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Registros recuperados: 15
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Cyclones and Anticyclones in Seismic Imaging 5
Barbosa Aguiar, A. C.; Menesguen, Claire; Le Gentil, Sylvie; Schopp, Richard; Carton, Xavier.
Nearly all the subsurface eddies detected in seismic imaging of sections in the northeast Atlantic have been assumed to be anticyclones containing Mediterranean Water (MW). Fewer MW cyclones have been observed and studied. In this study, the work of previous numerical studies is extended to investigate some characteristics of layering surrounding MW cyclones, using a primitive equation model with equal diffusivities for salinity and temperature to suppress the effects of double diffusion. It is shown that, after a stable state is reached, both anticyclones and cyclones display similar patterns of layering: stacked thin layers of high acoustic reflectivity located above and below the core of each vortex, which do not match isopycnals. The authors conclude...
Tipo: Text Palavras-chave: Geographic location/entity; North Atlantic Ocean; Circulation/ Dynamics; Small scale processes; Atm/Ocean Structure/ Phenomena; Eddies; Vortices; Observational techniques and algorithms; Acoustic measurements/effects; Models and modeling; Primitive equations model.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00281/39190/37746.pdf
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Destabilization of an oceanic meddy-like vortex: energy transfers and significance of numerical settings 5
Menesguen, Claire; Le Gentil, Sylvie; Marchesiello, P.; Ducousso, N..
The increase of computational capabilities led recent studies to implement very high resolution simulations that gave access to new scale interaction processes, particularly those associated with the transfer of energy from the oceanic mesoscales to smaller scales through an interior route to dissipation which is still under-explored. In this context, we study spin down simulations of a mesoscale interior vortex, unstable to a mixed baroclinic-barotropic instability. Even though the global energy is almost conserved, some energy is transferred down to dissipation scales during the development of instabilities. However, in our parameter regime, there is no substantial forward energy cascade sustained by unbalanced dynamics. Rather than exploring the...
Tipo: Text
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00435/54690/56128.pdf
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Diagnosis of vertical velocities in the upper ocean from high resolution sea surface height 5
Klein, Patrice; Isern-fontanet, Jordi; Lapeyre, Guillaume; Roullet, G.; Danioux, Eric; Chapron, Bertrand; Le Gentil, Sylvie; Sasaki, H..
A surface Quasi-Geostrophy based (eSQG) method to diagnose the vertical velocity field from Sea Surface Height (SSH) is assessed using high resolution simulations. These simulations concern a turbulent eddy field with large Rossby numbers and energetic wind-driven motions. Results indicate that low-frequency vertical velocities (and also horizontal motions) can be reconstructed within a range of scales between 20 km and 400 km from the surface down to 500 m. The only information needed is a single high-resolution SSH snapshot and information on the large-scale vertical stratification. Inertial motions are naturally filtered because they do not contaminate SSH as we demonstrate. These results are encouraging and further strengthen previous studies using the...
Tipo: Text
Ano: 2009 URL: http://archimer.ifremer.fr/doc/00000/11094/7418.pdf
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First transitions in circular Couette flow with axial stratification 5
Hua, Bach-lien; Le Gentil, Sylvie; Orlandi, P.
The first flow regimes which have been observed experimentally for a circular Couette flow with a stable, axial stratification in density are investigated through direct numerical simulations of the three-dimensional Navier-Stokes equations for a Boussinesq fluid. The setup of two concentric cylinders has a nondimensional gap width of epsilon=(b-a)/a=0.289; the outer cylinder is tired and the stratification in density in the axial direction is linear. The main effect of an axial density stratification is to reduce the height of the Taylor vortices and to cause the formation of density layers of small aspect ratio. For large enough Prandtl number, the primary bifurcation from circular Couette flow is found to be axisymmetric and of Hopf-type in the direct...
Tipo: Text
Ano: 1997 URL: http://archimer.ifremer.fr/doc/00336/44750/57508.pdf
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Impact of Small-Scale Structures on Two Energetic Dynamical Oceanic Regimes 5
Klein, Patrice; Hua, Bach-lien; Le Gentil, Sylvie; Sasaki, Hideharu.
The big challenge of the next decade for the oceanic sciences is to adopt a multi-scale approach because of the strong nonlinearity of the oceanic fluid. This can be undertaken only through numerical simulations with ultra-high resolution. Within this context, the purpose of our projects is to fully explore two energetic dynamical oceanic regimes that have a major impact on the general oceanic circulation: the mesoscale eddy regime at mid-latitudes and the equatorial regime. Expected results will help for the configuration of realistic numerical simulations to be performed in 2006 by the OFES group on the Earth Simulator and they should benefit to future climate models. These studies make use of the Primitive Equations model ROMS (Regional Ocean Modelling...
Tipo: Text Palavras-chave: Mesoscale oceanic eddies; Equatorial dynamics.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/00067/17783/15306.pdf
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Impact of Small-scale Structures on Two Energetic Dynamical Oceanic Regimes (2007) 5
Klein, Patrice; Hua, Bach-lien; Le Gentil, Sylvie; Fruman, Mark; Menesguen, Claire; Sasaki, Hideharu.
The big challenge of the next decade for the oceanic sciences is to adopt a multi-scale approach because of the strong nonlinearity of the oceanic fluid. This can be undertaken only through numerical simulations with ultra-high resolution. Within this context, the purpose of our project is to fully explore two energetic dynamical oceanic regimes that have a major impact on the general oceanic circulation: the mesoscale eddy regime at mid-latitudes and the equatorial regime. Results will help for the configuration of realistic numerical simulations to be performed in 2007-2008 by the OFES group on the Earth Simulator and also should benefit to future climate models. These studies make use of the Primitive Equations model ROMS (Regional Ocean Modelling...
Tipo: Text Palavras-chave: Mesoscale oceanic eddies; Equatorial dynamics.
Ano: 2007 URL: http://archimer.ifremer.fr/doc/00067/17784/15307.pdf
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Impact of small-scale structures on two energetic dynamical regimes 5
Klein, Patrice; Hua, Bach-lien; Le Gentil, Sylvie; Roullet, Guillaume; Fruman, Mark; Menesguen, Claire; Sasaki, Hideharu.
Tipo: Text
Ano: 2008 URL: http://archimer.ifremer.fr/doc/00067/17785/15308.pdf
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Layering and turbulence surrounding an anticyclonic oceanic vortex: in situ observations and quasi-geostrophic numerical simulations 5
Hua, Bach-lien; Menesguen, Claire; Le Gentil, Sylvie; Schopp, Richard; Marsset, Bruno; Aiki, Hidenori.
Evidence of persistent layering, with a vertical stacking of sharp variations in temperature, has been presented recently at the vertical and lateral periphery of energetic oceanic vortices through seismic imaging of the water column. The stacking has vertical scales ranging from a few metres up to 100 m and a lateral spatial coherence of several tens of kilometres comparable with the vortex horizontal size. Inside this layering, in situ data display a [k(h)(-5/3)k(h)(2)] scaling law of horizontal scales for two different quantities, temperature and a proxy for its vertical derivative, but for two different ranges of wavelengths, between 5 and 50 km for temperature and between 500 m and 5 km for its vertical gradient. In this study, we explore the dynamics...
Tipo: Text Palavras-chave: Geostrophic turbulence; Quasi; Geostrophic flows; Stratified flows.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00159/27070/25322.pdf
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Low-mode internal tide propagation in a turbulent eddy field 5
Dunphy, Michael; Ponte, Aurelien; Klein, Patrice; Le Gentil, Sylvie.
Understanding how internal tides distort and lose coherence as they propagate through the ocean has been identified as a key issue for interpreting data from the upcoming wide-swath altimeter mission SWOT. This study addresses that issue through the analysis of numerical experiments where a low mode internal tide propagates through a quasi-geostrophic turbulent jet. We present a set of reduced equations based on vertical mode projections that describe the dynamics of the low-mode internal tides as they propagate through the slower turbulent field. Diagnostics of the terms responsible for the interaction between the wave and the slow circulation are computed from the numerical outputs. The large scale change of stratification, on top of eddies and jet...
Tipo: Text
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00342/45364/44853.pdf
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Low-mode internal tides and balanced dynamics disentanglement in altimetric observations: Synergy with surface density observations 5
Ponte, Aurelien; Klein, Patrice; Dunphy, Michael; Le Gentil, Sylvie.
The performance of a tentative method that disentangles the contributions of a low-mode internal tide on sea level from that of the balanced mesoscale eddies is examined using an idealized high resolution numerical simulation. This disentanglement is essential for proper estimation from sea level of the ocean circulation related to balanced motions. The method relies on an independent observation of the sea surface water density whose variations are 1/dominated by the balanced dynamics and 2/correlate with variations of potential vorticity at depth for the chosen regime of surface-intensified turbulence. The surface density therefore leads via potential vorticity inversion to an estimate of the balanced contribution to sea level fluctuations. The...
Tipo: Text
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00374/48487/48761.pdf
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Ocean Scale Interactions from Space 5
Klein, Patrice; Lapeyre, Guillaume; Siegelman, Lia; Qiu, Bo; Fu, Lee‐lueng; Torres, Hector; Su, Zhan; Menemenlis, Dimitris; Le Gentil, Sylvie.
Satellite observations of the last two decades have led to a major breakthrough emphasizing the existence of a strongly energetic mesoscale turbulent eddy field in all the oceans. This ocean mesoscale turbulence (OMT) is characterized by cyclonic and anticyclonic eddies (with a 100‐‐300 km size and depth scales of ~500‐‐1000 m) that capture approximatively 80% of the total kinetic energy and is now known to significantly impact the large‐scale ocean circulation, the ocean's carbon storage, the air‐sea interactions and therefore the Earth climate as a whole. However, OMT revealed by satellite observations has properties that differ from those related to classical geostrophic turbulence theories. In the last decade, a large number of theoretical and...
Tipo: Text
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00488/59951/63202.pdf
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Optimal Perturbations of an Oceanic Vortex Lens 5
Meunier, Thomas; Menesguen, Claire; Carton, Xavier; Le Gentil, Sylvie; Schopp, Richard.
The stability properties of a vortex lens are studied in the quasi geostrophic (QG) framework using the generalized stability theory. Optimal perturbations are obtained using a tangent linear QG model and its adjoint. Their fine-scale spatial structures are studied in details. Growth rates of optimal perturbations are shown to be extremely sensitive to the time interval of optimization: The most unstable perturbations are found for time intervals of about 3 days, while the growth rates continuously decrease towards the most unstable normal mode, which is reached after about 170 days. The horizontal structure of the optimal perturbations consists of an intense counter-shear spiralling. It is also extremely sensitive to time interval: for short time...
Tipo: Text Palavras-chave: Vortex lenses; Intrathermocline eddies; Instability; Optimal perturbations.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00454/56605/58297.pdf
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Reconstruction of the 3-D Dynamics From Surface Variables in a High-Resolution Simulation of North Atlantic 5
Fresnay, S.; Ponte, Aurelien; Le Gentil, Sylvie; Le Sommer, J..
Several methods that reconstruct the three-dimensional ocean dynamics from sea level are presented and evaluated in the Gulf Stream region with a 1/60° realistic numerical simulation. The use of sea level is motivated by its better correlation with interior pressure or quasigeostrophic potential vorticity (PV) compared to sea surface temperature and sea surface salinity, and, by its observability via satellite altimetry. The simplest method of reconstruction relies on a linear estimation of pressure at depth from sea level. Another method consists in linearly estimating PV from sea level first and then performing a PV inversion. The last method considered, labeled SQG for surface quasigeostrophy, relies on a PV inversion but assumes no PV anomalies. The...
Tipo: Text Palavras-chave: Ocean dynamics; Quasi-geostrophy; Potential vorticity; Sea surface height; Correlation analysis; Spectral analysis.
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00425/53632/54468.pdf
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The Vertical Pump Organized by the Mesoscale Oceanic Eddies 5
Klein, Patrice; Hua, Bach-lien; Le Gentil, Sylvie; Sasaki, Hideharu.
The purpose of this project is to study the dynamics of the upper oceanic layers (the first 1000m below the surface) and principally to get new insights on the effectiveness of the oceanic vertical pump at a basin scale through numerical experiments using ultra-high resolution. If the magnitude of this vertical pump when using such a resolution is much larger than anticipated, then the expected results should have an important impact on basin-scale SST and circulation through the vertical fluxes of heat and potential vorticity. Indeed preliminary studies already indicate the significant contribution of this eddy vertical pump to the modification of the surface layers heat content ([1], [2]). Thus the expected new results should be of importance for climate...
Tipo: Text Palavras-chave: Mesoscale oceanic eddies; Submesoscale dynamics; Vertical pump.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/00067/17782/15304.pdf
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Tracer stirring around a meddy: The formation of layering 5
Meunier, Thomas; Menesguen, Claire; Schopp, Richard; Le Gentil, Sylvie.
The dynamics of the formation of layering surrounding meddy-like vortex lenses is investigated using primitive equation (PE), quasigeostrophic (QG), and tracer advection models. Recent in situ data inside a meddy confirmed the formation of highly density-compensated layers in temperature and salinity at the periphery of the vortex core. Very high-resolution PE modeling of an idealized meddy showed the formation of realistic layers even in the absence of double-diffusive processes. The strong density compensation observed in the PE model, in good agreement with in situ data, suggests that stirring might be a leading process in the generation of layering. Passive tracer experiments confirmed that the vertical variance cascade in the periphery of the vortex...
Tipo: Text Palavras-chave: Circulation/ Dynamics; Advection; Dynamics; Atm/Ocean Structure/ Phenomena; Vortices; Models and modeling; Primitive equations model; Quasigeostrophic models; Tracers.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00255/36599/35160.pdf
Registros recuperados: 15
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