[gradsusr] LON-LAT for European sector

[Clark, Douglas B.]

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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