Most Promising Concept of Hail Suppression
Two popularly attempted approaches to hail suppression by seeding clouds with Agl nuclei are (1) over-seeding to achieve full glaciation and (2) embryo competition. However, most hail suppression projects based on these concepts were inconclusive: hailfall increased, decreased, or there was no noticeable effect. Such inconsistent results cause one to question the validity of these concepts. This paper suggests a new concept: freezing a large number of accumulated, millimeter-size supercooled drops by contact nucleation by the timely introduction of Agl nuclei into the heart of the potential hail cloud. The large amount of latent heat of fusion liberated in a short time would increase rapidly the buoyancy and accelerate the updraft. The ice embryos would be carried to higher cloud levels, colder than -30 C. The supercooled droplets from the lower part of the cloud would freeze before reaching such embryos. This, in effect, kills accretional growth of the embryos, eliminating the formation of medium and large size hailstones. Numerical calculations show the effectiveness of this hail suppression concept.