Glaciation of mixed-phase clouds by dry ice to cool the Arctic

Arctic stratus or stratocumulus mixed-phase clouds have a substantial effect on the Arctic radiation budget1 and winter sea ice growth is sensitive to long wavelength radiative forcing.2 Clouds with a liquid water profile greater than 30 g m-2 are blackbody absorbers for terrestrial long wavelength radiation and increase the terrestrial forcing by roughly 40 W m-2 over clear skies or ice-only clouds.1, 3 This report proposes glaciating Arctic mixed-phase clouds by seeding with dry ice during the winter months of November through February to restore summer sea ice and Arctic albedo. Seeding is performed by aircraft above the clouds dropping 1 kg km-1 of dry ice pellets in parallel tracks spaced by 1.2 km. Each track creates a curtain of ice crystals that diffuse through the cloud, glaciating the cloud by the Wegener-Bergeron-Findeisen process. The ice crystal and water vapor concentrations are simulated during a 4 day period after seeding for different assumptions of the eddy diffusion coefficient.