The Importance of Natural Glaciation on the Modification of Tropical Maritime Cumuli by Silver Iodide Seeding

Abstract

In order to determine if natural glaciation proceeds rapidly or extensively enough in tropical maritime cumuli to influence attempts to modify their dynamical behavior by seeding with silver iodide, a detailed study was made of the clouds observed during the 1965 Project Stormfury experiments. From photographic coverage, notes on visual observations, and instrumentation on-board penetrating aircraft, data were compiled on cloud liquid water content, volume-median drop size, in-cloud temperature profile, and the dynamical 1ife histories of both seeded and non-seeded clouds. The validity d applying Koenig's numerical splintering model to tropical maritime cumuli, as well as an assessment of the effectiveness of silver iodide seeding, were determined by comparing the dynamical behavior of paired seeded and non-seeded clouds with glaciation times predicted by the model. Dynamical studies were initiated on two independently developed parametrized numerical cumulus models, and an excellent correlation between predicted and observed cumulas growth was found if no natural glaciation at temperatures > - 15C was assumed. The results of this study suggest that natural glaciation does not proceed rapidly and/or extensively enough in the critical cloud updraft areas to alter the effectiveness of modifying tropical maritime cumuli by causing artificial glaciation with silver iodide.