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  • 2015-2019  (28)
  • 2005-2009  (2)
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  • 1
    Online-Ressource
    Online-Ressource
    The Conrad Rise as an obstruction to the Antarctic Circumpolar Current (2008)
    Dazugehörige Bände
    Details Verfügbarkeit
    In: Geophysical research letters, Hoboken, NJ : Wiley, 1974, 35(2008), 1944-8007
    In: volume:35
    In: year:2008
    In: extent:6
    Beschreibung / Inhaltsverzeichnis: The Antarctic Circumpolar Current (ACC) carries water freely around the whole continent of Antarctica, but not without obstructions. Some, such as the Drake Passage, constrict its path, while others, such as mid-ocean ridges, may induce meandering in the current's cores and may cause the genesis of mesoscale turbulence. It has recently been demonstrated that some regions that are only relatively shallow may also have a major effect on the flow patterns of the ACC. This is here shown to be particularly true for the Conrad Rise. Using the trajectories of surface drifters, altimetry and the simulated velocities from a numerical model, we show that the ACC bifurcates at the western side of this Rise. In this process it forms two intense jets at the two meridional extremities of the Rise with a relatively stagnant water body over the Rise itself. Preliminary results from a recent cruise provide compelling support for this portrayal.
    Materialart: Online-Ressource
    Seiten: 6 , graph. Darst
    ISSN: 1944-8007
    URL: http://onlinelibrary.wiley.com/doi/10.1029/2008GL035382/epdf
    DOI: 10.1029/2008GL035382
    Sprache: Englisch
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
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    Simulating the Agulhas system in global ocean models – nesting vs. multi-resolution unstructured meshes (2018)
    ELSEVIER SCI LTD
    In:  EPIC3Ocean Modelling, ELSEVIER SCI LTD, 121, pp. 117-131, ISSN: 1463-5003
    Details
    Publikationsdatum: 2018-02-28
    Beschreibung: Many questions in ocean and climate modelling require the combined use of high resolution, global coverage and multi-decadal integration length. For this combination, even modern resources limit the use of traditional structured-mesh grids. Here we compare two approaches: A high-resolution grid nested into a global model at coarser resolution (NEMO with AGRIF) and an unstructured-mesh grid (FESOM) which allows to variably enhance resolution where desired. The Agulhas system around South Africa is used as a testcase, providing an energetic interplay of a strong western boundary current and mesoscale dynamics. Its open setting into the horizontal and global overturning circulations also requires global coverage. Both model configurations simulate a reasonable large-scale circulation. Distribution and temporal variability of the wind-driven circulation are quite comparable due to the same atmospheric forcing. However, the overturning circulation differs, owing each model’s ability to represent formation and spreading of deep water masses. In terms of regional, high-resolution dynamics, all elements of the Agulhas system are well represented. Owing to the strong nonlinearity in the system, Agulhas Current transports of both configurations and in comparison with observations differ in strength and temporal variability. Similar decadal trends in Agulhas Current transport and Agulhas leakage are linked to the trends in wind forcing. Although the number of 3D wet grid points used in FESOM is similar to that in the nested NEMO, FESOM uses about two times the number of CPUs to obtain the same model throughput (in terms of simulated model years per day). This is feasible due to the high scalability of the FESOM code.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Format: application/pdf
    Standort Signatur Einschränkungen Verfügbarkeit
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    ARTIKEL (OA)
  • 3
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    Designing variable ocean model resolution based on the observed ocean variability (2016)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, 8(2), pp. 904-916
    Details
    Publikationsdatum: 2016-09-19
    Beschreibung: If unstructured meshes are refined to locally represent eddy dynamics in ocean circulation models, a practical question arises on how to vary the resolution and where to deploy the refinement. We propose to use the observed sea surface height variability as the refinement criterion. We explore the utility of this method (i) in a suite of idealized experiments simulating a wind-driven double gyre flow in a stratified circular basin and (ii) in simulations of global ocean circulation performed with FESOM. Two practical approaches of mesh refinement are compared. In the first approach the uniform refinement is confined within the areas where the observed variability exceeds a given threshold. In the second one the refinement varies linearly following the observed variability. The resolution is fixed in time. For the double gyre case it is shown that the variability obtained in a high-resolution reference run can be well captured on variable-resolution meshes if they are refined where the variability is high and additionally upstream the jet separation point. The second approach of mesh refinement proves to be more beneficial in terms of improvement downstream the midlatitude jet. Similarly, in global ocean simulations the mesh refinement based on the observed variability helps the model to simulate high variability at correct locations. The refinement also leads to a reduced bias in the upper-ocean temperature.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Format: application/pdf
    Standort Signatur Einschränkungen Verfügbarkeit
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    ARTIKEL (OA)
  • 4
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    Simulating the Agulhas system in global ocean models – nesting vs. multi-resolution unstructured meshes (2018)
    Elsevier
    In:  Ocean Modelling, 121 . pp. 117-131.
    Details
    Publikationsdatum: 2021-02-08
    Beschreibung: Highlights: • Comparison of global NEMO and FESOM configurations with emphasis on the Agulhas system. • Both models simulate a reasonable and comparable large-scale circulation. • Both models have individual strengths and weaknesses to match the observations of the WBC system. • The numerical cost of FESOM is twice the one of NEMO. Abstract: Many questions in ocean and climate modelling require the combined use of high resolution, global coverage and multi-decadal integration length. For this combination, even modern resources limit the use of traditional structured-mesh grids. Here we compare two approaches: A high-resolution grid nested into a global model at coarser resolution (NEMO with AGRIF) and an unstructured-mesh grid (FESOM) which allows to variably enhance resolution where desired. The Agulhas system around South Africa is used as a testcase, providing an energetic interplay of a strong western boundary current and mesoscale dynamics. Its open setting into the horizontal and global overturning circulations also requires global coverage. Both model configurations simulate a reasonable large-scale circulation. Distribution and temporal variability of the wind-driven circulation are quite comparable due to the same atmospheric forcing. However, the overturning circulation differs, owing each model's ability to represent formation and spreading of deep water masses. In terms of regional, high-resolution dynamics, all elements of the Agulhas system are well represented. Owing to the strong nonlinearity in the system, Agulhas Current transports of both configurations and in comparison with observations differ in strength and temporal variability. Similar decadal trends in Agulhas Current transport and Agulhas leakage are linked to the trends in wind forcing. Although the number of 3D wet grid points used in FESOM is similar to that in the nested NEMO, FESOM uses about two times the number of CPUs to obtain the same model throughput (in terms of simulated model years per day). This is feasible due to the high scalability of the FESOM code.
    Materialart: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.ocemod.2017.12.002
    Standort Signatur Einschränkungen Verfügbarkeit
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    OceanRep: Artikel in einer Fachzeitschrift - begutachtet
  • 5
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    Ocean currents generate large footprints in marine palaeoclimate proxies (2015)
    Nature Publishing Group
    In:  Nature Communications, 6 (6521).
    Details
    Publikationsdatum: 2019-02-25
    Beschreibung: Fossils of marine microorganisms such as planktic foraminifera are among the cornerstones of palaeoclimatological studies. It is often assumed that the proxies derived from their shells represent ocean conditions above the location where they were deposited. Planktic foraminifera, however, are carried by ocean currents and, depending on the life traits of the species, potentially incorporate distant ocean conditions. Here we use high-resolution ocean models to assess the footprint of planktic foraminifera and validate our method with proxy analyses from two locations. Results show that foraminifera, and thus recorded palaeoclimatic conditions, may originate from areas up to several thousands of kilometres away, reflecting an ocean state significantly different from the core site. In the eastern equatorial regions and the western boundary current extensions, the offset may reach 1.5 °C for species living for a month and 3.0 °C for longer-living species. Oceanic transport hence appears to be a crucial aspect in the interpretation of proxy signals.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1038/ncomms7521
    Standort Signatur Einschränkungen Verfügbarkeit
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    OceanRep: Artikel in einer Fachzeitschrift - begutachtet
  • 6
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    Variability of the Boundary Circulation Systems and AMOC at 11°S (2016)
    In:  [Poster] In: CLIVAR-PIRATA-PREFACE Tropical Atlantic Variability Conference, 28.11.-01.12.2016, Paris, France .
    Details
    Publikationsdatum: 2017-07-17
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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    OceanRep: Poster
  • 7
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    Lateral eddy diffusivity estimates from simulated and observed drifter trajectories - a case study for the Agulhas Current system (2017)
    In:  [Poster] In: EGU General Assembly 2017, 23.-28.04.2017, Vienna, Austria .
    Details
    Publikationsdatum: 2019-09-23
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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    OceanRep: Poster
  • 8
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    Atlantic multi-decadal oscillation covaries with Agulhas leakage (2015)
    Nature Publishing Group
    In:  Nature Communications, 6 (10082).
    Details
    Publikationsdatum: 2019-02-25
    Beschreibung: The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, ‘Agulhas leakage’, forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870–2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales; the former leading by 15 years. This is relevant for climate in the North Atlantic
    Materialart: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1038/ncomms10082
    Standort Signatur Einschränkungen Verfügbarkeit
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    OceanRep: Artikel in einer Fachzeitschrift - begutachtet
  • 9
    facet.materialart.
    Unbekannt
    Designing variable ocean model resolution based on the observed ocean variability (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Advances in Modeling Earth Systems, 8 (2). pp. 904-916.
    Details
    Publikationsdatum: 2019-07-17
    Beschreibung: If unstructured meshes are refined to locally represent eddy dynamics in ocean circulation models, a practical question arises on how to vary the resolution and where to deploy the refinement. We propose to use the observed sea surface height variability as the refinement criterion. We explore the utility of this method (i) in a suite of idealized experiments simulating a wind-driven double gyre flow in a stratified circular basin and (ii) in simulations of global ocean circulation performed with FESOM. Two practical approaches of mesh refinement are compared. In the first approach the uniform refinement is confined within the areas where the observed variability exceeds a given threshold. In the second one the refinement varies linearly following the observed variability. The resolution is fixed in time. For the double gyre case it is shown that the variability obtained in a high-resolution reference run can be well captured on variable-resolution meshes if they are refined where the variability is high and additionally upstream the jet separation point. The second approach of mesh refinement proves to be more beneficial in terms of improvement downstream the midlatitude jet. Similarly, in global ocean simulations the mesh refinement based on the observed variability helps the model to simulate high variability at correct locations. The refinement also leads to a reduced bias in the upper-ocean temperature
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2016MS000650
    Standort Signatur Einschränkungen Verfügbarkeit
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    OceanRep: Artikel in einer Fachzeitschrift - begutachtet
  • 10
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    Contribution of increased Agulhas leakage to tropical Atlantic warming (2015)
    AMS (American Meteorological Society)
    In:  Journal of Climate, 28 (24). pp. 9697-9706.
    Details
    Publikationsdatum: 2020-08-04
    Beschreibung: The upper tropical Atlantic Ocean has markedly warmed since the 1960s. It has been shown that this warming was not due to local heat fluxes, and that the trade winds that drive the coastal and equatorial upwelling have intensified rather than weakened. Remote forcing might thus have played an important role. Here model experiments are used to investigate the contribution from an increased inflow of warm Indian Ocean water through Agulhas leakage. A high-resolution hindcast experiment with interannually varying forcing for the time period 1948 to 2007, in which Agulhas leakage increases by about 45% from the 1960s to the early 2000s, reproduces the observed warming trend. To tease out the role of Agulhas leakage, a sensitivity experiment designed to only increase Agulhas leakage is used. Compared to a control simulation it shows a pronounced warming in the upper tropical Atlantic Ocean. A Lagrangian trajectory analysis confirms that a significant portion of Agulhas leakage water reaches the upper 300m of the tropical Atlantic Ocean within two decades, and that the tropical Atlantic warming in the sensitivity experiment is mainly due to water of Agulhas origin. Therefore, it is suggested that the increased trade winds since the 1960s favor upwelling of warmer subsurface waters, which in parts originate from the Agulhas, leading to higher SSTs in the tropics
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1175/JCLI-D-15-0258.1
    Standort Signatur Einschränkungen Verfügbarkeit
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