An eddy-permitting model of the Atlantic circulation: Evaluating open boundary conditions Auteur(s) : Treguier, Anne-marie Barnier, B De Miranda, A Molines, J Grima, N Imbard, M Madec, G Messager, Christophe Éditeur(s) : American Geophysical Union Résumé : As part of the French CLIPPER project, an eddy permitting model of the Atlantic circulation has been run for 22 years. The domain has open boundaries at Drake passage and at 30 degreesE, from Africa to Antarctica. The simulated mean circulation, as well as the eddy activity, is satisfactory for a 1/3 degrees model resolution, and the meridional heat transport at 30 degreesS is within the range estimated from observations. We use the "mixed" open boundary algorithm of Barnier et al. [1998], which has both a radiation condition and a relaxation to climatology. The climatological boundary forcing strongly constrains the solution in the whole domain. The model heat balance adjusts through the surface (heat flux retroaction term) more than the open boundaries. The radiation phase velocities calculated within the algorithm are analyzed. This shows, quite surprisingly, that both the eastern and western boundaries have a similar behavior, regardless of the preferred directions for advection (mainly eastward) and wave propagation (mainly westward). Our results confirm that open boundary algorithms behave differently according to the dynamics of the region considered. The passive boundary condition that Penduff et al. [2000] applied successfully in the north eastern Atlantic does not work in the present South Atlantic model. We emphasize the need for a careful prescription of the climatology at the open boundary, for which a new approach based on synoptic sections is implemented. Journal of Geophysical Union - Research C - Oceans (0148-0227) (American Geophysical Union), 2001-10 , Vol. 106 , N. C10 , P. 22115-22129 Droits : 2001 American Geophysical Union http://archimer.ifremer.fr/doc/2001/publication-454.pdf DOI:10.1029/2000JC000376 http://archimer.ifremer.fr/doc/00000/454/ | Partager |
Climate change projections using the IPSL-CM5 Earth System Model: from CMIP3 to CMIP5 Auteur(s) : Dufresne, J-l. Foujols, M-a. Denvil, S. Caubel, A. Marti, O. Aumont, Olivier Balkanski, Y. Bekki, S. Éditeur(s) : Springer Résumé : We present the global general circulation model IPSL-CM5 developed to study the long-term response of the climate system to natural and anthropogenic forcings as part of the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). This model includes an interactive carbon cycle, a representation of tropospheric and stratospheric chemistry, and a comprehensive representation of aerosols. As it represents the principal dynamical, physical, and bio-geochemical processes relevant to the climate system, it may be referred to as an Earth System Model. However, the IPSL-CM5 model may be used in a multitude of configurations associated with different boundary conditions and with a range of complexities in terms of processes and interactions. This paper presents an overview of the different model components and explains how they were coupled and used to simulate historical climate changes over the past 150 years and different scenarios of future climate change. A single version of the IPSL-CM5 model (IPSL-CM5A-LR) was used to provide climate projections associated with different socio-economic scenarios, including the different Representative Concentration Pathways considered by CMIP5 and several scenarios from the Special Report on Emission Scenarios considered by CMIP3. Results suggest that the magnitude of global warming projections primarily depends on the socio-economic scenario considered, that there is potential for an aggressive mitigation policy to limit global warming to about two degrees, and that the behavior of some components of the climate system such as the Arctic sea ice and the Atlantic Meridional Overturning Circulation may change drastically by the end of the twenty-first century in the case of a no climate policy scenario. Although the magnitude of regional temperature and precipitation changes depends fairly linearly on the magnitude of the projected global warming (and thus on the scenario considered), the geographical pattern of these changes is strikingly similar for the different scenarios. The representation of atmospheric physical processes in the model is shown to strongly influence the simulated climate variability and both the magnitude and pattern of the projected climate changes. Climate Dynamics (0930-7575) (Springer), 2013-05 , Vol. 40 , N. 9-10 , P. 2123-2165 Droits : The Author(s) 2013. This article is published with open access at Springerlink.com http://archimer.ifremer.fr/doc/00138/24966/23079.pdf DOI:10.1007/s00382-012-1636-1 http://archimer.ifremer.fr/doc/00138/24966/ | Partager Voir aussi Climate Climate change Climate projections Earth System Model CMIP5 CMIP3 Greenhouse gases Aerosols Carbon cycle Allowable emissions Télécharger |
Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution Auteur(s) : Barnier, B Madec, G Penduff, T Molines, J Treguier, Anne-marie Le Sommer, J Beckmann, A Biastoch, A Éditeur(s) : Springer Résumé : Series of sensitivity tests were performed with a z-coordinate, global eddy-permitting (1/4 degrees) ocean/sea-ice model (the ORCA-R025 model configuration developed for the DRAKKAR project) to carefully evaluate the impact of recent state-of-the-art numerical schemes on model solutions. The combination of an energy-enstrophy conserving (EEN) scheme for momentum advection with a partial step (PS) representation of the bottom topography yields significant improvements in the mean circulation. Well known biases in the representation of western boundary currents, such as in the Atlantic the detachment of the Gulf Stream, the path of the North Atlantic Current, the location of the Confluence, and the strength of the Zapiola Eddy in the south Atlantic, are partly corrected. Similar improvements are found in the Pacific, Indian, and Southern Oceans, and characteristics of the mean flow are generally much closer to observations. Comparisons with other state-of-the-art models show that the ORCA-R025 configuration generally performs better at similar resolution. In addition, the model solution is often comparable to solutions obtained at 1/6 or 1/10 degrees resolution in some aspects concerning mean flow patterns and distribution of eddy kinetic energy. Although the reasons for these improvements are not analyzed in detail in this paper, evidence is shown that the combination of EEN with PS reduces numerical noise near the bottom, which is likely to affect current-topography interactions in a systematic way. We conclude that significant corrections of the mean biases presently seen in general circulation model solutions at eddy-permitting resolution can still be expected from the development of numerical methods, which represent an alternative to increasing resolution. Ocean Dynamics (1616-7341) (Springer), 2006-12 , Vol. 56 , N. 5-6 , P. 543-567 Droits : © Springer 2006. Part of Springer Science+Business Media http://archimer.ifremer.fr/doc/2006/publication-3514.pdf DOI:10.1007/s10236-006-0082-1 http://archimer.ifremer.fr/doc/00000/3514/ | Partager |