20010216: ngm vs ngm211

>From: Tom Priddy <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200102161411.f1GEBXL16592

>From: Tom Priddy
>         Dr Wang
>
>
>Please tell me the difference between the ngm and ngm211 models. How do
>we
>grab the ngm211 in our pqact.conf. Can we use the same decoder?
>


Tom,

The NGM model is available on several different output grid projections 
on NOAAPORT (the IDD). These include grid numbers 202, 207, 211, and 213.
Fples of the region of coverage for each of these grids see:
http://www.unidata.ucar.edu/packages/gempak/examples/models/grids/


Since all grids in a gempak grid file must be the same projection,
each of the 4 different grids must be stored in a different file. 
As a result, I provide the convention of storing the data sets like:
YYYYMMDDHH_ngm@@@.gem. Both dcgrib and dcgrib 2 will substitute the 
appropriate grid number from the data into the @@@ template similar to
the way the YYYYMMDDHH template is replaced by the date.

For decoder examples for NGM, see:
http://www.unidata.ucar.edu/packages/gempak/tutorial/pqact/decoders.tbl

The documentation above shows the WMO patterns for pqact.conf:
# NGM model output 
# Grid #211 CONUS   80km: ^[YZ].Q.*/mNGM
# Grid #207 Alaska  95km: ^[YZ].N.*/mNGM
# Grid #202 CONUS  190km: ^[YZ].I.*/mNGM
# Grid #213 CONUS 47.5km: ^[YZ].H.*/mNGM

The grid 211 is signified by the "Q" character in the 3rd position of the WMO 
header.

Typing "dcgrib -h" or "dcgrib2 -h" shows the valid templates for the decoders:
        YYYY            Year with century
        YY              Year without the century
        MM              Month number
        DD              Day
        HH              Hour
        NN              Minute
        ###             Generating process model id (PDS Octet 5)
        @@@             Grid number (PDS Octet 7)
        %%%             Generating subcenter (PDS Octet 26)


You could use a separate pqact.conf action for each of the different grid 
projections,
with their own output file names. The "@@@" template allows you to pass any NGM
grib to the dcgrib/dcgrib2 decoders and have the decoder determine the correct 
output 
file.


Steve Chiswell