Production of the CMIP6 aerosol forcing files

The forcing sets of data for tropospheric aerosols for CMIP6 were generated by a historical simulation over the period 1850-2014, using LMDZORINCA in the 6.0.12ttop configuration.

Because of the total cumbersome duration of the total historical simulation, five different segments were run in parallel: 1847-1882, 1880-1915, 1913-1948, 1946-1981 and 1979-2014. Each of them included a three-year period of spin-up (starting conditions with concentrations in SO2 and aerosols set to naught); the output data of the spin-up periods were not considered in the final operations.

The aerosol concentrations output from the five simulations underwent a smoothing process: a sliding, weighted average was operated over a three-year window centered on the year of interest, with weights defined as [0.25; 0.5; 0.25]. The shell script used to perform this operation can be found at ​http://forge.ipsl.jussieu.fr/igcmg/svn/TOOLS/CMIP6_FORCING/AER_TROP_CONCENTRATIONS/aerosols_from_inca.sh This average operation was calculated month-to-month, i.e. Jan_out(Y) = 0.25*Jan_in(Y-1) + 0.5*Jan_in(Y) + 0.25*Jan_in(Y+1), and so on for the other eleven months, eventually yielding a 12-month file for each year. (For 1850 (resp. 2014), the Y-1 (resp. Y+1) year was taken equal to Y.)