[gradsusr] LON-LAT for European sector

[Djordje Romanic]

Dear Doug,

Now I see... I made a slip during the calculation. Namely, I've used
NCEP/NCAR reanalysis data to calculate relative topography, and to do that
I've used the command:

***************************
sdfopen
http://nomad1.ncep.noaa.gov:9090/dods/_expr_{reanalyses/reanalysis-1/6hr/pgb/pgb}{hgtprs(lev=500)-hgtprs(lev=1000)}{0
:360,-90:90,1000:1000,00z1jan1961:00z1jan1991}
***************************
However, the longitude in the original file (on nomad server) goes only up
to 357.5. BUT, even if I replace 360 with 357.5 in the above command I get
the same result---WHY?
Dear Doug, since I have more than a month of work behind me and all of that
work was done usung the above command (with lon=360) and the result is the
same as it would be 357.5 instead of 360, but the difference is in writing
the result in a file, is it possible to change something in the CTL file and
to correct a mistake? You were right, if in the previous command is 357.5,
than I am able to set lon from -30 to 60. Since eveything else is the same,
except this ploting issue, please is it possible to correct that so that I
don't have to do the same tremandeus work from the beginning?

Regards,
Djordje



2011/5/9 Clark, Douglas B. <dbcl at ceh.ac.uk>

>  Djordje,
>
> I’m not sure, but I suspect that the problem might be related to the fact
> that the xdef entry in the ctl file appears to specify a grid that covers
> more than 360degrees of longitude, in that 145x2.5=362.5. So I think GrADS
> has failed to identify that the grid should be cyclic in longitude or just
> can’t work out which data to use in the “overlap” area. I certainly couldn’t
> get anything to plot across 0E when I hacked up an example, even when I
> tried a few standard “tricks”.
>
> (The fact that the grid is rather large in latitude too, >180deg, probably
> doesn’t matter because there’s no need for GrADS to wrap round in latitude.
> Also note that for a “basic” gridded data file, the t,z,y,x bit in the var
> line is not used, as far as I know – I tend to put “99” in there instead.)
>
> IF you only had one time level in the data file (which only has a single
> variable on a single level in it), you might be able to change the xdef line
> to have nx=144 so that GrADS thinks it only has data for 360deg – BUT THAT
> WILL NOT work for your current example which has >1 time.
>
> I think you’ll probably have to trim the grid to 360deg before going into
> GrADS if you want to plot across 0E.
>
> If the data file RTmavglobal(1961-1990).grd was written using fwrite  to
> output a subset of a larger file, then I think you will be able to proceed
> by explicitly setting ‘set x 1 144’ before you write the file. Otherwise
> GrADS will likely have added an extra column of data because of how it
> normally sets up for a global grid.
>
> Doug
>
>
>
> *From:* gradsusr-bounces at gradsusr.org [mailto:
> gradsusr-bounces at gradsusr.org] *On Behalf Of *Djordje Romanic
> *Sent:* 09 May 2011 08:54
> *To:* GrADS Users Forum
> *Subject:* [gradsusr] LON-LAT for European sector
>
>
>
> Dear Users,
>
>
>
> I have a *.grd file (relative topography data) covering the whole globe.
> His CTL file is as follows:
>
>
>
> ***************************************************************************
>
> dset ^RTmavglobal(1961-1990).grd
>
> undef 9.999e+20
>
> xdef 145 linear 0 2.5
>
> ydef 73 linear -90 2.5
>
> zdef 1 levels 1000
>
> tdef 43709 linear 0Z31jan1961 360mn
>
> vars 1
>
> RT 1 t,z,y,x **Relative topography 500/1000 [hPa]
>
> endvars
>
> **************************************************************************
>
> The data on global map (LAT -90 90; LON 0 360) are attached (global.jpeg).
> Now, from the global file I want to extract the data for the European sector
> (longitude interval is from 30W to 60E and latitude interval is from 0 90N),
> but after the following commands:
>
> ***********************************************************************
>
> set lon -30 60
>
> set lat 0 90
>
> d rt
>
> ************************************************************************
>
> I get the image that does not have the data East of the 0 meridian(attached
> as file euro.jpeg).
>
> Please, can someone help me with this issue? What is causing this?
>
> Kind regards,
>
> Djordje
>
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