How to perturb the initial conditions in LMDZOR?

Why?

Simulations in LMDZOR start with a prescribed atmospheric temperature. This initial temperature is estimated in the ELI experiment. The model results are rather sensitive to the initial conditions. However, the initial condition does not account for the specifics of the land surface. Therefore, one could reason that the initial conditions estimated during the ELI experiment are just one possible realisation from a population of initial conditions. The sensitivity of the model result to the initial conditions can then be tested by running the model for a (small) population of slightly different initial conditions. Such runs could be used as a sensitivity test but they could likewise be used as a proxy for the uncertainty on the simulated climate variables.

How?

At present the easiest way to perturb the initial conditions of LMDZOR seems to consist of adjusting the results of the ELI experiments.

Step-by-step

Run the ELI experiment, for example ELI-128x118x39-2010-R1. Instructions of how to set-up such an experiment can be found at ​https://forge.ipsl.jussieu.fr/orchidee/wiki/Documentation/UserGuide/PresentDay. The suffix R1 denotes that this is the first realization from a population of possible, equally likely initial conditions. Copy and rename ELI-128x118x39-2010-R1 to ELI-128x118x39-2010-R2

cd /ccc/store/cont003/dsm/p529luy/IGCM_OUT/LMDZ/
cp -rf ELI-128x118x39-2010-R1 ELI-128x118x39-2010-R2
cd ELI-128x118x39-2010-R2/ATM/Output/Restart/
rename 2010-R1 2010-R2 *.nc
cd ../Boundary
rename 2010-R1 2010-R2 *.nc

The folder /ccc/store/cont003/dsm/p529luy/IGCM_OUT/LMDZ/ELI-128x118x39-2010-R2 should now look as an independent folder. The initial atmospheric conditions are given in /ccc/store/cont003/dsm/p529luy/IGCM_OUT/LMDZ/ELI-128x118x39-2010-R2/ATM/Output/Restart/ in the file JOBNAME_YEAR_start.nc as the variable called TETA. Subsequently we will open this file, perturb TETA by a random field of small perturbations and then save the file with a perturbed value for TETA. Several libraries with ncdf4 functionality (confirmed for nco, R and python) contain commands that enable you to manipulate a variable in a netcdf file. In this example a python script was used to perform these tasks.

copy the config change COMP/lmdz.card ELI