4 New functionality offered

• Better support of components for which only a subset of processes participate in the coupling

  In OASIS3.3, components for which only a subset of processes participated in the coupling were supported in a very restricted way. In fact, this subset had to be composed of the N first processes and N had to be specified in the namcouple. Now, the subset of processes can be composed of any of the component processes and does not have to be pre-defined in the namcouple. New routines oasis_create_couplcomm and oasis_set_couplcomm are now available to create or set a coupling communicator gathering only these processes (see section ). (Note: this wass further improved in OASIS3-MCT_3.0.)

• Exact restart for LOCTRANS transformations

  If needed, LOCTRANS transformations write partially transformed fields in the coupling restart file at the end of a run to ensure an exact restart of the next run (see section 4.1). For that reason, coupling restart filenames are now required for all namcouple entries that use LOCTRANS (with non INSTANT values). This is the reason an optional restart file is now provided on the OUTPUT namcouple input line. If the coupling periods of two (or more) coupling fields are different, it is necessary to define two (or more) restart files, one for each field.

• Support to couple multiple fields via a single communication.

  This is supported through colon delimited field lists in the namcouple, for example

  ATMTAUX:ATMTAUY:ATMHFLUX TAUX:TAUY:HEATFLUX 1 3600 3 rstrt.nc EXPORTED

  in a single namcouple entry. All fields will use the namcouple settings for that entry. In the component model codes, these fields are still sent (“put”) or received (“get”) one at a time. Inside OASIS3-MCT, the fields are stored and a single mapping and send or receive instruction is executed for all fields. This is useful in cases where multiple fields have the same coupling transformations and to reduce communication costs by aggregating multiple fields into a single communication. If a LOCTRAN transformation is needed for these multiple fields, it is necessary to define a restart file for these multiple fields. The coupling fields must be sent and received in the same order as they are defined in the corresponding single entry of the namcouple (not relevant in further versions of OASIS3-MCT).

• Matching one source filed with multiple targets

  A coupling field sent by a source component model can be associated with more than one target field and model (get). In that case, the source model needs to send (“put”) the field only once and the corresponding data will arrive at multiple targets as specified in the namcouple configuration file. Different coupling frequencies and transformations are allowed for different coupling exchanges of the same field. If coupling restart files are required (either if a LAG or if a LOCTRANS transformation is specified), it is mandatory to specify different files for the different fields.

  The inverse feature is not allowed, i.e. a single target (get) field CANNOT be associated with multiple source (put) fields.

• The debug files

  The debug mode was greatly improved as compared to OASIS3.3. The level of debug information written out to the OASIS3-MCT debug files for each model process is defined by the $NLOGPRT value in the namcouple. All details are provided in section 3.2.