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PostPosted: Fri Apr 25, 2014 4:26 am 
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Joined: Fri Apr 11, 2014 6:28 am
Posts: 6
I have done with PRECIS run which has generated a great quantity of data for various climatic variables in .pp format. While converting that .pp file to .ctl and .dat file (using xconv), subsequently plotting using Gradsc software, I am facing a problem i.e. the run were performed over India domain but on contour plotting in Gradsc software it is showing shifting of regions to somewhere in Africa. Is something went wrong initially?

Let me know if you need any more information.


PS : Not able to upload the file :oops: , showing error :oops:


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PostPosted: Fri Apr 25, 2014 9:51 am 
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Joined: Thu Feb 06, 2014 12:29 pm
Posts: 118
Hi Praveen,

The output from PRECIS uses a rotated north pole grid. The idea is that the "real" north pole in the Arctic is shifted such that the equator then runs through the centre of the regional model domain. In your PRECIS domain, the new artificial equator runs through India. This is because at the equator, the grid boxes are the most equivalent in size and thus the model is the most stable. (As you approach the north or south pole the grid boxes decrease in their area because the meridians are converging).

In the real latitude-longitude coordinate system, the north pole is in the arctic (90 degrees north, 0 degrees east) and the "origin" (0 degree north, 0 degrees east) is off the coast of Ghana. That is why when you are transforming the PRECIS data and then plotting with Grads you see Africa.

More info here
http://www.metoffice.gov.uk/climatechange/science/monitoring/ukcp09/download/gridformat25.html

The solution is to regrid your data to the regular lat-lon coordinate system using ppregrid, then use pp2ctl.

(I see you have already removed the outer 8 point rim using pprr, which is a mandatory step. I assume that you have files *.rr8.pp somewhere - change the command below accordingly).

e.g. to regrid all soil moisture content output data (stash code 08208) you can do this:

Code:
cd $HOME
mkdir SMC_regrid
cd $ARCHIVEDIR/cubag/08208        # or wherever you have put the rim removed data
ppregrid -d 0.44,0.44 -e $HOME/SMC_regrid *.rr8.pp


In $HOME/SMC_regrid you will now have rim-removed and regridded (to the regular lat-lon coordinate syste) files that can me run through pp2ctl.

I have gzipped and added one of your output files so that future users can have a look. They will need to gunzip the file.

Thanks
David


Attachments:
cubaga.pae9dec.08208.pp.gz [459.52 KiB]
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