Comparisons of the Behavior of AgI-Type Ice Nucleating Aerosols in Laboratory-Simulated Clouds

Paul J DeMott


A variety of commonly used ice nucleants have been tested for comparable simulated adiabatic parcel ascents in the Colorado State University dynamic cloud chamber. Atmospheric adiabatic expansion and cooling of a parcel of air is simulated by evacuation and wall temperature control within the working volume. Ice nucleation characteristics have been studied for the injection of nuclei preceding the formation of clouds at a temperature near 0°C and following nuclei injection directly into cooling cloud parcels. A summary and comparison of the nucleation rates and mechanisms observed for four different ice nucleating aerosols is presented. In some cases, the results observed in the simulations of real cloud processes were quite different than found previously in the static conditions of the CSU isothermal cloud chamber containing an artificially generated cloud. In particular, complexed hygroscopic nucleating aerosols (2Agl.Nal and 2AgI.KI) display much higher nucleation rates during expansional cooling than for injection into supercooled isothermal cloud. Some implications of the experimental results to the expected results of seeding atmospheric clouds are discussed.

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