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| Registros recuperados: 21 | |
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| Yim, Eunok; Billant, Paul; Menesguen, Claire. |
| This paper investigates the stability of an axisymmetric pancake vortex with Gaussian angular velocity in radial and vertical directions in a continuously stratified-rotating fluid. The different instabilities are determined as a function of the Rossby number Ro, Froude number Fh, Reynolds number Re and aspect ratio α. Centrifugal instability is not significantly different from the case of a columnar vortex due to its short-wavelength nature: it is dominant when the absolute Rossby number |Ro| is large and is stabilized for small and moderate |Ro| when the generalized Rayleigh discriminant is positive everywhere. The Gent–McWilliams instability, also known as internal instability, is then dominant for the azimuthal wavenumber m=1 when the Burger number... |
| Tipo: Text |
Palavras-chave: Geophysical and geological flows; Vortex flows; Vortex instability. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00347/45817/46635.pdf |
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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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| Carton, Xavier; Sokolovskiy, Mikhail; Menesguen, Claire; Aguiar, Ana; Meunier, Thomas. |
| The stability of circular vortices to normal mode perturbations is studied in a multi-layer quasi-geostrophic model. The stratification is fitted on the Gulf of Cadiz where many Mediterranean Water (MW) eddies are generated. Observations of MW eddies are used to determine the parameters of the reference experiment; sensitivity tests are conducted around this basic case. The objective of the study is two-fold: (a) determine the growth rates and nonlinear evolutions of unstable perturbations for different three-dimensional (3D) velocity structures of the vortices, (b) check if the different structure of our idealized vortices, mimicking MW cyclones and anticyclones, can induce different stability properties in a model that conserves parity symmetry, and... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00216/32711/31363.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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| 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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| 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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| Menesguen, Claire; Le Gentil, Sylvie; Marchesiello, P.; Ducousso, N.. |
| The increase of computational capabilities led recent studies to implement very high resolution simulations that gave access to new scale interaction processes, particularly those associated with the transfer of energy from the oceanic mesoscales to smaller scales through an interior route to dissipation which is still under-explored. In this context, we study spin down simulations of a mesoscale interior vortex, unstable to a mixed baroclinic-barotropic instability. Even though the global energy is almost conserved, some energy is transferred down to dissipation scales during the development of instabilities. However, in our parameter regime, there is no substantial forward energy cascade sustained by unbalanced dynamics. Rather than exploring the... |
| Tipo: Text |
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| Ano: 2018 |
URL: http://archimer.ifremer.fr/doc/00435/54690/56128.pdf |
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| L'Hegaret, Pierre; Carton, Xavier; Ambar, Isabel; Menesguen, Claire; Hua, Bach Lien; Cherubin, Laurent; Aguiar, Ana; Le Cann, Bernard; Daniault, Nathalie; Serra, Nuno. |
| A collision of Mediterranean Water dipoles in the Gulf of Cadiz is studied here, using data from the MedTop and Semane experiments. First, a Mediterranean Water eddy (meddy) was surveyed hydrologically in November 2000 southwest of Cape Saint Vincent. Then, this meddy drifted northeastward from this position, accompanied by a cyclone (detected only via altimetry), thus forming a first dipole. In February 2001, a dipole of Mediterranean Water was measured hydrologically just after its formation near Portimão Canyon. This second dipole drifted southwestward. The western and eastern meddies had hydrological radii of about 22 and 25 km, respectively, with corresponding temperature and salinity maxima of (13.45°C, 36.78) and (11.40°C, 36.40). Rafos float... |
| Tipo: Text |
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| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00204/31565/29986.pdf |
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| Menesguen, Claire; Mcwilliams, J.c.; Molemaker, M. Jeroen. |
| Oceanic large- and meso-scale flows are nearly balanced in forces between Earth’s rotation and density stratification effects (i.e. geostrophic, hydrostatic balance associated with small Rossby and Froude numbers). In this regime advective cross-scale interactions mostly drive energy toward larger scales (i.e. inverse cascade). However, viscous energy dissipation occurs at small scales. So how does the energy reservoir at larger scales leak toward small-scale dissipation to arrive at climate equilibrium? Here we solve the linear instability problem of a balanced flow in a rotating and continuously stratified fluid far away from any boundaries (i.e. an interior jet). The basic flow is unstable not only to geostrophic baroclinic and barotropic instabilities,... |
| Tipo: Text |
Palavras-chave: Baroclinic flows; Critical layers; Stratified flows. |
| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00128/23906/21847.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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| 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 |
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| Storer, Benjamin; Poulin, Francis J.; Menesguen, Claire. |
| The stability of lens-shaped vortices is revisited in the context of an idealized quasigeostrophic model. We compute the stability characteristics with higher accuracy and for a wider range of Burger numbers (Bu) than what was previously done. It is found that there are four distinct Bu regions of linear instability. Over the primary region of interest (0.1 < Bu < 10), we confirm that the first and second azimuthal modes are the only linearly unstable modes, and they are associated with vortex tilting and tearing, respectively. Moreover, the most unstable first azimuthal mode is not precisely captured by the linear stability analysis because of the extra condition that is imposed at the vortex center, and accurate calculations of the second azimuthal... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00448/55987/57453.pdf |
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| Wang, Peng; Mcwilliams, James C.; Menesguen, Claire. |
| The linear instability of several rotating, stably stratified, interior vertical shear flows (U) over bar (z) is calculated in Boussinesq equations. Two types of baroclinic, ageostrophic instability, AI1 and AI2, are found in odd-symmetric (U) over bar (z) for intermediate Rossby number (R-0). AI1 has zero frequency; it appears in a continuous transformation of the unstable mode properties between classic baroclinic instability (BCI) and centrifugal instability (CI). It begins to occur at intermediate R-0 values and horizontal wavenumbers (k, l) that are far from l = 0 or k = 0, where the growth rate of BCI or CI is the strongest. AI1 grows by drawing kinetic energy from the mean flow, and the perturbation converts kinetic energy to potential energy. The... |
| Tipo: Text |
Palavras-chave: Baroclinic flows; Instability; Waves in rotating fluids. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00211/32230/30753.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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| 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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| Registros recuperados: 21 | |
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