Macroscopic Approach to Cloud Droplet Growth by Condensation - A Study by a semi-real scale Experimental System

Formation and growth of water droplets were studied using a semi-real scale experimental system; the main component of the system was a 430 m vertical shaft used to perform cloud formation experiments at a spatial scale close to that of the real atmosphere. By generating an updraft with humid air, a cloud was observed to form at a height of 35 m from the bottom. The number concentration, and size distribution of water droplets were recorded. In some experiments, NaCl particles were intentionally injected into the air stream to increase the number of condensation nuclei. The effects of this on the number and size distribution of droplets were studied. The droplet growth rate was estimated on the basis of these effects. It was found that in the shaft, the humidity of the air stream was below the saturation level. Thus, macroscopically, condensation and growth proceeded without supersaturation, which is usually assumed in traditional microscopic cloud physics for water droplet growth. The growth process was considered as a chemical reaction to deal with this condition. An attempt was made to obtain information about the rate constant.