[gradsusr] error with zinterp.gs and gfs_hd nomads

[Jennifer Adams]

On Apr 13, 2011, at 9:25 AM, Adrian Scherzinger wrote:

> hi
>
> i have to make wind maps on a certain height above ground with  
> gradsdods
> and the nomads gfs_hd (0.5) data. To solve this, i use the zinterp.gs
> function for an area which is quite big (lat 40 70, lon -15 40). The
> calculation of one timestep takes around 20 minutes.
That's because you've made a large 3-D request from a GDS of data in  
GRIB2 format, which takes a long time, especially if you are using  
'gradsdods', an old deprecated build, which is not optimized for doing  
I/O from an opendap server. You are doing the I/O on row by row basis,  
slamming the server with small requests. zinterp.gs is not designed to  
work with remote data sets.


> however, after one or two timesteps, the zinterp.gs function just  
> takes
> a few seconds and gradsdods just delivers "entire grid empty" data.
> the same script with nomads gfs 1 degree or 2.5 degree data is working
> fine for all timesteps.
It may be because the server has enabled a DOS after your 20 minutes  
of 1-row requests. The administrator of the nomads GDS may be willing  
to check the logs for an explanation of why your data requests are  
failing.

My suggestion:
1. Upgrade to the latest version of GrADS
2. Use a separate script to create a local data set (using fwrite or  
sdfwrite) that is the subset of gfs_hd grid, only the lat/lon/levels  
that you need for zinterp.gs to work. Optimize this for hitting the  
server a minimum number of times, and don't ask for more than one  
level per request -- that will slow down your script.
3. After you have a created a local data set, then run zinterp.gs.

--Jennifer




>
> what is going wrong?
>
> thanks for any help
> adrian
>
> -- 
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>
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--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org



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