A Study of Aerosol Indirect Effect for Cumulus Clouds on a Global Scale

Using case study approach my investigation on aerosol's effects on fair weather cumulus clouds shows that not only can aerosol reduce cloud droplet sizes like in the case of stratiform clouds, but also they can increase droplet sizes. Atmospheric water vapor loading explains nearly 70% of variations in the dependence of droplet size on aerosol loading for cases over Eastern United States. This finding withstands serious scrutinizing under different scenarios of artificial correlations. A further study on a global scale indicates that only two areas, Eastern US and coastal region of Southeast China, show increasing trend of droplet size with aerosol loading. Results from other regions agree well with findings from past studies further ruling out artificial correlation. Relationship between aerosol loading and cloud liquid water path differs significantly for marine stratocumulus clouds and continental cumuli. Two possible explanations for our findings are confirmed by state-of-the-art cloud resolving model simulations.