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20021106: Exploring content of gempak grid files...



Christian,

To look at the entire content of a grid file, use the GDINFO
program. Set GDFILE to the name of the file you are looking at,
and set GLEVEL, GVCORD, GFUNC, GDATTIM each to "all". A quick
way to do this is type "restore defaults/gdinfo" at the 
gempak-gdinfo> prompt.

The $GEMTBL/grid/gribkey.tbl is the file I use to store
the grid products according to model number and grid.

Each gempak grid file has a can hold grids of a single navigation.
In the case of the AVN & wind wave grids on 21-24, each of the 4
grids represents a quarter of a larger global grid which the
dcgrib2 decoder will stitch together. The MRF grids 25 & 26 (E & F)
similarly are NHem and SHem sections. The navigation of the GEMPAK file
will be that of the stitched together grid (the 2.5x5 and 5x5
degree CED grid respectively).

The AVN and MRF are historic uses of NCEPs global spectral model.

As of this summer, all NCEP spectral runs are a single GFS (global forecast
system) where the spectral resolution starts at T254, then reduces
to T170 past 72 hours, and to T126 past 120 hours. There are no
longer separate AVN and MRF runs, but the grid IDs are still
being created from the GFS for backwards compatibility.

See the GDINF0 for actual contents.

Steve Chiswell



>From: =?ISO-8859-1?Q?Christian_Pag=E9?= <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200211061842.gA6Ig6X01482

>Hi,
>
>Today I have many newbie questions regarding data available on ldm and 
>decoded for gempak...
>
>I added a lot of grid gempak files in my ldm to explore available data.
>But I have some difficulty to explore that using gdfile: I tried with 
>glevel=all in gdfile, but I always get that all is not a valid level, 
>though that in the gempak documentation it is written that it should 
>work.
>
>I added these products which I don't know what they contain exactly and 
>I don't know how to visualize them easily with gempak:
>#
>#  Spectral grids - grids A,B,C,D Global grid  Forecasts (wind & waves, 
>temperature)
>##
>HRS    ^H[A-Z][ABCD][A-Z][0-9][0-9] KWB. ([0-3][0-9])([0-2][0-9])..
>       PIPE    /io/gempak/nawips/bin/irix/dcgrib2 -d data/gempak/logs/dcgrib.l
> og
>       -e GEMTBL=/io/gempak/GEMPAK5.6.H/gempak/tables
>       data/gempak/model/YYYYMMDDHH_spec.gem
>
> From which model does this come from? Are these forecasts only for 
>water surfaces? Ocean?
>
>#
># Bitmap ocean
>#
>HRS    ^H[HKLTUV][T-W][ACEIK]93 KWB. ([0-3][0-9])([0-2][0-9])
>       PIPE    /io/gempak/nawips/bin/irix/dcgrib2 -d data/gempak/logs/dcgrib.l
> og
>       -e GEMTBL=/io/gempak/GEMPAK5.6.H/gempak/tables
>       data/gempak/model/YYYYMMDDHH_ocn2.gem
>#
># Ocean
>HRS    ^O..... KWBJ
>       PIPE    /io/gempak/nawips/bin/irix/dcgrib2 -d data/gempak/logs/dcgrib.l
> og
>       -e GEMTBL=/io/gempak/GEMPAK5.6.H/gempak/tables
># ICE
>HRS    ^O..... KWBM
>       PIPE    /io/gempak/nawips/bin/irix/dcgrib2 -d data/gempak/logs/dcgrib.l
> og
>       -e GEMTBL=/io/gempak/GEMPAK5.6.H/gempak/tables
>
>What are the fields in this file? Is it a forecast or an analysis?
>
>What is the difference between the Spectral AVN and the AVN? Are these 
>separate runs?
>
>#
>#  MRF grids - Extended range grids E and F
>#
>HRS    ^H.[EF][A-Z][0-9][0-9] KWB. ([0-3][0-9])([0-2][0-9])..
>       PIPE    /io/gempak/nawips/bin/irix/dcgrib2 -d data/gempak/logs/dcgrib.l
> og
>       -e GEMTBL=/io/gempak/GEMPAK5.6.H/gempak/tables
>
>Why these grids are separate from other MRF grids? They cover which 
>forecast hours? Are they on the same grid as the others?
>
>Thanks a lot for your help again...
>
>Christian Pagé
>address@hidden
>http://meteocentre.com/    http://meteoalerte.com/
>
>Etudiant au Doctorat en Sciences de l'environnement UQAM
>+1 514 987 3000 ext. 2376
>