A laboratory investigation of vapor-grown ice crystals at low atmospheric temperatures

An experimental system for controlled growth of small ice crystals has been developed and used to produce new measurements of ice crystal growth at low atmospheric temperature. The experimental arrangement allows for temperatures as low as -65°C and can produce ice supersaturations in excess of liquid water saturation at all sub-freezing temperatures. This well-insulated system is combined with a novel use of quadrupole electrodynamic levitation to monitor the evolution of single ice particles as they grow and evaporate. Measurements have been made on crystals growing on glass fibers as well as levitated crystals at various temperatures meant to simulate the possible environment of a cirrus cloud. It has been found that the growth and evaporation rates of the particles can be approximately modeled using a modified version of the classical capacitance model. The comparison of model calculations with data provides strong evidence for low kinetic deposition coefficients. These results offer some important insights into bulk cirrus behavior and offer a way to improve microphysical parameterizations in cold-cloud modeling.