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20060124: CONDUIT data stream

Jennie,

I think you are confusing a graphic of grid #104 (for NAM) with
grid #4 which is a global .5x.5 degree lat/lon grid.

The GRID #4 is the same lat/lon projection as GRID #3, just with
row/columns at .5 degree rather than 1 degree (eg 4x as many points).
GRIB2 is much better in regard to file size for the larger grid
size. In fact, NCEP will be transitioning all of its data to
GRIB2, except that which they have to provide to the GTS under WMO
agreements.

NCEP provides libraries to decode GRIB2 (as well as convert GRIB2 to GRIB1). 
See: http://www.nco.ncep.noaa.gov/pmb/codes/GRIB2/

Currently, we are sending the same GFS data at 2 resolutions
(grid #3 and grid #4) for F000-F084. That consumes a lot of user bandwidth.
Now that NCEP is running the GFS model at T384 through 180 hours, they will
be able to produce the top resolution grid #4 through 180 hours, so
CONDUIT will want to transmit that when available. At that time, the complete
0-180 GFS data set will be redundant on grid 3 so it makes sense to remove
that and use the bandwith for other data sets. The GRIB2 .5 degree data set 
will 
have been available for over a year and a half, giving users adequate time to 
transition legacy code to the higher resolution.

If you don't have the resources to transition to grid #4, or convert the GRIB2
to GRIB1 using the NCEP program mentioned above, you should also be aware that
NCEP has introduced additional levels/parameters etc to the GFS output
(both GRID #3 and GRID #4), so you should ensure that legacy applications you 
might
be using with GFS grid #3 are able to handle those newer parametere/levels
(or at least not die during inopportune moments)!

Steve Chiswell
Unidata User Support





>From: address@hidden (Jennie L. Moody)
>Organization: UCAR/Unidata
>Keywords: 200601242007.k0OK727s003856

>Hey Steve,
>
>I talked with Tom Yoksas the end of last week about my need to
>gain access to GFS runs through the idd CONDUIT feed for an
>upcoming spring campaign.  I have some non-unidata applications
>(not IDS, GEMPAK, McIDAS) that I want to run using grids.  I have
>been trying to sort out just what grids are available on what
>projections, and in what format (I have some pre-processor code
>to read the grib1 format, but have never used the grib2).   
>
>Before I jump in and drown, I have been trying to read everything
>that seems relevant regarding the CONDUIT feed.  I just saw a
>link today to an agenda for a meeting that will be held next week
>in Atlanta(AMS).  It mentions some up-coming changes, or
>development plans for CONDUIT, changes that will be implemented
>by NCEP.  These have me a bit confused.  I will quote here from
>what I read at 
>http://www.unidata.ucar.edu/projects/CONDUIT/CONDUIT_development_plans.html
>
>GFS Grids: 30 days pending availability
>
>    * Increase GFS 0.5 degree global grids in GRIB2 from 84 hours
>to 180 hours.
>    * The 0.5 degree GFS data has been available in CONDUIT from
>0 to 84 hours since September 2004. The extension of the number
>of forecast hours available at ~37 MB per forecast time will
>yield a net 1.3 GB increase per model run.
>    * Remove redundant GFS 1.0 degree global grids in GRIB1 from
>0 to 180 hours at ~23 MB per forecast time will yield a net 1.4
>GB decrease per model run.
>    * NCEP plans to produce the 0.5 degree data set to 180 hours
>following the lifting of moratorium at a time to be determined. 
>
>So, this raises a few questions for me.
>Does it mean that I should not plan on working with (which on my
>end, means writing code to access the GFS data on a given grid
>with a given resolution) the GFS 1.0 degree global grids, since
>it sounds like they could actually GO AWAY (be removed) in the
>March-April-May time frame (exactly when I would like to be
>looking at/using them?)
>
>My understanding of the GFS grids available on CONDUIT (all
>gleaned from Unidata web pages at this point) leads me to believe
>that the 1 degree data and the 0.5 degree data are on pretty
>different projections (the graphic you link to that shows model
>grids indicates that GFS 003 is mercator, and GFS 004 is
>conformal or something like that).  Also, as I noted, these two
>different GFS grids (the 1 degree and the 0.5 degree) are in two
>different formats, Grib1 and Grib2.  
>
>I was thinking that I would go ahead and set up a new ldm on my
>new workstation, and get just one feed going to pull in the GFS 1
>degree mercator grid files.  This would be a really bad idea if
>these grids are being sunset.
>
>Please let me know your thoughts, and if I have misunderstood
>things (I hope I have, I would really like to proceed down the
>path noted above)!
>
>Thanks.  
>Jennie
>address@hidden
>
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