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  • Wiley  (5)
  • Elsevier  (3)
  • 2015-2019  (8)
  • 2018  (8)
  • 1
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    Lagrangian ocean analysis: fundamentals and practices (2018)
    Elsevier
    In:  Ocean Modelling, 121 . pp. 49-75.
    Details
    Publication Date: 2021-02-08
    Description: Highlights: • Lagrangian ocean analysis is a powerful way to analyse the output of ocean circulation models • We present a review of the Kinematic framework, available tools, and applications of Lagrangian ocean analysis • While there are unresolved questions, the framework is robust enough to be used widely in ocean modelling Abstract: Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.ocemod.2017.11.008
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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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
    Publication Date: 2021-02-08
    Description: 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.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.ocemod.2017.12.002
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Seasonal Cycles of Oceanic Transports in the Eastern Subpolar North Atlantic (2018)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 123 (2). pp. 1471-1484.
    Details
    Publication Date: 2021-02-08
    Description: The variability of the Atlantic Meridional Overturning Circulation (AMOC) may play a role in sea surface temperature predictions on seasonal to decadal time scales. Therefore, AMOC seasonal cycles are a potential baseline for interpreting predictions. Here we present estimates for the seasonal cycle of transports of volume, temperature, and freshwater associated with the upper limb of the AMOC in the eastern subpolar North Atlantic on the Extended Ellett Line hydrographic section between Scotland and Iceland. Due to weather, ship‐based observations are primarily in summer. Recent glider observations during other seasons present an opportunity to investigate the seasonal variability in the upper layer of the AMOC. First, we document a new method to quality control and merge ship, float, and glider hydrographic observations. This method accounts for the different spatial sampling rates of the three platforms. The merged observations are used to compute seasonal cycles of volume, temperature, and freshwater transports in the Rockall Trough. These estimates are similar to the seasonal cycles in two eddy‐resolving ocean models. Volume transport appears to be the primary factor modulating other Rockall Trough transports. Finally, we show that the weakest transports occur in summer, consistent with seasonal changes in the regional‐scale wind stress curl. Although the seasonal cycle is weak compared to other variability in this region, the amplitude of the seasonal cycle in the Rockall Trough, roughly 0.5–1 Sv about a mean of 3.4 Sv, may account for up to 7–14% of the heat flux between Scotland and Greenland.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2017JC013350
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    The impact of Agulhas leakage on the central water masses in the Benguela upwelling system from a high‐resolution ocean simulation (2018)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 123 . pp. 9416-9428.
    Details
    Publication Date: 2021-02-08
    Description: We analyze the contribution of the Agulhas Current on the central water masses of the Benguela upwelling system (BUS) over the last decades in a high-resolution ocean simulation driven by atmospheric reanalysis. The BUS is an Eastern Boundary Upwelling System where upwelling of cold nutrient-rich water favors biomass growth. The two distinct subregions, North and South Benguela, differ in nutrient and oxygen properties of the upwelling water mass. Our analysis indicates that the contribution of Agulhas water to the upwelling is very strong in both subregions. Although the water masses feeding the upwelling have a common origin, their pathways are distinct in both regions. Whereas for the central waters of South Benguela the path is rather direct from where it is formed, the central waters of North Benguela takes a longer route through the equatorial current system. Not only the travel time from the Agulhas Current to the BUS is longer but also the central water mass is twice as old for the northern part when compared to the southern. Our analysis traces the pathways, history, and origin of the central water masses feeding upwelling in the BUS and emphasizes the direct impact of the Agulhas Current on the upwelling region. The variability of that link between the Indian Ocean and the South Atlantic is likely to change the nutrient and oxygen content, as well as temperature and salinity of the water masses in the upwelling region.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2018JC014218
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia (2018)
    Wiley
    In:  Global Ecology and Biogeography, 27 (7). pp. 814-827.
    Details
    Publication Date: 2022-01-21
    Description: Aim: Invasive species are of increasing global concern. Nevertheless, the mechanisms driving further distribution after the initial establishment of non‐native species remain largely unresolved, especially in marine systems. Ocean currents can be a major driver governing range occupancy, but this has not been accounted for in most invasion ecology studies so far. We investigate how well initial establishment areas are interconnected to later occupancy regions to test for the potential role of ocean currents driving secondary spread dynamics in order to infer invasion corridors and the source–sink dynamics of a non‐native holoplanktonic biological probe species on a continental scale. Location: Western Eurasia. Time period: 1980s–2016. Major taxa studied: ‘Comb jelly’ Mnemiopsis leidyi. Methods: Based on 12,400 geo‐referenced occurrence data, we reconstruct the invasion history of M. leidyi in western Eurasia. We model ocean currents and calculate their stability to match the temporal and spatial spread dynamics with large‐scale connectivity patterns via ocean currents. Additionally, genetic markers are used to test the predicted connectivity between subpopulations. Results: Ocean currents can explain secondary spread dynamics, matching observed range expansions and the timing of first occurrence of our holoplanktonic non‐native biological probe species, leading to invasion corridors in western Eurasia. In northern Europe, regional extinctions after cold winters were followed by rapid recolonizations at a speed of up to 2,000 km per season. Source areas hosting year‐round populations in highly interconnected regions can re‐seed genotypes over large distances after local extinctions. Main conclusions: Although the release of ballast water from container ships may contribute to the dispersal of non‐native species, our results highlight the importance of ocean currents driving secondary spread dynamics. Highly interconnected areas hosting invasive species are crucial for secondary spread dynamics on a continental scale. Invasion risk assessments should consider large‐scale connectivity patterns and the potential source regions of non‐native marine species.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: other
    Format: text
    DOI: 10.1111/geb.12742
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    The Deep Western Boundary Current in the Labrador Sea From Observations and a High-Resolution Model (2018)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2022-03-09
    Description: Long‐term observations from a 17 year long mooring array at the exit of the Labrador Sea at 53°N are compared to the output of a high‐resolution model (VIKING20). Both are analyzed to define robust integral properties on basin and regional scale, which can be determined and evaluated equally well. While both, the observations and the model, show a narrow DWBC cyclonically engulfing the Labrador Sea, the model's boundary current system is more barotropic than in the observations and spectral analysis indicates stronger monthly to interannual transport variability. Compared to the model, the observations show a stronger density gradient, hence a stronger baroclinicity, from center to boundary. Despite this, the observed temporal evolution of the temperature in the central Labrador Sea is reproduced. The model results yield a mean export of North Atlantic Deep Water (NADW) (33.0 +/‐ 5.7 Sv), which is comparable to the observed transport (31.2 +/‐ 5.5 Sv) at 53°N. The results also include a comparable spatial pattern and March mixed layer depth in the central Labrador Sea (maximum depth ∼ 2000 m). During periods containing enhanced deep convection (1990's) our analyses show increased correlation between LSW and LNADW model transport at 53°N. Our results indicate that the transport variability in LSW and LNADW at 53°N is a result of a complex modulation of wind stress and buoyancy forcing on regional and basin wide scale.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Agulhas Current Meanders Facilitate Shelf-Slope Exchange on the Eastern Agulhas Bank (2018)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2022-03-09
    Description: Large solitary meanders are arguably the dominant mode of variability in the Agulhas Current. Observational studies have shown that these large meanders are associated with strong upwelling velocities and affect the shelf circulation for over 100 days per year. Here 10-year time series from two ocean general circulation models are used to create a composite picture of the Agulhas Current and its interactions with the shelf circulation in meandering and nonmeandering modes. Both models show good agreement with the size, propagation speed, and frequency of observed meanders. These composite meanders are then used to examine the response of shelf waters to the onset of large meanders, with the use of model output enabling the dynamics at depth to be explored. Results show a composite mean warming of up to 3°C of depth-averaged temperature along the shelf edge associated with an intrusion of the current jet onto the shelf driven by an intensification of the flow along the leading edge of large meanders. However, this intensification of flow results in cooling of bottom waters, driving cold events at the shelf break of 〈10°C at 100 m. Thus, the intensification of the current jet associated with large meander events appears to drive strong up and downwelling events across the inshore front of the Agulhas Current, facilitating shelf-slope exchange.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Lagrangian ocean analysis : fundamentals and practices (2018)
    Elsevier
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ocean Modelling 121 (2018): 49-75, doi:10.1016/j.ocemod.2017.11.008.
    Description: Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.
    Description: EvS has received funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (grant agreement No 715386). This research for PJW was supported as part of the Energy Exascale Earth System Model (E3SM) project, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. Funding for HFD was provided by Grant No. DE-SC0012457 from the US Department of Energy. PB acknowledges support for this work from NERC grant NE/R011567/1. SFG is supported by NERC National Capability funding through the Extended Ellett Line Programme.
    Keywords: Ocean circulation ; Lagrangian analysis ; Connectivity ; Particle tracking ; Future modelling
    Repository Name: Woods Hole Open Access Server
    Type: Article
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