A Simplified Concept of Hygroscopic Seeding

H D Orville, Chengshu Wang, F J Kopp


A bulk-water microphysical convective cloud model is used to investigate the maximum effect of hygroscopic seeding. Using the fact that the desired cloud seeding effect is to transform the cloud from a continental one to a maritime one makes hygroscopic seeding a particularly easy process to simulate in bulk-water microphysics cloud models. In those types of cloud models, one only has to change the autoconversion threshold (i.e., the onset of coalescence) and the number concentration and dispersion characteristics of the cloud water to switch from a continental-type cloud to a maritime-type cloud. The continental cloud has no autoconversion, the maritime cloud an extremely efficient autoconversion process. Admittedly, this tests two extreme situations and makes the assumption that the effects of hygroscopic seeding will be somewhere between the two extremes, the maximum effect being represented by the maritime-type cloud. Very preliminary results indicate that the hygroscopic seeding would be quite efficient on small to moderate size clouds but its effect is much less definite on larger clouds. The dynamics of the clouds are crucial to the results.

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