Numerical simulations of the Mediterranean sea outflow: impact of the entrainment parameterization in an isopycnic coordinate ocean model

Papadakis, Matheos; Chassignet, Eric P.; Hallberg, Robert

doi:10.1016/s1463-5003(02)00042-2

Cited by 48 publications

(39 citation statements)

References 31 publications

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“…TE is derived from the bulk entrainment parameterization of Turner (1986) and Ellison and Turner (1959) and assumes that the net entrainment is proportional to the velocity shear times a function of the shear Richardson number (Ri; Hallberg 2000), provided that Ri is less than some critical value. TE gives qualitatively reasonable depictions of gravity current entrainment in some circumstances (Papadakis et al 2003;Legg et al 2006) but leads to excessive shear-driven entrainment in the Pacific Equatorial Undercurrent when applied globally.…”

Section: Physical Processes In Overflowsmentioning

confidence: 92%

Improving Oceanic Overflow Representation in Climate Models: The Gravity Current Entrainment Climate Process Team

Legg¹,

Briegleb²,

Chang³

et al. 2009

Bull. Amer. Meteor. Soc.

171

155

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Section: Physical Processes In Overflowsmentioning

confidence: 92%

Improving Oceanic Overflow Representation in Climate Models: The Gravity Current Entrainment Climate Process Team

Legg¹,

Briegleb²,

Chang³

et al. 2009

Bull. Amer. Meteor. Soc.

171

155

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show abstract

“…Jiang and Garwood (1998) concluded that topographic variations induce significant changes in the mixing and entrainment between density currents and ambient fluid. Sigma-and isopycnic-coordinate ocean general circulation models have been used to simulate the Mediterranean overflow (Jungclaus and Mellor 2000;Papadakis et al 2003) employing various mixing parameterizations Yamada 1982 andHallberg 2000, respectively).…”

Section: A Model Philosophymentioning

confidence: 99%

Turbulent Mixing in the Red Sea Outflow Plume from a High-Resolution Nonhydrostatic Model

Özgökmen

Johns

Peters

et al. 2003

Journal of Physical Oceanography

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Given the motivation that overflow processes, which supply source waters for most of the deep and intermediate water masses in the ocean, pose significant numerical and dynamical challenges for ocean general circulation models, an intercomparison study is conducted between field data collected in the Red Sea overflow and a highresolution, nonhydrostatic process model. The investigation is focused on the part of the outflow that flows along a long narrow channel, referred to as the ''northern channel,'' that naturally restricts motion in the lateral direction such that the use of a two-dimensional model provides a reasonable approximation to the dynamics. This channel carries about two-thirds of the total Red Sea overflow transport, after the overflow splits into two branches in the western Gulf of Aden. The evolution of the overflow in the numerical simulations can be characterized in two phases: the first phase is highly time dependent, during which the density front associated with the overflow propagates along the channel. The second phase corresponds to that of a statistically steady state. The primary accomplishment of this study is that the model adequately captures the general characteristics of the system: (i) the gradual thickening of the overflow with downstream distance, (ii) the advection of high salinity and temperature signals at the bottom along the channel with little dilution, and (iii) ambient water masses sandwiched between the overflow and surface mixed layer. To quantify mixing of the overflow with the ambient water masses, an entrainment parameter is determined from the transport increase along the slope and is expressed explicitly as a function of mean slope angle. Bulk Richardson numbers are estimated both from data and model and are related to the entrainment parameter. The range of entrainment parameter and its functional dependence on bulk Richardson number in this study are found to be in reasonable agreement with those reported from various laboratory experiments and that based on measurements of the Mediterranean overflow. The results reveal a complex dynamical interaction between shear-induced mixing and internal waves and illustrate the high computational and modeling requirements for numerical simulation of overflows to capture (at least in part) turbulent transports explicitly.

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“…1. Although the magnitude of the entrainment ratio is of central importance to understanding how many deepwater masses form (Price and Barringer 1994;Baines 2001;Papadakis et al 2003;Wells and Wettlaufer 2007;Wells and Nadarajah 2009;Legg et al 2009), there has not previously been any unifying theory to predict either the magnitude of E or to determine how E depends upon the stability of the flow. The results to date are based on empirical observations from laboratory and field studies (Cenedese and Adduce 2010).…”

Section: Introductionmentioning

confidence: 99%

The Relationship between Flux Coefficient and Entrainment Ratio in Density Currents

Wells

Cenedese

Caulfield

2010

Journal of Physical Oceanography

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The authors explore the theoretical and empirical relationship between the nonlocal quantities of the entrainment ratio E, the appropriately depth-and time-averaged flux coefficient G, and the bulk Froude number Fr o in density currents. The main theoretical result is thatwhere u is the angle of the slope over which the density current flows, C L is the ratio the turbulent length scale to the depth of the density current, and C U is the ratio of the turbulent velocity scale to the mean velocity of the density current. In the case of high bulk Froude numbers G ; Fr À2o and (C U 3 /C L ) 5 C ; 1, so E ; 0.1, consistent with observations of a constant entrainment ratio in unstratified jets and weakly stratified plumes. For bulk Froude numbers close to one, G is constant and has a value in the range of 0.1-0.3, which means that E ; Fr o 2 , again in agreement with observations and previous experiments. For bulk Froude numbers less than one, G decreases rapidly with bulk Froude number, explaining the sudden decrease in entrainment ratios that has been observed in all field and experimental observations.

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Numerical simulations of the Mediterranean sea outflow: impact of the entrainment parameterization in an isopycnic coordinate ocean model

Cited by 48 publications

References 31 publications

Improving Oceanic Overflow Representation in Climate Models: The Gravity Current Entrainment Climate Process Team

Improving Oceanic Overflow Representation in Climate Models: The Gravity Current Entrainment Climate Process Team

Turbulent Mixing in the Red Sea Outflow Plume from a High-Resolution Nonhydrostatic Model

The Relationship between Flux Coefficient and Entrainment Ratio in Density Currents

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