To support the WMO/UNEP Scientific Assessment of Ozone Depletion Report 2022, we are asking modelling groups to perform a number of simulations to allow for both an assessment of the models, the first comprehensive assessment of model performance since CCMVal-2 in 2010, and longer scenario simulations to project ozone recovery.

All the details of the setup and forcings for the first model experiment, the REF-D1 historical hindcast simulation covering 1960 – 2018 and using forcing as closely following the observed historical evolution, can be found here.

An excel spreadsheet version of the data request for all model experiments can be found here. Model data is to be provided in version 4 netCDF, with all metadata following the CF (Climate and Forecast) conventions. As such, we strongly recommend groups use the CMOR utility for the generation of the netCDF files and a version of the data request for use with the CMOR utility will be available soon.

Ancillary Information on REF-D1 Forcings

The required forcings, largely following datasets produced for the historical period of CMIP6 up to 2014 and then SSP2-4.5 for 2015 – 2018, are detailed in the REF-D1 experimental description. Here, a bit of additional information is provided on particular datasets that deviate from the standard CMIP6 recommendations.

Near-surface methane concentration

A slightly modified time series for the near-surface methane mixing ratio has been recommended for REF-D1 over the period 2015 – 2018. This data has been created by scaling the original SSP2-4.5 methane data by a globally constant scaling factor to bring the year-to-year changes in methane in line with more recent observations given in the annual WMO GHG bulletin and the NOAA/ESRL Global Monitoring Laboratory Atmospheric Greenhouse Gas Index. A comparison of the global average CO2, CH4 and N2O near-surface concentrations from the different Tier 1 and 2 CMIP6 SSPs against these observations for 2012 – 2019, can be found here. The python script that was used to modify the original v1.2.1 SSP 2-4.5 methane data files can be found here.

Ozone Depleting Substances

The WMO-2018 scenario of global-average near-surface mixing ratios was based on observations up to the beginning of 2017, with projected values used for subsequent years. To more accurately reflect the recent behaviour of different ODSs, flask network observations from NOAA ESRL were used to extend the WMO-2018 time series for 2017 – 2018 for CFC-11, CFC-12, CCl4, HCFC-22 and CH3Cl. For convenience, the original WMO-2018 time series was also extrapolated backwards from 1955 to 1949. A comparison of the original WMO-2018 baseline scenario and the revised time series for  the REF-D1 simulation can be found here, and the python script that was used to revise the WMO-2018 time series can be found here.

Quasi-Biennial Oscillation

The time series of equatorial zonal winds to be used for introducing a QBO into models that do not internally generate their own has been extended from the dataset produced for CCMI-1. The python script that was used to extend the dataset using the Singapore winds from FUB can be found here, and plots of the CCMI-1 and the extended time series can be found here.