Spurious diapycnal mixing in terrain-following coordinate models: The problem and a solution

Marchesiello, Patrick; Debreu, Laurent; Couvelard, Xavier

doi:10.1016/j.ocemod.2008.09.004

Cited by 155 publications

(135 citation statements)

References 32 publications

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“…This result suggests that entrainment and mixing of lighter surface waters must exist within the eddies and allow the depth of the floats to decrease and for the floats to follow shallower currents. However, the ROMS model setup with a thirdorder upwind horizontal advection scheme is notorious for numerical vertical mixing effects [e.g., Marchesiello et al, 2009]; hence, no attempt is made in this study to quantify diapycnal processes altering the water masses within the deep circulation. …”

Section: Discussionmentioning

confidence: 99%

The deep circulation of the Faroe‐Shetland Channel: Opposing flows and topographic eddies

Broadbridge

Toumi

2015

JGR Oceans

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New insights into the deep circulation of the Faroe‐Shetland channel are gained from a high‐resolution regional ocean model. The simulation shows a more complex structure of the deep flow field than previously thought: a flow reversal of the deep and intermediate waters to the northeast on the Faroese flank of the channel and persistent topographic eddies that force the deep currents into a gyre‐like structure. This flow reversal opposes the previously accepted understanding of a purely southwestward deep flow but is in agreement with velocity measurements. The southwestward transport of the overflow waters is found to be facilitated almost exclusively by a strong and narrow current on the Shetland side of the channel. Float release experiments show that up to 38% of the overflow water takes longer than a purely southwestward flow regime suggests and up to 13% takes twice as long. From the release of tracers, a substantial amount of lateral mixing is evident within the channel, predominantly facilitated by the topographic eddies.

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Section: Discussionmentioning

confidence: 99%

The deep circulation of the Faroe‐Shetland Channel: Opposing flows and topographic eddies

Broadbridge

Toumi

2015

JGR Oceans

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“…internal tides, may be prevalent. A solution to this is to use a non-diffusive advection scheme coupled with a rotated biharmonic diffusion scheme (Marchesiello et al, 2009). Another issue is the need for vertical mixing schemes that can accommodate wide variations in layer thickness and still retain low mixing in the ocean interior.…”

Section: Vertical Coordinatesmentioning

confidence: 99%

Prospects for improving the representation of coastal and shelf seas in global ocean models

et al. 2017

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Abstract. Accurately representing coastal and shelf seas in global ocean models represents one of the grand challenges of Earth system science. They are regions of immense societal importance through the goods and services they provide, hazards they pose and their role in global-scale processes and cycles, e.g. carbon fluxes and dense water formation. However, they are poorly represented in the current generation of global ocean models. In this contribution, we aim to briefly characterise the problem, and then to identify the important physical processes, and their scales, needed to address this issue in the context of the options available to resolve these scales globally and the evolving computational landscape.We find barotropic and topographic scales are well resolved by the current state-of-the-art model resolutions, e.g. nominal 1/12 • , and still reasonably well resolved at 1/4 • ; here, the focus is on process representation. We identify tides, vertical coordinates, river inflows and mixing schemes as four areas where modelling approaches can readily be transferred from regional to global modelling with substantial benefit. In terms of finer-scale processes, we find that a 1/12 • global model resolves the first baroclinic Rossby radius for only ∼ 8 % of regions < 500 m deep, but this increases to ∼ 70 % for a 1/72 • model, so resolving scales globally requires substantially finer resolution than the current state of the art.We quantify the benefit of improved resolution and process representation using 1/12 • global-and basin-scale northern North Atlantic nucleus for a European model of the ocean (NEMO) simulations; the latter includes tides and a k-ε vertical mixing scheme. These are compared with global stratification observations and 19 models from CMIP5. In terms of correlation and basin-wide rms error, the high-resolution models outperform all these CMIP5 models. The model with tides shows improved seasonal cycles compared to the highresolution model without tides. The benefits of resolution are particularly apparent in eastern boundary upwelling zones.To explore the balance between the size of a globally refined model and that of multiscale modelling options (e.g. finite element, finite volume or a two-way nesting approach), we consider a simple scale analysis and a conceptual grid refining approach. We put this analysis in the context of evolving computer systems, discussing model turnaround time, scalability and resource costs. Using a simple cost model compared to a reference configuration (taken to be a 1/4 • global model in 2011) and the increasing performance of the UK Research Councils' computer facility, we estimate an unstructured mesh multiscale approach, resolving process scales down to 1.5 km, would use a comparable share of the computer resource by 2021, the two-way nested multiscale approach by 2022, and a 1/72 • global model by 2026. However, we also note that a 1/12 • global model would not have a comparable computational cost to a 1 • global model in 2017 until 2027. Hence, we conc...

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“…ROMS is based in the Boussinesq and hydrostatic approximations to solve the imcopressible incompressible primitive equations, and it is coupled with advection/difussiondiffusion schemes for potential temperature, salinity and biological tracers, as well as a non linear equation of state. The advection scheme is the same as that described in Marchesiello et al (2009), which involves the split of advection and diffusion as a biharmonic operator, i.e., no explicit diffusion was implemented. Vertical mixing consists in the K-profile parameterization scheme (Large et al, 1994).…”

Section: Hydrodynamic Modelmentioning

confidence: 99%

Seasonal cycle of plankton production in the Iberian margin based on a high resolution ocean model

Reboreda

Nolasco

Castro

et al. 2014

Journal of Marine Systems

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Spurious diapycnal mixing in terrain-following coordinate models: The problem and a solution

Cited by 155 publications

References 32 publications

The deep circulation of the Faroe‐Shetland Channel: Opposing flows and topographic eddies

The deep circulation of the Faroe‐Shetland Channel: Opposing flows and topographic eddies

Prospects for improving the representation of coastal and shelf seas in global ocean models

Seasonal cycle of plankton production in the Iberian margin based on a high resolution ocean model

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