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Registros recuperados: 27
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A New Platform for the Determination of Air–Sea Fluxes (OCARINA): Overview and First Results ArchiMer
Bourras, D.; Branger, H.; Reverdin, Gilles; Marie, Louis; Cambra, R.; Baggio, L.; Caudoux, C.; Caudal, G.; Morisset, S.; Geyskens, N.; Weill, Alain; Hauser, D..
The present paper describes a new type of floating platform that was specifically designed for estimating air–sea fluxes, investigating turbulence characteristics in the atmospheric surface boundary layer, and studying wind–wave interactions. With its design, it can be deployed in the open ocean or in shallow-water areas. The system is designed to be used from a research vessel. It can operate for ~10 h as a drifting wave rider and 3 h under power. Turbulence and meteorological instrument packages are placed at a low altitude (1–1.5 m). It was deployed for validation purposes during the Front de Marée, Variabilité (FROMVAR), 2011 experiment off the west coast of Brittany, France. Wind friction velocity and surface turbulent buoyancy flux were estimated...
Tipo: Text Palavras-chave: In situ atmospheric observations; Surface observations; In situ oceanic observations.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00192/30283/28759.pdf
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A numerical model for ocean ultra-low frequency noise: Wave-generated acoustic-gravity and Rayleigh modes ArchiMer
Ardhuin, Fabrice; Lavanant, Thibaut; Obrebski, Mathias; Marie, Louis; Royer, Jean-yves; D'Eu, Jean-francois; Howe, Bruce M.; Lukas, Roger; Aucan, Jerome.
The generation of ultra-low frequency acoustic noise (0.1 to 1 Hz) by the nonlinear interaction of ocean surface gravity waves is well established. More controversial are the quantitative theories that attempt to predict the recorded noise levels and their variability. Here a single theoretical framework is used to predict the noise level associated with propagating pseudo-Rayleigh modes and evanescent acoustic-gravity modes. The latter are dominant only within 200 m from the sea surface, in shallow or deep water. At depths larger than 500 m, the comparison of a numerical noise model with hydrophone records from two open-ocean sites near Hawaii and the Kerguelen islands reveal: (a) Deep ocean acoustic noise at frequencies 0.1 to 1 Hz is consistent with the...
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Ano: 2013 URL: http://archimer.ifremer.fr/doc/00176/28748/27211.pdf
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A study of the phase instability of quasi-geostrophic Rossby waves on the infinite beta-plane to zonal flow perturbations ArchiMer
Marie, Louis.
The problem of the linear instability of quasi-geostrophic Rossby waves to zonal flow perturbations is investigated on an infinite beta-plane using a phase dynamics formalism. Equations governing the coupled evolutions of a zonal velocity perturbation and phase and amplitude perturbations of a finite-amplitude wave are obtained. The analysis is valid in the limit of infinitesimal, zonally invariant perturbation components, varying slowly in the meridional direction and with respect to time. In the case of a slow sinusoidal meridional variation of the perturbation components, analytical expressions for the perturbation growth rates are obtained, which are checked against numerical codes based on standard Floquet theory.
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Ano: 2010 URL: http://archimer.ifremer.fr/doc/00008/11903/8612.pdf
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Amélioration de la gestion des conditions de frontières ouvertes biogéochimiques dans les modèles physiques et biogéochimiques couplés régionaux afin de reproduire les principaux processus d’échanges côte - large. Action vers une Modélisation Intégrée Côtière Opérationnelle (AMICO). ArchiMer
Pinazo, Christel; Ross, Oliver; Diaz, F.; Doglioli, A.m.; D'Ortenzio, F.; Estournel, C.; Forget, P.; Garnier, Valerie; Gutknecht, E.; Kersale, M.; Kessouri, F.; Lathuilière, C.; Marie, Louis; Marmain, J.; Marsaleix, P.; Perruche, C.; Petrenko, A.; Reffray, G.; Sourisseau, Marc; Taillandier, V.; Taupier-letage, I.; Testor, P.; Thouvenin, Benedicte; Ulses, C.; Eldin, G..
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00292/40336/41772.pdf
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An hydrodynamic shear instability in stratified disks ArchiMer
Dubrulle, B; Marie, Louis; Normand, C; Richard, D; Hersant, F; Zahn, Jp.
We discuss the possibility that astrophysical accretion disks are dynamically unstable to non-axisymmetric disturbances with characteristic scales much smaller than the vertical scale height. The instability is studied using three methods: one based on the energy integral, which allows the determination of a sufficient condition of stability, one using a WKB approach, which allows the determination of the necessary and sufficient condition for instability and a last one by numerical solution. This linear instability occurs in any inviscid stably stratified differential rotating fluid for rigid, stress-free or periodic boundary conditions, provided the angular velocity Omega decreases outwards with radius r. At not too small stratification, its growth rate...
Tipo: Text Palavras-chave: Accretion; Accretion disks hydrodynamic instabilities turbulence.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/00253/36469/35013.pdf
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Assessing spatial and temporal variability of phytoplankton communities' composition in the Iroise Sea ecosystem (Brittany, France): A 3D modeling approach. Part 1: Biophysical control over plankton functional types succession and distribution ArchiMer
Cadier, Mathilde; Gorgues, Thomas; Sourisseau, Marc; Edwards, Christopher A.; Aumont, Olivier; Marie, Louis; Memery, Laurent.
Understanding the dynamic interplay between physical, biogeochemical and biological processes represents a key challenge in oceanography, particularly in shelf seas where complex hydrodynamics are likely to drive nutrient distribution and niche partitioning of phytoplankton communities. The Iroise Sea includes a tidal front called the ‘Ushant Front’ that undergoes a pronounced seasonal cycle, with a marked signal during the summer. These characteristics as well as relatively good observational sampling make it a region of choice to study processes impacting phytoplankton dynamics. This innovative modeling study employs a phytoplankton-diversity model, coupled to a regional circulation model to explore mechanisms that alter biogeography of phytoplankton in...
Tipo: Text Palavras-chave: Iroise Sea; Tidal mixing front; Biogeochemical modeling; Phytoplankton; Functional groups; Seasonal cycle.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00352/46367/45986.pdf
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Biophysical Interactions Control the Size and Abundance of Large Phytoplankton Chains at the Ushant Tidal Front ArchiMer
Landeira, Jose Maria; Ferron, Bruno; Lunven, Michel; Morin, Pascal; Marie, Louis; Sourisseau, Marc.
Phytoplankton blooms are usually dominated by chain-forming diatom species that can alter food pathways from primary producers to predators by reducing the interactions between intermediate trophic levels. The food-web modifications are determined by the length of the chains; however, the estimation is biased because traditional sampling strategies damage the chains and, therefore, change the phytoplankton size structure. Sedimentological studies around oceanic fronts have shown high concentrations of giant diatom mats (>1 cm in length), suggesting that the size of diatom chains is underestimated in the pelagic realm. Here, we investigate the variability in size and abundance of phytoplankton chains at the Ushant tidal front (NW France) using the Video...
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Ano: 2014 URL: http://archimer.ifremer.fr/doc/00186/29730/28148.pdf
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Circulation on the shelf and the upper slope of the Bay of Biscay ArchiMer
Le Boyer, Arnaud; Charria, Guillaume; Le Cann, Bernard; Lazure, Pascal; Marie, Louis.
Here, we used measurements taken with an array of 10 acoustic Doppler current profilers deployed from July 2009 to August 2011 to describe the tidally filtered circulation over the shelf and upper slope on the French side off the French coasts of the Bay of Biscay. The measurements provided an overview of the shelf and slope circulation throughout the entire water column over a large range of spatial and time scales. The average circulation over the shelf and upper slope of the Bay of Biscay was poleward following the topography with a speed of the order of 3 cm s(-1). This average circulation had marked seasonal variability. In summer, the currents were equatorward on the outer shelf near surface. Deeper in the water column, the flow remained poleward. In...
Tipo: Text Palavras-chave: Bay of Biscay; Observation; Shelf and slope circulation; Vertical profile; ADCP; Wind driven circulation.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00139/24976/26395.pdf
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Cyclogeostrophic balance in the Mozambique Channel ArchiMer
Penven, Pierrick; Halo, Issufo; Pous, Stephane; Marie, Louis.
Three methods are proposed for the inclusion of inertia when deriving currents from sea surface height (SSH) in the Mozambique Channel: gradient wind, perturbation expansion, and an iterative method. They are tested in a model and applied to satellite altimetry. For an eddy of 25 cm amplitude and 100 km radius, typical of Mozambique Channel rings at 18°S, the error made with geostrophy is 40% for the anticyclones and 20% for the cyclones. Inertia could reach one third of the pressure gradient. Geostrophy underestimates subsurface currents by up to 50 cm s−1, resulting in errors of 30–40%. The iterative method results in errors of <5% for the most part of the structure. The error RMS in velocities based on 8 years of model SSH is in excess of 30 cm s−1...
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Ano: 2014 URL: http://archimer.ifremer.fr/doc/00175/28617/27045.pdf
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Enhanced Turbulence Associated with the Diurnal Jet in the Ocean Surface Boundary Layer ArchiMer
Sutherland, Graig; Marie, Louis; Reverdin, Gilles; Christensen, Kai H.; Brostrtom, Goran; Ward, Brian.
Detailed observations of the diurnal jet, a surface intensification of the wind-driven current associated with the diurnal cycle of sea surface temperature (SST), were obtained during August and September 2012 in the subtropical Atlantic. Adiurnal increase in SST of 0.2 degrees to 0.5 degrees C was observed, which corresponded to a diurnal jet of 0.15 m s(-1). The increase in near-surface stratification limits the vertical diffusion of the wind stress, which in turn increases the near-surface shear. While the stratification decreased the turbulent dissipation rate epsilon below the depth of the diurnal jet, there was an observed increase in epsilon within the diurnal jet. The diurnal jet was observed to increase the near-surface shear by a factor of 5,...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00358/46872/46758.pdf
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Evidence for Forcing-Dependent Steady States in a Turbulent Swirling Flow ArchiMer
Saint-michel, Brice; Dubrulle, B.; Marie, Louis; Ravelet, F.; Daviaud, F..
We study the influence on steady turbulent states of the forcing in a von Karman flow, at constant impeller speed, or at constant torque. We find that the different forcing conditions change the nature of the stability of the steady states and reveal dynamical regimes that bear similarities to low-dimensional systems. We suggest that this forcing dependence may be applicable to other turbulent systems.
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Ano: 2013 URL: http://archimer.ifremer.fr/doc/00172/28352/26652.pdf
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Experimental measurement of the scale-by-scale momentum transport budget in a turbulent shear flow ArchiMer
Marie, Louis; Daviaud, F.
We report measurements linking velocity fluctuations with the turbulent drag in a turbulent closed flow, namely the von Karman flow. Making use of the angular momentum balance equation in integral form, we obtain a simple expression for the torque applied by the forcing mechanism, which we check against quantitative laser Doppler velocimetry measurements. We then decompose the angular momentum flux into contributions coming from the different spectral components of the flow. We provide evidence of the fact that the turbulent drag is dominantly generated by coherent structures at the largest scales of the flow. (C) 2004 American Institute of Physics.
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Ano: 2004 URL: http://archimer.ifremer.fr/doc/00254/36475/35019.pdf
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Flux dynamics of planktic foraminiferal tests in the south-eastern Bay of Biscay (northeast Atlantic margin) ArchiMer
Kuhnt, Tanja; Howa, Helene; Schmidt, Sabine; Marie, Louis; Schiebel, Ralf.
The temporal and water depth related dynamics of planktic foraminiferal fluxes in the south-eastern Bay of Biscay are discussed for a two year sampling period (June 2006-June 2008). Two sediment traps deployed at 800 m and 1700 m water depth at a mooring in 2000 m of water depth, were analyzed for the flux of planktic foraminiferal species >150 mu m, in comparison with the total mass flux. Total flux of planktic foraminifera shows seasonal maxima in spring/early summer (>2000 Ind.m(-2) d(-1)) and minima from late summer through winter (<10 Ind.m(-2) d(-1)). The flux of planktic foraminiferal tests in the intermediate to deep water column at the inner Bay of Biscay comprises an intermittent and regionally variable signal of seasonal surface water...
Tipo: Text Palavras-chave: Planktic foraminifera; Bay of Biscay; Sediment traps; Particulate mass flux; Pb-210; Seasonality; Lateral advection.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00125/23593/21785.pdf
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Galerkin analysis of kinematic dynamos in the von Karman geometry ArchiMer
Marie, Louis; Normand, C; Daviaud, F.
We investigate dynamo action by solving the kinematic dynamo problem for velocity fields of the von Karman type between two coaxial counter-rotating propellers in a cylinder. A Galerkin method is implemented that takes advantage of the symmetries of the flow and their subsequent influence on the nature of the magnetic field at the dynamo threshold. Distinct modes of instability have been identified that differ by their spatial and temporal behaviors. Our calculations give the result that a stationary and antisymmetric mode prevails at the dynamo threshold. We then present a quantitative analysis of the results based on the parametric study of four interaction coefficients obtained by reduction of our initially large eigenvalue problem. We propose these...
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Ano: 2006 URL: https://archimer.ifremer.fr/doc/00253/36474/35014.pdf
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Generation of a magnetic field by dynamo action in a turbulent flow of liquid sodium ArchiMer
Monchaux, R.; Berhanu, M.; Bourgoin, M.; Moulin, M.; Odier, Ph.; Pinton, J. -f.; Volk, R.; Fauve, S.; Mordant, N.; Petrelis, F.; Chiffaudel, A.; Daviaud, F.; Dubrulle, B.; Gasquet, C.; Marie, Louis; Ravelet, F..
We report the observation of dynamo action in the von Karman sodium experiment, i.e., the generation of a magnetic field by a strongly turbulent swirling flow of liquid sodium. Both mean and fluctuating parts of the field are studied. The dynamo threshold corresponds to a magnetic Reynolds number R-m similar to 30. A mean magnetic field of the order of 40 G is observed 30% above threshold at the flow lateral boundary. The rms fluctuations are larger than the corresponding mean value for two of the components. The scaling of the mean square magnetic field is compared to a prediction previously made for high Reynolds number flows.
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Ano: 2007 URL: http://archimer.ifremer.fr/doc/00253/36472/35017.pdf
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Influence of Reynolds number and forcing type in a turbulent von Karman flow ArchiMer
Saint-michel, Brice; Dubrulle, B.; Marie, Louis; Ravelet, F.; Daviaud, F..
We present a detailed study of a global bifurcation occuring in a turbulent von Karman swirling flow. In this system, the statistically steady states progressively display hysteretic behaviour when the Reynolds number is increased above the transition to turbulence. We examine in detail this hysteresis using asymmetric forcing conditions-rotating the impellers at different speeds. For very high Reynolds numbers, we study the sensitivity of the hysteresis cycle-using complementary particle image velocimetry and global mechanical measurements-to the forcing nature, imposing either the torque or the speed of the impellers. New mean states, displaying multiple quasi-steady states and negative differential responses, are experimentally observed in torque...
Tipo: Text Palavras-chave: Turbulence; Instability; Negative response; Symmetry.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00204/31503/29904.pdf
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Intense deformation field at oceanic front inferred from directional sea surface roughness observations ArchiMer
Rascle, Nicolas; Molemaker, Jeroen; Marie, Louis; Nouguier, Frederic; Chapron, Bertrand; Lund, Bjorn; Mouche, Alexis.
Fine scale current gradients at the ocean surface can be observed by sea surface roughness. More specifically, directional surface roughness anomalies are related to the different horizontal current gradient components. This paper reports results from a dedicated experiment during the LASER (LAgrangian Submesoscale ExpeRiment) drifter deployment. A very sharp front, 50 m wide, is detected simultaneously in drifter trajectories, sea surface temperature and sea surface roughness. A new observational method is applied, using sun glitter reflections during multiple airplane passes to reconstruct the multi-angle roughness anomaly. This multi-angle anomaly is consistent with wave-current interactions over a front, including both cross-front convergence and...
Tipo: Text Palavras-chave: Sea surface roughness; Surface current; Remote sensing; Sun glitter; High resolution; Oceanic fronts.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00386/49767/50301.pdf
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Mixed and mixing layer depths in the ocean surface boundary layer under conditions of diurnal stratification ArchiMer
Sutherland, G.; Reverdin, Gilles; Marie, Louis; Ward, Ben.
A comparison between mixed (MLD) and mixing (XLD) layer depths is presented from the SubTRopical Atlantic Surface Salinity Experiment (STRASSE) cruise in the subtropical Atlantic. This study consists of 400 microstructure profiles during fairly calm and moderate conditions (2 < U10 < 10 m s−1) and strong solar heating O(1000 W m−2). The XLD is determined from a decrease in the turbulent dissipation rate to an assumed background level. Two different thresholds for the background dissipation level are tested, 10−8 and 10−9 m2 s−3, and these are compared with the MLD as calculated using a density threshold. The larger background threshold agrees with the MLD during restratification but only extends to half the MLD during nighttime convection, while the...
Tipo: Text Palavras-chave: Ocean surface boundary layer; Mixed and mixing layer depths; Buoyancy.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00240/35101/33594.pdf
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Multifrequency seismic detectability of seasonal thermoclines assessed from ARGO data ArchiMer
Ker, Stephan; Le Gonidec, Y.; Marie, Louis.
Seismic Oceanography is a developing research topic where new acoustic methods allow high-resolution teledetection of the thermohaline structure of the ocean. First implementations to study the Ocean Surface Boundary Layer have recently been achieved but remain very challenging due to the weakness and shallowness of such seismic reflectors. In this article, we develop a multifrequency seismic analysis of hydrographic datasets collected in a seasonally stratified midlatitude shelf by ARGO network floats to assess the detectability issue of shallow thermoclines. This analysis, for which sensitivity to the data reduction scheme used by ARGO floats for the transmission of the profiles is discussed, allows characterizing both the depth location and the...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00347/45801/45446.pdf
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Multiscale seismic reflectivity of shallow thermoclines ArchiMer
Ker, Stephan; Le Gonidec, Yves; Marie, Louis; Thomas, Yannick; Gibert, Dominique.
Seismic Oceanography is coming of age as an established technique of observation of the thermohaline structure of the ocean. The present paper deals with the seismic reflectivity of the Armorican Shelf seasonal thermocline, west of France, based on two seismic experiments performed with a sparker source. The peak frequency was 500 Hz for the ASPEX experiment, where the thermocline was located at 27 m water depth, and reduced to 400 Hz associated to a higher source level for the IFOSISMO experiment, where the thermocline was 12 m deeper. Despite this settings, only the first experiment could clearly highlight the thermocline reflector, providing the first seismic observation of a shallow oceanic structure. To better understand the limitation of...
Tipo: Text Palavras-chave: Thermocline; Seismic method; Wavelet analysis; Acoustic.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00254/36535/35066.pdf
Registros recuperados: 27
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