Stratospheric aerosol files for LMDz can be created by running on ciclad the script 
./volc.sh 
which itself prepares two more files and submit a job on ciclad which may take a couple of days to run.

The stratospheric AOD data originates from data prepared by Beiping Luo ETZH for CMIP6. 
See http://www.wcrp-climate.org/wgcm-cmip/wgcm-cmip6
and ftp://iacftp.ethz.ch/pub_read/luo/CMIP6/
The data were provided in June 2016 and were not versioned (but were later referred as v2). 
A new version (v3) was made available on 15 September 2017 due to a glitch in the 1970s data. 
The new version also modified the trend in the background aerosol.

Beiping calculated for the solar radiation 8 bands (bands 1-6 for the SW 6 bands 
model and 7-8 for the SW 2 bands model) and likewise for the 16 bands of the RRTM LW model. 

The data are processed in IDL on ciclad for different resolutions 
of the IPSL model and aerosol optical properties are generated for AOD, 
omega and g per model layer (SW), and absorption AOD per model layer (LW).

The stratospheric aerosol data extends into the troposphere but a mask is applied 
in the LMDz model to remove tropospheric data. The data are interpolated on the vertical 
from the CMIP6 altitude coordinate (z, resolution 0.5 km) to the model coordinate (sigma). 
This is done using a monthly (10-year mean) climatology of the geopotential height. 
zalt_LR_l79.nc = 10 yr climatology from a coupled IPSL-CM6.0.12 simulation
zalt_zonmean_LR_l79.nc = zonal mean of the above file  (cdo zonmean zalt.nc zalt_zonmean.nc)
zalt_zonmean_LR_l79_rev.nc = same as above but ferret'ized so that can be read in idl

In September 2017 the processing idl routine was to v4 changed to rely on climatological LMDz altitudes
that vary monthly and with latitude (based on GEOP variable Z=GEOP/RG/1000 [in km]). 
Start from a file geop.nc with monthly GEOP variable
cdo divc,9810. geop_LR.nc zalt_LR_l79.nc
cdo zonmean zalt_LR_l79.nc zalt_zonmean_LR_l79.nc
ferret'ize file to make it readable by ferret : zalt_zonmean_LR_l79_rev.nc 
We have files for LR, MR, HR model versions.
The variable is called GEOP but is now the altitude in km as required by the interpolation scheme.

The data are fed on ciclad (currently in /data/$USER/CMIP6/VOLC/)

Annual files: taulwstrat.2D.$year.nc and taulwstrat.2D.$year.nc
to be used for historical simulations

Average 1850-2014 conditions (no seasonal cycle): taulwstrat.2D.ave.nc and tauswstrat.2D.ave.nc
to be used for piControl, pdControl and for scenario runs (past a 10 year transition from 2014 conditions)
subject to changes in the protocol

Following the CMIP6 protocol, a linear transition between 2014 and average conditions is 
performed and should be used for the period 2015-2023. Average conditions should then be used for
2024 onwards.

CMIP6 stratospheric aerosols are activated in LMDz with flag_aerosol_strat=2

Files to be renamed as taulwstrat.2D.nc and tauswstrat.2D.nc for use by LMDz 
No additional interpolation between months is done. 

Olivier Boucher 
27/07/2016
Revised 10/09/2017
Revised 04/10/2017
Revised 15/04/2018
Revised 18/09/2018
Revised 11/12/2018