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  • Copernicus Publications (EGU)  (20)
  • Geophysical Fluid Dynamics Laboratory (GFDL)  (2)
  • Kiel : Universitätsbibliothek Kiel  (2)
  • 1
    Online Resource
    Online Resource
    The impact of submesoscale flows on mesoscale Agulhas dynamics (2020)
    Kiel : Universitätsbibliothek Kiel
    Details Availability
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (ix, 208 Seiten) , Illustrationen, Diagramme
    URL: https://nbn-resolving.org/urn:nbn:de:gbv:8-mods-2020-00151-7
    URL: https://d-nb.info/1209542870/34
    URL: https://macau.uni-kiel.de/receive/macau_mods_00000504
    URN: urn:nbn:de:gbv:8-mods-2020-00151-7
    DDC: 551.462
    Language: English
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  • 2
    Online Resource
    Online Resource
    Lagrangian connectivity of the upper limb of the overturning circulation studied with high-resolution ocean models (2018)
    Kiel : Universitätsbibliothek Kiel
    Details Availability
    Keywords: Hochschulschrift ; Mathematische Modellierung ; Meer
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (xiv, 120 Seiten) , Illustrationen
    URL: https://nbn-resolving.org/urn:nbn:de:gbv:8-diss-238711
    URL: https://d-nb.info/1196621896/34
    URL: https://macau.uni-kiel.de/receive/dissertation_diss_00023871
    URN: urn:nbn:de:gbv:8-diss-238711
    DDC: 550
    Language: English
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  • 3
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    Major sources of North Atlantic Deep Water in the subpolar North Atlantic from Lagrangian analyses in a high–resolution ocean model (2022)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2022-09-20
    Description: North Atlantic Deep Water (NADW) is a crucial component of the Atlantic Meridional Overturning Circulation and, therefore, is an important factor of the climate system. In order to estimate the mean relative contributions, sources and pathways of the three different deep water mass components (namely Labrador Sea Water, Northeast Atlantic Deep Water and Denmark Strait Overflow Water) at the southern exit of the Labrador Sea, Lagrangian particle experiments were performed. The particles were seeded according to the strength of the velocity field along the 53° N section and computed 40 years backward in time in the three-dimensional velocity and hydrography field. Water masses were defined within the model output in the central Labrador Sea and the subpolar North Atlantic. The resulting transport pathways, their sources and corresponding transit time scales were inferred. Our experiments show that the majority of NADW passing 53° N is associated with diapycnal mass flux, accounting for 14.3 Sv (48 %), where 6.2 Sv originate from the Labrador Sea, compared to 4.7 Sv from the Irminger Sea. The second largest contribution originates from the mixed layer with 7.2 Sv (24 %), where the Labrador Sea contribution (5.9 Sv) dominates over the Irminger Sea contribution (1.0 Sv). Another 5.7 Sv (19 %) of NADW cross the Greenland–Scotland Ridge within the NADW density class, where about 2/3 pass Denmark Strait, while 1/3 cross the Iceland Scotland Ridge. The NADW exported at 53° N is hence dominated by entrainment through diapycnal mass flux and the mixed layer origin in the Labrador Sea.
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    An observed 20-year time series of Agulhas leakage (2014)
    Copernicus Publications (EGU)
    In:  Ocean Science, 10 (4). pp. 601-609.
    Details
    Publication Date: 2019-09-23
    Description: We provide a time series of Agulhas leakage anomalies over the last 20-years from satellite altimetry. Until now, measuring the interannual variability of Indo-Atlantic exchange has been the major barrier in the investigation of the dynamics and large scale impact of Agulhas leakage. We compute the difference of transport between the Agulhas Current and Agulhas Return Current, which allows us to deduce Agulhas leakage. The main difficulty is to separate the Agulhas Return Current from the southern limb of the subtropical "supergyre" south of Africa. For this purpose, an algorithm that uses absolute dynamic topography data is developed. The algorithm is applied to a state-of-the-art ocean model. The comparison with a Lagrangian method to measure the leakage allows us to validate the new method. An important result is that it is possible to measure Agulhas leakage in this model using the velocity field along a section that crosses both the Agulhas Current and the Agulhas Return Current. In the model a good correlation is found between measuring leakage using the full depth velocities and using only the surface geostrophic velocities. This allows us to extend the method to along-track absolute dynamic topography from satellites. It is shown that the accuracy of the mean dynamic topography does not allow us to determine the mean leakage but that leakage anomalies can be accurately computed.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.5194/os-10-601-2014
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Variability in the subtropical-tropical cells and its effect on near-surface temperature of the equatorial Pacific: a model study (2008)
    Copernicus Publications (EGU)
    In:  Ocean Science, 4 (1). pp. 73-88.
    Details
    Publication Date: 2015-02-26
    Description: A set of experiments utilizing different implementations of the global ORCA-LIM model with horizontal resolutions of 2°, 0.5° and 0.25° is used to investigate tropical and extra-tropical influences on equatorial Pacific SST variability at interannual to decadal time scales. The model experiments use a bulk forcing methodology building on the global forcing data set for 1958 to 2000 developed by Large and Yeager (2004) that is based on a blend of atmospheric reanalysis data and satellite products. Whereas representation of the mean structure and transports of the (sub-) tropical Pacific current fields is much improved with the enhanced horizontal resolution, there is only little difference in the simulation of the interannual variability in the equatorial regime between the 0.5° and 0.25° model versions, with both solutions capturing the observed SST variability in the Niño3-region. The question of remotely forced oceanic contributions to the equatorial variability, in particular, the role of low-frequency changes in the transports of the Subtropical Cells (STCs), is addressed by a sequence of perturbation experiments using different combinations of fluxes. The solutions show the near-surface temperature variability to be governed by wind-driven changes in the Equatorial Undercurrent. The relative contributions of equatorial and off-equatorial atmospheric forcing differ between interannual and longer, (multi-) decadal timescales: for the latter there is a significant impact of changes in the equatorward transport of subtropical thermocline water associated with the lower branches of the STCs, related to variations in the off-equatorial trade winds. A conspicuous feature of the STC variability is that the equatorward transports in the interior and along the western boundary partially compensate each other at both decadal and interannual time scales, with the strongest transport extrema occurring during El Niño episodes. The behaviour is rationalized in terms of a wobbling in the poleward extents of the tropical gyres, which is manifested also in a meridional shifting of the bifurcation latitudes of the North and South Equatorial Current systems.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/os-4-73-2008
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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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
  • 7
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    Stevens Open Boundary Conditions (1996)
    Geophysical Fluid Dynamics Laboratory (GFDL)
    In:  In: MOM 2 Version 2.0 (Beta) - Documentation User’s Guide and Reference Manual - Release date: Nov 7,1996. , ed. by Pacanowski, R. C. GDFL Ocean Technical Report, 3.2 . Geophysical Fluid Dynamics Laboratory (GFDL), Princeton, USA, pp. 141-150.
    Details
    Publication Date: 2020-04-24
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 8
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    Stevens Open Boundary Conditions (1999)
    Geophysical Fluid Dynamics Laboratory (GFDL)
    In:  In: MOM 3.0 Manual. , ed. by Pacanowski, R. C. and Griffies, S. M. GFDL Ocean Group Technical Report, 4 . Geophysical Fluid Dynamics Laboratory (GFDL), Princeton, USA, pp. 245-252.
    Details
    Publication Date: 2020-03-24
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 9
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    The Flexible Ocean and Climate Infrastructure Version 1 (FOCI1): Mean State and Variability (2020)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2023-02-08
    Description: A new Earth system model, the Flexible Ocean and Climate Infrastructure (FOCI), is introduced. A first version of FOCI consists of a global high-top atmosphere (ECHAM6.3) and an ocean model (NEMO3.6) as well as sea ice (LIM2) and land surface model components (JSBACH), which are coupled through the OASIS3-MCT software package. FOCI includes a number of optional modules which can be activated depending on the scientific question of interest. In the atmosphere, interactive stratospheric chemistry can be used (ECHAM6-HAMMOZ) to study, for example, the effects of the ozone hole on the climate system. In the ocean, a biogeochemistry model (MOPS) is available to study the global carbon cycle. A unique feature of FOCI is the ability to explicitly resolve mesoscale ocean eddies in specific regions. This is realized in the ocean through nesting; first examples for the Agulhas Current and the Gulf Stream systems are described here. FOCI therefore bridges the gap between coarse-resolution climate models and global high-resolution weather prediction and ocean-only models. It allows to study the evolution of the climate system on regional and seasonal to (multi-) decadal scales. The development of FOCI resulted from a combination of the long-standing expertise in ocean and climate modeling in several research units and divisions at GEOMAR. FOCI will thus be used to complement and interpret long-term observations in the Atlantic, enhance the process understanding of the role of mesoscale oceanic eddies for large-scale oceanic and atmospheric circulation patterns, study feedback mechanisms with stratospheric processes, estimate future ocean acidification, improve the simulation of the Atlantic Meridional Overturning Circulation changes and their influence on climate, ocean chemistry and biology. In this paper we present both the scientific vision for the development of FOCI as well as some technical details. This includes a first validation of the different model components using several configurations of FOCI. Results show that the model in its basic configuration runs stably under pre-industrial control as well as under historical forcing, and produces a mean climate and variability which compares well with observations, reanalysis products and other climate models. The nested configurations reduce some long-standing biases in climate models and are an important step forward to include the atmospheric response in multi-decadal eddy-rich configurations.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Analysis of the position and strength of westerlies and trades with implications for Agulhas leakage and South Benguela upwelling (2019)
    Copernicus Publications (EGU)
    In:  Earth System Dynamics, 10 (4). pp. 847-858.
    Details
    Publication Date: 2022-01-31
    Description: The westerlies and trade winds over the South Atlantic and Indian Ocean are important drivers of the regional oceanography around southern Africa, including features such as the Agulhas Current, the Agulhas leakage, and the Benguela upwelling. Agulhas leakage constitutes a fraction of warm and saline water transport from the Indian Ocean into the South Atlantic. The leakage is stronger during intensified westerlies. Here, we analyze the wind stress of different observational and modeled atmospheric data sets (covering the last 2 millennia, the recent decades, and the 21st century) with regard to the intensity and position of the southeasterly trades and the westerlies. The analysis reveals that variations of both wind systems go hand in hand and that a poleward shift of the westerlies and trades and an intensification of westerlies took place during the recent decades. Furthermore, upwelling in South Benguela is slightly intensified when trades are shifted poleward. Projections for strength and position of the westerlies in the 21st century depend on assumed CO2 emissions and on their effect relative to the ozone forcing. In the strongest emission scenario (RCP8.5) the simulations show a further southward displacement, whereas in the weakest emission scenario (RCP2.6) a northward shift is modeled, possibly due to the effect of ozone recovery dominating the effect of anthropogenic greenhouse forcing. We conclude that the Agulhas leakage has intensified during the last decades and is projected to increase if greenhouse gas emissions are not reduced. This will have a small impact on Benguela upwelling strength and may also have consequences for water mass characteristics in the upwelling region. An increased contribution of Agulhas water to the upwelling water masses will import more preformed nutrients and oxygen into the upwelling region.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/esd-10-847-2019
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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