Observed feasibility of fine and coarse aerosol-driven marine cloud brightening across different cloud regimes

Marine cloud brightening (MCB), rooted in aerosol-cloud interactions, is proposed as a rapid cooling strategy to combat global warming. However, uncertainties remain regarding its applicability across different cloud regimes and the potential counteracting effects of unfiltered coarse marine particles. Combining nearly a decade (2004-2013) of geostationally satellite observations and global reanalysis data, we compared the responses of three warm cloud regimes—marine stratocumulus (MSC), trade wind cumulus (Cu), and equatorial convection (Convection)—to fine aerosols (FA) and coarse sea salt aerosols (CSA). FA consistently strengthens cloud cooling in whatever cloud regimes, whereas CSA enhances cooling in dry MSC and Cu but induces warming in humid Cv, where precipitation dominates the cloud water loss. Further, a 50% FA increase induces a significant cooling of -14.7 W·m^-2 in MSC, as well as a moderate cooling of -5.1 W·m^-2 and -4.1 W·m^-2 in Cu and Cv regions, far exceeding CSA effects (e.g., +1.5 W·m^-2 in Cv). These results confirm that combining FA and CSA injections enhances cooling in MSC and Cu, whereas CSA injection in Cv should be avoided to prevent reduced radiative cooling. The cloud physics behind these aerosol-cloud interactions involves the balance between cloud droplet formation, cloud cover, albedo (reflectivity), precipitation, and evaporation processes, all of which are shaped by the aerosol size and the moisture content above the cloud. These findings offer key insights for climate modeling and intervention strategies.