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  • 1
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    On the seasonal variability and eddies in the North Brazil Current: insights from model intercomparison experiments (2001)
    In:  EPIC3Progress in Oceanography, 48, pp. 195-230
    Details
    Publication Date: 2019-07-17
    Description: The time dependent circulation of the North Brazil Current is studied with three numerical ocean circulation models, which differ by the vertical coordinate used to formulate theprimitive equations. The models are driven with the same surface boundary conditions and their horizontal grid-resolution (isotropic, 1/3° at the equator) is in principle fine enough topermit the generation of mesoscale eddies. Our analysis of the mean seasonal currents concludes that the volume transport of the North Brazil Current (NBC) at the equator isprincipally determined by the strength of the meridional overturning, and suggests that the return path of the global thermohaline circulation is concentrated in the NBC. Models whichsimulate a realistic overturning at 24°N of the order of 16-18 Sv also simulate a realistic NBC transport of nearly 35 Sv comparable to estimates deduced from the most recentobservations. In all models, the major part of this inflow of warm waters from the South Atlantic recirculates in the zonal equatorial current system, but the models also agree on theexistence of a permanent coastal mean flow to the north-west, from the equator into the Carribean Sea, in the form of a continuous current or a succession of eddies. Importantdifferences are found between models in their representation of the eddy field. The reasons invoked are the use of different subgrid-scale parameterisations, and differences instability of the NBC retroflection loop because of differences in the representation of the effect of bottom friction according to the vertical coordinate that is used. Finally, even ifdifferences noticed between models in the details of the seasonal mean circulation and water mass properties could be explained by differences in the eddy field, nonetheless themajor characteristics (mean seasonal currents, volume and heat transports) appears to be at first order driven by the strength of the thermohaline circulation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Seasonal cycle of meridional heat transport in the subtropical North Atlantic: a model intercomparison in relation to observations near 25 (2001)
    In:  EPIC3Progress in Oceanography, 48(2), pp. 231-253, ISSN: 0079-6611
    Details
    Publication Date: 2019-07-17
    Description: Three different, eddy-permitting numerical models are used to examine the seasonal variation ofmeridional mass and heat flux in the North Atlantic, with a focus on the transport mechanisms inthe subtropics relating to observational studies near 25°N. The models, developed in theDYNAMO project, cover the same horizontal domain, with a locally isotropic grid of 1/3° resolutionin longitude, and are subject to the same monthly-mean atmospheric forcing based on athree-year ECMWF climatology. The models differ in the vertical-coordinate scheme(geopotential, isopycnic, and sigma), implying differences in lateral and diapycnic mixingconcepts, and implementation of bottom topography. As shown in the companion paper ofWillebrand et al. (2001), the model solutions exhibit significant discrepancies in the annual-meanpatterns of meridional mass and heat transport, as well as in the structure of the western boundarycurrent system.Despite these differences in the mean properties, the seasonal anomalies of the meridional fluxesare in remarkable agreement, demonstrating a robust model behavior that is primarily dependenton the external forcing, and independent of choices of numerics and parameterization. The annualrange is smaller than in previous model studies in which wind stress climatologies based on marineobservations were used, both in the equatorial Atlantic (1.4 PW) and in the subtropics (0.4-0.5PW). This is a consequence of a weaker seasonal variation in the zonal wind stresses based onthe ECMWF analysis than those derived from climatologies of marine observations.The similarities in the amplitude and patterns of the meridional transport anomalies betwen thedifferent model realizations provide support for previous model conclusions concerning themechanism of seasonal and intraseasonal heat flux variations: they can be rationalized in terms of atime-varying Ekman transport and their predominantly barotropic compensation at depth. Analysisfor 25°N indicates that the net meridional flow variation at depth is concentrated near the westernboundary, but cannot be inferred from transport measurements in the western boundary currentsystem, because of significant and complex recirculations over the western half of the basin. Themodel results instead suggest that the main requirement for estimating the annual cycle of heatflux through a transoceanic section, and the major source of error in model simulations, is anaccurate knowledge of the wind stress variation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Circulation characteristics in three eddy-permitting models of the North Atlantic (2001)
    In:  EPIC3Progress in Oceanography, 48(2), pp. 123-161, ISSN: 0079-6611
    Details
    Publication Date: 2019-07-17
    Description: A systematic intercomparison of three realistic eddy-permitting models of the North Atlanticcirculation has been performed. The models use different concepts for the discretization of thevertical coordinate, namely geopotential levels, isopycnal layers, terrain-following (sigma)coordinates, respectively. Although these models were integrated under nearly identicalconditions, the resulting large-scale model circulations show substantial differences. The resultsdemonstrate that the large-scale thermohaline circulation is very sensitive to the modelrepresentation of certain localised processes, in particular to the amount and water massproperties of the overflow across the Greenland-Scotland region, to the amount of mixing withina few hundred kilometers south of the sills, and to several other processes at small or sub-gridscales. The different behaviour of the three models can to a large extent be explained as aconsequence of the different model representation of these processes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Agulhas eddy fluxes in a 1/6 deg. Atlantic model (2003)
    In:  EPIC3Deep-sea research ii, 50(1), pp. 251-280, ISSN: 0967-0645
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    DYNAMO - Dynamics of North Atlantic Models Simulation and assimilation with high resolution models (1997)
    In:  EPIC3Berichte aus dem Institut für Meereskunde Kiel, 294, 333 p., ISSN: 0341-8561
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    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 6
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    The Ocean Reanalyses Intercom parison Project (ORA - IP) (2015)
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    Publication Date: 2022-06-20
    Description: Uncertainty in ocean analysis methods and deficiencies in the observing system are major obstacles for the reliable reconstruction of the past ocean climate. The variety of existing ocean reanalyses is exploited in a multi-reanalysis ensemble to improve the ocean state estimation and to gauge uncertainty levels. The ensemble-based analysis of signal-to-noise ratio allows the identification of ocean characteristics for which the estimation is robust (such as tropical mixed-layer-depth,upper ocean heat content), and where large uncertainty exists (deep ocean, Southern Ocean, sea-ice thickness, salinity), providing guidance for future enhancement of the observing and data assimilation systems.
    Description: This work has been partially funded by the European Commission funded projects MyOcean, MyOcean2 and COMBINE; by the GEMINA project-funded bythe Italian Ministry for Environment; by the NERC-funded VALOR project; by the NERC-funded NCEO program; by the Research Program on Climate Change adaptation of the Ministry of Education, Culture, Sports, Science and Technology of the Japanese government; by the Joint UK DECC/Defra Met Office Hadley Centre Climate Programme (GA01101); by NASA’s Modeling Analysis and Prediction Program under WBS 802678.02.17.01.25 and by the NASA Physical Oceanography Program; by the NOAA's Climate Observation Division (COD); by the LEFE/GMMC French national program.
    Description: Published
    Description: s80-s97
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: open
    Keywords: Global ocean–sea-ice modelling ; Ocean model comparisons ; DATA ASSIMILATION SCHEME ; multi-analysis ensemble ; Ocean climate ; 03. Hydrosphere::03.01. General::03.01.04. Ocean data assimilation and reanalysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Unexpected impacts of the Tropical Pacific array on reanalysis surface meteorology and heat fluxes (2014)
    John Wiley & Sons
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 6213–6220, doi:10.1002/2014GL061302.
    Description: The Tropical Pacific mooring array has been a key component of the climate observing system since the early 1990s. We identify a pattern of strong near surface humidity anomalies, colocated with the array, in the widely used European Center for Medium Range Weather Forecasting Interim atmospheric reanalysis. The pattern generates large, previously unrecognized latent and net air-sea heat flux anomalies, up to 50 Wm−2 in the annual mean, in reanalysis derived data sets employed for climate studies (TropFlux) and ocean model forcing (the Drakkar Forcing Set). As a consequence, uncertainty in Tropical Pacific ocean heat uptake between the 1990s and early 2000s at the mooring sites is significant with mooring colocated differences in decadally averaged ocean heat uptake as large as 20 Wm−2. Furthermore, these results have major implications for the dual use of air-sea flux buoys as reference sites and sources of assimilation data that are discussed.
    Description: SKG and NT were supported by the Russian Science Foundation project 14-17-00697.
    Description: 2015-03-03
    Keywords: Tropical Pacific ; Heat flux ; Mooring array ; Reanalysis
    Repository Name: Woods Hole Open Access Server
    Type: Article
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