Consulta: subjectFacets:"Vortices"
Registros recuperados: 8
Data/hora: 01/06/2024 06:20:34

The Role of Curvature in Modifying Frontal Instabilities. Part II: Application of the Criterion to Curved Density Fronts at Low Richardson Numbers
Provedor de dados: 5
Autores: 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′ &lt; 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

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

The Role of Curvature in Modifying Frontal Instabilities. Part I: Review of Theory and Presentation of a Nondimensional Instability Criterion
Provedor de dados: 5
Autores: 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 &lt; 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

Interaction between an eddy and a zonal jet - Part I. One-and-a-half-layer model
Provedor de dados: 5
Autores: Vandermeirsch, Frederic; Carton, Xavier; Morel, Yves.
The interaction between a stable zonal jet and a vortex is studied numerically with two one-and-a-half layer models, one with quasi-geostrophic dynamics, the other with shallow-water equations. In both models, simulations on the f-plane evidence three regimes occuring with increasing vortex strength: (regime 1) weak vortices do not cross the jet and steadily drift along it; (regime 2) stronger vortices cross the jet, tear an opposite-sign meander from the jet with which they pair as a dipole; the trajectory of this dipole depends on the strength of the initial vortex; since most dipoles are asymmetric, they veer back towards the jet axis where they are split apart in the ambient shear; (regime 3) even stronger vortices cross the jet and tear a vorticity...
Tipo: Text
Palavras-chave: Potential vorticity; Vortices; Jets; Nonlinear equations; Stratified flow; Rotating fluids.
Ano: 2003
URL: http://archimer.ifremer.fr/doc/2003/publication-440.pdf

Interaction between an eddy and a zonal jet - Part II. Two-and-a-half-layer model
Provedor de dados: 5
Autores: Vandermeirsch, Frederic; Carton, Xavier; Morel, Yves.
In a two-and-a-half-layer quasi-geostrophic model, a process study is conducted on the interaction between a vortex and a zonal jet, both with constant potential vorticity. The vortex is a stable anticyclone, initially located north of the eastward jet. The potential vorticity of the jet is allowed to have various vertical structures, while the vortex is concentrated in only one layer. The flow parameters are set to values characteristic of the Azores region.   First, the jet is stable. Weak vortices steadily drift north of the jet without crossing it while strong vortices can cross the jet and tear off a cyclone with which they pair as a heton (baroclinic dipole). This heton often breaks later in the shear exerted by the jet; the two vortices finally...
Tipo: Text
Palavras-chave: Potential vorticity; Vortices; Jets; Nonlinear equations; Stratified flow; Rotating fluids.
Ano: 2003
URL: http://archimer.ifremer.fr/doc/2003/publication-441.pdf

From Mixing to the Large Scale Circulation: How the Inverse Cascade Is Involved in the Formation of the Subsurface Currents in the Gulf of Guinea
Provedor de dados: 5
Autores: Assene, Fernand; Morel, Yves; Delpech, Audrey; Aguedjou, Micael; Jouanno, Julien; Cravatte, Sophie; Marin, Frederic; Ménesguen, Claire; Chaigneau, Alexis; Dadou, Isabelle; Alory, Gael; Holmes, Ryan; Bourlès, Bernard; Koch-larrouy, Ariane.
In this paper, we analyse the results from a numerical model at high resolution. We focus on the formation and maintenance of subsurface equatorial currents in the Gulf of Guinea and we base our analysis on the evolution of potential vorticity (PV). We highlight the link between submesoscale processes (involving mixing, friction and filamentation), mesoscale vortices and the mean currents in the area. In the simulation, eastward currents, the South and North Equatorial Undercurrents (SEUC and NEUC respectively) and the Guinea Undercurrent (GUC), are shown to be linked to the westward currents located equatorward. We show that east of 20∘ W, both westward and eastward currents are associated with the spreading of PV tongues by mesoscale vortices. The...
Tipo: Text
Palavras-chave: Equatorial atlantic; NEUC (North Equatorial Undercurrents); SEUC (South Equatorial Undercurrents); Vortices; Mixing; Friction.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00645/75697/76601.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