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| Registros recuperados: 14 | |
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| Colin De Verdiere, Alain; Huck, Thierry; Pogossian, Souren; Ollitrault, Michel. |
| The vertically integrated potential energy of an incompressible stratified fluid formulated in density coordinates can be simply written as a weighted vertical sum of the squares of the vertical displacements of density surfaces, a general expression valid for arbitrary displacements. The sum of this form of potential energy and kinetic energy is then a conserved quantity for the multilayer shallow water model. The formulation in density coordinates is a natural one to find the Lorenz reference state of available potential energy (APE).We describe the method to compute the APE of an ocean state and provide two applications. The first is the classical double-gyre, wind-driven circulation simulated by a shallow water model at high resolution.We show that the... |
| Tipo: Text |
Palavras-chave: Energy transport; Ocean circulation; Ocean dynamics; Isopycnal coordinates. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00464/57521/59707.pdf |
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| Hochet, Antoine; Huck, Thierry; Arzel, Olivier; Sevellec, Florian; Colin De Verdiere, Alain; Mazloff, Matthew; Cornuelle, Bruce. |
| The North Atlantic is characterized by basin-scale multidecadal fluctuations of the sea surface temperature with periods ranging from 20 to 70 years. One candidate for such a variability is a large-scale baroclinic instability of the temperature gradients across the Atlantic associated with the North Atlantic Current. Because of the long time scales involved, most of the studies devoted to this problem are based on low resolution numerical models leaving aside the effect of explicit meso-scale eddies. How high-frequency motions associated with the meso-scale eddy field affect the basin-scale low-frequency variabiliy is the central question of this study. This issue is addressed using an idealized configuration of an Ocean General Circulation Model at... |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00635/74701/74640.pdf |
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| Sevellec, Florian; Huck, Thierry; Colin De Verdiere, Alain. |
| The freshwater flux intensity is used as the main control parameter to destabilize the ThermoHaline Circulation (THC): as it increases, the classical bifurcation scenario, thermal stable steady state, millennial oscillation and haline stable steady state are reproduced in a 2D zonally-averaged ocean model under mixed boundary conditions. Both bifurcations arise through global bifurcations leading to an infinite period of the limit cycle. Here we highlight a centennial oscillation important for the instability of the thermal phase of the millennial oscillation and which could be considered as a precursor to the collapse of the THC. It is suggested that the existence or the absence of this centennial oscillation leads to dramatic changes in the collapse time... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00038/14912/12623.pdf |
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| 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 |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-6116.pdf |
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| Colin De Verdiere, Alain; Meunier, Thomas; Ollitrault, Michel. |
| A direct method is presented to obtain the meridional overturning and heat transport in oceanic basins from observations under the sole assumptions of geostrophy and hydrostatics. The method is made possible because of the rising Argo float displacements database that can provide a reference level at 1000 dbar for the time mean circulation at 1 degrees x 1 degrees resolution. To achieve the overturning and heat transport objectives, the absolute geostrophic time mean circulation must have nondivergent barotropic transports and this requires the solutions of two Poisson equations with suitable boundary conditions, one for the geopotential at 1000 dbar and one for the barotropic stream function. Applied to the subpolar Atlantic for the period 2000-2009, an... |
| Tipo: Text |
Palavras-chave: Oceanic heat transport; Meridional overturning; Subpolar Atlantic. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00589/70139/68105.pdf |
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| Marchal, Olivier; Waelbroeck, Claire; Colin De Verdiere, Alain. |
| Three sediment records of sea surface temperature (SST) are analyzed that originate from distant locations in the North Atlantic, have centennial-to-multicentennial resolution, are based on the same reconstruction method and chronological assumptions, and span the past 15 000 yr. Using recursive least squares techniques, an estimate of the time-dependent North Atlantic SST field over the last 15 kyr is sought that is consistent with both the SST records and a surface ocean circulation model, given estimates of their respective error (co)variances. Under the authors' assumptions about data and model errors, it is found that the 10 degrees C mixed layer isotherm, which approximately traces the modern Subpolar Front, would have moved by ~15 degrees of... |
| Tipo: Text |
Palavras-chave: Inverse methods; Kalman filters; Climate variability; Circulation/ Dynamics; Geographic location/entity; Oceanic variability; Variability; Mathematical and statistical techniques; Fronts; North Atlantic Ocean. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00318/42922/42423.pdf |
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| Arhan, Michel; Colin De Verdiere, Alain; Memery, L. |
| A quasi-meridional hydrographic section carried out between 60-degrees and 20-degrees-N offshore from the European and African continental slopes is analyzed in terms of water masses and zonal transports in and out of the eastern boundary. Outstanding features of the meridional distribution of water masses are focused on, such as the transition between North Atlantic and South Atlantic Central Waters at 20-degrees-25-degrees-N, the properties and anticyclonic circulation of the Rockall Channel mode water, and the northern boundary of the large-scale Mediterranean Water plume at about 50-degrees-N. An eastward transport of about 11 X 10(6) m3 s-1 is found to enter the eastern boundary layer at densities lower than 27.25 and feed southward alongshore... |
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| Ano: 1994 |
URL: http://archimer.ifremer.fr/doc/00196/30717/29449.pdf |
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| Ollitrault, Michel; Colin De Verdiere, Alain. |
| The mean ocean circulation near 1000-m depth is estimated with 100-km resolution from the Argo float displacements collected before 1 January 2010. After a thorough validation, the 400 000 or so displacements found in the 950–1150 dbar layer and with parking times between 4 and 17 days allow the currents to be mapped at intermediate depths with unprecedented details. The Antarctic Circumpolar Current (ACC) is the most prominent feature, but western boundary currents (and their recirculations) and alternating zonal jets in the tropical Atlantic and Pacific are also well defined. Eddy kinetic energy (EKE) gives the mesoscale variability (on the order of 10 cm2 s−2 in the interior), which is compared to the surface geostrophic altimetric EKE showing e-folding... |
| Tipo: Text |
Palavras-chave: Circulation; Dynamics; Currents; Dynamics; Large-scale motions; Ocean circulation. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00174/28512/26877.pdf |
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| Herbette, Steven; Hochet, Antoine; Huck, Thierry; Colin De Verdiere, Alain; Collin, Jeremy; Shillington, Frank. |
| When a source-sink dipole forces a fluid on a beta-plane limited by a western boundary, the linear steady solution can be obtained analytically and consists of zonally elongated gyres that extend west of the forcing and close as western boundary currents. The nondimensional parameter Ro(upsilon) = U/(4 beta a(2)) (with U the zonal velocity of the flow and 2a the distance between the source and sink) is used to characterize the nonlinearity of the flow. When Ro(upsilon) reaches 0.1, the numerical shallow-water solution shows that the configuration with the source to the north of the sink becomes unstable, while the reverse configuration remains steady. Indeed, that reverse configuration remains steady for much larger values of the nonlinearity parameter... |
| Tipo: Text |
Palavras-chave: Beta-plane double-gyre; Source-sink rotating tank experiments; Jet instability; Hopf bifurcation. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00211/32182/30652.pdf |
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| Registros recuperados: 14 | |
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