Decadal prediction skill using a high-resolution climate model

The ability of a high-resolution coupled atmosphere–ocean general circulation model (with a horizontal resolution of a quarter of a degree in the ocean and of about 0.5° in the atmosphere) to predict the annual means of temperature, precipitation, sea-ice volume and extent is assessed based on initialized hindcasts over the 1993–2009 period. Significant skill in predicting sea surface temperatures is obtained, especially over the North Atlantic, the tropical Atlantic and the Indian Ocean. The Sea Ice Extent and volume are also reasonably predicted in winter (March) and summer (September). The model skill is mainly due to the external forcing associated with well-mixed greenhouse gases. A decrease in the global warming rate associated with a negative phase of the Pacific Decadal Oscillation is simulated by the model over a suite of 10-year periods when initialized from starting dates between 1999 and 2003. The model ability to predict regional change is investigated by focusing on the mid-90’s Atlantic Ocean subpolar gyre warming. The model simulates the North Atlantic warming associated with a meridional heat transport increase, a strengthening of the North Atlantic current and a deepening of the mixed layer over the Labrador Sea. The atmosphere plays a role in the warming through a modulation of the North Atlantic Oscillation: a negative sea level pressure anomaly, located south of the subpolar gyre is associated with a wind speed decrease over the subpolar gyre. This leads to a reduced oceanic heat-loss and favors a northward displacement of anomalously warm and salty subtropical water that both concur to the subpolar gyre warming. We finally conclude that the subpolar gyre warming is mainly triggered by ocean dynamics with a possible contribution of atmospheric circulation favoring its persistence

Tropical Channel NEMO-OASIS-WRF Coupled Simulations at Very High Resolution

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simulation des grandes echelles de l'ecoulement instationnaire turbulent dans une tuyere 3D transsonique

A realistic 3D internal, unsteady, turbulent and compressible ow was simulated using the Large Eddy Simulation (LES). This work was supported by the Consortium Industrie- Recherche en Turbomachines (CIRT) and was conducted in a collaboration with the LEMFI. The selected test-case was a 3D convergent-divergent transsonic nozzle. Indeed there were available experimental results (ONERA) and numerical simulations using RANS approach (LEMFI) that could be used for comparisons with our simulation. Also this configuration contained the main physical phenomena encountered in turbomachinery. The nozzle is a rectangular channel with a swept three-dimensional bump on the lower wall. A 3D shock wave/boundary layer interaction takes place downstream the bump, lea- ding to a large separation. In the LES approach, the large unsteady and energetic scales are calculated. The contri- bution of the unresolved small scales is modeled using the mixed scale model, developped at the LIMSI-CNRS. Time integration of the equations is preformed by a second order explicit Runge-Kutta scheme. The spatial discretization of the Euler fluxes is obtained by a second order TVD Harten-Yee scheme while the viscous fluxes are discretized by a central scheme. The LES of such flow has given some interesting unsteady results. The temporal evolution of the turbulent eddies, convected by the mean flow, has been observed. The large sepa- ration became unstable and the shock wave oscillations were captured by the LES. The methodology was then validated by comparing our results on the isentropic Mach number, the mean velocity and the Reynolds stress tensor to the numerical results given by the statistical modelisation of Launder-Shima (LEMFI) and experiments (ONERA). The kinetic energy balance was also analyzed and compared to the statistical one, in the separation zone. The LES results on the balance of k have shown that this approach pre- dicts correctly the large fluctuations of the pressure in the shock wave measured in the midle of the channel, on the opposite of the statistical ones.Cette thèse porte sur la simulation numérique d'un écoulement interne compressible, ins- tationnaire et turbulent à l'aide de la Simulation des Grandes Echelles (SGE). Dans cette approche, les grandes échelles énergétiques et instationnaires de l'écoulement sont calcu- lées, tandis que les petites échelles sont modélisées. L'objectif de ce travail, réalisé en collaboration avec le Consortium Industrie-Recherche dans les Turbomachines (CIRT) et le LEMFI, est d'analyser les potentialités de la SGE pour le calcul d'écoulements confinés en géométrie 3D en vue d'applications aux turboma- chines. Le cas d'étude retenu pour la validation de la méthodologie est l'écoulement dans une tuyère 3D transsonique pour lequel il existe de nombreux résultats statistiques (LEMFI) et expérimentaux (ONERA). La tuyère est caractérisée par une bosse en flèche sur la paroi basse génératrice d'effets 3D. L'écoulement, sans rotation, présente cependant les phénomènes physiques complexes d'interaction onde de choc/couche limite et de large dé- collement, comme ceux rencontrés au sein des turbomachines. La SGE est obtenue à partir d'un modèle de sous maille d'échelles mixtes développé au LIMSI-CNRS. La discrétisa- tion temporelle des équations est réalisée par un schéma de Runge-Kutta explicite d'ordre deux. Les flux Euler sont discrétisés par un schéma TVD d'Harten-Yee d'ordre deux tandis que les flux visqueux le sont par un schéma centré. La SGE a permis d'obtenir des informations instationnaires sur l'écoulement, et de mettre en évidence la formation et le lâcher de tourbillons dans la tuyère. La solution insta- tionnaire est différente de la solution stationnaire RANS obtenue avec une modélisation statistique classique et montre l'oscillation du choc et la déstabilisation du décollement au cours du temps. Les résultats de la SGE obtenus sur le nombre de Mach isentropique, les profils de la vitesse moyenne et les tensions de Reynolds sont discutés et comparés aux résultats expérimentaux (ONERA) et statistiques, obtenus avec le modèle de Launder- Shima (LEMFI). Le bilan de l'énergie cinétique turbulente (k) est analysé et comparé à celui donné par la modélisation statistique, dans le décollement. Les résultats de la SGE montrent des différences notables avec les résultats statistiques dans le c÷ur de la tuyère : les termes de fluctuations de pression importants mesurés dans le choc sont pris en compte par la SGE

SIMULATION DES GRANDES ECHELLES DE L'ECOULEMENT INSTATIONNAIRE TURBULENT DANS UNE TUYERE 3D TRANSSONIQUE

PARIS-BIUSJ-Physique recherche (751052113) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocSudocFranceF

Conservative Regridding When Grid Cell Edges Are Unknown -- Case of SCRIP

16 pages, 1 figureNowadays, climate models rely on couplers. Each complete climate model is broken into different sub-models (oceanic, atmospheric,...), each one working on a different grid. The coupler brings these models together and interpolates the physical quantities between the grids. However, neither the coupler nor sometimes the sub-models themselves know precisely the grid cell edges. They only know the grid cell corners (vertices) and the true grid cell areas. Thus, the coupler has to make assumptions about the grid cell edges in order to compute the grid cell intersections. For first-order schemes, the most straightforward way to interpolate scalar quantities is to directly use these approximate grid cell intersections, that don' take the true grid cell areas into account. It is the method used in the "conservative" regridding option implemented in the widely used spherical interpolation package SCRIP. We show that is doesn't preserve integrals in the general case, whether the coupler using the SCRIP-generated weights transmits directly the intensive quantity, or its extensive counterpart (that is the same quantity multiplied by the true area of the individual source grid cell). We show how to modify the interpolation scheme to preserve integrals in the general case

Large eddy simulation of shock boundary layer interaction in a transonic internal flow

The paper presents a study of the dynamics of non-stationary shock wave and its interaction with the boundary layer in a transonic flow inside a channel with a bump. The turbulent flow is handled using Large Eddy Simulations (LES). The computations are done with the recently developed multidimensional upwind scheme and with two other commercial codes. The aim is to improve the understanding of the mechanism of shock wave dynamics, viscous/inviscid and the presence of solution hysteresis. The numerical results are compared to available experimental data

L’expérience de la fatigue chronique de patients atteints de SFC/EM, d’une MICI et de sujets tout-venant : étude quantitative et qualitative du discours préalable à la création d’une échelle d’évaluation de l’asthénie chronique

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Multithreaded or thread safe OASIS version including performance optimisations to adapt to many‐core architectures (D2.3)

<p><strong>Abstract</strong></p> <p>The developments realised in OASIS3‐MCT to improve its parallel efficiency are detailed. These will be available in the next release OASIS3‐MCT_4.0 planned for spring 2018. The most important improvements concern the communication scheme and the hybrid MPI+OpenMP parallelisation of theSpherical Coordinate Remapping and Interpolation Package (SCRIP) library. The new communication method, which can now use the mapping weights to define the intermediate mapping decomposition, takes longer to initialise but offers significant gain at run time, especially for high‐resolution cases running on a high number of tasks. The parallelisation introduced in the SCRIP library for the mapping weight calculation allows a reduction in the weight calculation time of 2 to 3 orders of magnitude for high‐resolution grids. Also, significant gains are obtained in the initialisation phase by updating the MCT library from version 2.8 to 2.10.beta1 and additional debugging. New methods introduced in the CONSERV post‐processing operation ensuring the global conservation of the coupling fields lower the calculation costs by one order of magnitude while still ensuring good level of reproducibility. Finally, additional results obtained with IS‐ENES2 coupling technology benchmarks show that OASIS3‐MCT performs as well as, and even better at very high number of cores, than other coupling technologies and<br> that its behaviour on Marconi KNL is fully satisfactory.</p> <p><strong>About this document</strong></p> <ul> <li>Work package in charge: WP2 Scalability</li> <li>Actual delivery date for this deliverable: 28 March 2018</li> <li>Dissemination level: PU (for public use)</li> <li>Lead author: Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS): Sophie Valcke</li> <li>Other contributing authors: Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS): Laure Coquart, Anthony Craig, Gabriel Jonville, Eric Maisonnave, Andrea Piacentini</li> <li>Internal reviewers: Sveriges Meteorologiska och Hydrologiska Institut (SMHI): Uwe Fladrich,  BULL/ATOS (BULL): David Guibert, Erwan Raffin, Deutsches Klimarechenzentrum (DKRZ): Philipp Neumann</li> </ul