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Author Ali, A. ; Christensen, K.H. ; Breivik, Ø. ; Malila, M. ; Raj, R.P. ; Bertino, L. ; Chassignet, E.P. ; Bakhoday-Paskyabi, M.
Title A comparison of Langmuir turbulence parameterizations and key wave effects in a numerical model of the North Atlantic and Arctic Oceans Type $loc['typeJournal Article']
Year 2019 Publication Ocean Modelling Abbreviated Journal Ocean Modelling
Volume 137
Issue Pages 76-97
Keywords Langmuir mixing parameterization Mixed layer depth Sea surface temperature Ocean heat content Stokes penetration depth
Abstract Five different parameterizations of Langmuir turbulence (LT) effect are investigated in a realistic model of the North Atlantic and Arctic using realistic wave forcing from a global wave hindcast. The parameterizations mainly apply an enhancement to the turbulence velocity scale, and/or to the entrainment buoyancy flux in the surface boundary layer. An additional run is also performed with other wave effects to assess the relative importance of Langmuir turbulence, namely the Coriolis-Stokes forcing, Stokes tracer advection and wave-modified momentum fluxes. The default model (without wave effects) underestimates the mixed layer depth in summer and overestimates it at high latitudes in the winter. The results show that adding LT mixing reduces shallow mixed layer depth (MLD) biases, particularly in the subtropics all year-around, and in the Nordic Seas in summer. There is overall a stronger relative impact on the MLD during winter than during summer. In particular, the parameterization with the most vigorous LT effect causes winter MLD increases by more than 50% relative to a control run without Langmuir mixing. On the contrary, the parameterization which assumes LT effects on the entrainment buoyancy flux and accounts for the Stokes penetration depth is able to enhance the mixing in summer more than in winter. This parametrization is also distinct from the others because it restrains the LT mixing in regions of deep MLD biases, so it is the preferred choice for our purpose. The different parameterizations do not change the amplitude or phase of the seasonal cycle of heat content but do influence its long-term trend, which means that the LT can influence the drift of ocean models. The combined impact on water mass properties from the Coriolis-Stokes force, the Stokes drift tracer advection, and the wave-dependent momentum fluxes is negligible compared to the effect from the parameterized Langmuir turbulence.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1463-5003
ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 1001
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Author Guerra, L.A.A. ; Paiva, A.M. ; Chassignet, E.P.
Title On the translation of Agulhas rings to the western South Atlantic Ocean Type $loc['typeJournal Article']
Year 2018 Publication Deep Sea Research Part I: Oceanographic Research Papers Abbreviated Journal Deep Sea Research Part I: Oceanographic Research Papers
Volume 139
Issue Pages 104-113
Keywords
Abstract The shedding of Agulhas rings is the primary process connecting the Indian and Atlantic oceans. The rings transport warm and salty waters that feed the surface limb of the Atlantic Meridional Overturning Circulation. Early studies suggest that Agulhas rings decay and diffuse their contents within the South Atlantic subtropical gyre. In this paper, we update the ring census using an automated algorithm to detect and track eddies over more than 23 years of satellite altimetry data (1993-2016) and calculate their main characteristics. While 140 rings spawned from the Agulhas Retroflection, their following splitting and merging resulted in 74 long-lived rings that crossed the Walvis Ridge and translated towards the west. Eventually, three rings reached the western boundary. For one of them, we use in situ measurements to document its interaction with the Brazil Current and two cyclonic eddies, which resulted in a current velocity increase by three times. Although already hypothesized, this interaction had not been demonstrated with in situ evidence until now.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0967-0637
ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 994
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Author Xu, X. ; Chassignet, E.P. ; Firing, Y.L. ; Donohue, K.
Title Antarctic Circumpolar Current transport through Drake Passage: What can we learn from comparing high-resolution model results to observations? Type $loc['typeJournal Article']
Year 2020 Publication Journal of Geophysical Research: Oceans Abbreviated Journal J. Geophys. Res. Oceans
Volume 125
Issue 7
Pages
Keywords
Abstract Uncertainty exists in the time‐mean total transport of the Antarctic Circumpolar Current (ACC), the world�s strongest ocean current. The two most recent observational programs in Drake Passage, DRAKE and cDrake, yielded transports of 141 and 173.3 Sv, respectively. In this paper, we use a realistic 1/12° global ocean simulation to interpret these observational estimates and reconcile their differences. We first show that the modeled ACC transport in the upper 1000 m is in excellent agreement with repeat shipboard acoustic Doppler current profiler (SADCP) transects and that the exponentially decaying transport profile in the model is consistent with the profile derived from repeat hydrographic data. By further comparing the model results to the cDrake and DRAKE observations, we argue that the modeled 157.3 Sv transport, i.e. approximately the average of the cDrake and DRAKE estimates, is actually representative of the time‐mean ACC transport through the Drake Passage. The cDrake experiment overestimated the barotropic contribution in part because the array undersampled the deep recirculation southwest of the Shackleton Fracture Zone, whereas the surface geostrophic currents used in the DRAKE estimate yielded a weaker near‐surface transport than implied by the SADCP data. We also find that the modeled baroclinic and barotropic transports are not correlated, thus monitoring either baroclinic or barotropic transport alone may be insufficient to assess the temporal variability of the total ACC transport.
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Language Summary Language Original Title
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Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 1107
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Author Le Sommer, Julien ; Chassignet, E.P. ; Wallcraft, A. J.
Title Ocean Circulation Modeling for Operational Oceanography: Current Status and Future Challenges Type $loc['typeBook Chapter']
Year 2018 Publication New Frontiers in Operational Oceanography Abbreviated Journal
Volume Issue Pages 289-305
Keywords OCEAN MODELING ; OCEAN CIRCULATION ; PARAMETERIZATIONS
Abstract This chapter focuses on ocean circulation models used in operational oceanography, physical oceanography and climate science. Ocean circulation models area particular branch of ocean numerical modeling that focuses on the representation of ocean physical properties over spatial scales ranging from the global scale to less than a kilometer and time scales ranging from hours to decades. As such, they are an essential build-ing block for operational oceanography systems and their design receives a lot of attention from operational and research centers.
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Publisher GODAE OceanView
Place of Publication Tallahassee, FL
Editor Chassignet, E. P., A. Pascual, J. Tintoré, and J. Verron
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 948
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Author Davidson, F. ; Alvera-Azcárate, A. ; Barth, A. ; Brassington, G.B. ; Chassignet, E.P. ; Clementi, E. ; De Mey-Frémaux, P. ; Divakaran, P. ; Harris, C. ; Hernandez, F. ; Hogan, P. ; Hole, L.R. ; Holt, J. ; Liu, G. ; Lu, Y. ; Lorente, P. ; Maksymczuk, J. ; Martin, M. ; Mehra, A. ; Melsom, A. ; Mo, H. ; Moore, A. ; Oddo, P. ; Pascual, A. ; Pequignet, A.-C. ; Kourafalou, V. ; Ryan, A. ; Siddorn, J. ; Smith, G. ; Spindler, D. ; Spindler, T. ; Stanev, E.V. ; Staneva, J. ; Storto, A. ; Tanajura, C. ; Vinayachandran, P.N. ; Wan, L. ; Wang, H. ; Zhang, Y. ; Zhu, X. ; Zu, Z.
Title Synergies in Operational Oceanography: The Intrinsic Need for Sustained Ocean Observations Type $loc['typeJournal Article']
Year 2019 Publication Frontiers in Marine Science Abbreviated Journal Front. Mar. Sci.
Volume 6
Issue Pages
Keywords
Abstract Operational oceanography can be described as the provision of routine oceanographic information needed for decision-making purposes. It is dependent upon sustained research and development through the end-to-end framework of an operational service, from observation collection to delivery mechanisms. The core components of operational oceanographic systems are a multi-platform observation network, a data management system, a data assimilative prediction system, and a dissemination/accessibility system. These are interdependent, necessitating communication and exchange between them, and together provide the mechanism through which a clear picture of ocean conditions, in the past, present, and future, can be seen. Ocean observations play a critical role in all aspects of operational oceanography, not only for assimilation but as part of the research cycle, and for verification and validation of products. Data assimilative prediction systems are advancing at a fast pace, in tandem with improved science and the growth in computing power. To make best use of the system capability these advances would be matched by equivalent advances in operational observation coverage. This synergy between the prediction and observation systems underpins the quality of products available to stakeholders, and justifies the need for sustained ocean observations. In this white paper, the components of an operational oceanographic system are described, highlighting the critical role of ocean observations, and how the operational systems will evolve over the next decade to improve the characterization of ocean conditions, including at finer spatial and temporal scales.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 2296-7745
ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 1083
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Author Fox-Kemper, B. ; Adcroft, A. ; Böning, C.W. ; Chassignet, E.P. ; Curchitser, E. ; Danabasoglu, G. ; Eden, C. ; England, M.H. ; Gerdes, R. ; Greatbatch, R.J. ; Griffies, S.M. ; Hallberg, R.W. ; Hanert, E. ; Heimbach, P. ; Hewitt, H.T. ; Hill, C.N. ; Komuro, Y. ; Legg, S. ; Le Sommer, J. ; Masina, S. ; Marsland, S.J. ; Penny, S.G. ; Qiao, F. ; Ringler, T.D. ; Treguier, A.M. ; Tsujino, H. ; Uotila, P. ; Yeager, S.G.
Title Challenges and Prospects in Ocean Circulation Models Type $loc['typeJournal Article']
Year 2019 Publication Frontiers in Marine Science Abbreviated Journal Front. Mar. Sci.
Volume 6
Issue Pages
Keywords Southern Ocean ; Overturning Circulation: Regional sea level ; submesoscale ; ice shelves ; turbulence
Abstract We revisit the challenges and prospects for ocean circulation models following Griffies et al. (2010). Over the past decade, ocean circulation models evolved through improved understanding, numerics, spatial discretization, grid configurations, parameterizations, data assimilation, environmental monitoring, and process-level observations and modeling. Important large scale applications over the last decade are simulations of the Southern Ocean, the Meridional Overturning Circulation and its variability, and regional sea level change. Submesoscale variability is now routinely resolved in process models and permitted in a few global models, and submesoscale effects are parameterized in most global models. The scales where nonhydrostatic effects become important are beginning to be resolved in regional and process models. Coupling to sea ice, ice shelves, and high-resolution atmospheric models has stimulated new ideas and driven improvements in numerics. Observations have provided insight into turbulence and mixing around the globe and its consequences are assessed through perturbed physics models. Relatedly, parameterizations of the mixing and overturning processes in boundary layers and the ocean interior have improved. New diagnostics being used for evaluating models alongside present and novel observations are briefly referenced. The overall goal is summarizing new developments in ocean modeling, including how new and existing observations can be used, what modeling challenges remain, and how simulations can be used to support observations.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 2296-7745
ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 1011
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Author Dukhovskoy, D.S. ; Yashayaev, I. ; Proshutinsky, A. ; Bamber, J.L. ; Bashmachnikov, I.L. ; Chassignet, E.P. ; Lee, C.M. ; Tedstone, A.J.
Title Role of Greenland Freshwater Anomaly in the Recent Freshening of the Subpolar North Atlantic Type $loc['typeJournal Article']
Year 2019 Publication Journal of Geophysical Research: Oceans Abbreviated Journal J. Geophys. Res. Oceans
Volume 124
Issue 5
Pages 3333-3360
Keywords Greenland ice sheet melting ; freshwater anomaly ; subpolar North Atlantic ; subpolar gyre ; passive tracer numerical experiment ; freshwater budget
Abstract The cumulative Greenland freshwater flux anomaly has exceeded 5000 km3 since the 1990s. The volume of this surplus fresh water is expected to cause substantial freshening in the North Atlantic. Analysis of hydrographic observations in the subpolar seas reveal freshening signals in the 2010s. The sources of this freshening are yet to be determined. In this study, the relationship between the surplus Greenland freshwater flux and this freshening is tested by analyzing the propagation of the Greenland freshwater anomaly and its impact on salinity in the subpolar North Atlantic based on observational data and numerical experiments with and without the Greenland runoff. A passive tracer is continuously released during the simulations at freshwater sources along the coast of Greenland to track the Greenland freshwater anomaly. Tracer budget analysis shows that 44% of the volume of the Greenland freshwater anomaly is retained in the subpolar North Atlantic by the end of the simulation. This volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50�100 m. However, in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations. Therefore, the simulations suggest that the accelerated Greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of fresh water have contributed to the freshening. Impacts on salinity in the subpolar seas of the freshwater transport through Fram Strait and precipitation are discussed.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 2169-9275
ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 1029
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Author Rahaman, H. ; Srinivasu, U. ; Panickal, S. ; Durgadoo, J.V. ; Griffies, S.M. ; Ravichandran, M. ; Bozec, A. ; Cherchi, A. ; Voldoire, A. ; Sidorenko, D.. ; Chassignet, E.P. ; Danabasoglu, G. ; Tsujino, H. ; Getzlaff, K. ; Ilicak, M. ; Bentsen, M. ; Long, M.C. ; Fogli, P.G. ; Farneti, R. ; Danilov, S. ; Marsland, S.J. ; Valcke, S. ; Yeager, S.G. ; Wang, Q.
Title An assessment of the Indian Ocean mean state and seasonal cycle in a suite of interannual CORE-II simulations Type $loc['typeJournal Article']
Year 2020 Publication Ocean Modelling Abbreviated Journal Ocean Modelling
Volume 145
Issue Pages
Keywords
Abstract
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1463-5003
ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 1087
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Author LaCasce, J.H. ; Escartin, J. ; Chassignet, E.P. ; Xu, X.
Title Jet instability over smooth, corrugated and realistic bathymetry Type $loc['typeJournal Article']
Year 2018 Publication Journal of Physical Oceanography Abbreviated Journal J. Phys. Oceanogr.
Volume Issue Pages
Keywords
Abstract The stability of a horizontally- and vertically-sheared surface jet is examined, with a focus on the vertical structure of the resultant eddies. Over a flat bottom, the instability is mixed baroclinic/barotropic, producing strong eddies at depth which are characteristically shifted downstream relative to the surface eddies. Baroclinic instability is suppressed over a large slope for retrograde jets (with a flow anti-parallel to topographic wave propagation), and to a lesser extent for prograde jets (with flow parallel to topographic wave propagation), as seen previously. In such cases, barotropic (lateral) instability dominates if the jet is sufficiently narrow. This yields surface eddies whose size is independent of the slope but proportional to the jet width. Deep eddies still form, forced by interfacial motion associated with the surface eddies, but they are weaker than under baroclinic instability and are vertically aligned with the surface eddies. A sinusoidal ridge acts similarly, suppressing baroclinic instability and favoring lateral instability in the upper layer.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0022-3670
ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ user @
Serial 998
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Author Xu, X. ; Chassignet, E.P., Wang, F.
Title On the variability of the Atlantic meridional overturning circulation transports in coupled CMIP5 simulations Type $loc['typeJournal Article']
Year 2018 Publication Climate Dynamics Abbreviated Journal Clim Dyn.
Volume 51
Issue 11
Pages 6511-6531
Keywords NAO-AMOC ; CMIP5 ; NAO index ; AMOC index ; meridional pressure gradient ; magnitude ; structure change of the NAO.
Abstract The Atlantic meridional overturning circulation (AMOC) plays a fundamental role in the climate system, and long-term climate simulations are used to understand the AMOC variability and to assess its impact. This study examines the basic characteristics of the AMOC variability in 44 CMIP5 (Phase 5 of the Coupled Model Inter-comparison Project) simulations, using the 18 atmospherically-forced CORE-II (Phase 2 of the Coordinated Ocean-ice Reference Experiment) simulations as a reference. The analysis shows that on interannual and decadal timescales, the AMOC variability in the CMIP5 exhibits a similar magnitude and meridional coherence as in the CORE-II simulations, indicating that the modeled atmospheric variability responsible for AMOC variability in the CMIP5 is in reasonable agreement with the CORE-II forcing. On multidecadal timescales, however, the AMOC variability is weaker by a factor of more than 2 and meridionally less coherent in the CMIP5 than in the CORE-II simulations. The CMIP5 simulations also exhibit a weaker long-term atmospheric variability in the North Atlantic Oscillation (NAO). However, one cannot fully attribute the weaker AMOC variability to the weaker variability in NAO because, unlike the CORE-II simulations, the CMIP5 simulations do not exhibit a robust NAO-AMOC linkage. While the variability of the wintertime heat flux and mixed layer depth in the western subpolar North Atlantic is strongly linked to the AMOC variability, the NAO variability is not.
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Call Number COAPS @ rl18 @
Serial 981
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