Emergent Constraints for Aerosol Indirect Effects

It has been a challenge to constrain aerosol indirect effects through direct constraints on simulated aerosol and cloud fields in current climate. Our previous work proposed a new metric called rain frequency susceptibility to provide an emergent constraint for cloud lifetime effects of aerosols. In this study, we compared rain frequency susceptibility with several other metrics proposed in the literature for constraining cloud lifetime effects of aerosols. WE have found that rain frequency susceptibility provides a better constraint than some other proposed metrics. We further found that the magnitude of rain frequency susceptibility from satellite observations depends on whether cloud droplet number concentrations or aerosol index are used in its definition. Our results show that constraining model results using rain frequency susceptibility from both definitions provides further insights on model discrepancies with observations.