal and trajectory analyses are used to understand the mean flow of mixed layer and thermocline waters between the subtropics and Tropics. Subtropical/tropical water pathways are not simply direct meridional routes; the existence of vigorous zonal current systems obviously complicates the picture. In the surface mixed layer, upwelled equatorial waters flow into the subtropical gyre mainly through the midlatitude western boundary current (the model Kuroshio). There is additionally an interior ocean pathway, through the Subtropical Countercurrent (an eastward flow across the middle of the subtropical gyre), that directly feeds subtropical subduction sites. Below the mixed layer, the water pathways in the subtropical thermocline essentially reflect the anticyclonic gyre circulation where we find that the model subtropical gyre separates into two circulation centers. The surface circulation also features a doublecell pattern, with the poleward cell centered at about 30ЊN and the equatorward component contained between 15Њ and 25ЊN. In addition, thermocline waters that can be traced to subtropical subduction sites move toward the Tropics almost zonally across the basin, succeeding in flowing toward the equator only along relatively narrow north-south conduits. The low-latitude western boundary currents serve as the main southward circuit for the subducted subtropical thermocline water. However, the model does find a direct flow of thermocline water into the Tropics through the ocean interior, confined to the far western Pacific (away from the low-latitude western boundary currents) across 10ЊN. This interior pathway is found just to the west of a recirculating gyre in and just below the mixed layer in the northeastern Tropics. This equatorward interior flow and a flow that can be traced directly to the western boundary are then swept eastward by the deeper branches of the North Equatorial Countercurrent, finally penetrating to the equator in the central and eastern Pacific. Most of these results are consistent with available observations and recently published theoretical and idealized numerical experiments, although the interior pathway of subtropical thermocline water into the Tropics found in this experiment is not apparent in other published numerical simulations. Potential vorticity dynamics are useful in explaining the pathways taken by subtropical thermocline water as it flows into the Tropics. In particular, a large-scale zonally oriented ''island'' of homogenous potential vorticity, whose signature is determined by thin isop...

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A Continuously Stratified Thermocline Model Incorporating a Mixed Layer of Variable Thickness and Density

Cited by 13 publications

References 0 publications

Does eddy subduction matter in the northeast Atlantic Ocean?

Does eddy subduction matter in the northeast Atlantic Ocean?

Sharp Frontal Interfaces in the Near-Surface Layer of the Ocean in the Western Equatorial Pacific Warm Pool

A Numerical Simulation of the Mean Water Pathways in the Subtropical and Tropical Pacific Ocean

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