Abstract. The quality of the representation of greenhouse gas (GHG) transport in
atmospheric general circulation models (GCMs) drives the potential of inverse
systems to retrieve GHG surface fluxes to a large extent. In this work, the
transport of CO2 is evaluated in the latest version of the Laboratoire de
Météorologie Dynamique (LMDz) GCM,
developed for the Climate Model Intercomparison Project 6 (CMIP6) relative to
the LMDz version developed for CMIP5. Several key changes have been
implemented between the two versions, which include a more elaborate
radiative scheme, new subgrid-scale parameterizations of convective and
boundary layer processes and a refined vertical resolution. We performed a
set of simulations of LMDz with different physical parameterizations, two
different horizontal resolutions and different land surface schemes, in order
to test the impact of those different configurations on the overall transport
simulation. By modulating the intensity of vertical mixing, the physical
parameterizations control the interhemispheric gradient and the amplitude of
the seasonal cycle in the Northern Hemisphere, as emphasized by the
comparison with observations at surface sites. However, the effect of the new
parameterizations depends on the region considered, with a strong impact over
South America (Brazil, Amazonian forest) but a smaller impact over Europe,
East Asia and North America. A finer horizontal resolution reduces the
representation errors at observation sites near emission hotspots or along
the coastlines. In comparison, the sensitivities to the land surface model
and to the increased vertical resolution are marginal.
On the impact of recent developments of the LMDz atmospheric general circulation model on the simulation of CO<sub>2</sub> transport
