Towards predictive understanding of atmospheric circulation change

Abstract:

Intermodel spread in projected rainfall change under global warming remains large in the CMIP5 ensemble. Unlike the ensemble mean that is affected by both the wet-get-wetter and warmer-get wetter mechanisms, moisture budget analyses reveal that model uncertainties in tropical rainfall change is dominated by intermodel discrepancies in the dynamical contribution by the atmospheric circulation change. Intermodel Singular Value Decomposition analyses further show a tight coupling between the ocean warming pattern and tropical circulation change. Two robust modes emerge: one with an inter-hemispheric asymmetric structure and one with an equatorial peak. The interhemispheric-asymmetric mode is accompanied by trade wind changes consistent with wind-evaporation-SST feedback. We suggest that the tropical coupled asymmetric mode is triggered by the muted surface warming in the Southern Ocean due to the locally enhanced heat uptake. Zonally asymmetric circulation adjustments will also be discussed.