How entraining density currents influence the stratification in a one-dimensional ocean basin

Wåhlin, Anna; Cenedese, Claudia

doi:10.1016/j.dsr2.2005.10.019

Cited by 25 publications

(24 citation statements)

References 37 publications

(86 reference statements)

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“…Furthermore, for low F r and low Re, it had a comparable order of magnitude to mixing observed in the ocean. As already pointed out by Wåhlin & Cenedese (2006) and Hughes & Griffiths (2006), the subcritical mixing observed in CWAO and in some of the present experiments, could be of fundamental importance when determining the final water mass characteristics (for example density) of a dense current descending the continental slope following a long path. Therefore, a weak, but non-zero, entrainment can substantially change the final density and, consequently, the location of important water masses, such as NADW, in the open ocean water column.…”

Section: Discussionmentioning

confidence: 68%

“…This new parameterization will, consequently, differ substantially from the Ellison & Turner (1959) parameterization still widely used. The Wåhlin & Cenedese (2006) comparison of the Ellison & Turner (1959) and CWAO low-Froudenumber parameterization suggests that major differences in the basin stratification could occur, in the case of small slopes, depending on the parameterization used.…”

Section: Discussionmentioning

confidence: 99%

“…Wåhlin & Cenedese (2006) and Hughes & Griffiths (2006) pointed out that subcritical mixing could be of fundamental importance in determining the final properties of the dense current, especially if its path length to the bottom of the ocean, or to its level of neutral buoyancy, is long. Weak subcritical entrainment, if it occurs over long distances, could be as effective as strong supercritical entrainment occurring near a sill or a constriction.…”

Section: Introductionmentioning

confidence: 99%

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Mixing in a density-driven current flowing down a slope in a rotating fluid

2008

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We discuss laboratory experiments investigating mixing in a density-driven current flowing down a sloping bottom, in a rotating homogenous fluid. A systematic study spanning a wide range of Froude, 0.8 < Fr < 10, and Reynolds, 10 < Re < 1400, numbers was conducted by varying three parameters: the bottom slope; the flow rate; and the density of the dense fluid. Different flow regimes were observed, i.e. waves (non-breaking and breaking) and turbulent regimes, while changing the above parameters. Mixing in the density-driven current has been quantified within the observed regimes, and at different locations on the slope. The dependence of mixing on the relevant non-dimensional numbers, i.e. slope, Fr and Re, is discussed. The entrainment parameter, E, was found to be dependent not only on Fr, as assumed in previous studies, but also on Re. In particular, mixing increased with increasing Fr and Re. For low Fr and Re, the magnitude of the mixing was comparable to mixing in the ocean. For large Fr and Re, mixing was comparable to that observed in previous laboratory experiments that exhibited the classic turbulent entrainment behaviour.

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Section: Discussionmentioning

confidence: 68%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mixing in a density-driven current flowing down a slope in a rotating fluid

2008

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“…In particular, it assumes that the amount of entrainment in a dense current descending down a slope depends on both the Froude number Fr and Reynolds number Re of the flow and that entrainment occurs for subcritical Fr (,1). The subcritical entrainment observed in Cenedese et al (2004) and Cenedese and Adduce (2008) has been suggested (Wå hlin and Cenedese 2006;Hughes and Griffiths 2006;Lauderdale et al 2008) to be of fundamental importance for the water mass characteristics, such as density, of a dense current descending the continental slope. A weak, but nonzero, entrainment can change the final density and, consequently, the depth and location of important water masses in the open ocean.…”

Section: A New Parameterizationmentioning

confidence: 99%

A New Parameterization for Entrainment in Overflows

Cenedese

Adduce²

2010

Journal of Physical Oceanography

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Dense overflows entrain surrounding waters at specific locations, for example, sills and constrictions, but also along the descent over the continental slope. The amount of entrainment dictates the final properties of these overflows, and thus is of fundamental importance to the understanding of the formation of deep water masses. Even when resolving the overflows, coarse resolution global circulation and climate models cannot resolve the entrainment processes that are often parameterized. A new empirical parameterization is suggested, obtained using an oceanic and laboratory dataset, which includes two novel aspects. First, the parameterization depends on both the Froude number (Fr) and Reynolds number of the flow. Second, it takes into account subcritical (Fr , 1) entrainment. A weak, but nonzero, entrainment can change the final density and, consequently, the depth and location of important water masses in the open ocean. This is especially true when the dense current follows a long path over the slope in a subcritical regime, as observed in the southern Greenland Deep Western Boundary Current. A streamtube model employing this new parameterization gives results that are more consistent with previous laboratory and oceanographic observations than when a classical parameterization is used. Finally, the new parameterization predictions compare favorably to recent oceanographic measurements of entrainment and turbulent diapycnal mixing rates, using scaling arguments to relate the entrainment ratio to diapycnal diffusivities.

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“…4 Now as the new overflow entrainment parameterizations are implemented into coupled climate models, we are beginning to investigate the influence of overflow entrainment on the large-scale circulation and, therefore, climate. We are guided by work carried out in idealized ocean models, which suggest that overflow entrainment can significantly influence the MOC and large-scale ocean stratification (Hughes and Griffiths 2006;Wahlin and Cenedese 2006). Early results from the NCAR and GFDL OGCMs 4 These earlier studies did not include physically based parameterizations of the entrainment in overflows but rather focused on limiting the excessive spurious entrainment in the z-coordinate models.…”

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confidence: 99%