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Jullien S.,French National Center for Space Studies | Menkes C.E.,Institute Of Recherche Pour Le Developpement | Menkes C.E.,University Pierre and Marie Curie | Marchesiello P.,French National Center for Space Studies | And 8 more authors.
Journal of Physical Oceanography | Year: 2012

The present study investigates the integrated ocean response to tropical cyclones (TCs) in the South Pacific convergence zone through a complete ocean heat budget. The TC impact analysis is based on the comparison between two long-term (1979-2003) oceanic simulations forced by a mesoscale atmospheric model solution in which extreme winds associated with cyclones are either maintained or filtered. The simulations provide a statistically robust experiment that fills a gap in the current modeling literature between coarse-resolution and short-term studies. The authors' results show a significant thermal response of the ocean to at least 500-m depth, driven by competing mixing and upwelling mechanisms. As suggested in previous studies, vertical mixing largely explains surface cooling induced by TCs. However, TC-induced upwelling of deeper waters plays an unexpected role as it partly balances the warming of subsurface waters induced by vertical mixing. Below 100 m, vertical advection results in cooling that persists long after the storm passes and has a signature in the ocean climatology. The heat lost through TC-induced vertical advection is exported outside the cyclogenesis area with strong interannual variability. In addition, 60% of the heat input below the surface during the cyclone season is released back to the oceanic mixed layer through winter entrainment and then to the atmosphere. Therefore, seasonal modulation reduces the mean surface heat flux due to TCs to about 331023 PW in this region exposed to 10%-15% of the world's cyclones. The resulting climatological anomaly is a warming of about 0.18°C in the subsurface layer and cooling below the thermocline (less than 0.18°C). © 2012 American Meteorological Society. Source

Gliere A.,CEA Grenoble | Roux J.-M.,CEA Grenoble | Achard J.-L.,Laboratoire des Ecoulements Geophysiques et Industriels
Microfluidics and Nanofluidics | Year: 2013

A conducting drop in partial wetting regime, placed on the lower electrode of a parallel-plate capacitor and surrounded by a dielectric fluid, is considered. The drop, initially flattened by gravity, is elongated by the electrostatic force and possibly lifts-off when a uniform DC electric field is applied. The electrostatic force and the lift-off condition were calculated in two previous articles, respectively, for undeformable and for slightly deformable drops in the absence of gravity (zero Eötvos number). In this paper, numerical models are put to work to study accurately the complex lift-off process resulting from the competition between gravitational, electrical and capillary forces. Large deformations of the drop surface at any value of the Eötvos number may be addressed by such a numerical procedure. Computational results allow assessing the accuracy and limits of previous analytical and asymptotic relations. © 2013 Springer-Verlag Berlin Heidelberg. Source

Verhille G.,Ecole Normale Superieure de Lyon | Plihon N.,Ecole Normale Superieure de Lyon | Bourgoin M.,Laboratoire des Ecoulements Geophysiques et Industriels | Odier P.,Ecole Normale Superieure de Lyon | Pinton J.-F.,Ecole Normale Superieure de Lyon
New Journal of Physics | Year: 2010

We study magnetohydrodynamics in a von Kármán flow driven by the rotation of impellers made of material with varying electrical conductivity and magnetic permeability. Gallium is the working fluid and magnetic Reynolds numbers of order unity are achieved. We find that specific induction effects arise when the impellers' electric and magnetic characteristics differ from that of the fluid. Implications with regard to the VKS dynamo are discussed. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Salort J.,CNRS Neel Institute | Baudet C.,Laboratoire des Ecoulements Geophysiques et Industriels | Castaing B.,Ecole Normale Superieure de Lyon | Chabaud B.,CNRS Neel Institute | And 11 more authors.
Physics of Fluids | Year: 2010

We present velocity spectra measured in three cryogenic liquid H4e steady flows: grid and wake flows in a pressurized wind tunnel capable of achieving mean velocities up to 5 m/s at temperatures above and below the superfluid transition, down to 1.7 K, and a "chunk" turbulence flow at 1.55 K, capable of sustaining mean superfluid velocities up to 1.3 m/s. Depending on the flows, the stagnation pressure probes used for anemometry are resolving from one to two decades of the inertial regime of the turbulent cascade. We do not find any evidence that the second-order statistics of turbulence below the superfluid transition differ from the ones of classical turbulence, above the transition. © 2010 American Institute of Physics. Source

Scott R.B.,University of Texas at Austin | Scott R.B.,French National Center for Scientific Research | Ferry N.,Mercator Ocean | Drevillon M.,Mercator Ocean | And 6 more authors.
Ocean Dynamics | Year: 2012

We compared the estimates of surface drifter trajectories from 1 to 7 days in the equatorial Atlantic over an 18-month period with five eddying ocean general circulation model (OGCM) reanalyses and oneobservational product. The cumulative distribution of trajectory error was estimated using over 7,000 days of drifter trajectories. The observational product had smaller errors than any of the individual OGCM reanalyses. Three strategies for improving trajectory estimates using the ensemble of five operational ocean analysis and forecasting products were explored: two methods using a multi-model ensemble estimate and also spatial low-pass filtering. The results were insensitive to the method used to create the ensemble estimates, and by most measures, the results were better than the observational product. Comparison of relative skill of the various OGCM reanalyses suggested promising avenues for exploration for further improvements: forcing with higher frequency wind stress and quality control of input data. One of the lowest horizontal resolution OGCMs, with 1/4° longitude horizontal resolution, made the best trajectory estimates. The individual OGCMs were dominated by errors at spatial scales smaller than about 100 to 200 km, i.e., less than the local deformation radius. But buried in those errors were valuable signals that could be retrieved by combining all the OGCM velocity fields to produce a multimodel ensemble-based estimate. This estimate had skill down to spatial scales about 75 km. Results from this study are consistent with previous work showing that ensemble-mean forecast skill is superior to individual forecasts. © Springer-Verlag 2012. Source

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