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Model output

Excerpt

The instructions in this article show how to convert OpenIFS GRIB output to netCDF for use in other analysis and visualisation software.

The OpenIFS model outputs files in GRIB format. These files are a mix of GRIB 1 & GRIB 2 format messages. They also contain multiple vertical coordinates: pressure levels, sub-surface levels etc as well as fields on reduced Gaussian grids which causes a problem with some 3rd party tools as the same GRIB variable code is used for each axis. The instructions below show how to work around this.

The ICMGG files contain all the gridpoint fields. The ICMSH files are the spherical harmonics of the wind fields, pressure and temperature.

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Info
The MetView application is available for analysis and visualisation of OpenIFS output.
Please see 'Using MetView with OpenIFS' for more details.
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Grib-api tools

grib_to_netcdf

This command will convert one or more GRIB files to netCDF is available with the ECMWF grib_api software (versions above 1.11.0 are recommended. It is not available in versions less than 1.10.0). For more details please see: grib_to_netcdf description.

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To convert from vorticity and divergence to winds, please see CDO instructions below.

CDO commands

These instructions assume the use of a recent version of Climate Data Operators (CDO) (available from Max-Planck-Institut, Germany).

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Code Block
titleExample cdo command for inspecting GRIB file
$ cdo sinfo ICMSHfrq2+000000.grb 
   File format: GRIB
    -1 : Institut Source   Param       Time Typ  Grid Size Num  Levels Num
     1 : ECMWF    unknown  11.3        var  P16     65792   1      60   1
     2 : ECMWF    unknown  39.3        var  P16     65792   1      60   1
     3 : ECMWF    unknown  43.3        var  P16     65792   1      60   1
     4 : ECMWF    unknown  44.3        var  P16     65792   1      60   1
     5 : ECMWF    unknown  152.128     var  P16     65792   1       1   2
     6 : ECMWF    unknown  6.3         var  P16     65792   1       1   2
   Horizontal grids :
     1 : spectral     > size      : dim = 65792  truncation = 255  spc = 32896
                                    complexPacking = 1
   Vertical grids :
     1 : hybrid            level : 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 
                                   20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 
                                   36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 
                                   52 53 54 55 56 57 58 59 60 
     2 : hybrid            level : 1 
   Time axis :  1 step
     RefTime =  1999-12-24 12:00:00  Units = hours  Calendar = PROLEPTIC
  YYYY-MM-DD hh:mm:ss  YYYY-MM-DD hh:mm:ss  YYYY-MM-DD hh:mm:ss  YYYY-MM-DD hh:mm:ss
  1999-12-24 12:00:00
cdo sinfo: Processed 6 variables over 1 timestep. ( 0.04s )

Example 1 - Converting a single file

In this example a single GRIB file with model level data, on a regular Gaussian grid is converted to netCDF with vorticity & divergence replaced by u & v and model level data interpolated to pressure levels.

Code Block
grib_set -s editionNumber=1 file file.grb
cdo -t ecmwf -f nc copy file.grb file.nc
cdo -t ecmwf dv2uvl file.nc file_uv.nc
cdo -t ecmwf sp2gpl file_uv.nc file_uv_gg.nc
cdo -t ecmwf ml2pl,92500,85000,50000,20000 file_uv_gg.nc file_uv_gg_pl.nc

Example 2 - Converting series of files

The following script shows how to loop over several output files using the steps above to convert to netCDF:

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