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

International audienc

6. Performance et parallélisation

International audienc

6. Performance et parallélisation

La puissance de calcul est la clef de voûte de la modélisation du climat. Depuis l’origine, cette science a suivi les progrès de l’informatique et en a largement bénéficié. Symétriquement, en tant qu’utilisatrice des supercalculateurs les plus puissants au monde, elle a longtemps contribué à leur développement. Tirer parti de toutes les ressources de calcul disponibles est donc une préoccupation majeure qui transparaît dans le code informatique lui-même : choix du langage, performance des alg..

Improving ocean modeling software NEMO 4.0 benchmarking and communication efficiency

International audienceCommunications in distributed memory supercomputers are still limiting scalability of geophysical models. Considering the recent trends of the semiconductor industry, we think this problem is here to stay. We present the optimizations that have been implemented in the 4.0 version of the ocean model NEMO to improve its scalability. Thanks to the collaboration of oceanographers and HPC experts, we identified and removed the unnecessary communications in two bottleneck routines, the computation of free surface pressure gradient, and the forcing in the straight or unstructured open boundaries. Since a wrong parallel decomposition choice could undermine computing performance, we impose its automatic definition in all cases, including when subdomains containing land points only are excluded from the decomposition. For a smaller audience of developers and vendors, we propose a new benchmark configuration, which is easy to use while offering the full complexity of operational versions

Les modèles climatiques gagnent en précision

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Ocean-Atmosphere Modelization over the Grid

apport de recherch

Ocean-Atmosphere Application Scheduling within DIET

apport de recherch

HyMeX - The regional coupled system WRF-NEMO over the Mediterranean (MORCE plateform): impacts of mesoscale coupled processes on the water budget estimation

The Mediterranean climate and water cycle are strongly affected by fine-scale and coupled processes, which generally involve all the Earth system compartments (ocean - atmosphere - land surface). Their investigation by modelling needs the development of accurate coupled and mesoscale numerical systems. We build at IPSL the MORCE (Model Of the Regional Coupled Earth system) plateform over the Mediterranean area. It includes the regional air-sea coupled system WRF-OASIS-NEMO. The horizontal resolutions are 20km for the non-hydrostatic atmospheric model WRF and 1/12o for the eddy-resolving ocean circulation model NEMO-MED12. The Sea Surface Temperature (SST) and fluxes exchanges between the two models are managed via the OASIS coupler. Three simulations are currently available: (1)The downscaling of the ERA-interim reanalyses (1989-2008) by WRF. This simulation is also part of the Med-CORDEX project; (2)The NEMO-MED12 simulation for the same period, driven by air-sea fluxes provided by simulation (1) every 3 hours; (3)The two-way interactive coupled run (MORCE experiment). The coupling frequency chosen is 3 hours. The comparison of the uncoupled/coupled runs is done to evaluate the role of mesoscale coupled processes on the water budget. Compared to reanalyses, the coupled system better represents the mean SST, especially in summer. The coupling produces mesoscale patterns in the turbulent fluxes that slightly modify the general and thermohaline circulations. In the atmospheric model, the SST modifications between uncoupled and coupled runs induce strong retroactions on the Precipitation (P) and Evaporation (E) fields. We found a significant spatial correspondence between the SST anomalies and the P and E anomalies. The fine-scale P anomalies extend over the coastal area, but the extension seems to be limited by the surrounding orography. The wind speed is also decreased in the coupled mode over the whole domain, except over some SST anomaly hot-spots. Finally, the annual cycles of P, E and E-P over sea show weak differences. This highlights that the coupled processes major role is the redistribution of the water at mesoscale