Asian monsoon amplifies semi-direct effect of biomass burning aerosols on low cloud formation

Low clouds play a key role in the Earth-atmosphere energy balance and influence agricultural production and solar-power generation. Smoke aloft has been found to enhance marine stratocumulus over the Southeast Atlantic in austral spring through aerosol-cloud interactions, but its role in regions with strong human activities and complex monsoon circulation remains unclear. Here we show that biomass burning aerosols aloft strongly increase the low-cloud coverage over both land and ocean in subtropical southeastern Asia. The degree of this enhancement and its spatial extent are comparable to that in the Southeast Atlantic, even though biomass burning emissions in Southeast Asia are only one-third of those in Southern Africa. Our results indicate that a coupling of aerosol-cloud-boundary-layer feedback with the monsoon is the main reason for the strong semi-direct effect and enhanced low-cloud formation in Asia.