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| Baey, Jean-michel; Carton, Xavier. |
| The stability of elliptically perturbed circular vortices is investigated in a two-layer shallow-water model, with constant background rotation. The fluid is bounded above and below by rigid and flat surfaces. The linear stability analysis shows that elliptical perturbations are most unstable for moderate Burger numbers and vorticity shears. Shorter waves dominate for more sheared vortices. Shallow-water and quasigeostrophic growth rates exhibit a striking similarity, except at each end of the Burger number domain. There, cyclones (anticyclones) with finite Rossby numbers are more (less) unstable than their quasi-geostrophic counterparts. A simple model gives a first-order trend for this bias. Nonlinear model runs with initially perturbed vortices also... |
| Tipo: Text |
Palavras-chave: Stability analysis; Vortex; Shallow water. |
| Ano: 2002 |
URL: http://archimer.ifremer.fr/doc/2002/publication-645.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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| Caballero, Ainhoa; Ferrer, Luis; Rubio, Anna; Charria, Guillaume; Taylor, Benjamin H.; Grima, Nicolas. |
| The presence of a quasi-stationary anticyclonic eddy within the southeastern Bay of Biscay (centred around 44°30′N-4°W) has been reported on various occasions in the bibliography. The analysis made in this study for the period 2003–2010, by using in situ and remote sensing measurements and model results shows that this mesoscale coherent structure is present almost every year from the end of winter-beginning of spring, to the beginning of fall. During this period it remains in an area limited to the east by the Landes Plateau, to the west by Le Danois Bank and Torrelavega canyon and to the northwest by the Jovellanos seamount. All the observations and analysis made in this contribution, suggest that this structure is generated between Capbreton and... |
| Tipo: Text |
Palavras-chave: Bay of Biscay; Eddies; SWODDIES; Topographic effects; Vortex; Mesoscale; Altimetry; Satellite oceanography; Drifters; ROMS. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00161/27260/25469.pdf |
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| Flament, Pierre; Lumpkin, Rick; Tournadre, Jean; Armi, Laurence. |
| Observations of the downstream evolution of an oceanic zonal horizontal shear flow at a Reynolds number of about 10(11), formed as the westward North Equatorial Current passes the island of Hawai'i, reveal finite-amplitude anticyclonic vortices resulting from instability of the shear. The initial orbital period of the vortices is exactly one pendulum day (3.1 days at this latitude), centrifugal instability presumably inhibiting stronger vortices from forming. As they move downstream, they appear to pair and merge into successively larger vortices, in a geometric sequence of longer orbital periods; three subharmonic transitions are suggested with final orbital periods near 6, 12 and 24 days. |
| Tipo: Text |
Palavras-chave: Vortex; Oceanic shear flow. |
| Ano: 2001 |
URL: http://archimer.ifremer.fr/doc/2001/publication-644.pdf |
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| De Marez, Charly; Meunier, Thomas; Morvan, Mathieu; L’hégaret, Pierre; Carton, Xavier. |
| We investigate the stability of a composite cyclone representative of Arabian Sea eddies using a high resolution primitive equation model. We observe that the eddy is unstable with respect to a mixed barotropic/baroclinic instability, leading to the growth of an azimuthal mode 2 perturbation. The latter deforms the eddy, which eventually evolves into a tripole after about 4 months of simulation. The presence of a critical level for the most unstable mode generates sharp fronts in the surface mixed layer where the Rossby number is large. These fronts then become unstable, and this generates submesoscale cyclones and filaments. Near these fronts, diapycnal mixing occurs, causing the potential vorticity to change sign locally, and symmetric instability to... |
| Tipo: Text |
Palavras-chave: Mesoscale; Eddy; Instability; Submesoscale; Vortex. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00598/70967/69196.pdf |
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