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| Registros recuperados: 23 | |
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| Menesguen, Claire; Hua, Bach-lien; Carton, Xavier; Klingelhoefer, Frauke; Schnurle, Philippe; Reichert, C.. |
| The North Atlantic temperature and salinity distributions are strongly influenced by the existence of Mediterranean eddies (meddies) which significantly contribute to the transport of the warm and salty Mediterranean Water along different pathways. The most common pathways are observed to be North and West of the Canary Current. However, a 2011 seismic reflection cruise conducted by BGR and Ifremer near the North-Western African margin of Morocco, MIRROR Leg 2, revealed the presence of a meddy south of the Azores front and very close to the Morocco coastline. This unusual location of a strong Mediterranean Water anomaly is confirmed by other data. Moreover, meddies are long-lived structures whose dynamics and dissipation are not yet completely understood.... |
| Tipo: Text |
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| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00074/18499/16046.pdf |
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| Hua, Bach-lien; Klein, Patrice; Lapeyre, Guillaume. |
| Geophysical turbulent fluids are characterized by the presence of organized energetic structures which control tracer transport and stirring, while enabling a tracer cascade down to the smallest scales. In order to understand the physical mechanisms involved in this turbulent tracer cascade, we focus on the dynamics underlying the formation of tracer gradients which are necessarily associated to this cascade. We show that the dynamics of tracer gradients in physical space is mainly governed by their orientation with respect to the compressional eigenvector of the strain tensor. This relative angle results from the competition between strain and the "effective rotation" (due to both vorticity and rotation of strain axes). The implication is that tracer... |
| Tipo: Text |
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| Ano: 2001 |
URL: http://archimer.ifremer.fr/doc/00067/17786/15309.pdf |
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| 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 |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-5913.pdf |
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| Le Traon, Pierre-yves; Klein, Patrice; Hua, Bach-lien; Dibarboure, G. |
| In high-eddy-energy regions, it is generally assumed that sea level wavenumber spectra compare well with quasigeostrophic (QG) turbulence models and that spectral slopes are close to the expected k(-5) law. This issue is revisited here. Sea level wavenumber spectra in the Gulf Stream, Kuroshio, and Agulhas regions are estimated using the most recent altimeter datasets [the Ocean Topography Experiment (TOPEX)/ Poseidon, Jason-1, the Environmental Satellite (Envisat), and the Geosat Follow-On]. The authors show that spectral slopes in the mesoscale band are significantly different from a k(-5) law, in disagreement with the QG turbulence theory. However, they very closely follow a k(-11/3) slope, which indicates that the surface quasigeostrophic theory (SQG)... |
| Tipo: Text |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-4118.pdf |
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| 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 |
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| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-7406.pdf |
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| Menesguen, Claire; Hua, Bach-lien; Papenberg, C.; Klaeschen, D.; Geli, Louis; Hobbs, R.. |
| The fine resolution of long geoseismic sections should permit the characterization of oceanic turbulence properties over several decades of horizontal scales. The range of horizontal scales actually probed by three different acoustic sources is found to be directly linked to their frequency content. The horizontal inertial range with a spectral slope of k(h)(-5/3) extend up to 3 km wavelength for the most intense acoustic reflectors which surround strong anticyclonic eddies. The in situ data analysis is confirmed by high resolution numerical simulations of oceanic anticyclonic vortices, in a rotating temperature-stratified fluid (no salt), which show the spontaneous emergence of a concentration of acoustic reflectors above and below the eddy. These show an... |
| Tipo: Text |
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| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6922.pdf |
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| D'Orgeville, Marc; Hua, Bach-lien; Sasaki, H. |
| The response of the deep equatorial ocean to an oscillatory baroclinic western boundary current is investigated in a continuously stratified primitive equation model. The symmetry of the current about the equator is such that mixed Rossby-gravity (MRG) waves are excited in the western part of the equatorial ocean. Depending on the forcing frequency, short to long scale (when compared to equatorial Rossby radius) monochromatic (MRG) waves are selected. The subsequent MRG wave destabilization generally leads to a much higher vertical mode response than the forced MRG wave mode. In a channel, short MRG waves are destabilized by shear instability (Hua et al., 2007). In a basin, the destabilization occurs in the vicinity of the western boundary and leads to... |
| Tipo: Text |
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| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2534.pdf |
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| D'Orgeville, Marc; Hua, Bach-lien. |
| This study revisits the problem of the zonally symmetric instability on the equatorial beta-plane. Rather than treating the classical problem of a steady basic flow, it treats a sequence of problems of increasing complexity in which the basic flow is oscillatory in time with a frequency omega(0). First, for the case of a homogeneous fluid, a time-oscillating barotropic shear forcing may excite a subharmonic parametric resonance of inertial oscillations. Because of the continuous distribution of inertial oscillation frequencies, this resonance occurs at critical inertial latitudes y(c). such that beta y(c) = +/-omega(0)/2. Next the effects of stratification, characterized by Brunt-Vaisala frequency N, are taken into account. It is shown analytically (in... |
| Tipo: Text |
Palavras-chave: Equatorial wave; Dynamical model; Oscillating shear flows. |
| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/2005/publication-433.pdf |
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| 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 |
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| Ano: 2004 |
URL: http://archimer.ifremer.fr/doc/00000/10892/9229.pdf |
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| 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 |
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| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00336/44750/57508.pdf |
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| Geli, Louis; Cosquer, Emmanuel; Hobbs, R. W.; Klaeschen, D.; Papenberg, C.; Thomas, Yannick; Menesguen, Claire; Hua, Bach-lien. |
| A small volume (117 cu-inch) seismic source producing signal predominantly in the 150-200 Hz frequency window was used during the GO calibration experiment in the Gulf of Cadiz (April-May 2007). The data show the small scale (< 10 m in the z direction) internal structure of the ocean. High-resolution images display seismic reflectors that often appear as distinct, horizontal, short (similar to a few hundred meters to a few km long) segments, lying at different depths, while low-resolution (similar to 20 to 30 Hz) display long, horizontal reflectors (similar to a few tens of km), sometimes linked by short, apparently "dipping" segments. The present data suggest that this apparent dipping effect is due to the insufficient separation power (similar to... |
| Tipo: Text |
Palavras-chave: High resolution; Seismics; Oceanography. |
| Ano: 2009 |
URL: https://archimer.ifremer.fr/doc/2009/publication-7297.pdf |
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| 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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| 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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| 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 |
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| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-7405.pdf |
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| 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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| Hua, Bach-lien. |
| This note attempts to connect the skewness of the probability distribution function (PDF) of pressure, which is commonly observed in two-dimensional turbulence, to differences in the geometry of the strain and vorticity fields. This paper illustrates analytically the respective roles of strain and vorticity in shaping the PDF of pressure, in the particular case of a joint normal distribution of velocity gradients. The latter assumption is not valid in general in direct numerical simulations (DNS) of two-dimensional turbulence but may apply to geostrophic turbulence in presence of a differential rotation (beta effect). In essence, minus the Laplacian of pressure is the difference of squared strain and vorticity, a quantity which is named the generalized... |
| Tipo: Text |
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| Ano: 1994 |
URL: http://archimer.ifremer.fr/doc/00196/30691/30393.pdf |
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| 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 |
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| Capet, Xavier; Klein, Patrice; Hua, Bach-lien; Lapeyre, Guillaume; Mcwilliams, James C. |
| The relevance of surface quasi-geostrophic dynamics (SQG) to the upper ocean and the atmospheric tropopause has been recently demonstrated in a wide range of conditions. Within this context, the properties of SQG in terms of kinetic energy (KE) transfers at the surface are revisited and further explored. Two well-known and important properties of SQG characterize the surface dynamics: (i) the identity between surface velocity and density spectra (when appropriately scaled) and (ii) the existence of a forward cascade for surface density variance. Here we show numerically and analytically that (i) and (ii) do not imply a forward cascade of surface KE (through the advection term in the KE budget). On the contrary, advection by the geostrophic flow primarily... |
| Tipo: Text |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-4623.pdf |
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| Hua, Bach-lien. |
| The purpose of this note is to investigate the use of Lagrangian potential vorticity conservation as a numerically independent method for checking a posteriori the dynamical consistency of an eddy-resolving GCM simulation. This is performed for a series of simulations with increasing horizontal and vertical resolution. The result that higher vertical modes play a catalytic role in the largest scales of eddy-driven flows is independently confirmed through this Lagrangian test. |
| Tipo: Text |
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| Ano: 1994 |
URL: http://archimer.ifremer.fr/doc/00196/30752/29304.pdf |
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| Registros recuperados: 23 | |
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