Recent Progresses in Modelling the Global Ocean/Sea-Ice Circulation at Eddy Permitting Resolution
Bernard Barnier(1) , Thierry Penduff(1) , jean Marc Molines(1) , Anne Marie Treguier(2) , and Gurvan MADEC(3)
(2) LPO-CNRS, IFREMER Centre de Brest, 29280 Plouzane, France
(3) LOCEAN/CNRS, 4 place Jussieu, 75252 Paris, France
Solutions of numerical models of the ocean general circulation always showed a significant dependency upon numerical schemes and physical parameterizations that are used. Series of sensitivity tests have been performed with a z-coordinate, global eddy permitting (1/4°) 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 scheme for momentum advection with a partial step 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. Comparison 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° resolution on some aspects concerning mean flow patterns and distribution of eddy kinetic energy. 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.