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Tip

If you have already followed the Introduction Tutorial on GRIB decoding with ecCodes GRIB tools: inspecting GRIB files there is no need to redo these preliminary steps.

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Expand
titleClick here to see solution...

To copy only those messages for parameter T from the GRIB file tz_an_pl.grib1 use grib_copy with the -w option to specify a shortName=t:

No Format
$>  grib_copy -w shortName=t tz_an_pl.grib1 t_an_pl.grib1

Similarly to copy only those messages for parameter Z, use:

No Format
$> grib_copy -w shortName=z tz_an_pl.grib1 z_an_pl.grib1

Or, more simply, and because the file contains only parameters T and Z, one can use:

No Format
$> grib_copy tz_an_pl.grib1 "[shortName]_an_pl.grib1"

Using grib_ls of the two files confirms that the contents are correct. For example:

No Format
$> grib_ls -p centre,paramId,typeOfLevel,level,date,dataType,time,shortName t_an_pl.grib1
t_an_pl.grib1
centre       paramId      typeOfLevel  level        date         dataType     time         shortName    
ecmf         130          isobaricInhPa  1000         20170219     an           1200         t           
ecmf         130          isobaricInhPa  850          20170219     an           1200         t           
ecmf         130          isobaricInhPa  700          20170219     an           1200         t           
ecmf         130          isobaricInhPa  500          20170219     an           1200         t           
ecmf         130          isobaricInhPa  400          20170219     an           1200         t           
ecmf         130          isobaricInhPa  300          20170219     an           1200         t           
6 of 6 messages in t_an_pl.grib1
  
6 of 6 total messages in 1 files


You can take this further and split the file tz_an_pl.grib1 into separate files for each parameter/pressure level combination with:

No Format
$> grib_copy tz_an_pl.grib1 "[shortName]_[level].grib[edition]"

$> ls ?_*.grib1
t_1000.grib1  t_400.grib1  t_700.grib1  z_1000.grib1  z_400.grib1  z_700.grib1
t_300.grib1   t_500.grib1  t_850.grib1  z_300.grib1   z_500.grib1  z_850.grib1

Each file contains one message only, e.g.:

No Format
$> grib_ls -p centre,paramId,typeOfLevel,level,date,dataType,time,shortName t_1000.grib1
t_1000.grib1
centre       paramId      typeOfLevel  level        date         dataType     time         shortName    
ecmf         130          isobaricInhPa  1000         20170219     an           1200         t           
1 of 1 messages in t_1000.grib1

1 of 1 total messages in 1 files


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Info
iconfalse

Using grib_set to change key values

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Expand
titleClick here to see solution...

Use grib_ls to inspect the contents of the file tp.grib1, printing also the paramId with the –P option:

No Format
$> grib_ls -P paramId tp.grib1
tp.grib1
paramId      edition      centre       typeOfLevel  level        dataDate     stepRange    dataType     shortName    packingType  gridType     
142          1            ecmf         surface      0            20170221     24           fc           lsp          grid_simple  regular_ll  
1 of 1 messages in tp.grib1

1 of 1 total messages in 1 files

Alternatively, you could inspect the parameter namesapce with grib_ls:

No Format
$> grib_ls -n parameter tp.grib1
tp.grib1
centre      paramId     units       name        shortName   
ecmf        142         m           Large-scale precipitation  lsp        
1 of 1 messages in tp.grib1

1 of 1 total messages in 1 files

The shortName is set to lsp and paramId to 142, i.e., large-scale precipitation.

Info

The field was created using MARS compute to sum the convective and large-scale (stratiform) precipitation. When using MARS compute, the output field maintains the information from the GRIB header of the first input field so, in this case, we see that the field has paramId 142 even though the message is now supposed to contain the total precipitation.

To change the parameter to total precipitation, use grib_set as follows:

No Format
$> grib_set -s shortName=tp tp.grib1 tp_new.grib1

Check with grib_ls:

No Format
$> grib_ls -P paramId tp_new.grib1               
tp_new.grib1
paramId      edition      centre       typeOfLevel  level        dataDate     stepRange    dataType     shortName    packingType  gridType     
228          1            ecmf         surface      0            20170221     24           fc           tp           grid_simple  regular_ll  
1 of 1 messages in tp_new.grib1
   
1 of 1 total messages in 1 files


Tip

Note that changing the shortName has also changed the value of paramId. The same could be achieved by setting paramId=228:

No Format
$> grib_set -s paramId=228 tp.grib tp_new.grib



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Info
iconfalse

Converting GRIB data to netCDF with grib_to_netcdf

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