[gradsusr] lats4d issues

[Arlindo da Silva]

On Mon, Aug 2, 2010 at 1:59 PM, Matt Brewer <mcbrewer83 at yahoo.com> wrote:

> Folks,
> I am using lats4d to convert NCEP's NARR data (grib) to netCDF. It only
> kind of worked. This is what I type into the command line:
>
> lats4d -i narr-a_221_19790101_0000_000.sub -o narr2009.nc -ftype ctl -lon
> -160 -90 -lat 25 65  -time 0z1jan2009 21z31dec2009 -mxtimes 2920 -levs 925mb
> -xvars ugrdprs vgrdprs ugrd10m vgrd10m msletmsl prmslmsl
>
> This works fine except for one issue. It seems to be totally messing up the
> axis dimensions, causing data to be in incorrect lat/lon locations.Notice
> how I asked for data from 160W to 90W and 25N to 65N, so with the longitude,
> that is a span of 70 degrees, and for latitude, it is 40 degrees. So I
> should get back a geopot. height matrix of 121x211 (there are data points
> every 1/3rd degree). It seems, in matlab at least, that I get an array of
> 122x212. And so what happens is the first point on the second array actually
> gets saved in the 212th place in the first array, so the second line starts
> out with what is supose to be the second point in the array. Make sense?
> When I put the nc file into grads, it has similar issues as well....so
> something wierd is going on when I run the lats4d script....I just don't
> know what. So if anyone has any ideas of what is goin on, please help!!!
>
>
The first step is to make sure GrADS is reading your GRIB file correctly. Go
ahead, start GrADS, open your GRIB file, plot it and see if it is doing it
correctly:

ga-> open narr-a_221_19790101_0000_000.sub
ga-> d something

If this is pre-projected data, make sure your PDEF is correct. Once you sort
this out, the netcdf version should produce the same results. (Our
regression tests do just that: reads a GRIB file, converts to netcdf, then
reads the netcdf file back and checks if it gets exactly the same values.)

One important detail: when asking for help, you need to let us know the
particular version of grads, lats4d, and your operating system; basically,
the otput of "q config".

   Arlindo




> Matt
>
>
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>


-- 
Arlindo da Silva
dasilva at alum.mit.edu
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