Beginning with version 2.0, MPAS-Atmosphere can be compiled and run in single-precision, offering faster model execution and smaller input and output files. Please note, however, that single-precision MPAS-Atmosphere has received only limited testing as of the 2.0 release.
To compile a single-precision MPAS-Atmosphere executable, it is necessary to first add -DSINGLE_PRECISION to the definition of MODEL_FORMULATION at the top of the main Makefile. We've found that some versions of the ifort compiler have difficulties with certain parts of the MPAS-A solver in single precision, and consequently, it may also be necessary to add -DSINGLE_PRECISION_IFORT to the specification of MODEL_FORMULATION if using the ifort compiler. Additionally, any compiler flags, such as -fdefault-real-8, -r8, or -real-size 64 must be removed from the compiler target that will be used. For example, if compiling with the gfortran compiler, one would change the line
"FFLAGS_OPT = -O3 -m64 -ffree-line-length-none -fdefault-real-8 -fdefault-double-8 -fconvert=big-endian -ffree-form" \
in the top-level Makefile to
"FFLAGS_OPT = -O3 -m64 -ffree-line-length-none -fconvert=big-endian -ffree-form" \
before compiling the init_atmsophere_model and atmosphere_model executables as usual.
Running MPAS-Atmosphere in single-precision requires the user to begin with single-precision SCVT grid files, and all pre-processing steps must be run using a single-precision version of init_atmosphere_model with these grid files. In order to obtain suitable grid files, any existing double-precision SCVT grid file that was downloaded from the MPAS-Atmosphere meshes download page may be run through the double_to_float_grid converter program to produce a single-precision grid file. Using the double-precision grid files with single-precision executables will not work.
Any questions related to building and running MPAS-Atmosphere should be directed to the MPAS-Atmosphere Help forum. Posting to the forum requires a free google account. Alternatively, questions may be sent from any e-mail address to "mpas-atmosphere-help AT googlegroups.com". Please note that in either case, questions and their answers will appear on the online forum.