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| Registros recuperados: 25 | |
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| 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... |
| Tipo: Text |
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| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00357/46814/46679.pdf |
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| 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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| 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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| Buckingham, Christian; Gula, Jonathan; Carton, Xavier. |
| We continue our study of the role of curvature in modifying frontal stability. In Part I, we obtained an instability criterion valid for curved fronts and vortices in gradient wind balance (GWB): Φ′ = L′q′ < 0, where L′ and q′ are the nondimensional absolute angular momentum and Ertel potential vorticity (PV), respectively. In Part II, we investigate this criterion in a parameter space representative of low-Richardson-number fronts and vortices in GWB. An interesting outcome is that, for Richardson numbers near 1, anticyclonic flows increase in q′, while cyclonic flows decrease in q′, tending to stabilize anticyclonic and destabilize cyclonic flow. Although stability is marginal or weak for anticyclonic flow (owing to multiplication by L′), the... |
| Tipo: Text |
Palavras-chave: Eddies; Fronts; Instability; Ocean circulation; Potential vorticity; Frontogenesis/frontolysis; Vortices; Angular momentum. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00677/78919/81286.pdf |
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| 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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| 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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| 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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| 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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| 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... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00456/56804/58672.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00382/49328/49708.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00589/70153/68140.pdf |
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| Buckingham, Christian; Gula, Jonathan; Carton, Xavier. |
| In this study, we examine the role of curvature in modifying frontal stability. We first evaluate the classical criterion that the Coriolis parameter f multiplied by the Ertel potential vorticity (PV) q is positive for stable flow and that instability is possible when this quantity is negative. The first portion of this statement can be deduced from Ertel’s PV theorem, assuming an initially positive fq. Moreover, the full statement is implicit in the governing equation for the mean geostrophic flow, as the discriminant, fq, changes sign. However, for curved fronts in cyclogeostrophic or gradient wind balance (GWB), an additional term enters the discriminant owing to conservation of absolute angular momentum L. The resulting expression, (1 + Cu)fq < 0 or... |
| Tipo: Text |
Palavras-chave: Instability; Ocean dynamics; Potential vorticity; Turbulence; Frontogenesis/frontolysis; Fronts; Vortices; Angular momentum. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00677/78920/81288.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00644/75652/76523.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00609/72075/70786.pdf |
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| 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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| 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... |
| Tipo: Text |
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| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00358/46879/46760.pdf |
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| Registros recuperados: 25 | |
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