Exploring the Effect of Aerosol on Marine Cloud Cover Using a Counterfactual Approach

<p>Aerosol&#8211;cloud interactions in marine stratocumulus clouds (Sc) are among the most challenging frontiers in cloud&#8211;climate research.&#160;In particular, the cloud cover susceptibility to droplet concentration remained under-represented in the literature.&#160;We developed methodologies to estimate what&#160;would have been the cloud cover and&#160;the associated&#160;radiative&#160;<span>effect</span> of currently observed Sc, but in a hypothetical cleaner world. The first methodology uses a realistic Lagrangian large eddy simulation coupled with satellite observations and provides a process-oriented analysis. The other uses a <span>simple</span> model and provides a global estimate of the radiative impact. We found that overcast Sc decks would have broken up sooner had they not been influenced by anthropogenic aerosol, thereby causing a significant effective radiative forcing.</p>