The growth of ice particles in a mixed phase environment based on laboratory observations

Abstract

This paper describes new laboratory observations about the size evolution of ice crystals and cloud droplets immersed in a mixed-phase cloud. The experiments were performed by using a cloud chamber facility for three temperatures − 6 °C, − 10 °C and − 20 °C, in order to explore the basic crystal growth habits (columns and hexagonal plates). The sizes of the cloud droplets, ice-columns and hexagonal ice-plates were examined for growth times between 50 and 300 s. The results show evidence that after ice crystal nucleation, the cloud droplets reduce gradually their sizes by the evaporation process; while the ice crystals grow as a consequence of the water vapor diffusion process. The ice crystal growths at different temperatures were compared with the results reported by other authors. The experimental data were also compared with a theoretical model of the growth rate of ice crystals. It was observed that the numerical model provides a description of the ice columns' growth in fairly good agreement with the laboratory observations, while it predicts that the hexagonal plates evolve with maximum sizes larger than those observed in the experiments. In general, it has been noted that the results obtained from the model are very sensitive to the parameter that denotes the ratio between the condensation coefficient for the basal face and prism face. It is a critical coefficient that needs to be carefully addressed in cloud modeling.