A CHEMICAL TRACER EXPERIMENT IN OROGRAPHIC CLOUDS

Abstract

In the summer of 1954, and experiment was conducted on the Island of Maui, Territory of Hawaii, in which a chemical tracer technique was exployed to ?tag? water droplets sprayed into an orographic cloud from a site near the base of a large cliff, oriented normal to the trade winds. A sampling method was used which permitted the individual drops to be identified and their size measured when they fell to the ground downwind from the spray site. The object of the experiment was to obtain data on the growth and final size distribution of the droplets. Samples of the spray were obtained up to six miles downwind from the spray site, and the lateral boundaries of the spray plume were determined approximately. Sampling results were negative during conditions when moderate to heavy rain prevailed or, at the other extreme, when the orographic cloud was weakly developed. A tendency for increasing drop size with distance from the spray site was indicated by the data.