Sensitivity of a GCM to changes in the droplet effective radius parameterization

Abstract

The French Community Climate model (ARPEGE‐climat) has been used in relation to four different warm cloud droplet effective radius parameterizations in order to simulate the January and July climatologies. Two of these parameterizations depend upon the cloud character (maritime or continental). The comparison between the results of the different simulations reveals that the model is very sensitive to the effective radius parameterization change. This change induces differences up to 30Wm −2 in the global values of the radiative fluxes at the top of the atmosphere and at the surface level. Important differences are also induced in the zonally averaged short‐wave cloud radiative forcing, cloudiness and precipitation. At smaller scales, non negligible precipitation and surface temperature changes are also observed. The comparison between the simulation results obtained by using model versions containing the above parameterizations reveals that two of them considerably improve the agreement between model and climatological cloudiness, thus allowing a pertinent choice of the most appropriate cloud droplet effective radius parameterization.