Abstract
A numerical model is constructed to simulate the evolution of pre-ice-nucleation conditions within a settling cloud chamber. Drop nucleation, growth, evaporation, sedimentation, and vertical and radial heat and moisture diffusion are included in the model. Measured vertical temperature profiles and a prescribed condensation nucleus distribution serve as inputs to the model. Time-height cross sections of saturation ratio, liquid water content and drop concentration, and time evolution of drop size spectra at various locations are presented. The results show that maximum supersaturation is attained in a shallow layer just above the maximum curvature of the temperature profile, i.e., near the top of the brass cylinder. Subsaturation with respect to water but supersaturation with respect to ice exists in the cloud-filled iso-thermal portion of the chamber. Although the ice phase is not included in the model, the results suggest that the dominance of a particular mode of ice nucleation may be a function of the initial condensation nucleus spectrum.
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