[gradsusr] Converting and displaying a data subset

[Stephan Steyn]

I am using grib2ctl.pl and GrADS in order to convert ERA5 reanalysis data (e.g. 2m temperature at 12Z) from a .grib format to a .dat format.
The grib file contains global data (x=1440 and y=721 for a 0.25x0.25 degree grid).
When I use convert.gs to create the .dat file for the whole dataset everything works fine and the data is displayed correctly thereafter.
However, I don't have the computing power to ingest such a huge dataset and would rather work with a subset for a window area.
Now, when I run a modified convert.gs to create the .dat file for the smaller domain (e.g. x=96 to 128 and y=234 to 264) I don't get any error messages and everything seems to still work fine.
But upon displaying the data I get funny zonal isotherms for temp and constant field displays for wind.
Any ideas please?

Modified script for converting for smaller window area (original domain in comments):
  function main()
  'reinit'
  rname1='ERA5_sfcvar12_'
  rname2='newERA5_sfc12_'
  ext1='.ctl'
  ext2='.dat'
  jaar=1979
  mnth=12
  fname1=rname1%jaar%mnth%ext1
  fname2=rname2%jaar%mnth%ext2
  tlabel=DEC1979
  'open /run/media/stephan/SS_Transcend/ERA5/'fname1''
  'set x 96 128'
**  was originally 'set x 1 1440'
** in order to set lon 0.00 359.75
  'set y 234 264'
**  was originally 'set y 1 721'
** in order to set lat -90.00 90.00
  'set time 'tlabel''
  'set gxout fwrite'
  'set fwrite /run/media/stephan/SS_Transcend/ERA5/'fname2''
  tyd=1
  while (tyd <= 31)
   'set t 'tyd
*** surface 10 metre U wind component [m/s]
   'd no10Usfc'
*** surface 10 metre V wind component [m/s]
   'd no10Vsfc'
*** surface 2 metre dewpoint temperature [K]
   'd no2Dsfc'
*** surface 2 metre temperature [K]
   'd no2Tsfc'
   tyd=tyd+1
  endwhile
  'close 1'
  'reinit'
  'quit'

Stephan Steyn

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