Introduction

In the beginning, grib fields were identified by a name, a level and some timing information. Life was simple and the people were happy. This was soon to pass, for the ensemble people had to specify the ensemble number and the probability of events. The dust people needed to specify dust density by composition and by size. Thinking big, ensembles of dust models were in the future albeit obscured by the haze. Consequently the old name (ex. HGT, TMP) was often no longer a good way to specify a specific field. For example, a TMP field could be measured in degrees K or fraction if the TMP had a probability modifier. The -set_ext_name and -ext_name options are a way to help fix this problem. Using these two options, you can get a extended name with many of the modfiers added to the name. This option will have to be updated when more modifiers are used to distiguish the fields.

The -var option prints the VARIABLE name of the grib message. Common names would be HGT and TMP for the geopotential height and the temperature. For most knowing the variable name, the level and the timimg information is all you need. Then things became more complicated. Eventually a file came along which had only one variable type (MASSDEN, mass density) but had a couple of important qualifier chemical type (H2O/O3/N02) and ensemble member ID. The -AAIG output was useless because its output used the variable name.

To fix the -AAIG output, an extended name was introduced. You can see the extended name by the -ext_name option.

-sh-2.05b$ ./wgrib2 chem.grb2 
1:0:d=2009012600:MASSDEN:surface:anl:ENS=hi-res ctl chemical=Water Vapour
-sh-2.05b$ ./wgrib2 chem.grb2 -ext_name
1:0:MASSDEN.hi-res_ctl.Water_Vapour
-sh-2.05b$ ./wgrib2 chem.grb2 -misc 
1:0:ENS=hi-res ctl:chemical=Water Vapour

Usage

-ext_var
-set_ext_name 0/1
-var

Examples

-sh-2.05b$ ./wgrib2 chem.grb2 -var
1:0:MASSDEN
-sh-2.05b$ ./wgrib2 chem.grb2 -ext_name
1:0:MASSDEN.hi-res_ctl.Water_Vapour