In 1991, CERFACS decided to tackle coupled climate modelling and to develop a software interface to couple existing numerical General Circulation Models of the ocean and of the atmosphere. Today, the OASIS3 coupler, which is the result of more than 15 years of evolution is used by about 30 modelling groups in Europe, Australia, Asia and North America, on the different computing platforms used by the climate modelling community. The list of coupled models realized with OASIS3 and previous versions and the platforms onto which they were run on in the few past years can be found in Appendix C.
OASIS3 sustained development is ensured by a collaboration between CERFACS and the Centre National de la Recherche Scientifique (CNRS) and its maintainance and user support is presently reinforced with additinal resources coming from IS-ENES project funded by the EU (FP7 - GA no 228203), into which the parallel OASIS4 version of the coupler is also currently being developed.
OASIS3 is a portable set of Fortran 77, Fortran 90 and C routines. Portability and flexibility are OASIS3 key design concepts. At run-time, OASIS3 acts as a separate executable, which main function is to interpolate the coupling fields exchanged between the component models, and as a communication library linked to the component models, the OASIS3 PRISM Model Interface Library (PSMILe). OASIS3 supports 2D coupling fields in the longitude and latitude dimensions. To communicate with OASIS3, or directly with another model, or to perform I/O actions, a component model needs to include few specific PSMILe calls. OASIS3 PSMILe supports in particular parallel communication between a parallel component model and OASIS3 interpolation executable based on Message Passing Interface (MPI) and file I/O using the mpp_io library from GFDL. New with this version, the OASIS3 interpolation executable can be run on many processes, each process interpolating a subset of the coupling fields, resulting in a parallelisation of OASIS3 on a field-per-field basis. For each coupling exchange, OASIS3 performs the transformations and regridding needed to express the source field on the grid of the target model. The current OASIS3_3 version and its toy coupled model TOYOASIS3 were compiled and run on NEC SX6, IBM Power4, CRAY XD1, and Linux PC (XXX list to be updated).