Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

OASIS3 coupler

The OASIS3 coupler is a software package allowing synchronized exchanges of coupling information between numerical models representing different sub-systems of the climatic system. In particular, OASIS3 performs the transformations needed to express, on the grid of a target model, the coupling fields produced by a source model on its grid. Different transformations and 2D interpolations (gaussian weighted nearest neighbour, bilinear, bi-cubic, conservative re-mapping, etc) are available in OASIS3, thanks in particular to its interfacing with the SCRIP 1.4 library. OASIS3 is a portable set of Fortran 77, Fortran 90 and C routines. At run-time, OASIS3 acts as a separate mono process executable, which main function is to interpolate the coupling fields, and as a library linked to the component models, the PRISM Model Interface Library, PSMILe.

The models themselves may remain as separate executables, keeping their own main options as in the uncoupled mode. To communicate with OASIS3, or directly between them, or to perform I/O actions, the component models need to include few specific PSMILe calls. OASIS3 PSMILe supports:

- Parallel communication between a parallel component model and OASIS3 main process based on Message Passing Interface (MPI);

- Direct communication between parallel component models when no transformations are required, also based on MPI;

- Automatic sending and receiving actions at appropriate times, time integration or accumulation of the coupling fields;

- I/O actions from/to files thanks to the mpp_io library from GFDL.

Flexibility is ensured by the fact that all options for a particular coupled simulation (i.e. the component models, the coupling fields, the coupling sequencing and periods, the interpolations and other transformations), are defined externally before the run by the user in an external configuration text file. This configuration file is read at the beginning of the run by OASIS3 and transferred to the model PSMILe libraries; during the run. OASIS3 and the model PSMILe libraries then perform appropriate actions automatically.

OASIS3, and in particular its PSMILe library, is an evolution realized in the PRISM project of the OASIS coupler developed and maintained since more than 10 years in CERFACS (Toulouse, France).

OASIS3 and its toy coupled model have been compiled and successfully run on Fujitsu VPP5000, NEC SX6, SGI Octane and 03000, IBM Power4, COMPAQ Alpha cluster and Linux PC cluster. OASIS3 has been extensively used in the PRISM demonstration runs and is currently used by approximately 10 climate-modelling groups in Europe, USA, Canada, Australia, India and Brazil.

Sharing standard coupling software between different institutions brings along many benefits:

- Assembling Earth System Models based on component models sharing a common coupling software is technically easier;

- Each institution benefits, at relatively low cost, from the central development of the coupler by dedicated IT experts;

- Sharing common software increases interaction between the different institutions;

- Computer manufacturers are inclined to work on software widely used across the climate modelling community, increasing thereby its portability.

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