How_to_find_parameter_name

[odiaconu]

Hi, I am a user of ECMWF models in MET. I always had the problem of correctly identifying the name of the parameter in grib or netcdf files; I waste a lot of time trying to find the appropriate name and level. I am using before setting in config the plot_data_plane to choose them. . Please, is there another way to identify these two faster and easier? Thank you very much in avance for any idea

[jprestop]

Hi @odiaconu.

Thank you for explaining that you are having trouble correctly identifying the name of the parameter in grib or netcdf files. I do not know the current method that you are using to identify this information, but I will provide some information below.

Are you familiar with the wgrib tool for GRIB files (similarly wgrib2 for GRIB2 files) and the ncdump tool for NetCDF files?

Generally, the GRIB1 and GRIB2 tables in MET are consistent with those provided with wgrib and wgrib2. In fact, MET issue #2780 for version 12.0.0 updated MET’s GRIB tables in the data/table_files directory to make them more consistent with these tools.
If you do find a discrepancy between the variable names between MET and wgrib/wgrib2, please let us know via GitHub Discussions.

For GRIB files, using a the wgrib tool with the "-V" (verbose) option, the output for the 2t_20240331_1800.grb file that you submitted for your other Discussion (MET12.0.0 - plot_data_plane #2860) looks like:

$ wgrib -V 2t_20240331_1800.grb
rec 1:0:date 2024033118 2T kpds5=167 kpds6=1 kpds7=0 levels=(0,0) grid=255 sfc ECext=1 class=23 type=analysis stream=1025 Version=0001 anl:
  2T=2 metre temperature [K]
  timerange 0 P1 0 P2 0 TimeU 1  nx 281 ny 201 GDS grid 0 num_in_ave 0 missing 0
  center 98 subcenter 0 process 145 Table 128 scan: WE:NS winds(N/S) 
  latlon: lat  70.000000 to 20.000000 by 0.250000  nxny 56481
          long -30.000000 to 40.000000 by 0.250000, (281 x 201) scan 0 mode 128 bdsgrid 1
  min/max data 243.008 311.881  num bits 16  BDS_Ref 243.008  DecScale 0 BinScale -9

With that output, you can see the variable name "2T" for "2 metre temperature [K]". The level value shows "(0,0)". Scrolling down in the "fcst" section of the MET Configuration File Overview chapter describes the various level types for GRIB data entries:

The “level” entry specifies a level type and value:

• ANNN for accumulation interval NNN
• ZNNN for vertical level NNN
• ZNNN-NNN for a range of vertical levels
• PNNN for pressure level NNN in hPa
• PNNN-NNN for a range of pressure levels in hPa
• LNNN for a generic level type
• RNNN for a specific GRIB record number

So the level is a formatted string that begins is A, Z, P, L, or R. And that is followed by a single value (NNN) or a range of values (NNN-NNN). For example, setting the obs level = "P500"; indicates that you only want to use observations for pressure level exactly equal to 500. Whereas, level = "P475-500"; indicate that you want to use any observations falling in that pressure range.

Levels starting with "Z" filter the observations based on their height. So level = "Z18-20"; would use observations whose height is between 18 and 20.

In this way, the user can filter down which observations are included in the verification based on their pressure or height level.

You could instead use the following values to call plot_data_plane:

• The GRIB1_ptv entry is an integer specifying the GRIB1 parameter table version number.
• The GRIB1_code entry is an integer specifying the GRIB1 code (wgrib kpds5 value).

Looking at this sample output above, notice the line which reads "Table 128", that is the GRIB1 parameter table version number and note the line that indicates the kpds5 value of 167. You could then try running this MET command to plot your data:

plot_data_plane 2t_20240331_1800.grb 2t_20240331_1800.ps 'GRIB1_ptv=128; GRIB1_code=167; level="Z0";'

For NetCDF files, in the same "fcst" section, scrolling down to the "NetCDF (from MET tools, CF-compliant, p_interp, and wrf_interp):" information it describes:

• The “name” entry specifies the NetCDF variable name.
• The “level” entry specifies the dimensions to be used:
• • (i,…,j,,) for a single field, where i,…,j specifies fixed dimension values and , specifies the two dimensions for the gridded field. @ specifies the vertical level value or time value instead of offset, (i,…,@NNN,,). For example:

field = [
     {
       name       = "QVAPOR";
       level      = "(0,5,*,*)";
     },
     {
       name       = "TMP_P850_ENS_MEAN";
       level      = [ "(*,*)" ];
     }
   ];

field = [
     {
       name       = "QVAPOR";
       level      = "(@20220601_1200,@850,*,*)";
     },
     {
       name       = "TMP_P850_ENS_MEAN";
       level      = [ "(*,*)" ];
     }
   ];

For NetCDF files, using the ncdump tool, with the "-h" option (for header information), using this file as an example, running ncdump -h produces the following output:

$ ncdump -h ERA5_2020072412_Cld.nc
netcdf ERA5_2020072412_Cld {
dimensions:
	longitude = 1440 ;
	latitude = 721 ;
	time = 1 ;
variables:
	float longitude(longitude) ;
		longitude:units = "degrees_east" ;
		longitude:long_name = "longitude" ;
	float latitude(latitude) ;
		latitude:units = "degrees_north" ;
		latitude:long_name = "latitude" ;
	int time(time) ;
		time:units = "hours since 1900-01-01 00:00:00.0" ;
		time:long_name = "time" ;
		time:calendar = "gregorian" ;
	short cbh(time, latitude, longitude) ;
		cbh:scale_factor = 0.227045915798148 ;
		cbh:add_offset = 7461.72404723253 ;
		cbh:_FillValue = -32767s ;
		cbh:missing_value = -32767s ;
		cbh:units = "m" ;
		cbh:long_name = "Cloud base height" ;
	short hcc(time, latitude, longitude) ;
		hcc:scale_factor = 1.52594875864068e-05 ;
		hcc:add_offset = 0.499992370256207 ;
		hcc:_FillValue = -32767s ;
		hcc:missing_value = -32767s ;
		hcc:units = "(0 - 1)" ;
		hcc:long_name = "High cloud cover" ;
	short lcc(time, latitude, longitude) ;
		lcc:scale_factor = 1.52594875864068e-05 ;
		lcc:add_offset = 0.499992370256207 ;
		lcc:_FillValue = -32767s ;
		lcc:missing_value = -32767s ;
		lcc:units = "(0 - 1)" ;
		lcc:long_name = "Low cloud cover" ;
	short mcc(time, latitude, longitude) ;
		mcc:scale_factor = 1.52594875864068e-05 ;
		mcc:add_offset = 0.499992370256207 ;
		mcc:_FillValue = -32767s ;
		mcc:missing_value = -32767s ;
		mcc:units = "(0 - 1)" ;
		mcc:long_name = "Medium cloud cover" ;
	short tcc(time, latitude, longitude) ;
		tcc:scale_factor = 1.52594875864068e-05 ;
		tcc:add_offset = 0.499992370256207 ;
		tcc:_FillValue = -32767s ;
		tcc:missing_value = -32767s ;
		tcc:units = "(0 - 1)" ;
		tcc:long_name = "Total cloud cover" ;
		tcc:standard_name = "cloud_area_fraction" ;

// global attributes:
		:Conventions = "CF-1.6" ;
		:history = "2022-08-05 20:16:00 GMT by grib_to_netcdf-2.25.1: /opt/ecmwf/mars-client/bin/grib_to_netcdf.bin -S param -o /cache/data5/adaptor.mars.internal-1659730560.623973-5461-3-c6dc3aed-2162-4560-bfdb-7eca9e0f9175.nc /cache/tmp/c6dc3aed-2162-4560-bfdb-7eca9e0f9175-adaptor.mars.internal-1659730560.1068156-5461-5-tmp.grib" ;
}

I see the variable name "cbh" for "Cloud base height". For the level, the asterisks belong in the slots for the two spatial dimensions. Those are typically the latitude and longitude dimensions. For all other dimensions, the user must specify some value to indicate which slice of that dimension should be used. You can do this by specifying the 0-based index for that dimension. In this case, I can run plot_data_plane in the following way:

$ plot_data_plane ERA5_2020072412_Cld.nc ERA5_2020072412_Cld.ps  'name="cbh"; level="(0,*,*)";'
DEBUG 1: Start plot_data_plane by jpresto(7414) at 2025-01-14 16:44:51Z  cmd: plot_data_plane ERA5_2020072412_Cld.nc ERA5_2020072412_Cld.ps name="cbh"; level="(0,*,*)"; 
DEBUG 1: Opening data file: ERA5_2020072412_Cld.nc
DEBUG 2: 
DEBUG 2: NcCfFile::getData(NcVar *, const LongArray &, DataPlane &) const -> data was flipped to north.
DEBUG 1: Creating postscript file: ERA5_2020072412_Cld.ps
DEBUG 1: Finish plot_data_plane by jpresto(7414) at 2025-01-14 16:44:52Z

I hope this information is useful. Please let us know if you have any other questions.

[odiaconu]

Thank you very much. These infos are very useful. I am using wgrib and wgrib2 . Thanks a lot !