Much of the underlying implementation of OASIS3 was refactored to leverage the Model Coupling Toolkit (MCT). OASIS3-MCT is a coupling library to be linked to the component models and that carries out the coupling field transformations (e.g. remappings/interpolations) in parallel on either the source or target processes and that performs all communication in parallel directly between the component models; there is no central coupler executable anymore14.
With MAPPING, OASIS3-MCT has the ability to read a predefined set of weights and addresses (mapping file) specified in the namcouple to perform the interpolation/remapping. The user also has the flexibility to choose the location and the parallelization strategy of the remapping with specific MAPPING options (see section ).
But as before, OASIS3-MCT_1.0 can also generate the mapping file using the SCRIP library (, ). When this is the case, the mapping file generation is done on one process of the model components; all previous SCRIPR remapping schemes available in OASIS3.3 are still supported besides BICUBIC and CONSERV/SECOND. (Note: these remapping schemes, not available in OASIS3-MCT_1.0 were reactivated in OASIS3-MCT_2.0, see .)
Only MPI1 start mode is allowed. As before with the MPI1 mode, all component models must be started by the user in the job script in a pseudo-MPMD mode; in this case, they will automatically share the same MPI_COMM_WORLD communicator and an internal communicator created by OASIS3-MCT needs to be used for internal parallelization (see section ).