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Registros recuperados: 25
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Potential Vorticity diagnostics based on balances between volume integral and boundary conditions ArchiMer
Morel, Yves; Gula, Jonathan; Ponte, Aurelien.
Taking advantage of alternative expressions for potential vorticity (PV) in divergence forms, we derive balances between volume integral of PV and boundary conditions, that are then applied to practical computations of PV: • we propose a new method for diagnosing the Ertel potential vorticity from model output, that preserves the balances; • we show how the expression of PV can be derived in general coordinate systems. This is here emphasised with isopycnic coordinates by generalising the PV expression to the general Navier-Stokes equations; • we propose a generalised derivation for the Haynes-McIntyre impermeability theorem, which highlights the role of the bottom boundary condition choice (e.g. no-slip vs free-slip) and mixing near the bottom boundary...
Tipo: Text Palavras-chave: Potential vorticity; Boundary conditions; General circulation; Vortex; Fronts; Boundary layers.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00494/60525/63988.pdf
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Internal tide cycle and topographic scattering over the North Mid‐Atlantic Ridge ArchiMer
Lahaye, Noe; Gula, Jonathan; Roullet, Guillaume.
Internal tides are a predominant source of high‐frequency variability and diapycnal mixing in the ocean. Understanding their dynamics and lifecycle is necessary to better understand their role in the ocean circulation. In this paper, we describe and quantify internal tide generation, propagation and dissipation in a sector of the North Mid‐Atlantic Ridge, using high‐resolution numerical simulations with realistic bathymetry and stratification. We show that the generation and dissipation of internal tides, as well as the distribution of internal tides amongst vertical modes, exhibit high spatial variability. We find that topographic scattering leads to a significant transfer of energy towards high vertical modes and thereby enhances internal tide...
Tipo: Text Palavras-chave: Energy dissipation & Mixing; Internal tides; Internal waves; Topographic scattering.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00658/77003/78259.pdf
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Interaction of the Gulf Stream with small scale topography: a focus on lee waves ArchiMer
De Marez, Charly; Lahaye, Noe; Gula, Jonathan.
The generation of lee waves in the Gulf Stream along the U.S. seaboard is investigated using high resolution realistic simulations. The model reproduces the surface signature of the waves, which compares favourably with observations from satellite sun glitter images in the region. In particular, a large number of internal waves are observed above the Charleston Bump. These waves match well with the linear theory describing topographically-generated internal waves, which can be used to estimate the associated vertical transport of momentum and energy extracted from the mean flow. Finally, small scale topographic features are shown to have a significant impact on the mean flow in this region of the Gulf Stream, and the specific role of lee waves in this...
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Ano: 2020 URL: https://archimer.ifremer.fr/doc/00609/72075/70786.pdf
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Submesoscale streamers exchange water on the north wall of the Gulf Stream ArchiMer
Klymak, Jody M.; Shearman, R. Kipp; Gula, Jonathan; Lee, Craig M.; D'Asaro, Eric A.; Thomas, Leif N.; Harcourt, Ramsey R.; Shcherbina, Andrey Y.; Sundermeyer, Miles A.; Molemaker, Jeroen; Mcwilliams, James C..
The Gulf Stream is a major conduit of warm surface water from the tropics to the subpolar North Atlantic. Here we observe and simulate a submesoscale (<20km) mechanism by which the Gulf Stream exchanges water with subpolar water to the north. Along isopycnals, the front has a sharp compensated temperature-salinity contrast, with distinct mixed water between the two water masses 2 and 4km wide. This mixed water does not increase downstream despite substantial energy available for mixing. A series of streamers detrain this water at the crest of meanders. Subpolar water replaces the mixed water and resharpens the front. The water mass exchange accounts for a northward flux of salt of 0.5-2.5 psum(2)s(-1), (large-scale diffusivity O (100m(2)s(-1))). This is...
Tipo: Text Palavras-chave: Ocean mixing; Gulf Stream; Submesoscale mixing; Eddies.
Ano: 2016 URL: https://archimer.ifremer.fr/doc/00600/71201/69570.pdf
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The life cycle of submesoscale eddies generated by topographic interactions ArchiMer
Morvan, Mathieu; L'Hégaret, Pierre; Carton, Xavier; Gula, Jonathan; Vic, Clement; Sokolovskiy, Mikhail; Koshel, Konstantin.
The Persian Gulf Water and Red Sea Water are salty and dense waters recirculating at subsurface in the Gulf of Oman and the Gulf of Aden respectively, under the influence of mesoscale eddies which dominate the surface flow in both semi-enclosed basins. In situ measurements combined with altimetry indicate that the Persian Gulf Water is driven by mesoscale eddies in the form of filaments and submesoscale structures. In this paper, we study the formation and the life cycle of intense submesoscale vortices and their impact on the spread of Persian Gulf Water and Red Sea Water. We use a three-dimensional hydrostatic model with submesoscale-resolving resolution to study the evolution of submesoscale vortices. Our configuration is an idealized version of the...
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Ano: 2019 URL: https://archimer.ifremer.fr/doc/00589/70153/68140.pdf
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Submesoscale Coherent Vortices in the Gulf Stream ArchiMer
Gula, Jonathan; Blacic, Tanya M.; Todd, Robert E..
Seismic images and glider sections of the Gulf Stream front along the U.S. eastern seaboard capture deep, lens‐shaped submesoscale features. These features have radii of 5–20 km, thicknesses of 150–300 m, and are located at depths greater than 500 m. These are typical signatures of anticyclonic submesoscale coherent vortices. A submesoscale‐resolving realistic simulation, which reproduces submesoscale coherent vortices with the same characteristics, is used to analyze their generation mechanism. Submesoscale coherent vortices are primarily generated where the Gulf Stream meets the Charleston Bump, a deep topographic feature, due to the frictional effects and intense mixing in the wake of the topography. These submesoscale coherent vortices can transport...
Tipo: Text Palavras-chave: Submesoscale coherent vortices; Glider; Seismic observations; Gulf Stream; Topographic interactions; Charleston Bump.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00484/59597/62599.pdf
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The Gulf Stream North Wall: Ageostrophic Circulation and Frontogenesis ArchiMer
Mcwilliams, James C.; Gula, Jonathan; Molemaker, Maarten Jeroen.
Eastward zonal jets are common in the ocean and atmosphere, for example, the Gulf Stream and jet stream. They are characterized by atypically strong horizontal velocity, baroclinic vertical structure with an upward flow intensification, large change in the density stratification meridionally across the jet, large-scale meanders around a central latitude, narrow troughs and broad crests, and a sharp and vertically sloping northern (poleward) "wall" defined by horizontal maxima in the lateral gradients of both velocity and density. Measurements and realistic oceanic simulations show these features in the Gulf Stream downstream from its western boundary separation point. A diagnostic theory based on the conservative balance equations is developed to calculate...
Tipo: Text Palavras-chave: Ageostrophic circulations; Frontogenesis/frontolysis; Ocean models.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00486/59786/62925.pdf
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CROSSROAD. Climatic ROle of Subpolar Slopes: a Regional Observational Array off NewfoundlanD ArchiMer
Desbruyeres, Damien; Mercier, Herle; Thierry, Virginie; Lherminier, Pascale; Gula, Jonathan; Cyr, F; Kieke, D; Holliday, P; Smeed, D.
An observational experimental setup will be proposed to investigate the dynamics and thermodynamics of the deep western boundary current in the “transition zone” of the North Atlantic, around Flemish Cap, Newfoundland. Located between the international RAPID and OSNAP mooring arrays, this region represents a unique choke point for most of the North Atlantic large-scale currents and water masses involved in the Atlantic Meridional Overturning Circulation (AMOC). Horizontal export and latitudinal coherence, water mass transformation and vertical motions, as well as shelf-slope-interior exchanges will be studied with repeat hydrography, moorings, drifting and profiling floats, and gliders. Multidisciplinary approaches are likely, including biogeochemistry and...
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Ano: 2019 URL: https://archimer.ifremer.fr/doc/00503/61502/65316.pdf
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Deep Currents in the Rift Valley of the North Mid-Atlantic Ridge ArchiMer
Lahaye, Noe; Gula, Jonathan; Thurnherr, Andreas M.; Reverdin, Gilles; Bouruet-aubertot, Pascale; Roullet, Guillaume.
Over mid-ocean ridges, the interaction between the currents and the topography gives rise to complex flows, which drive the transport properties of biogeochemical constituents, and especially those associated with hydrothermal vents, thus impacting associated ecosystems. This paper describes the circulation in the rift valley along the Azores sector of the North Mid-Atlantic Ridge, using a combination of in-situ data from several surveys and realistic high-resolution modeling. It confirms the presence of a mean deep current with an up-valley branch intensified along the right inner flank of the valley (looking downstream), and a weaker down-valley branch flowing at shallower depth along the opposite flank. The hydrographic properties of the rift-valley...
Tipo: Text Palavras-chave: Deep currents; Transport; Deep turbulence; Internal waves and tides; Realistic modeling; In situ observation.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00584/69630/67486.pdf
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The Submesoscale Kinetic Energy Cascade: Mesoscale Absorption of Submesoscale Mixed Layer Eddies and Frontal Downscale Fluxes ArchiMer
Schubert, René; Gula, Jonathan; Greatbatch, Richard J.; Baschek, Burkard; Biastoch, Arne.
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 wintertime 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...
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Ano: 2020 URL: https://archimer.ifremer.fr/doc/00644/75652/76523.pdf
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Dispersion of deep-sea hydrothermal vent effluents and larvae by submesoscale and tidal currents ArchiMer
Vic, Clement; Gula, Jonathan; Roullet, Guillaume; Pradillon, Florence.
Deep-sea hydrothermal vents provide sources of geochemical materials that impact the global ocean heat and chemical budgets, and support complex biological communities. Vent effluents and larvae are dispersed and transported long distances by deep ocean currents, but these currents are largely undersampled and little is known about their variability. Submesoscale (0.1–10 km) currents are known to play an important role for the dispersion of biogeochemical materials in the ocean surface layer, but their impact for the dispersion in the deep ocean is unknown. Here, we use a series of nested regional oceanic numerical simulations with increasing resolution (from δx=6km to δx=0.75km) to investigate the structure and variability of highly-resolved deep currents...
Tipo: Text Palavras-chave: Submesoscales; Tides; Hydrothermal vent; Lagrangian dispersion; Lucky Strike; Mid-Atlantic Ridge; Connectivity; Bathymodiolus.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00419/53001/53949.pdf
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Generation of submesoscale frontal eddies in the Agulhas Current ArchiMer
Tedesco, Pauline; Gula, Jonathan; Ménesguen, Claire; Penven, Pierrick; Krug, M..
This study addresses the dynamics of the Agulhas inshore front in the submesoscale range upstream of 26°E. Submesoscale frontal eddies are observed in the vicinity of Port Elizabeth (26°E) from satellite images and in observations collected from under‐water gliders. Using a submesoscale‐resolving numerical model (dx ~ 0.75 km) we are able to simulate similar submesoscale eddies. Barotropic instability is confirmed as the generation mechanism by a 1D linear stability analysis and an eddy kinetic energy budget. Kinetic energy is transferred from the mean flow to the eddies through the mean horizontal shear, which is a signature of barotropic instability. When the Agulhas Current is in a non‐meandering state, submesoscale eddy generation is a recurrent...
Tipo: Text Palavras-chave: Submesoscale; Numerical Modelling; Barotropic Instability; Agulhas Current; Frontal Eddies.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00514/62520/66827.pdf
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Topographic generation of submesoscale centrifugal instability and energy dissipation ArchiMer
Gula, Jonathan; Molemaker, Maarten Jeroen; Mcwilliams, James C..
Most of the ocean kinetic energy is contained in the large scale currents and the vigorous geostrophic eddy field, at horizontal scales of order 100 km. To achieve equilibrium the geostrophic currents must viscously dissipate their kinetic energy at much smaller scale. However, geostrophic turbulence is characterized by an inverse cascade of energy towards larger scale, and the pathways of energy toward dissipation are still in question. Here, we present a mechanism, in the context of the Gulf Stream, where energy is transferred from the geostrophic flow to submesoscale wakes through anticyclonic vertical vorticity generation in the bottom boundary layer. The submesoscale turbulence leads to elevated local dissipation and mixing outside the oceanic...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00357/46814/46679.pdf
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Control and Stabilization of the Gulf Stream by Oceanic Current Interaction with the Atmosphere ArchiMer
Renault, Lionel; Molemaker, Maarten Jeroen; Gula, Jonathan; Masson, Sebastien; Mcwilliams, James C..
The Gulf Stream (GS) is known to have a strong influence on climate, for example, by transporting heat from the tropics to higher latitudes. Although the GS transport intensity presents a clear interannual variability, satellite observations reveal its mean path is stable. Numerical models can simulate some characteristics of the mean GS path, but persistent biases keep the GS separation and postseparation unstable and therefore unrealistic. This study investigates how the integration of ocean surface currents into the ocean–atmosphere coupling interface of numerical models impacts the GS. The authors show for the first time that the current feedback, through its eddy killing effect, stabilizes the GS separation and postseparation, resolving long-lasting...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00358/46879/46760.pdf
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Barotropic vorticity balance of the North Atlantic subpolar gyre in an eddy-resolving model ArchiMer
Le Corre, Mathieu; Gula, Jonathan; Tréguier, Anne-marie.
The circulation in the North Atlantic subpolar gyre is complex and strongly influenced by the topography. The gyre dynamics are traditionally understood as the result of a topographic Sverdrup balance, which corresponds to a first-order balance between the planetary vorticity advection, the bottom pressure torque, and the wind stress curl. However, these dynamics have been studied mostly with non-eddy-resolving models and a crude representation of the bottom topography. Here we revisit the barotropic vorticity balance of the North Atlantic subpolar gyre using a new eddy-resolving simulation (with a grid space of ≈2 km) with topography-following vertical coordinates to better represent the mesoscale turbulence and flow–topography interactions. Our findings...
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Ano: 2020 URL: https://archimer.ifremer.fr/doc/00629/74062/73537.pdf
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Sea‐surface signature of internal tides ArchiMer
Lahaye, Noe; Gula, Jonathan; Roullet, Guillaume.
The upper ocean is energetic at scales below the Rossby deformation radius owing to the existence of internal waves and submesoscale fronts and vortices. These contribute significantly to energy dissipation, tracer mixing and exchanges between the ocean surface layer, the ocean interior, and the atmospheric boundary layer. Internal waves and submesoscale motions both undergo strong spatial and seasonal variations, driven by different mechanisms. Here, we investigate the sea surface signature of internal waves and its seasonality using linear wave theory and a high‐resolution realistic simulation. In summer, internal waves are greatly amplified near the surface mostly due to a thin mixed layer bounded by a seasonal pycnocline. This surface amplification is...
Tipo: Text Palavras-chave: Internal tide; Submesosacle dynamics; Seasonality.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00486/59746/62847.pdf
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Dampening of Submesoscale Currents by Air-Sea Stress Coupling in the Californian Upwelling System ArchiMer
Renault, Lionel; Mcwilliams, James C.; Gula, Jonathan.
Oceanic submesoscale currents (SMCs) occur on an scale of 0.1-10 km horizontally and have a large influence on the oceanic variability and on ecosystems. At the mesoscale (10-250 km), oceanic thermal and current feedbacks are known to have a significant influence on the atmosphere and on oceanic dynamics. However, air-sea interactions at the submesoscale are not well known because the small size of SMCs presents observational and simulation barriers. Using high-resolution coupled oceanic and atmospheric models for the Central California region during the upwelling season, we show that the current feedback acting through the surface stress dominates the thermal feedback effect on the ocean and dampens the SMC variability by approximate to 17% +/- 4%. As for...
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Ano: 2018 URL: https://archimer.ifremer.fr/doc/00456/56804/58672.pdf
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Small-scale open-ocean currents have large effects on wind-wave heights ArchiMer
Ardhuin, Fabrice; Gille, Sarah T.; Menemenlis, Dimitris; Rocha, Cesar B.; Rascle, Nicolas; Chapron, Bertrand; Gula, Jonathan; Molemaker, Jeroen.
Tidal currents and large-scale oceanic currents are known to modify ocean wave properties, causing extreme sea states that are a hazard to navigation. Recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies, fronts and filaments at scales 10 to 100∼km. Based on realistic numerical models, we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km, including important variations down to 10 km. Model results are consistent with wave height variations along satellite altimeter tracks, resolved at scales larger than 50 km. The spectrum of significant wave heights is found to be of the order of 70〈Hs〉2/(g2〈Tm0,-1〉2) times...
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Ano: 2017 URL: http://archimer.ifremer.fr/doc/00382/49328/49708.pdf
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Effects of the submesoscale on the potential vorticity budget of ocean mode waters ArchiMer
Wenegrat, Jacob O.; Thomas, Leif N.; Gula, Jonathan; Mcwilliams, James C..
Non-conservative processes change the potential vorticity (PV) of the upper ocean, and later, through the subduction of surface waters into the interior, affect the general ocean circulation. Here we focus on how boundary layer turbulence, in the presence of submesoscale horizontal buoyancy gradients, generates a source of potential vorticity at the ocean surface through a balance known as the Turbulent ThermalWind. This source of PV injection at the submesoscale can be of similar magnitude to PV fluxes from the wind and surface buoyancy fluxes, and hence can lead to a net injection of PV onto outcropped isopycnals even during periods of surface buoyancy loss. The significance of these dynamics is illustrated using a high-resolution realistic model of the...
Tipo: Text Palavras-chave: Ageostrophic circulations; Atmosphere-ocean interaction; Fronts; Ocean dynamics; Potential vorticity; Boundary layer.
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00452/56347/57937.pdf
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A Persistent Deep Anticyclonic Vortex in the Rockall Trough Sustained by Anticyclonic Vortices Shed From the Slope Current and Wintertime Convection ArchiMer
Smilenova, Angelina; Gula, Jonathan; Le Corre, Mathieu; Houpert, Loïc; Reecht, Yves.
Tipo: Text Palavras-chave: Mesoscale eddy; Eddy merger; Instability; Potential vorticity transformations; Topographic effects; Water masses mixing; Rockall Trough.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00655/76734/77881.pdf
Registros recuperados: 25
Primeira ... 12 ... Última
 

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