source: CMIP6/RFMIP/piClim-anthro/CM616-LR-piClim-anthroO3-4-2RadCall/README_2RadCall_ghg_per @ 5822

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

Notes for GHG:
============

1/ See config.card_preind for how to prescribe ghg_per values for the 2nd call (here preindustrial) : 
Example :
N2O_ppb_per = 2.7302e+02
and not :
N2O_ppb_per = _AUTO_: DEFAULT = 2.7302e+02
Using " _AUTO_ " will lead the model to crash because there is no option of "_AUTO_" values for "_per" in DRIVER/lmdz.driver,       
except for co2_ppm_per. 
co2_ppm_per is calculated as 4x varying CO2 if a CO2 file is available for reading via lmdz.card         
(typically the historical/scenario CO2 file). 
If this file is absent, the DEFAULT value defined in config.def is used
(typically = 4xCO2_preind ; in RFMIP we use CO2_preind).

2/ Radiation variables are available for TOA and SRF, with "ghg" suffix for the 2nd call.
The tropopause variables (t_, p_, z_tropopause) and the 3D radiation variables from 2nd call (*ghg) are also available, but not the 3D variables from the 1st call.
So IRF for GHG can be calculated for TOA and SRF only.
For complete IRF calculations (TOA, SRF and tropopause), see (1-year) run :
/ccc/cont003/home/gencmip6/p25sima/RFMIPi/modipsl/config/LMDZOR_v6/CM616-LR-piClim-anthroO3-4-2RadCall-IRFtropo

3/ To set up a 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).