A parameter consists of a Discipline( ie Meteorological_products), 
a Category( ie Temperature ) and a number that refers to a 
name( ie Temperature), Description( ie Temperature at 2 meters), and 
Units( ie K ).  

There is a difference on how the parameters are read into the
grib library for GRIB(1|2). GRIB1 has a seperate table for each Center, 
Sub-Center, and version number. Usually the Center/Sub-Center pair has more 
than one version number and therefore more than one table. On the other hand,
GRIB2 has only one table with the parameters under the Discipline, Category, and
number headings. To make Parameters consistent, GRIB1 parameters have a static
Discipline (Meteorological Products) and a static Category (Meteorological 
Parameters). 

The above paragraph is not really important unless one plans on programming
the parameter APIs.  Then one should look at ucar/TableLookup.java,
ucar/grib1/Grib1Lookup.java, and ucar/grib2/Grib2Lookup.java.

Because it is huge task to keep all parameter tables up to date, there are
some routine calls to add tables/parameters to the existing ones. If the 
additions are already in the jar, then the new addition will overwrite the
jar entries.

1. Adding GRIB1 Parameter tables and parameters:

The routine for a user to read in his own Grib1 table is:

GribPDSParamTable.addParameterUserLookup(String UserGribTabPath)

The UserGribTabPath can be path, url, etc. and the routine expects a file
with format:

158:     0:               2:    fnmoc_2.tab

and the table ie. fnmoc_2.tab can be a relative or absolute path.  The tables 
are in ncep format:

-1:158:-1:2
0:var0:undefined
1:PRES:Pressure [Pa]
2:PRMSL:Pressure reduced to MSL [Pa]
3:PTEND:Pressure tendency [Pa/s]
4:PVORT:Pot. vorticity [km^2/kg/s]
5:ICAHT:ICAO Standard Atmosphere Reference Height [M]
6:GP:Geopotential [m^2/s^2]
...

2. The GRIB2 routine for a user to read in his own parameters is:

ParameterTable.addParametersUser(String UserGribTable)

This is a sample table, the lines starting with # are not include in table.
# Parameters are listed by row, fields are separated by tabs:
# Discipline, Catagory, Parmeter Number, Name, Units, & Description
#
#Dis	Cat	Parm #	Name		Units	Desc
0	0	0	Temperature	K	Temperature

This is the list of Discipline and Categories available. It would be wise to 
check resources/grib/tables/grib2StdQuantities.xml before adding parameters. 
If one uses new parameters outside their facility, then check with NCEP first.
#
#    <discipline id="Meteorological_products" number="0">
#        <category id="Temperature" number="0">
#           <quantity id="Temperature" number="0" unit="K"
#               description="Temperature" />
#           <quantity id="Virtual_temperature" number="1" unit="K"
#               description="Virtual temperature" />
#        </category>
#        <category id="Moisture" number="1">
#        </category>
#        <category id="Momentum" number="2">
#        </category>
#        <category id="Mass" number="3">
#        </category>
#        <category id="Short-wave_Radiation" number="4">
#        </category>
#        <category id="Long-wave_Radiation" number="5">
#        </category>
#        <category id="Cloud" number="6">
#        </category>
#        <category id="Thermodynamic_Stability_indices" number="7">
#        </category>
#        <category id="Kinematic_Stability_indices" number="8">
#        </category>
#        <category id="Temperature_Probabilities" number="9">
#        </category>
#        <category id="Moisture_Probabilities" number="10">
#        </category>
#        <category id="Momentum_Probabilities" number="11">
#        </category>
#        <category id="Mass_Probabilities" number="12">
#        </category>
#        <category id="Aerosols" number="13">
#        </category>
#        <category id="Trace_gases" number="14">
#        </category>
#        <category id="Radar" number="15">
#        </category>
#        <category id="Forecast_Radar_Imagery" number="16">
#        </category>
#        <category id="Electro-dynamics" number="17">
#        </category>
#        <category id="Nuclear_and_radiology" number="18">
#        </category>
#        <category id="Physical_atmospheric_properties" number="19">
#        </category>
#        <category id="ASCII_character_string" number="253">
#        </category>
#    </discipline>
#    <discipline id="Hydrological_products" number="1">
#        <category id="Hydrology" number="0">
#        </category>
#        <category id="Hydrology_probabilities" number="1">
#        </category>
#    </discipline>
#    <discipline id="Land_surface_products" number="2">
#        <category id="Vegetation_and_Biomass" number="0">
#        </category>
#        <category id="Agri-aquacultural_Special_Products_" number="1">
#        </category>
#        <category id="Soil_Products" number="3">
#        </category>
#    </discipline>
#    <discipline id="Space_Products" number="3">
#        <category id="Image_format_products" number="0">
#        </category>
#        <category id="Quantitative_products" number="1">
#        </category>
#    </discipline>
#    <discipline id="Oceanographic_products" number="10">
#        <category id="Waves" number="0">
#        </category>
#        <category id="Currents" number="1">
#        <category id="Ice" number="2">
#        </category>
#        <category id="Surface_Properties" number="3">
#        </category>
#        <category id="Sub-surface_Properties" number="4">
#        </category>
#    </discipline>
#

3. Another way of Changing/adding tables/parameters

Another way of changing the tables/parameters is to extract the table from the
grib.jar file, make the changes, and then enter it back into the grib.jar. This
process doesn't require any routine calls and it works well because all the
tables are ascii text. But, one needs to make sure that the table syntax is
followed or the table will not be processed correctly. Look at files:

for GRIB1 tables

resources/grib/tables/tablelookup.lst
resources/grib/tables/nceptab_130.tab

for GRIB2 table

resources/grib/tables/grib2StdQuantities.xml