WRF ARW User's Guide - MMM - UCAR

WPS
end if
write(unit=ounit) hdate, xfcst, map_source, field, &
units, desc, xlvl, nx, ny, iproj
write(unit=ounit) startloc, startlat, startlon, dx, dy, &
xlonc, truelat1, earth_radius
! 3) WRITE WIND ROTATION FLAG
write(unit=ounit) is_wind_grid_rel
! 4) WRITE 2-D ARRAY OF DATA
write(unit=ounit) slab
Creating and Editing Vtables
Although Vtables are provided for many common data sets, it would be impossible for
ungrib to anticipate every possible source of meteorological data in GRIB format. When
a new source of data is to be processed by ungrib.exe, the user may create a new Vtable
either from scratch, or by using an existing Vtable as an example. In either case, a basic
knowledge of the meaning and use of the various fields of the Vtable will be helpful.
Each Vtable contains either seven or eleven fields, depending on whether the Vtable is
for a GRIB Edition 1 data source or a GRIB Edition 2 data source, respectively. The
fields of a Vtable fall into one of three categories: fields that describe how the data are
identified within the GRIB file, fields that describe how the data are identified by the
ungrib and metgrid programs, and fields specific to GRIB Edition 2. Each variable to be
extracted by ungrib.exe will have one or more lines in the Vtable, with multiple lines for
data that are split among different level types – for example, a surface level and upper-air
levels. The fields that must be specified for a line, or entry, in the Vtable depends on the
specifics of the field and level.
The first group of fields – those that describe how the data are identified within the GRIB
file – are given under the column headings of the Vtable shown below.
GRIB1| Level| From | To |
Param| Type |Level1|Level2|
-----+------+------+------+
The "GRIB1 Param" field specifies the GRIB code for the meteorological field, which is
a number unique to that field within the data set. However, different data sets may use
different GRIB codes for the same field – for example, temperature at upper-air levels
has GRIB code 11 in GFS data, but GRIB code 130 in ECMWF data. To find the GRIB
code for a field, the g1print.exe and g2print.exe utility program may be used.
Given a GRIB code, the "Level Type", "From Level1", and "From Level2" fields are
used to specify which levels a field may be found at. As with the "GRIB1 Param" field,
the g1print.exe and g2print.exe programs may be used to find values for the level fields.
WRF-ARW V3: User’s Guide 3-32