Global transport of passive tracers in conventional and superparameterized climate models: Evaluation of multi-scale methods

The global transport of the surface-emitted short-lived passive tracers radon and methyl iodide is simulated in a cloud-resolving Global Climate Model (GCM) for the first time and compared against simulations with a conventional GCM in which cloud processes are not resolved. Both models are operated in chemical transport mode in which the large scale flow is set to observationally derived dynamic and thermodynamic fields from a meteorological reanalysis. Simulated vertical profiles of tracers concentrations from both models are compared with profiles observed in situ. The comparisons suggest that the cloud-resolving GCM is, to a small degree, better than the conventional GCM in reproducing the vertical gradients and hence the convective entrainment and detrainment of passive tracers. Contrasting only simulated climatological maps of tracers concentrations from the two models, we find consistent and appreciable relative differences that create a quadrupole pattern in the vertical direction. Relative to the conventional GCM, the tracer concentrations from the cloud-resolving GCM results are depleted from the surface to 1 km and from 4 to 12 Km and enriched from 1 to 4 km and above 12 km. This might have important implications for climate and atmospheric chemistry simulations but require further investigations.