Effect of coarse marine aerosols on stratocumulus clouds

Authors


Abstract

[1] In contrast to fine anthropogenic aerosols (radii ∼<0.5 μm), large aerosol particles are thought to enhance cloud droplet growth, promote precipitation formation and reduce cloud albedo. While shown in cloud simulation models, the impact of coarse aerosols on marine stratocumulus clouds lacks observational evidence. Here, by combining data from AMSR-E and MODIS, both aboard NASA's satellite Aqua, we link the amount of coarse marine aerosols emitted to the atmosphere through wind-driven processes with the size of cloud droplets, at the world's largest deck of marine stratocumulus clouds over the southeastern Pacific. For constrained meteorological conditions, approximately 1/2 of the change in droplet effective radius (reff) is attributed to increase in coarse marine aerosol optical depth (τcm), as surface winds intensify. Accordingly, a twofold increase in τcm is associated with a 1.4 μm +/−0.11 increase in reff. Our results suggest that climatic changes in surface winds may play an important role not only over land for wind-power estimation but also over the oceans by changing clouds reflectance and lifetime.

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