Support for choosing the precision mode of MPAS dycore via CIME

[kuanchihwang]

What is the feature/what would you like to discuss?

Since CAM-SIMA PR #327, the capability of running MPAS dycore in single precision mode has been introduced. However, to enable it, users have to manually uncomment the line # export CPPFLAGS += -DSINGLE_PRECISION in the Makefile at src/dynamics/mpas/assets/Makefile.in.CESM.

The ConfigCAM Python class can already parse the dyn_kind argument, which can be specified via the CAM_CONFIG_OPTS variable. Therefore, for better usability, we should allow users to choose the Fortran real kind in MPAS dycore by the usual CIME method:

./xmlchange --append CAM_CONFIG_OPTS="--dyn_kind REAL32" # For single precision
./xmlchange --append CAM_CONFIG_OPTS="--dyn_kind REAL64" # For double precision

Is there anyone in particular you want to be part of this conversation?

No response

Will this change (regression test) answers?

No

Will you be implementing this enhancement yourself?

Yes