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  • AGU (American Geophysical Union)  (19)
  • Springer  (8)
  • 2020-2024  (13)
  • 2005-2009  (14)
  • 1
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    Uptake and spreading of anthropogenic trace gases in a eddy-permitting model of the Atlantic Ocean (2007)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 112 . C09017.
    Details
    Publication Date: 2018-04-19
    Description: An eddy-permitting circulation model of the Atlantic Ocean was used to study the effect of mesoscale processes on the uptake and spreading of anthropogenic CO2 and CFC-11. A comparison with a coarser-resolution model version shows anthropogenic tracer distributions with qualitatively similar patterns, but much more structure (e.g., stronger longitudinal gradients) in the eddy-permitting model, improving the agreement with observations. The better representation of the formation of water masses such as subpolar-mode water in the eddy-permitting model has an influence on the distribution of anthropogenic CO2 over density classes, but no influence on the total inventory taken up. In the subpolar Atlantic, the air-sea flux of CFC-11 is dominated by deep-water formation, while the air-sea flux of anthropogenic CO2 extends over a larger part of the subpolar gyre and has a clear association with North Atlantic surface currents. An in-depth analysis of the mechanisms shaping this distribution showed that the entrainment of water from below into the mixed layer determines the structure in the subpolar North Atlantic, whereas the temporal correlation between surface heat fluxes and mixed-layer depth is more important in the subtropical gyre. The northward, integrated heat and anthropogenic CO2 transports in midlatitudes are closely correlated on seasonal to interannual timescales. This has implications for using the ongoing monitoring arrays of the thermohaline circulation for estimation of the transport of anthropogenic CO2.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2006JC003966
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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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
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    The Agulhas system as a key region of the global oceanic circulation (2006)
    Springer
    In:  In: High Performance Computing on Vector Systems. , ed. by Resch, M. Springer, Berlin, pp. 163-169. ISBN 978-3-540-29124-4
    Details
    Publication Date: 2017-04-06
    Type: Book chapter , PeerReviewed
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    OceanRep: Book chapter
  • 4
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    Signal propagation related to the North Atlantic Overturning (2005)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 32 . L09602.
    Details
    Publication Date: 2018-03-28
    Description: Changes of the meridional overturning circulation (MOC) due to surface heat flux variability related to the North Atlantic Oscillation (NAO) are analyzed in various ocean models, i.e., eddying and non‐eddying cases. A prime signature of the forcing is variability of the winter‐time convection in the Labrador Sea. The associated changes in the strength of the MOC near the subpolar front (45°N) are closely related to the NAO‐index, leading MOC anomalies by about 2–3 years in both the eddying and non‐eddying simulation. Further south the speed of the meridional signal propagation depends on model resolution. With lower resolution (non‐eddying case, 4/3° resolution) the MOC signal propagates equatorward with a mean speed of about 0.6 cm/s, similar as spreading rates of passive tracer anomalies. Eddy‐permitting experiments (1/3°) show a significantly faster propagation, with speeds corresponding to boundary waves, thus leading to an almost in‐phase variation of the MOC transport over the subtropical to subpolar North Atlantic.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2004GL021002
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Decadal to Multidecadal Variability of the Atlantic MOC: Mechanisms and Predictability (2007)
    AGU (American Geophysical Union)
    In:  In: Ocean Circulation: Mechanisms and Impacts - Past and Future Changes of the Ocean's Meridional Overturning. , ed. by Schmittner, A., Chiang, J. and Hemming, S. AGU Monograph, 173 . AGU (American Geophysical Union), Washington D.C., pp. 149-166. ISBN 978-0-87590-438-2
    Details
    Publication Date: 2020-07-28
    Description: The dynamics and predictability of the decadal to multidecadal Atlantic merid­ional overturning circulation (MOC) variability are described from observations and models. The investigation focuses on two modes that involve the MOC: One mode exhibits a quasi-decadal period, while the other is multidecadal. The two modes have completely different underlying dynamics, which is reflected in their rather different spatial characteristics. While the quasi-decadal mode represents a damped mode of the coupled ocean-atmosphere system, the multidecadal mode can be basically understood as the MOC response to the multidecadal forcing by the North Atlantic Oscillation (NAO). "Perfect model" predictability studies indicate a rather high predictability potential of the MOC variability on decadal timescales. Variations of the MOC are associated with variations in the meridional heat trans­port that drive sea surface temperature (SST) anomalies. SST anomalies in the North Atlantic thus exhibit a similar decadal predictability potential as the MOC. The decadal predictability carries over to the atmosphere. The probability density function of European surface air temperature anomalies, for instance, changes sig­nificantly with the state of the MOC. A reconstruction of the MOC for the 20th cen­tury from observed SSTs shows considerable variability on decadal timescales, but no strong sustained long-term trend. Furthermore, an assessment of the observed hydrographical changes in the Nordic Seas, with the aid of ocean general circula­tion model experiments and the analysis of recent scenario integrations with global climate models, indicates that the expected anthropogenic weakening of the MOC may not exceed the level of the internal variability within the next decades.
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 6
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    The Agulhas System as a Prime Example for the Use of Nesting Capabilities in Ocean Modelling (2009)
    Springer
    In:  In: High Performance Computing on Vector Systems 2009. , ed. by Resch, M., Roller, S., Benkert, K., Galle, M., Bez, W. and Kobayashi, H. Springer, Berlin, pp. 191-198. ISBN 978-3642039126
    Details
    Publication Date: 2012-07-05
    Type: Book chapter , PeerReviewed
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    OceanRep: Book chapter
  • 7
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    The Agulhas System as a Key Region of the Global Oceanic Circulation (2008)
    Springer
    Details
    Publication Date: 2023-11-08
    Description: The Agulhas system all the interface between the Indian and Atlantic Ocean is an important region in the global oceanic circulation with a recognized key role in global climate and climate change. The simulation of the Agulhas system was performed by a high-resolution regional model nested in a global coarse-resolution ocean model. It is shown that this model simulates all characteristics of the Agulhas regime in a highly realistic manner. Due to the two-way coupling of both models the importance of the Agulhas leakage on the large-scale thermohaline circulation was demonstrated.
    Type: Book chapter , PeerReviewed
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    OceanRep: Book chapter
  • 8
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    Late 20th Century Indian Ocean Heat Content Gain Masked by Wind Forcing (2020)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-02-08
    Description: Rapid increases in upper 700‐m Indian Ocean heat content (IOHC) since the 2000s have focused attention on its role during the recent global surface warming hiatus. Here, we use ocean model simulations to assess distinct multidecadal IOHC variations since the 1960s and explore the relative contributions from wind stress and buoyancy forcing regionally and with depth. Multidecadal wind forcing counteracted IOHC increases due to buoyancy forcing from the 1960s to the 1990s. Wind and buoyancy forcing contribute positively since the mid‐2000s, accounting for the drastic IOHC change. Distinct timing and structure of upper ocean temperature changes in the eastern and western Indian Ocean are linked to the pathway how multidecadal wind forcing associated with the Interdecadal Pacific Oscillation is transmitted and affects IOHC through local and remote winds. Progressive shoaling of the equatorial thermocline—of importance for low‐frequency variations in Indian Ocean Dipole occurrence—appears to be dominated by multidecadal variations in wind forcing.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    The Atlantic Meridional Overturning Circulation in High‐Resolution Models (2020)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2023-02-08
    Description: The Atlantic meridional overturning circulation (AMOC) represents the zonally integrated stream function of meridional volume transport in the Atlantic Basin. The AMOC plays an important role in transporting heat meridionally in the climate system. Observations suggest a heat transport by the AMOC of 1.3 PW at 26°N—a latitude which is close to where the Atlantic northward heat transport is thought to reach its maximum. This shapes the climate of the North Atlantic region as we know it today. In recent years there has been significant progress both in our ability to observe the AMOC in nature and to simulate it in numerical models. Most previous modeling investigations of the AMOC and its impact on climate have relied on models with horizontal resolution that does not resolve ocean mesoscale eddies and the dynamics of the Gulf Stream/North Atlantic Current system. As a result of recent increases in computing power, models are now being run that are able to represent mesoscale ocean dynamics and the circulation features that rely on them. The aim of this review is to describe new insights into the AMOC provided by high-resolution models. Furthermore, we will describe how high-resolution model simulations can help resolve outstanding challenges in our understanding of the AMOC.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Resolving and Parameterising the Ocean Mesoscale in Earth System Models (2020)
    Springer
    Details
    Publication Date: 2023-02-08
    Description: Purpose of Review: Assessment of the impact of ocean resolution in Earth System models on the mean state, variability, and future projections and discussion of prospects for improved parameterisations to represent the ocean mesoscale. Recent Findings: The majority of centres participating in CMIP6 employ ocean components with resolutions of about 1 degree in their full Earth System models (eddy-parameterising models). In contrast, there are also models submitted to CMIP6 (both DECK and HighResMIP) that employ ocean components of approximately 1/4 degree and 1/10 degree (eddy-present and eddy-rich models). Evidence to date suggests that whether the ocean mesoscale is explicitly represented or parameterised affects not only the mean state of the ocean but also the climate variability and the future climate response, particularly in terms of the Atlantic meridional overturning circulation (AMOC) and the Southern Ocean. Recent developments in scale-aware parameterisations of the mesoscale are being developed and will be included in future Earth System models. Summary: Although the choice of ocean resolution in Earth System models will always be limited by computational considerations, for the foreseeable future, this choice is likely to affect projections of climate variability and change as well as other aspects of the Earth System. Future Earth System models will be able to choose increased ocean resolution and/or improved parameterisation of processes to capture physical processes with greater fidelity.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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