...

so that the SST anomaly with respect to the climatology is added to the existing SST field over the Pacific, effectively doubling the strength of the El Nino signal there.

More complex scenarios

If more complex scenarios are necessary than supported by the above equation, the relevant code in sst_modif.mv to change is:

      g= g*lsmGrb +                                        # STL1 values over land points; provided by fInit
         ref[idxRef]*(1-lsmGrb) +                          # STL1 values over sea points, outside AND inside box mask
         (pert[idxPert]-ref[idxRef]) * maskGrb * weight    # weighted difference added to STL1 values INSIDE box mask

Running the script

To run the script, type the command:

...

Rename ICMCL files to run!

Final and important step, once the sst_modif.mv script has completed and you are satisfied with the changes in the SST field, remember to rename the files to replace the original, so that the model uses the modified file when starting:

...