960308: Aquiring the thinned AVN grids

Rick here is the rough history of the official notice of
the termination of the A-D grids that comprised the AVN:

On Tue, 4 Apr 1995, Peggy Bruehl wrote:

> This means that on April 18, all of the AVN global model output
> grids will disappear from the HRS data stream.  To provide global 
> model output coverage, the National Weather Service is broadcasting 
> eight 1.25x1.25 lat/lon grid octants, which when stitched together 
> provide a global "thinned grid".  A description of the
> "thinned grid" follows (from the GRIB ed 1 document by John 
> Stackpole): 


>NOUS40 KWBC 121446
>FOS NOTICE NO 661 04-12-95
>**************************NOTICE******************************
>
>HRS SUBSCRIBERS
>
>THE SCHEDULED REMOVAL OF THE  2.5 X 5.0 DEGREE FOS BULLETINS
>/2440/ FROM THE HRS ON APRIL 18...HAS BEEN CHANGED TO JUNE 5.
>
>**************************NMC NOTE***************************




*****************************************************************

Since longitudes converge as they approach the pole, thinned
grids apply a technique which decreases the number of grid points
along a latitude line as the latitudes approach the pole.

A process known as thickenning is used to generate values 
at regular grid points after the grids are received.

The current resolution of the AVN model is 1.25x1.25 degrees.
The present version of gribtonc supports a command line
parameter to specify the resolution to which you wish
to "thicken" the grids when stored in the NetCDF file.

The thickening resolution must be a multiple of the 1.25x1.25 resolution.
That is, you may choose to store the data at full resolution 1.25x1.25
degrees (which takes up more space), or you can store the data at
a resolution comparable to the old AVN grids 2.5x5.0 degrees (since 2.5 
and 5.0 are multiples of 1.25). 


Here is the pqact.conf pattern used to store the grids at 2.5x5.0 
resolution:

# AVN model on thinned grids, interpolated to global 5.0 x 2.5 regular grid
HRS     ^H.[I-P]... KWB. (..)(..).*(/mAVN|/mSSIAVN)
        PIPE    /usr/local/ldm/decoders/gribtonc
        -q "lin,dlat=2.5,dlon=5.0" etc/avn-x.cdl
        data/GRIB/(\1:yy)(\1:mm)\1\2_avn-x.nc


The "-q" parameter is used for the resolution option.
the "lin" option tells gribtonc to use a linear
fit to seam the octants together the dlat and
dlon are the delta lat and lons used.

As you can see from the pattern above, the quasi-thinned grids are
transmitted as grids I-P, where greids I, J, K, and L are in the
northern hemispere, and M, N, O, P are in the southern hemisphere.

Also note that the distribution center pattern has been changed from
KWBC to KWB. since the 4th letter will be used to denote the models
in the future.

*********************************************************************

To keep apprised of data stream changes you can subscribe to Unidata
email lists through the Unidata WWW page. Simply
use your forms capable browser to reach:
http://www.unidata.ucar.edu

Once connected, scroll down to the section:
Information of Interest to the Unidata Community
   Other Services 
      Subscribe to/unsubscribe from Unidata's Mailing Lists


Email lists which you may be most interested in are:
nws-changes: which provides information on changes in the NWS
ldm-users: which procides information about the LDM
datastream: which contains information about the data feeds 

of course you are welcomed to subscribe to any of the lists you find 
meet your uses.

You may also search back through archives of these email lists to
find old messages such as I listed at the top of this mail message,
or you can search through support messages for responses to
users problems which may be germain to a problem you are having.

************************************************************************


So, Now to get you up to speed so that you can receive decode these grids,

you will need to upgrade the following:

udunits (current version 1.10)
netcdf  (current version 2.2.4)

the above two are needed for the decoders package

decoders version 2.2.1 (which contains gribtonc and the cdl files)

The old version of gribtonc you have is before the introduction of
the thinned grids.


and eventually, we will want you to get LDM upgraded to LDM-5.0



All of these packages are available through anonymous ftp to 
ftp.unidata.ucar.edu.


download udunits from:
pub/udunits/udunits.tar.Z

download netcdf from
pub/netcdf/netcdf.tar.Z 

download decoders from 
pub/decoders/decoders.tar.Z

the cdl file used by gribtonc for the thinned grids is
in the decoders tar file as:
decoders-2.2.1/src/gribtonc/cdl/avn-x.cdl
 


Each of these packages contains instructions for building,
the package- which consists primarily of running the 
configure script, followed by making and installing the
package. Building the decoders requires netcdf and udunits,
so you will instructed how to specify the locations of these
libraries when building gribtonc.



After you get that working, you can download LDM-5.0
a compiled binary is available in pub/binary/sun4-sunos5/ldm.tar.Z


Typically, you unpack the ldm distribution under the ldm directory.
This will create a directory ldm-5.0 and its sub directories.

It is suggested that when you get to this point you move your
current ldm4.1.41 distribution that you mentioned is currently called
runtime, to ldm-4.1.41 

the convention is for runtime to be a link to the directory
of ldm that you are currently running. So presently runtime
would be linked to the ldm-4.1.41 directory.
We adopted this convention to make it easier to install
new versions of ldm, install them, then when you are all set up,
all you have to do is cange the runtime link to your new directory.

in ldm, bin is a link to runtim/bin, lib to runtim/lib, include to
runtime/include, man to runtime/man.

The only directory that is not linked is usually the etc directory.
This is because your cdl files, pqact.conf files etc are usually
the same from version to version.

When you upgrade to LDM5.0, you may want to print out a copy
of the site managers guide in the doc directory.

Your pqact.conf file will probably be fine when changing versions,
especially since you mentioned it was only 18 lines- so there isn't
much that could change.

You will create an ldmd.conf file in the etc directory that will
soecify your feed sites, permissions etc.

This replaces the old ldmadmin.conf, and ldmaccess.conf files in
LDM version 4.


*******************************************************************

As I mentioned on the phone, it is desireable for you to get to LDM5 
since it has several data recovery characteristics for 
retrieving data if the network is down for a short period.
However, it is not critical- yet. So Feel free to
work at your pace. The main thing is getting
the grids decoded into netcdf. Then when you are comfortable
with that, then you can tackle ldm5.0.

At that point you can configure your feed pattern to ask for only data 
that you are needing.
Since the thinned grids are in the HDS stream, while WMO is the
superset of all the FOS data, you can lessen the network load by 
specifying the
feed type, and the pattern requested from the upstream site.

If you have further questions or problems,
feel free to send them to address@hidden for
quickest response- since I may be out of the office,
and others here will be able to answer from the support 
email address.

Steve Chiswell
User Support
address@hidden