WRF - Developmental Testbed Center

simulations may use a constant SST field; this field need only be available at a singletime, and may be used by setting the constants_name variable to the path and filenameof the SST intermediate file. Typical uses of constants_name might look like&metgridconstants_name = '/data/ungribbed/constants/SST_FILE:2006-08-16_12'/or&metgridconstants_name = 'LANDSEA', 'SOILHGT'/The second metgrid capability – that of interpolating data from multiple sources – may beuseful in situations where two or more complementary data sets need to be combined toproduce the full input data needed by real. To interpolate from multiple sources of timevarying,meteorological data, the fg_name variable in the &metgrid namelist recordshould be set to a list of prefixes of intermediate files, including path information whennecessary. When multiple path-prefixes are given, and the same meteorological field isavailable from more than one of the sources, data from the last-specified source will takepriority over all preceding sources. Thus, data sources may be prioritized by the order inwhich the sources are given.As an example of this capability, if surface fields are given in one data source and upperairdata are given in another, the values assigned to the fg_name variable may looksomething like:&metgridfg_name = '/data/ungribbed/SFC', '/data/ungribbed/UPPER_AIR'/To simplify the process of extracting fields from GRIB files, the prefix namelistvariable in the &ungrib record may be employed. This variable allows the user to controlthe names of (and paths to) the intermediate files that are created by ungrib. The utility ofthis namelist variable is most easily illustrated by way of an example. Suppose we wishto work with the North American Regional Reanalysis (NARR) data set, which is splitinto separate GRIB files for 3-dimensional atmospheric data, surface data, and fixed-fielddata. We may begin by linking all of the "3D" GRIB files using the link_grib.cshscript, and by linking the NARR Vtable to the filename Vtable. Then, we may suitablyedit the &ungrib namelist record before running ungrib.exe so that the resultingintermediate files have an appropriate prefix:&ungribout_format = 'WPS',prefix = 'NARR_3D',/After running ungrib.exe, the following files should exist (with a suitable substitution forthe appropriate dates):WRF-NMM V3: User’s Guide 3-17