WRF - Developmental Testbed Center

from the originating center. Vtables for common GRIB model output files are providedwith the ungrib software.Vtables are provided for NAM 104 and 212 grids, the NAM AWIP format, GFS, theNCEP/NCAR Reanalysis archived at NCAR, RUC (pressure level data and hybridcoordinate data), AFWA's AGRMET land surface model output, ECMWF, and other datasets. Users can create their own Vtable for other model output using any of the Vtables asa template; further details on the meaning of fields in a Vtable are provided in the sectionon creating and editing Vtables.Ungrib can write intermediate data files in any one of three user-selectable formats: WPS– a new format containing additional information useful for the downstream programs; SI– the previous intermediate format of the WRF system; and MM5 format, which isincluded here so that ungrib can be used to provide GRIB2 input to the MM5 modelingsystem. Any of these formats may be used by WPS to initialize WRF, although the WPSformat is recommended.Program metgridThe metgrid program horizontally interpolates the intermediate-format meteorologicaldata that are extracted by the ungrib program onto the simulation domains defined by thegeogrid program. The interpolated metgrid output can then be ingested by the WRF realprogram. The range of dates that will be interpolated by metgrid are defined in the“share” namelist record of the WPS namelist file, and date ranges must be specifiedindividually in the namelist for each simulation domain. Since the work of the metgridprogram, like that of the ungrib program, is time-dependent, metgrid is run every time anew simulation is initialized.Control over how each meteorological field is interpolated is provided by theMETGRID.TBL file. The METGRID.TBL file provides one section for each field, andwithin a section, it is possible to specify options such as the interpolation methods to beused for the field, the field that acts as the mask for masked interpolations, and the gridstaggering (e.g., U, V in ARW; H, V in NMM) to which a field is interpolated.Output from metgrid is written in the WRF I/O API format, and thus, by selecting theNetCDF I/O format, metgrid can be made to write its output in NetCDF for easyvisualization using external software packages, including the new version of RIP4.Running the WPSNote: For software requirements and how to compile the WRF Preprocessing Systempackage, see Chapter 2.There are essentially three main steps to running the WRF Preprocessing System:WRF-NMM V3: User’s Guide 3-4