cordexfps-aerosol

This protocol targets to assess the role of the regional aerosol load in the future evolution of the regional climate. It can be seen as a sensitivity experiment to assess current practices in RCM in CORDEX. Indeed, currently, the aerosol forcing and its evolution in historical and scenario runs is not specified in the CORDEX experimental protocol. This creates inconsistencies in the way it is applied in the CORDEX RCMs with potential impacts on the simulated climate change signal. For example for the Med-CORDEX or Euro-CORDEX domains, most of the models do not use evolving aerosols in RCP historical and scenario runs (see Nabat et al. 2015a for Med-CORDEX and this document for Euro-CORDEX)

Protocol 1B of the CORDEX FPS-aerosol is now citable through its DOI: 10.5281/zenodo.4589266

The protocol proposed here relies on existing CORDEX simulations following the official CORDEX protocol for Med-CORDEX or Euro-CORDEX, whatever the spatial resolution:
- One simulation covering at least the period 1971-2000 for the historical run
- A second simulation covering the period 2021-2050 for the RCP8.5 run
Both simulations are required with some classical variable outputs. We also request from the participating groups to document the way they specify the aerosol in their model runs for CORDEX including a description of the spatio-temporal variability of this forcing. You can follow this example.

We also request the participating groups to provide their AOD (Aerosol Optical Depth) in netcdf (monthly-mean files) if any as well as radiative characteristics of their aerosols if possible (single scattering albedo, asymmetry parameter, angstrom exponent).

Note that only RCMs including an aerosol forcing can participate to this modelling exercice. This forcing can however be very simple (as in RCA), no need for a complex scheme. This may exclude models such as some versions of WRF and of RegCM.

For this protocol, it is requested to run an additional future scenario runs of 30 years (2021-2050) that is a perfect twin of the CORDEX standard run. Two options are proposed depending on the aerosol forcing applied in the standard CORDEX runs

Option 1: If you already have evolving aerosols in the scenario runs (such as in RACMO or ALADIN)

Take the AOD of the historical period, average it over the 30 years keeping its spatial and seasonal/monthly variability and apply it to the 2021-2050 period. The goal is to have the same mean AOD in the historical and scenario 30-year period.

Option 2: If you do not have evolving aerosols in the scenario runs (such as in RCA, PROMES, REMO, some WRF versions, HIRHAM, COSMO-CLM)

CNRM (contact pierre.nabat[at]meteo.fr) will provide you an AOD anomaly adapted to your model configuration to be added to your presente-climate AOD forcing. You will have to run the 2021-2050 period with the modified AOD forcing. This AOD forcing comes from a GCM with interactive aerosols and participating to the ACCMIP initiative (LMDZ-INCA, Szopa et al. 2013). It is the forcing applied in ALADIN runs.

The following simulations are requested:

• HIS1B (1971-2000) a historical simulation (existing in Euro-CORDEX or Med-CORDEX)
• SCE1B (2021-2050) RCP8.5 simulation (existing in Euro-CORDEX or Med-CORDEX)
• AER1B (2021-2050) RCP8.5 simulation with a different aerosol evolution (new simulation)

Please contact Pierre Nabat (pierre.nabat[at]meteo.fr) to get an evolution of aerosols adapted to your model configuration for simulation AER1B. These simulations have to be run with a regional climate model on a domain including the Med-CORDEX official domain (see details here), the Euro-CORDEX official domain being therefore accepted (see details here).

Example of naming for the output files :

• Existing CORDEX run: rsds_EUR-11_CNRM-CERFACS-CNRM-CM5_rcp85_r1i1p1_CNRM-ALADIN63_v1_mon_202101-203012.nc
• if option1: rsds_EUR-11_CNRM-CERFACS-CNRM-CM5_rcp85_r1i1p1_CNRM-ALADIN63_v1cstaer_mon_202101-203012.nc
• if option2: rsds_EUR-11_CNRM-CERFACS-CNRM-CM5_rcp85_r1i1p1_CNRM-ALADIN63_v1evoaer_mon_202101-203012.nc

Variables to be stored : see the columns "Protocol 1" of this table

Participants : see this table for protocol 1B

Nabat, P., Somot, S., Mallet, M., Sevault, F., Chiacchio, M., & Wild, M. (2015). Direct and semi-direct aerosol radiative effect on the Mediterranean climate variability using a coupled regional climate system model. Climate dynamics, 44(3-4), 1127-1155.

Szopa, S., Balkanski, Y., Schulz, M., Bekki, S., Cugnet, D., Fortems-Cheiney, A., … & Idelkadi, A. (2013). Aerosol and ozone changes as forcing for climate evolution between 1850 and 2100. Climate dynamics, 40(9-10), 2223-2250.