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  • 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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    GEOMAR CATALOGUE
    Link to Library Catalog
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  • 2
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    Submesoscale flows impact Agulhas leakage in ocean simulations (2021)
    Nature Publishing Group UK
    Details
    Publication Date: 2023-11-14
    Description: Agulhas leakage, the warm and salty inflow of Indian Ocean water into the Atlantic Ocean, is of importance for the climate-relevant Atlantic Meridional Overturning Circulation. South of Africa, the eastward turning Agulhas Current sheds Agulhas rings, cyclones and filaments of order 100 km that carry the Indian Ocean water into the Cape Basin and further into the Atlantic. Here, we show that the resolution of submesoscale flows of order 10 km in an ocean model leads to 40 % more Agulhas leakage and more realistic Cape Basin water-masses compared to a parallel non-submesoscale resolving simulation. Moreover, we show that submesoscale flows strengthen shear-edge eddies and in consequence lee cyclones at the northern edge of the Agulhas Current, as well as the leakage pathway in the region of the filaments that takes place outside of mesoscale eddies. This indicates that the increase in leakage can be attributed to stronger Agulhas filaments, when submesoscale flows are resolved.
    Description: Leakage of warm, salty waters from the Indian Ocean into the Atlantic increases by up to 40 % in high-resolution numerical ocean model simulations, suggesting that low-resolution models underestimate this key part of the global meridional overturning circulation.
    Description: Agence Nationale de la Recherche (French National Research Agency) https://doi.org/10.13039/501100001665
    Description: https://hdl.handle.net/20.500.12085/c572cde8-a82c-4c2d-9bd7-288dfc8f1939
    Description: https://www.aoml.noaa.gov/phod/gdp/data.php
    Description: https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=GLOBAL_REANALYSIS_PHY_001_030
    Description: https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=SEALEVEL_GLO_PHY_L4_REP_OBSERVATIONS_008_047
    Keywords: ddc:551.46 ; Climate and Earth system modelling ; Physical oceanography
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 3
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    The Impact of Submesoscale Flows on Mesoscale Agulhas Dynamics (2020)
    Details
    Publication Date: 2023-02-08
    Description: Mesoscale eddies are central to the oceanic circulation and the global climate. Of particular importance, in this respect, are mesoscale eddies in the Agulhas region south of Africa, as they govern the inflow of warm and salty Indian Ocean waters into the Atlantic Ocean. In this dissertation, it is shown that these eddies are strengthened by submesoscale flows. This highlights the importance of including submesoscale effects for a realistic representation of the mesoscale dynamics in ocean models. First, a general circulation ocean model for the Agulhas region is improved with respect to the simulation of submesoscale dynamics by increasing the vertical and horizontal resolution and reducing the model diffusion and dissipation. Second, a model validation based on horizontal-wavenumber spectra computed from high-resolution satellite sea-surface temperature and sea-surface height measurements is performed. It demonstrates that the simulated submesoscale and mesoscale circulation in the Cape Basin are extraordinary well represented in this model. A comparison to two parallel model experiments, of which the first only resolves the largest and the second no submesoscale flows, reveals that the mesoscale spectral density of sea-surface height increases the more submesoscales are resolved. The results of an eddy detection algorithm show that this can be attributed to a strengthening of the mesoscale eddies. Third, a coarse-graining approach for the transfer of kinetic energy between spatial scales is applied to the model outputs. The results indicate that the mesoscale eddies are strengthened in spring or early summer by the absorption of submesoscale eddies resulting from baroclinic mixed-layer instability in winter. Fourth, this analysis complemented with the computation of the transfer of kinetic energy between temporal scales reveals that submesoscale eddies emerging from barotropic instabilities at the northern boundary of the Agulhas Current are important for the strength of shear-edge eddies and further of lee cyclones that propagate into the Cape Basin. The model comparison shows that the combination of both strengthening effects contributes to an increase of the surface mesoscale kinetic energy in the Cape Basin by 28 %, if submesoscale processes are resolved.
    Type: Thesis , NonPeerReviewed
    Format: text
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    OceanRep: Thesis - not published by a publisher
  • 4
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    The Submesoscale Kinetic Energy Cascade: Mesoscale Absorption of Submesoscale Mixed-Layer Eddies and Frontal Downscale Fluxes (2020)
    AMS (American Meteorological Society) | Wiley
    Details
    Publication Date: 2023-02-08
    Description: Mesoscale eddies can be strengthened by the absorption of submesoscale eddies resulting from mixed-layer baroclinic instabilities. This is shown for mesoscale eddies in the Agulhas Current system by investigating the kinetic energy cascade with a spectral and a coarse-graining approach in two model simulations of the Agulhas region. One simulation resolves mixed-layer baroclinic instabilities and one does not. When mixed-layer baroclinic instabilities are included, the largest submesoscale near-surface fluxes occur in winter-time in regions of strong mesoscale activity for upscale as well as downscale directions. The forward cascade at the smallest resolved scales occurs mainly in frontogenetic regions in the upper 30 m of the water column. In the Agulhas ring path, the forward cascade changes to an inverse cascade at a typical scale of mixed-layer eddies (15 km). At the same scale, the largest sources of the upscale flux occur. After the winter, the maximum of the upscale flux shifts to larger scales. Depending on the region, the kinetic energy reaches the mesoscales in spring or early summer aligned with the maximum of mesoscale kinetic energy. This indicates the importance of submesoscale flows for the mesoscale seasonal cycle. A case study shows that the underlying process is the mesoscale absorption of mixed-layer eddies. When mixed-layer baroclinic instabilities are not included in the simulation, the open-ocean upscale cascade in the Agulhas ring path is almost absent. This contributes to a 20 %-reduction of surface kinetic energy at mesoscales larger than 100 km when submesoscale dynamics are not resolved by the model.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Robust estimates for the decadal evolution of Agulhas leakage from the 1960s to the 2010s (2022)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Agulhas leakage, the transport of warm and salty waters from the Indian Ocean into the South Atlantic, has been suggested to increase under anthropogenic climate change, due to strengthening Southern Hemisphere westerly winds. The resulting enhanced salt transport into the South Atlantic may counteract the projected weakening of the Atlantic overturning circulation through warming and ice melting. Here we combine existing and new observation- and model-based Agulhas leakage estimates to robustly quantify its decadal evolution since the 1960s. We find that Agulhas leakage very likely increased between the mid-1960s and mid-1980s, in agreement with strengthening winds. Our models further suggest that increased leakage was related to enhanced transport outside eddies and coincided with strengthened Atlantic overturning circulation. Yet, it appears unlikely that Agulhas leakage substantially increased since the 1990s, despite continuously strengthening winds. Our results stress the need to better understand decadal leakage variability to detect and predict anthropogenic trends.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Cloud-based framework for inter-comparing submesoscale-permitting realistic ocean models (2022)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: With the increase in computational power, ocean models with kilometer-scale resolution have emerged over the last decade. These models have been used for quantifying the energetic exchanges between spatial scales, informing the design of eddy parametrizations, and preparing observing networks. The increase in resolution, however, has drastically increased the size of model outputs, making it difficult to transfer and analyze the data. It remains, nonetheless, of primary importance to assess more systematically the realism of these models. Here, we showcase a cloud-based analysis framework proposed by the Pangeo project that aims to tackle such distribution and analysis challenges. We analyze the output of eight submesoscale-permitting simulations, all on the cloud, for a crossover region of the upcoming Surface Water and Ocean Topography (SWOT) altimeter mission near the Gulf Stream separation. The cloud-based analysis framework (i) minimizes the cost of duplicating and storing ghost copies of data and (ii) allows for seamless sharing of analysis results amongst collaborators. We describe the framework and provide example analyses (e.g., sea-surface height variability, submesoscale vertical buoyancy fluxes, and comparison to predictions from the mixed-layer instability parametrization). Basin- to global-scale, submesoscale-permitting models are still at their early stage of development; their cost and carbon footprints are also rather large. It would, therefore, benefit the community to document the different model configurations for future best practices. We also argue that an emphasis on data analysis strategies would be crucial for improving the models themselves.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Submesoscale flows impact Agulhas leakage in ocean simulations (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Agulhas leakage, the warm and salty inflow of Indian Ocean water into the Atlantic Ocean, is of importance for the climate-relevant Atlantic Meridional Overturning Circulation. South of Africa, the eastward turning Agulhas Current sheds Agulhas rings, cyclones and filaments of order 100 km that carry the Indian Ocean water into the Cape Basin and further into the Atlantic. Here, we show that the resolution of submesoscale flows of order 10 km in an ocean model leads to 40 % more Agulhas leakage and more realistic Cape Basin water-masses compared to a parallel non-submesoscale resolving simulation. Moreover, we show that submesoscale flows strengthen shear-edge eddies and in consequence lee cyclones at the northern edge of the Agulhas Current, as well as the leakage pathway in the region of the filaments that takes place outside of mesoscale eddies. This indicates that the increase in leakage can be attributed to stronger Agulhas filaments, when submesoscale flows are resolved.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
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