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  • 2020-2022  (4)
  • 1990-1994  (13)
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  • 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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    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
  • 3
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    Arctic Ocean Surface Energy Flux and the Cold 2 Halocline in Future Climate Projections (2020)
    american geophysical union
    In:  EPIC3Journal of geophysocal research oceans, american geophysical union, 125, ISSN: 2169-9291
    Details
    Publication Date: 2020-02-14
    Description: Ocean heat transport is often thought to play a secondary role for Arctic surface warm16 ing in part because warm water which ows northward is prevented from reaching the 17 surface by a cold and stable halocline layer. However, recent observations in various re18 gions indicate that occasionally, warm water is found directly below the surface mixed 19 layer. Here we investigate Arctic Ocean surface energy uxes and the cold halocline layer 20 in climate model simulations from the Coupled Model Intercomparison Project Phase 21 5 (CMIP5). An ensemble of 15 models shows decreased sea ice formation and increased 22 ocean energy release during fall, winter, and spring for a high-emission future scenario. 23 Along the main pathways for warm water advection, this increased energy release is not 24 locally balanced by increased Arctic Ocean energy uptake in summer. Because during 25 Arctic winter, the ocean mixed layer is mainly heated from below, we analyze changes 26 of the cold halocline layer in the monthly mean CMIP5 data. Fresh water acts to sta27 bilize the upper ocean as expected based on previous studies. We �nd that in spite of 28 this stabilizing e�ect, periods in which warm water is found directly or almost directly 29 below the mixed layer and which occur mainly in winter and spring become more fre30 quent in high-emission future scenario simulations, especially along the main pathways 31 for warm water advection. This could reduce sea ice formation and surface albedo. 32 Plain Language
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Wind Feedback Mediated by Sea Ice in the Nordic Seas (2020)
    In:  EPIC3Journal of Climate, 33(15), pp. 6621-6632
    Details
    Publication Date: 2020-07-08
    Description: Air-sea interactions play a critical role in the climate system. This study investigates wind-induced changes in the ocean surface temperature and sea ice cover feeding back onto the atmospheric circulation. This interaction was modeled in the Nordic seas, using a partial coupling method to constrain the ocean with prescribed wind forcing in an otherwise fully coupled Earth system model. This enabled the evaluation of not only the direct oceanic, but also the indirect atmospheric response to idealized forcing scenarios of perturbed winds over the Nordic seas. The results show that an anticyclonic wind anomaly forcing leads to significant surface cooling in the Greenland Sea mostly due to anomalous drift of sea ice. During winter, the cooling reduces the net surface heat flux to the atmosphere and increases sea level pressure. The pressure gradients result in anomalous geostrophic southerly winds, which locally are comparable both in direction and in velocity to the prescribed forcing anomalies, suggesting a positive feedback.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Feedback mechanisms affecting the thermohaline circulation (1994)
    In:  EPIC3Proc WRCP Conf on the Dynamics of the Arctic Climate System, Gothenburg, Sweden
    Details
    Publication Date: 2019-07-17
    Description: Changes in high latitude surface salinity have a strong effect on the North Atlantic Deep Water Formation (NADWF) which appears to be very important in driving the global thermohaline conveyor belt. Natural variations of sea surface salinity and sea ice have been observed in the North Atlantic, namely the Great Salt Anomaly (GSA) of the late sixties and seventies. When dealing with climate variability one must consider the sensitivity of the climate system to perturbations.In order to include the atmospheric heat transport mechanisms we coupled an atmosphere energy balance model with a 3-D ocean general circulation model which includes a thermodynamic sea ice model. We explore the feedback mechanisms in the ocean-atmosphere-sea ice system affecting the thermohaline circulation (THC) under perturbations in sea surface salinity at high latitudes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 6
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    Melting and freezing rates beneath Filchner-Ronne Ice Shelf from a 3-d ocean circulation model (1994)
    In:  EPIC3FRISP Report, Alfred-Wegener-Institut, Bremerhaven, 8, pp. 12-19
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 7
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    A primitive equation ocean circulation model using a general vertical coordinate transformation. Part 1: Description and testing of the model (1993)
    In:  EPIC3Journal of Geophysical Research, 98, pp. 14683-14701
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    A 1-d energy balance atmospheric model applied to ocean modelling (1993)
    In:  EPIC3Berichte aus dem Fachbereich Physik, 44 p.
    Details
    Publication Date: 2019-07-17
    Description: We present a simple, deterministic energy balance model in this report. The model is designed to represent the atmospheric component of the coupled atmosphere-ocean system. It is a one dimensional, global model with time and space resolutions of one year and 10^0 of latitude respectively. The model predicts the surface air temperature and estimates the surface freshwater flux diagnostically.The coupling between the atmospheric model and an ocean model is accomplished by heat and freshwater fluxes at their interface. The heat flux is calculated according to the difference in the surface air temperature and ocean surface temperature, while the freshwater flux is estimated from the latent heat transport in the atmosphere by a diagnostic equation since no explicit hydrologic cycle or water vapour budget is kept in the model. Two parameterizations for the latent heat transport are proposed, which distinguishes the two versions of the model. The assumptions made in the first version are that the total heat transport in the combined system is invariant and that the atmospheric sensible heat transport can be approximated by a diffusion process, whereas in the second version both atmospheric sensible heat and water vapour transport are treated as a diffusion process.Before proceeding with interactive runs, we study the behaviour of the model in a decoupled mode. Some experiments with initial conditions altered and external forcings changed are carried out to investigate the sensitivity and stability of the model. In particular, the influence of the ice-albedo feedback on model solutions is examined. The results of these experiments may be helpful both in understanding the characteristics of the model and in interpreting results when the model is coupled to an OGCM.2 x CO2 Experiment
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 9
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    Melting and freezing beneath ice shelves: Implications from a 3-d ocean circulation model (1994)
    In:  EPIC3Berichte aus dem Fachbereich Physik, 48 p.
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 10
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    A primitive equation ocean circulation model using a general vertical coordinate transformation, Part 2 application to an overflow problem (1993)
    In:  EPIC3Journal of Geophysical Research, 98, pp. 14703-14726
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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