Isoneutral Diffusion in a<i>z</i>-Coordinate Ocean Model

Griffies, Stephen M.; Gnanadesikan, Anand; Pacanowski, R. C.; Larichev, Vitaly D.; Dukowicz, John K.; Smith, Richard D.

doi:10.1175/1520-0485(1998)028<0805:idiazc>2.0.co;2

Cited by 230 publications

(218 citation statements)

References 33 publications

(44 reference statements)

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“…Isoneutral mixing of tracers is performed by the code of Griffies et al (1998). The small angle assumption is adopted to simplify the diffusion rotation tensor, as recommended for general oceanic applications by Gent and McWilliams (1990) and Griffies et al (1998).…”

Section: Sub-grid-scale Mixing and Stirring Of Tracers In The Ocean Imentioning

confidence: 99%

“…The small angle assumption is adopted to simplify the diffusion rotation tensor, as recommended for general oceanic applications by Gent and McWilliams (1990) and Griffies et al (1998). The isoneutral tracer diffusivity A I is set to 1000 m 2 s -1 , except in regions of steeply sloping neutral surfaces, where the diffusivity is reduced via the Gerdes et al (1991) taper to avoid numerical instability.…”

Section: Sub-grid-scale Mixing and Stirring Of Tracers In The Ocean Imentioning

confidence: 99%

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Current and future latitudinal gradients in stream macroinvertebrate richness across North America

et al. 2014

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Section: Sub-grid-scale Mixing and Stirring Of Tracers In The Ocean Imentioning

confidence: 99%

Section: Sub-grid-scale Mixing and Stirring Of Tracers In The Ocean Imentioning

confidence: 99%

Current and future latitudinal gradients in stream macroinvertebrate richness across North America

et al. 2014

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“…It has a free surface formulation for the barotropic mode [Webb, 1996] and 19 levels in the vertical, varying in thickness from 30 m near the surface to 500 m at depth. Tracer (temperature and salinity) mixing has components in the horizontal, vertical and along isoneutral surfaces [Griffies et al, 1998]. The values of the mixing coefficients are taken from England [1993].…”

Section: Climate Modelmentioning

confidence: 99%

Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere‐iceberg‐ocean model

2008

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[1] We introduce explicit icebergs from a dynamic and thermodynamic iceberg model into an intermediate complexity climate model, which includes the coupled atmosphere-ocean system. This modeling approach allows iceberg meltwater to be injected into the ocean on the basis of thermodynamical considerations along the iceberg trajectories. Icebergs are seeded from known ice sheets in both hemispheres. Adding icebergs to the present-day climate model has a minimal impact, but during the Last Glacial Maximum (LGM), Atlantic overturning strength is reduced by a third, while producing a model state that is consistent with a steady state climate. We test the sensitivity of the model at the LGM to additional Heinrich event-scale fluxes of icebergs from three possible sources: Hudson Strait, the Gulf of Saint Lawrence, and the Norwegian Channel Ice Stream (NCIS). The sensitivity of the ocean is similar for all locations, with differences dominated by the length of the iceberg meltwater pathways to the main ocean convection region. The NCIS events result in more variability and a distinctly different, more northerly, salinity anomaly. We compare these results to a more typical modeling approach, whereby meltwater is injected directly into the ocean at the iceberg source locations, and find that these floods overestimate the oceanic response compared to the iceberg events. Our results suggest that 0.3-0.4 Sv of additional freshwater flux, either as icebergs or freshwater, is required to shut down the North Atlantic meridional overturning, a larger freshwater flux than sometimes suggested because of the localized nature of the release of the freshwater.Citation: Levine, R. C., and G. R. Bigg (2008), Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere-iceberg-ocean model, Paleoceanography, 23, PA4213,

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“…The spatial discretization of the isopycnal mixing operators is a difficult problem that has been thoroughly tackled by Beckers et al (1998), Beckers et al (2000) and Griffies et al (1998). Following those studies, as well as Lemarié et al (2011), we consider here the so-called LINEAR1 method described in Beckers et al (2000).…”

Section: Discretization In Spacementioning

confidence: 99%

Are there inescapable issues prohibiting the use of terrain-following coordinates in climate models?

et al. 2012

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The use of σ-coordinate ocean models has historically been considered a disadvantage for large-scale climate studies. The main reason resides in the non-alignment of the vertical coordinate isosurfaces with either geopotential surfaces or isopycnals making it harder to accurately compute the horizontal pressure gradient, advection, and isoneutral tracer diffusion. Moreover, this class of model requires a vertical mixing parameterization robust to large changes in the vertical resolution between shallow and deep areas. In this paper we show that, with some adjustments of the tracer advection, the surface boundary layer parameterization and the vertical grid, a σ-coordinate model can achieve an accurate representation of the oceanic interior and mixed-layer dynamics. To do so, a new way of handling the temporal discretization of the rotated biharmonic operator is used to achieve tracer variance dissipation in an adiabatic and computationally efficient way. Furthermore, a redesign of the K-Profile surface layer Parameterization (KPP) to improve the regularity of the solution and the overall numerical efficiency of the scheme is introduced. To validate the new algorithmic developments, we perform a set of coarse-resolution realistic basin-scale Pacific simulations. Besides improving the conservation of water mass properties, the use of an isoneutral tracer hyperdiffusion is shown to have a negative feedback on the circulation error growth rate, thus significantly reducing the sensitivity of the model solution to the degree of topographic smoothing. The overall validation of our simulations, focusing on the key characteristics of the circulation in the Pacific Ocean, provides some evidence of the efficacy of a terrain-following coordinate for large scale applications.

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Isoneutral Diffusion in az-Coordinate Ocean Model

Cited by 230 publications

References 33 publications

Current and future latitudinal gradients in stream macroinvertebrate richness across North America

Current and future latitudinal gradients in stream macroinvertebrate richness across North America

Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere‐iceberg‐ocean model

Are there inescapable issues prohibiting the use of terrain-following coordinates in climate models?

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