Glaciation of liquid clouds, snowfall, and reduced cloud cover at industrial aerosol hot spots
Toll, Velle ; Rahu, Jorma ; Keernik, Hannes ; Trofimov, Heido ; Voormansik, Tanel ; Manshausen, Peter ; Hung, Emma ; Michelson, Daniel ; Christensen, Matthew W. ; Post, Piia ; Junninen, Heikki ; Murray, Benjamin J. ; Lohmann, Ulrike ; Watson-Parris, Duncan ; Stier, Philip ; Donaldson, Norman ; Storelvmo, Trude ; Kulmala, Markku ; Bellouin, Nicolas
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.</p>
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