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  • AMS (American Meteorological Society)  (7)
  • Elsevier  (3)
  • Springer  (3)
  • Cambridge University Press  (1)
  • DWD  (1)
  • 1
    Electronic Resource
    Electronic Resource
    The influence of numerical advection schemes on the results of ocean general circulation models (1991)
    Springer
    Climate dynamics 5 (1991), S. 211-226 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The dependence of results from coarse-resolution models of the North Atlantic circulation on the numerical advection algorithm is studied. In particular, the sensitivity of parameters relevant for climate simulations as e.g., meridional transport of mass and heat and main thermocline thickness is investigated. Three algorithms were considered: (a) a central difference scheme with constant values for horizontal and vertical diffusion, (b) an upstream scheme with no explicit diffusion, and (c) a flux-corrected transport (FCT) scheme with constant and strictly isopycnal diffusion. The temporal evolution of the three models on time scales of centuries is markedly different, the upstream scheme resulting in much shorter adjustment time whereas the central difference scheme is slower and controlled by vertical diffusion rather than advection. In the steady state, the main thermocline structure is much less diffusive in the FCT calculation which also has much lower heat transport. Both horizontal circulation and overturning in the meridional-vertical plane are strongest in the upstream-model. The results are discussed in terms of the effective vertical (diapycnal) mixing in the different models. A significant increase in vertical resolution would be required to eliminate the high sensitivity due to the numerical algorithms, and allow physically motivated mixing formulations to become effective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210006
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Neutral Density Revisited (1999)
    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 46 . pp. 33-54.
    Details
    Publication Date: 2019-09-23
    Description: The possibilities of defining and computing an approximately neutral density variable are reexamined in this paper. There are three desirable properties that a neutral density variable should possess. Firstly, the isosurfaces of this variable should coincide with (approximately) neutral surfaces. This would facilitate the analysis of hydrographic data on the most appropriate mixing and spreading surfaces. Secondly, the horizontal gradients of the neutral density should agree with the gradients of the in situ density, and thirdly the vertical gradient of the neutral density variable should be proportional to the static stability of the water column. A density variable that approximates the latter two properties can be used in ocean circulation models based on layer coordinates, and would reduce substantial errors in present isopycnal models due to the use of a potential density variable. No variable can possess all the three properties simultaneously. The variable γn introduced by Jackett and McDougall (1997, J. Phys. Oceanogr. 27, 237–263) satisfies the first of the properties exactly but is not designed for the use in models. Based on climatological data in the North Atlantic, an alternative neutral density variable ν̃(S, Θ) is defined, which is shown to approximate the two gradient criteria much better than any potential density. We suggest that this neutral density variable may be useful in isopycnal ocean models as an alternative to potential density, since it could significantly reduce errors in thermal wind relation and vertical stability
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(98)00113-1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Allgemeine Zirkulationsmodelle, Ozean (2003)
    DWD
    In:  Promet - Meteorologische Fortbildung, 29 (1-4). pp. 15-28.
    Details
    Publication Date: 2016-10-04
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    Parameterization of mesoscale eddies as inferred from a high-resolution circulation model (1996)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 26(10) . pp. 2281-2285.
    Details
    Publication Date: 2018-04-05
    Description: The compatibility of the Gent and McWilliams thickness mixing parameterization with perturbation thickness fluxes evaluated from eddy-resolving North Atlantic model results is investigated. After extensive spatial and temporal averaging, a linear correlation between the parameterized fluxes and those calculated directly from model fluctuations in the subtropics could be found. A direct estimate of a constant mixing parameter κ could be inferred in the order of 1.0 × 107 cm2 s−1.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/1520-0485(1996)026〈2281:POMEAI〉2.0.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Physical Climate Processes and Feedbacks (2001)
    Cambridge University Press
    In:  In: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernemental Panel on Climate Change. , ed. by Houghton, J. T., Ding, Y. and Griggs, D. J. Cambridge University Press, Cambridge, United Kingdom, pp. 417-470. ISBN 0521-01495-6
    Details
    Publication Date: 2020-03-30
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 6
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    The influence of numerical advection schemes on the results of ocean general circulation models (1991)
    Springer
    In:  Climate Dynamics, 5 (4). pp. 211-226.
    Details
    Publication Date: 2018-03-02
    Description: The dependence of results from coarse-resolution models of the North Atlantic circulation on the numerical advection algorithm is studied. In particular, the sensitivity of parameters relevant for climate simulations as e.g., meridional transport of mass and heat and main thermocline thickness is investigated. Three algorithms were considered: (a) a central difference scheme with constant values for horizontal and vertical diffusion, (b) an upstream scheme with no explicit diffusion, and (c) a flux-corrected transport (FCT) scheme with constant and strictly isopycnal diffusion. The temporal evolution of the three models on time scales of centuries is markedly different, the upstream scheme resulting in much shorter adjustment time whereas the central difference scheme is slower and controlled by vertical diffusion rather than advection. In the steady state, the main thermocline structure is much less diffusive in the FCT calculation which also has much lower heat transport. Both horizontal circulation and overturning in the meridional-vertical plane are strongest in the upstream-model. The results are discussed in terms of the effective vertical (diapycnal) mixing in the different models. A significant increase in vertical resolution would be required to eliminate the high sensitivity due to the numerical algorithms, and allow physically motivated mixing formulations to become effective.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/BF00210006
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Effects of increased horizontal resolution in a simulation of the North Atlantic Ocean (1994)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 24 . pp. 326-344.
    Details
    Publication Date: 2018-04-05
    Description: Global mean and eddy fields from a four-year experiment with a 1/6° × 1/5° horizontal resolution implementation of the CME North Atlantic model are presented. The time-averaged wind-driven and thermohaline circulation in the model is compared to the results of a 1/3° × 2/5° model run in very similar configuration. In general, the higher resolution results are found to confirm that the resolution of previous CME experiments is sufficient to describe many features of the large-scale circulation and water mass distribution quite well. While the increased resolution does not lead to large changes in the mean flow patterns, the variability in the model is enhanced significantly. On the other hand, however, not all aspects of the circulation have improved with resolution. The Azores Current Frontal Zone with its variability in the eastern basin is still represented very poorly. Particular attention is also directed toward the unrealistic stationary anticyclones north of Cape Hatteras and in the Gulf of Mexico.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/1520-0485(1994)024〈0326:EOIHRI〉2.0.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Ocean Dynamics (2012)
    Springer
    In:  Springer, Heidelberg, 704 pp. ISBN 978-3-642-23449-1
    Details
    Publication Date: 2012-06-12
    Type: Book , NonPeerReviewed
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    OceanRep: Book
  • 9
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    A diagnosis of thickness fluxes in an eddy-resolving model (2007)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 37 . pp. 727-742.
    Details
    Publication Date: 2020-08-04
    Description: Output from an eddy-resolving model of the North Atlantic Ocean is used to estimate values for the thickness diffusivity κ appropriate to the Gent and McWilliams parameterization. The effect of different choices of rotational eddy fluxes on the estimated κ is discussed. Using the raw fluxes (no rotational flux removed), large negative values (exceeding −5000 m2 s−1) of κ are diagnosed locally, particularly in the Gulf Stream region and in the equatorial Atlantic. Removing a rotational flux based either on the suggestion of Marshall and Shutts or the more general theory of Medvedev and Greatbatch leads to a reduction of the negative values, but they are still present. The regions where κ 〈 0 correspond to regions where eddies are acting to increase, rather than decrease (as in baroclinic instability) the mean available potential energy. In the subtropical gyre, κ ranges between 500 and 2000 m2 s−1, rapidly decreasing to zero below the thermocline in all cases. Rotational fluxes and κ are also estimated using an optimization technique. In this case, |κ| can be reduced or increased by construction, but the regions where κ 〈 0 are still present and the optimized rotational fluxes also remain similar to a priori values given by the theoretical considerations. A previously neglected component (ν) of the bolus velocity is associated with the horizontal flux of buoyancy along, rather than across, the mean buoyancy contours. The ν component of the bolus velocity is interpreted as a streamfunction for eddy-induced advection, rather than diffusion, of mean isopycnal layer thickness, showing up when the lateral eddy fluxes cannot be described by isotropic diffusion only. All estimates show a similar large-scale pattern for ν, implying westward advection of isopycnal thickness over much of the subtropical gyre. Comparing ν with a mean streamfunction shows that it is about 10% of the mean in midlatitudes and even larger than the mean in the Tropics.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/JPO2987.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Circulation Characteristics in Three Eddy-Permitting Models of the North Atlantic (2001)
    Elsevier
    In:  Progress in Oceanography, 48/2-3 . pp. 123-162.
    Details
    Publication Date: 2016-10-07
    Description: A systematic intercomparison of three realistic eddy-permitting models of the North Atlantic circulation has been performed. The models use different concepts for the discretization of the vertical coordinate, namely geopotential levels, isopycnal layers, terrain-following (sigma) coordinates, respectively. Although these models were integrated under nearly identical conditions, the resulting large-scale model circulations show substantial differences. The results demonstrate that the large-scale thermohaline circulation is very sensitive to the model representation of certain localised processes, in particular to the amount and water mass properties of the overflow across the Greenland–Scotland region, to the amount of mixing within a few hundred kilometers south of the sills, and to several other processes at small or sub-grid scales. The different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0079-6611(01)00003-9
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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