Simulation with double call to radiation for aerosols and GHG,
in order to calculate IRF (present_day - preindustrial).

For GHG (here CO2 only, cf PARAM/config.def_preind. To get IRF for well-mixed GHG, uncomment all "_per" lignes): 
Radiation variables are available for TOA and SRF only (no 3D vars), with "ghg" suffix for the 2nd call.
So IRF for GHG can be calculated for TOA and SRF only.
For complete IRF calculations (TOA, SRF and tropopause), see run (for 1 year only):
/ccc/cont003/home/gencmip6/p25sima/RFMIPi/modipsl/config/LMDZOR_v6/CM616-LR-piClim-anthroO3-4-2RadCall-IRFtropo

To set up a new simulation including variables for IRF at tropopause, best is to take example from 
piClim-histall/CM619-LR-piClim-histall-3 
See COMP/lmdz.card : 

  note the use of PARAM/*.xml_2RadCall files, 
     (key elements : new output file "histmthForIRFtropo", groups "fields_irf_aer_CMIPstyle", "fields_rad_ghg_* ", "*_tropopause" variables),

  and the post-processing (TS_MO) for :
     IRF variables for aerosols (with irf* names instead of the native "tospswad, topswai…") 
     and for GHG 2nd call variables (with "ghg" suffix).