Consulta: creatorFacets:"Schopp, Richard"
Registros recuperados: 12
Data/hora: 06/06/2024 18:23:13

Layering and turbulence surrounding an anticyclonic oceanic vortex: in situ observations and quasi-geostrophic numerical simulations
Provedor de dados: 5
Autores: 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

Intermittent layering in the Atlantic equatorial deep jets
Provedor de dados: 5
Autores: Menesguen, Claire; Hua, Bach-lien; Fruman, Mark; Schopp, Richard.
Equatorial observations in the Atlantic show three distinct vertical scales: quasi-barotropic eastward Extra-Equatorial Jets (EEJ), Equatorial Deep Jets (EDJ) of scale 500-800 m, and a smaller scale signal (50-100 m) of thin layers of well-mixed tracer fields. In the combined system of jets, westward EDJ correspond to zero-Potential Vorticity (PV) "niches," inside of which most of the thin well-mixed layers are found. Because of its correlation with zero-PV niches, the formation of layers is interpreted as due to inertial instability. The latter encompasses inertial barotropic instability due to meridional shear (either steady or parametric), baroclinic symmetric instability due to sloping isopyenals and vertical velocity shear, and effective-beta inertial...
Tipo: Text
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/publication-7405.pdf

Multiple Equilibria for Cross-Gyre Flow between Subpolar and Subtropical Gyres
Provedor de dados: 5
Autores: Schopp, Richard.
A simple Sverdrup-type two-layer model that allows the outcropping of isopycnals is forced by wind stress, is completed with a frictional western boundary layer, and is investigated along the zero wind-stress curl line separating the subpolar gyre from the subtropical gyre. The study focuses on the different cross-gyre flow patterns. Intermediate length-scale dynamics, which is able to take the dispersion of Rossby waves and the steepening of isopycnals into account, is used to analyze the evolution of these cross-gyre currents. In particular, these transients show that the solution, which exhibits an arrested Rossby wave, is unstable in the western part of the basin. Nevertheless, this solution is able to evolve to other more stable solutions present in...
Tipo: Text
Ano: 1993
URL: http://archimer.ifremer.fr/doc/00192/30372/29047.pdf

Extended deep equatorial layering as a possible imprint of inertial instability
Provedor de dados: 5
Autores: D'Orgeville, Marc; Hua, Bach-lien; Schopp, Richard; Bunge, L.
The deep equatorial track of the world ocean is subject to intense zonal flow fields that still remain to be better understood. Inertial instability has been invoked to explain some of its features. Here we present possible in situ imprints of such a mechanism in the equatorial Atlantic Ocean below the thermocline. We analyse the observed pattern of homogeneous density layers of 50 - 100 m vertical scale, which are characterized by a large meridional coherency up to 2degrees of latitude, a concentration in the vicinity of the equator and foremost a vertical localization within regions of well-mixed angular momentum ( westward jets). These distinctive properties suggest inertial instability to be a plausible mechanism for this extended layering. Numerical...
Tipo: Text
Ano: 2004
URL: http://archimer.ifremer.fr/doc/00000/10892/9229.pdf

Destabilization of mixed Rossby gravity waves and the formation of equatorial zonal jets
Provedor de dados: 5
Autores: Hua, Bach-lien; D'Orgeville, Marc; Fruman, Mark; Menesguen, Claire; Schopp, Richard; Klein, Patrice; Sasaki, H.
stability of mixed Rossby gravity (MRG) waves has been investigated numerically using three-dimensionally consistent high-resolution Simulations of the continuously stratified primitive equations. For short enough zonal wavelength, the westward phase propagating MRG wave is strongly destabilized by barotropic shear instability leading , to the formation of zonal jets. The large-scale instability of the zonally short wave,generates zonal jets because it consists primarily of sheared meridional motions, as shown recently for the short barotropic Rossby wave problem.   Simulations were done in a variety of domain geometries: a periodic re-entrant channel, a basin with a short MRG wave forced in its western part and a very long channel initialized with a...
Tipo: Text
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-5913.pdf

Cyclones and Anticyclones in Seismic Imaging
Provedor de dados: 5
Autores: 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

Low-frequency variations of the large-scale ocean circulation and heat transport in the North Atlantic from 1955-1998 in situ temperature and salinity data
Provedor de dados: 5
Autores: Huck, Thierry; Colin De Verdiere, Alain; Estrade, P.; Schopp, Richard.
Low-frequency variations of the large-scale ocean circulation in the Atlantic are reconstructed from NODC pentadal anomalies of temperature and salinity from 1955 to 1998 based on hydrographic data, in addition to atmospheric reanalysis surface forcing. Diagnostic ocean circulations are estimated from simple methods using dynamical model integrations: namely diagnostic, robust diagnostic, and short prognostic. Mean transports of heat and mass are sensitive to the method and model configuration, but their decadal variability is much more coherent and does not depend explicitly on the variations of the surface forcing, its influence being imprinted in the thermohaline structure. Multidecadal variations are of the order of 20%, with large transports in the...
Tipo: Text
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-6116.pdf

Optimal Perturbations of an Oceanic Vortex Lens
Provedor de dados: 5
Autores: 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

Tracer stirring around a meddy: The formation of layering
Provedor de dados: 5
Autores: 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

Slow quasigeostrophic unstable modes of a lens vortex in a continuously stratified flow
Provedor de dados: 5
Autores: Nguyen, Hai Yen; Hua, Bach-lien; Schopp, Richard; Carton, Xavier.
This work addresses the linear dynamics underlying the formation of density interfaces at the periphery of energetic vortices, well outside the vortex core, both in the radial and axial directions. We compute numerically the unstable modes of an anticyclonic Gaussian vortex lens in a continuously stratified rotating fluid. The most unstable mode is a slow mode, associated with a critical layer instability located at the vortex periphery. Although the most unstable disturbance has a characteristic vertical scale which is comparable to the vortex height, interestingly, the critical levels of the successively fastest growing modes are closely spaced at intervals along the axial direction that are much smaller than the vortex height.
Tipo: Text
Palavras-chave: Quasigeostrophic model; Vortices; Stratified flow; Critical level; Flow instability.
Ano: 2012
URL: http://archimer.ifremer.fr/doc/00074/18520/16331.pdf

Dynamics of the combined extra-equatorial and equatorial deep jets in the Atlantic
Provedor de dados: 5
Autores: Menesguen, Claire; Hua, Bach-lien; Fruman, Mark; Schopp, Richard.
The available meridional sections of zonal velocity with high vertical and meridional resolution reveal tall eastward jets at 2N and 2S, named the extra-eqaatorial jets (EEJ), straddling the stacked eastward and westward jets of smaller vertical scales right at the equator, the so-called equatorial deep jets (EDJ). In contrast to the semi-annual to interannual fluctuations in the zonal velocity component, the measured meridional velocity component is dominated by intraseasonal period. We argue here that the formation mechanism for both types of jets is linked to the intraseasonal variability in meridional velocity and the associated wave motions. A process study is complemented by high resolution primitive equation simulations based on a realistic...
Tipo: Text
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/publication-7406.pdf

Observations and mechanisms for the formation of deep equatorial and tropical circulation
Provedor de dados: 5
Autores: Menesguen, Claire; Delpech, Audrey; Marin, Frederic; Cravatte, Sophie; Schopp, Richard; Morel, Yves.
The Intermediate and Deep Equatorial and Tropical Circulations (DEC and DTC) consist of a complex system of zonal jets. This paper attempts at unifying existing observations and theories to present our current understanding of this jets system. Recent in‐situ observations suggesting a continuity between DEC and DTC are confronted against the various generation mechanisms that have been proposed in the literature. The key notion to differentiate these previous studies lies in the so‐called "cascade of mechanisms", i.e. the energy pathway and equilibration processes chain that lead to the jets from their initial energy source. Many studies see the Deep Equatorial Intra‐seasonal Variability (DEIV) as the initial energy source, highlighting its key role in...
Tipo: Text
Palavras-chave: Deep equatorial circulation; Deep tropical circulation; Zonal jets.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00482/59393/62159.pdf