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Run ungrib twice: for surface (GRIB1) and for model level (GRIB2) files

Ungrib run for

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surface fields

Ungrib section of namelist.wps file can look like this:

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$ ln -sf Vtable.ECMWF_sigma Vtable
$ link_grib.csh *sfc*
$ ungrib.exe

Where Vtable.ECMWF_sigma is updated for mix of GRIB1 and GRIB2 data produced IFS. The table should be download from this page because table with the same name in official release of WPS is outdated!

Ungrib run for

...

model level fields

Ungrib section of namelist.wps file should be modified to create intermediate files with different names in order to avoid overwriting of the intermediate files created in the first ungrib run.

&ungrib
 out_format = 'WPS',
 prefix = 'MFILE',
/

After making these changes, the ungrib can be safely run for the second time"

$ ln -sf Vtable.ECMWF_sigma Vtable
$ link_grib.csh *ml*
$ ungrib.exe

Calculate pressure at model levels

Using Using calc_ecmwf_p.exe utility tool available at WPS /"util/" directory, calculate pressure at ECMWF model levels. calc_ecmwf_p.exe expects to have file with name ecmwf_coeffs containing list of coefficients for all model levels. The file attached here contains coefficients for IFS 137 vertical model levels which is derived from L137 model level definitions.

Running geogrid

Geogrid should be run as usual without any modifications.

Running metgrid

If steps above were successful, in your run directory you should have "SFILE", "MFILE", and "PRES" files.

SFILE - contains surface fields, produced by the 1st ungrib run

MFILE - contains model levels fields, produced by the 2nd run of ungrib

PRES - contains pressure values on all model levels, produced by calc_ecmwf_p.exe

Before running metgrid, make sure to instruct metgrid to use all three type of files. This can be done by setting "fg_name" in the namelist.wps as shown below:

&metgrid
 fg_name = 'SFILE' 'MFILE' 'PRES'

Real and WRF

real.exe and erf.exe should be run as usual, without any modifications. Users just need to set namelist variables "num_metgrid_levels" and "num_metgrid_soil_levels" to match number of input levels created by WPS.