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  • 2005-2009  (16)
  • 2009  (16)
  • 1
    Online Resource
    Online Resource
    A weaker Agulhas Current leads to more Agulhas leakage (2009)
    Associated volumes
    Details Availability
    In: Geophysical research letters, Hoboken, NJ : Wiley, 1974, 36(2009), 1944-8007
    In: volume:36
    In: year:2009
    In: extent:4
    Description / Table of Contents: Time series of transports in the Agulhas region have been constructed by simulating Lagrangian drifter trajectories in a 1/10 degree two-way nested ocean model. Using these 34 year long time series it is shown that smaller (larger) Agulhas Current transport leads to larger (smaller) Indian-Atlantic inter-ocean exchange. When transport is low, the Agulhas Current detaches farther downstream from the African continental slope. Moreover, the lower inertia suppresses generation of anti-cyclonic vorticity. These two effects cause the Agulhas retroflection to move westward and enhance Agulhas leakage. In the model a 1 Sv decrease in Agulhas Current transport at 32°S results in a 0.7 ± 0.2 Sv increase in Agulhas leakage.
    Type of Medium: Online Resource
    Pages: 4 , graph. Darst.
    ISSN: 1944-8007
    URL: http://europa.agu.org/?view=article&uri=/journals/gl/gl0903/2008GL036614/2008GL036614.xml&t=2008GL036614
    DOI: 10.1029/2008GL036614
    Language: English
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  • 2
    Online Resource
    Online Resource
    Relating Agulhas leakage to the Agulhas Current retroflection location (2009)
    Associated volumes
    Details Availability
    In: Ocean science, Katlenburg-Lindau : Copernicus Publ., 2005, 5(2009), 4, Seite 511-521, 1812-0792
    In: volume:5
    In: year:2009
    In: number:4
    In: pages:511-521
    Description / Table of Contents: The relation between the Agulhas Current retroflection location and the magnitude of Agulhas leakage, the transport of water from the Indian to the Atlantic Ocean, is investigated in a high-resolution numerical ocean model. Sudden eastward retreats of the Agulhas Current retroflection loop are linearly related to the shedding of Agulhas rings, where larger retreats generate larger rings. Using numerical Lagrangian floats a 37 year time series of the magnitude of Agulhas leakage in the model is constructed. The time series exhibits large amounts of variability, both on weekly and annual time scales. A linear relation is found between the magnitude of Agulhas leakage and the location of the Agulhas Current retroflection, both binned to three month averages. In the relation, a more westward location of the Agulhas Current retroflection corresponds to an increased transport from the Indian Ocean to the Atlantic Ocean. When this relation is used in a linear regression and applied to almost 20 years of altimetry data, it yields a best estimate of the mean magnitude of Agulhas leakage of 13.2 Sv. The early retroflection of 2000, when Agulhas leakage was probably halved, can be identified using the regression.
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1812-0792
    URL: http://www.ocean-sci.net/5/511/2009/os-5-511-2009.pdf
    Language: English
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  • 3
    Online Resource
    Online Resource
    Lagrangian validation of numerical drifter trajectories using drifting buoys : application to the Agulhas system (2009)
    Associated volumes
    Details Availability
    In: Ocean modelling online, Amsterdam [u.a.] : Elsevier Science, 1999, 29(2009), 4, Seite 269-276, 1463-5011
    In: volume:29
    In: year:2009
    In: number:4
    In: pages:269-276
    Description / Table of Contents: The skill of numerical Lagrangian drifter trajectories in three numerical models is assessed by comparing these numerically obtained paths to the trajectories of drifting buoys in the real ocean. The skill assessment is performed using the two-sample KolmogorovSmirnov statistical test. To demonstrate the assessment procedure, it is applied to three different models of the Agulhas region. The test can either be performed using crossing positions of one-dimensional sections in order to test model performance in specific locations, or using the total two-dimensional data set of trajectories. The test yields four quantities: a binary decision of model skill, a confidence level which can be used as a measure of goodness-of-fit of the model, a test statistic which can be used to determine the sensitivity of the confidence level, and cumulative distribution functions that aid in the qualitative analysis. The ordering of models by their confidence levels is the same as the ordering based on the qualitative analysis, which suggests that the method is suited for model validation. Only one of the three models, a 1/10ʿ two-way nested regional ocean model, might have skill in the Agulhas region. The other two models, a 1/2° global model and a 1/8° assimilative model, might have skill only on some sections in the region.
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1463-5011
    URL: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VPS-4WD1C5N-1&_user=2387607&_coverDate=12/31/2009&_rdoc=5&_fmt=high&_orig=browse&_srch=doc-info(#toc#6214#2009#999709995#1268063#FLA#display#Volume)&_cdi=6214&_sort=d&_docanchor=&_ct=6&_acct=C000056415&_version=1&_urlVersion=0&_userid=2387607&md5=0e3c2040f208584caf179c8a10b7dfca
    DOI: 10.1016/j.ocemod.2009.05.005
    Language: English
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  • 4
    Online Resource
    Online Resource
    Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies (2009)
    Associated volumes
    Details Availability
    In: Nature, London [u.a.] : Nature Publ. Group, 1869, 462(2009), 7272, Seite 495-498, 1476-4687
    In: volume:462
    In: year:2009
    In: number:7272
    In: pages:495-498
    Description / Table of Contents: The transport of warm and salty Indian Ocean waters into the Atlantic Oceanthe Agulhas leakagehas a crucial role in the global oceanic circulation1 and thus the evolution of future climate. At present these waters provide the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation (MOC)2. There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages3 and model studies4 that the amount of Agulhas leakage and its corresponding effect on the MOC has been subject to substantial change, potentially linked to latitudinal shifts in the Southern Hemisphere westerlies5. A progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing6, but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage. Here we present the results of a highresolution ocean general circulation model7,8 to show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing. The increased leakage has contributed to the observed salinification9 of South Atlantic thermocline waters. Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic, with potential implications for the future evolution of the MOC.
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1476-4687
    DOI: 10.1038/nature08519
    Language: English
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  • 5
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    Relating Agulhas leakage to the Agulhas Current retroflection location (2009)
    Copernicus Publications (EGU)
    In:  Ocean Science, 5 . pp. 511-521.
    Details
    Publication Date: 2016-10-11
    Description: The relation between the Agulhas Current retroflection location and the magnitude of Agulhas leakage, the transport of water from the Indian to the Atlantic Ocean, is investigated in a high-resolution numerical ocean model. Sudden eastward retreats of the Agulhas Current retroflection loop are linearly related to the shedding of Agulhas rings, where larger retreats generate larger rings. Using numerical Lagrangian floats a 37 year time series of the magnitude of Agulhas leakage in the model is constructed. The time series exhibits large amounts of variability, both on weekly and annual time scales. A linear relation is found between the magnitude of Agulhas leakage and the location of the Agulhas Current retroflection, both binned to three month averages. In the relation, a more westward location of the Agulhas Current retroflection corresponds to an increased transport from the Indian Ocean to the Atlantic Ocean. When this relation is used in a linear regression and applied to almost 20 years of altimetry data, it yields a best estimate of the mean magnitude of Agulhas leakage of 13.2 Sv. The early retroflection of 2000, when Agulhas leakage was probably halved, can be identified using the regression.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/os-5-511-2009
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Improvements for High Resolution Ocean Research with NEMO (2009)
    J-STAGE
    In:  Interdisciplinary Information Sciences, 15 . pp. 85-90.
    Details
    Publication Date: 2019-09-23
    Description: NEMO is a fluid dynamics code used for oceanographic research. Within the TERAFLOP Workbench in cooperation with the Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR) in Kiel a performance assessment and improvement campaign was carried out, ranging from MPI to memory addressing in solvers. At The High Performance Computing Center Stuttgart (HLRS) tests were made using a large configuration of SX nodes running NEMO at 2.1 Teraflop/s. The improved code is running the test case 29% faster on 512 SX-8 CPUs.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4036/iis.2009.85
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Agulhas Leakage: The Neglected Player in the Variability of the Atlantic Meridional Overturning Circulation (2009)
    In:  [Invited talk] In: IAPSO Assembly, 19.-24.07, Montreal, Canada .
    Details
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 8
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    Variability and coherence of the Agulhas Undercurrent in a High-resolution Ocean General Circulation Model (2009)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 39 . pp. 2417-2435.
    Details
    Publication Date: 2020-08-04
    Description: The Agulhas Current system has been analyzed in a nested high-resolution ocean model and compared to observations. The model shows good performance in the western boundary current structure and the transports off the South African coast. This includes the simulation of the northward-flowing Agulhas Undercurrent. It is demonstrated that fluctuations of the Agulhas Current and Undercurrent around 50–70 days are due to Natal pulses and Mozambique eddies propagating downstream. A sensitivity experiment that excludes those upstream perturbations significantly reduces the variability as well as the mean transport of the undercurrent. Although the model simulates undercurrents in the Mozambique Channel and east of Madagascar, there is no direct connection between those and the Agulhas Undercurrent. Virtual float releases demonstrate that topography is effectively blocking the flow toward the north.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/2009JPO4184.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    A weaker Agulhas Current leads to more Agulhas leakage (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L03601.
    Details
    Publication Date: 2019-09-23
    Description: Time series of transports in the Agulhas region have been constructed by simulating Lagrangian drifter trajectories in a 1/10 degree two-way nested ocean model. Using these 34 year long time series it is shown that smaller (larger) Agulhas Current transport leads to larger (smaller) Indian-Atlantic inter-ocean exchange. When transport is low, the Agulhas Current detaches farther downstream from the African continental slope. Moreover, the lower inertia suppresses generation of anti-cyclonic vorticity. These two effects cause the Agulhas retroflection to move westward and enhance Agulhas leakage. In the model a 1 Sv decrease in Agulhas Current transport at 32 degrees S results in a 0.7 +/- 0.2 Sv increase in Agulhas leakage
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008GL036614
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Unknown
    The Agulhas system as a key region of the global oceanic circulation (2009)
    IFM-GEOMAR
    In:  IFM-GEOMAR Annual Report, 2008 . pp. 12-13.
    Details
    Publication Date: 2018-10-16
    Description: The Agulhas system transports warm and salty waters from the Indian to the Atlantic Ocean and therefore acts as a key element in the global oceanic circulation. Studies have shown that mesoscale processes are not only important for the correct description of the circulation around South Africa itself but also for its impact on the Gulf Stream system in the North Atlantic.
    Type: Article , NonPeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - without review
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