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Greater tropical ascent area reduction linked to higher equilibrium climate sensitivity in CMIP6

Presentation Date
Wednesday, December 9, 2020 at 4:00am



Among the latest generation of climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6), models with higher equilibrium climate sensitivity (ECS) tend to have greater tropical ascent area reduction per degree of warming. Models with higher ECS also tend to have greater increases in the fractional area occupied by intense precipitation and smaller decreases in tropical ascent strength. Changes in the shortwave cloud radiative effect (CRE) in the deep tropics dominate the intermodel spread in the net CRE, which appears to be driven by changes in low cloud fraction rather than high cloud properties. Correlation maps further reveal that the intermodel spread in low cloud fraction in the Indo-Pacific warm pool and Pacific inter-tropical convergence zone (ITCZ) regions is more significantly related to the intermodel spread in ECS than the intermodel spread in subtropical marine boundary layer low cloud fraction among CMIP6 models. These results suggest that the intermodel spread in tropical ascent area reduction and the response of tropical deep convection to warming across scales may be intimately tied to the intermodel spread in ECS through low cloud fraction changes. Results from perturbed physics experiments will be presented to elucidate potential mechanisms and physical processes linking both tropical and subtropical low cloud variability to convection parameterization.

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