Glaciation of liquid clouds, snowfall, and reduced cloud cover at industrial aerosol hot spots.
Toll V., Rahu J., Keernik H., Trofimov H., Voormansik T., Manshausen P., Hung E., Michelson D., Christensen MW., Post P., Junninen H., Murray BJ., Lohmann U., Watson-Parris D., Stier P., Donaldson N., Storelvmo T., Kulmala M., Bellouin N.
The ability of anthropogenic aerosols to freeze supercooled cloud droplets remains debated. In this work, we present observational evidence for the glaciation of supercooled liquid-water clouds at industrial aerosol hot spots at temperatures between -10° and -24°C. Compared with the nearby liquid-water clouds, shortwave reflectance was reduced by 14% and longwave radiance was increased by 4% in the glaciation-affected regions. There was an 8% reduction in cloud cover and an 18% reduction in cloud optical thickness. Additionally, daily glaciation-induced snowfall accumulations reached 15 millimeters. Glaciation events downwind of industrial aerosol hot spots indicate that anthropogenic aerosols likely serve as ice-nucleating particles. However, rare glaciation events downwind of nuclear power plants indicate that factors other than aerosol emissions may also play a role in the observed glaciation events.