Assessment of transport in the latest Chemistry Climate Model Initiative (CCMI-2022) simulations
D. Plummer, H. Akiyoshi, F. Dennison, S. Frith, B. Josse, J. Keeble, D. Kinnison, M. Marchand,
O. Morgenstern, A. Pfeiffer and E. Rozanov
Abstract: Chemistry climate models (CCMs) are routinely used
to study the present-day chemical state of the atmosphere andmake projections of how the chemical state may change in thefuture under different climate change and reactive gas emission
scenarios. As part of Phase Two of the Chemistry Climate ModelValidation (CCMVal-2) project the distribution of a number ofchemical species and diagnostic tracers (e.g. age of air) werecompared with available observations to assess the fidelity ofstratospheric transport in the participating models. It has been
more than 10 years since the CCMVal-2 assessment andchemistry climate models have continued to evolve. Here we
revisit and extend the assessment of the distribution of chemicaltracers from CCMVal-2 to look at the most recent set ofsimulations performed for the Chemistry Climate Model
Initiative to ask whether the ability of models to accuratelysimulate stratospheric transport has changed significantly.
The CCMI-2022 Experiments
refD1

A free-running historical hindcast simulation
covering 1960 – 2018, using observed SSTs/seaice and other forcings (including extended
datasets of stratospheric aerosols and solarforcing) designed to reproduce the past.

refD2

The baseline scenario covering 1960 – 2100 toprovide updated projections of ozone recovery.
This scenario follows the GHGs and reactive gas
emissions from SSP2-4.5 of CMIP6 and theWMO(2018) baseline projection for Ozone
Depleting Substances. SSTs and sea-ice arecalculated by each modelling group, using eitherprescribed datasets or interactively.

senD2-sai

Based on the refD2, but with modified fields forthe specified stratospheric aerosols reflecting
increased amounts from 2025 due toStratospheric Aerosol Intervention. SSTs/sea-ice
are to be specified as a repeating annual cycle
derived as the 2020 – 2030 average from thebaseline refD2 simulation.

Simulations currently available in the Centre for Environmental
Data Analysis (CEDA) data archive
Institute-ModelrefD1

CSIRO-ACCESSECCC-CMAM
DLR-EMAC
GSFC-GEOSCCM
NIES-MIROC32
CNRM-MOCAGENIWA-UKCA2IPSL-REPROBUS
ETH-SOCOLNCAS-UKESM1
NCAR-WACCM351134*
31133^

refD23314*
3senD2- senD2- senD2saissp126 ssp370
34*
311333^*Multiple realizations using combinations of different model versions anddifferent forcings but the same meteorology.
^Data not currently available in CEDA archive.

Some initial comparisons of CCMI-2022 with CCMVal-2

Figure 1. A comparison of total inorganic chlorine (Cly) at 1hPa, 70 - 80°Sin October. The left-hand panel shows the results from the CCMI-2022
REF-D1 simulation and the right-hand panel are results from theCCMVal-2 REF-B2 simulation as presented in Neu and Strahan (Chapter 5of SPARC CCMVal (2010)). At 1hPa in October almost all of the chlorine
has been released from the organic species and the total inorganic
chlorine should not exceed the maximum specified troposphericchlorine total of approximately 3.7ppb.
NOTE: The colours used for each model are not consistent between thetwo panels.

senD2-ssp370 Set up largely as the refD2 baseline scenario,
only following the low climate mitigation
scenario SSP3-7.0 of CMIP6 for GHGs andreactive gas emissions.
senD2-ssp126 Similar to senD2-ssp370, though following thehigh climate mitigation scenario SSP1-2.6 ofCMIP6.
Assigned high priority.

Figure 2. A comparison of total inorganic chlorine (Cly) at 50hPa, 70 80°S in October. The left-hand panel shows the results from the CCMI2022 REF-D1 simulation and the right-hand panel are results from theCCMVal-2 REF-B2 simulation as presented in Neu and Strahan (Chapter 5of SPARC CCMVal (2010)). Observations of Cly from Lary et al. (2007) are
shown as the black circles with uncertainties as derived in Waugh andEyring (2008).

For CCMI-2022 there are fewer models that appear to haveproblems conserving total chlorine (Figure 1, Cly at 1 hPa),
though the majority of models continue to underestimate
reactive chlorine in the Antarctic vortex (Figure 2).
References:
SPARC CCMVal (2010), SPARC Report on the Evaluation of Chemistry-Climate Models, V. Eyring, T. G. Shepherd, D. W. Waugh (Eds.), SPARC Report No. 5, WCRP-132, WMO/TD-No. 1526.
Lary, D. J., Waugh, D. W., Douglass, A. R., Stolarski, R. S., Newman, P. A. and Mussa, H., Variations in stratospheric inorganic chlorine between 1991 and 2006, Geophys. Res. Lett., 34, doi:10.1029/2007GL030053.
Waugh, D. W. and Eyring, V., Quantifying performance metrics for stratospheric-resolving chemistry-climate models, Atmos. Chem. Phys., 8, 5699-5713.