Constraints on interactions between aerosols and clouds on a global scale from a combination of MODIS-CERES satellite data and climate simulations

摘要

Satellite-based cloud top effective radius retrieved by the CERES ScienceTeam were combined with simulated aerosol concentrations from CCCma CanAM4 toexamine relationships between aerosol and cloud that underlie the firstaerosol indirect (cloud albedo) effect. Evidence of a strong negativerelationship between sulphate, and organic aerosols, with cloud top effectiveradius was found for low clouds, indicating both aerosol types arecontributing to the first indirect effect on a global scale. Furthermore,effects of aerosol on the cloud droplet effective radius are more pronouncedfor larger cloud liquid water paths. While CanAM4 broadly reproduces theobserved relationship between sulphate aerosols and cloud droplets, it doesnot reproduce the dependency of cloud top droplet size on organic aerosolconcentrations nor the dependency on cloud liquid water path. Simulationswith a modified version of the model yield a more realistic dependency ofcloud droplets on organic carbon. The robustness of the methods used in thestudy are investigated by repeating the analysis using aerosol simulated bythe GOCART model and cloud top effective radii derived from the MODIS ScienceTeam.