WRF - Developmental Testbed Center

not necessary to use a parallel io_form, but when one is used, each CPU will read/writeits input/output to a separate file, whose name is simply the name that would be usedduring serial execution, but with a four-digit processor ID appended to the name. Forexample, running geogrid on four processors with io_form_geogrid=102 would createoutput files named geo_em.d01.nc.0000, geo_em.d01.nc.0001, geo_em.d01.nc.0002, andgeo_em.d01.nc.0003 for the coarse domain.During distributed-memory execution, model domains are decomposed into rectangularpatches, with each processor working on a single patch. When reading/writing from/tothe WRF I/O API format, each processor reads/writes only its patch. Consequently, if aparallel io_form is chosen for the output of geogrid, metgrid must be run using the samenumber of processors as were used to run geogrid. Similarly, if a parallel io_form ischosen for the metgrid output files, the real program must be run using the same numberof processors. Of course, it is still possible to use a standard io_form when running onmultiple processors, in which case all data for the model domain will bedistributed/collected upon input/output. As a final note, when geogrid or metgrid are runon multiple processors, each processor will write its own log file, with the log file namesbeing appended with the same four-digit processor ID numbers that are used for the I/OAPI files.Checking WPS OutputWhen running the WPS, it may be helpful to examine the output produced by theprograms. For example, when determining the location of nests, it may be helpful to seethe interpolated static geographical data and latitude/longitude fields. As anotherexample, when importing a new source of data into WPS – either static data ormeteorological data – it can often be helpful to check the resulting interpolated fields inorder to make adjustments the interpolation methods used by geogrid or metgrid.By using the NetCDF format for the geogrid and metgrid I/O forms, a variety ofvisualization tools that read NetCDF data may be used to check the domain filesprocessed by geogrid or the horizontally interpolated meteorological fields produced bymetgrid. In order to set the file format for geogrid and metgrid to NetCDF, the usershould specify 2 as the io_form_geogrid and io_form_metgrid in the WPS namelistfile (Note: 2 is the default setting for these options):&shareio_form_geogrid = 2,/&metgridio_form_metgrid = 2,/Among the available tools, the ncdump, ncview, and new RIP4 programs may be ofinterest. The ncdump program is a compact utility distributed with the NetCDF librariesWRF-NMM V3: User’s Guide 3-20