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Zusammenfassung:
Recent research suggests cloud-radiation interaction as key for inter-model differences in tropical precipitation change with warming. This motivates the hypothesis that inter-model differences in the climatology of precipitation, and in its response to warming, should reduce in the absence of cloud-radiation interaction. The hypothesis is explored with the aquaplanet simulations by the Clouds On-Off Klimate Intercomparison Experiment performed by seven general circulation models, wherein atmospheric cloud radiative effects (ACREs) are active (ACRE-on) and inactive (ACRE-off). Contrary to expectation, models’ climatology of tropical precipitation are more diverse in the ACRE-off experiments, as measured by the position of the intertropical convergence zone (ITCZ), the subtropical precipitation minima, and the associated organization of the tropical circulation. Also the direction of the latitudinal shift of the ITCZ differs more in simulations with inactive cloud-radiative effects. Nevertheless, both in ACRE-on and ACRE-off the same relationship between tropical precipitation and the mean vertical-velocity (zonally, temporally and vertically averaged) emerges in all models. An analysis framework based on the moist static energy budget and used in the moisture space is then developed to understand what controls the distribution of the mean vertical-velocity. The results suggest that inter-model differences in tropical circulation and zonal mean precipitation patterns are most strongly associated with inter-model differences in the representation of shallow circulations that connect dry and moist regions.
