WRF - Developmental Testbed Center

Step 2: Extracting meteorological fields from GRIB files with ungribHaving already downloaded meteorological data in GRIB format, the first step inextracting fields to the intermediate format involves editing the “share” and “ungrib”namelist records of the namelist.wps file – the same file that was edited to define thesimulation domains. An example of the two namelist records is given below.&sharewrf_core = 'ARW',max_dom = 2,start_date = '2008-03-24_12:00:00','2008-03-24_12:00:00',end_date = '2008-03-24_18:00:00','2008-03-24_12:00:00',interval_seconds = 21600,io_form_geogrid = 2/&ungribout_format = 'WPS',prefix = 'FILE'/In the “share” namelist record, the variables that are of relevance to ungrib are thestarting and ending times of the coarse domain (start_date and end_date; alternatively,start_year, start_month, start_day, start_hour, end_year, end_month, end_day,and end_hour) and the interval between meteorological data files (interval_seconds).In the “ungrib” namelist record, the variable out_format is used to select the format ofthe intermediate data to be written by ungrib; the metgrid program can read any of theformats supported by ungrib, and thus, any of 'WPS', 'SI', and 'MM5' may be specifiedfor out_format, although 'WPS' is recommended. Also in the "ungrib" namelist, the usermay specify a path and prefix for the intermediate files with the prefix variable. Forexample, if prefix were set to 'ARGRMET', then the intermediate files created by ungribwould be named according to AGRMET:YYYY-MM-DD_HH, where YYYY-MM-DD_HHis the valid time of the data in the file.After suitably modifying the namelist.wps file, a Vtable must be supplied, and the GRIBfiles must be linked (or copied) to the filenames that are expected by ungrib. The WPS issupplied with Vtable files for many sources of meteorological data, and the appropriateVtable may simply be symbolically linked to the file Vtable, which is the Vtable nameexpected by ungrib. For example, if the GRIB data are from the GFS model, this could beaccomplished with> ln -s ungrib/Variable_Tables/Vtable.GFS VtableThe ungrib program will try to read GRIB files named GRIBFILE.AAA,GRIBFILE.AAB, …, GRIBFILE.ZZZ. In order to simplify the work of linking the GRIBfiles to these filenames, a shell script, link_grib.csh, is provided. The link_grib.csh scripttakes as a command-line argument a list of the GRIB files to be linked. For example, ifWRF-NMM V3: User’s Guide 3-8