Seeding Stratiform Clouds: The Effects of Cloud Parameters on Aiming

Abstract

It is shown that the trajectories of precipitation particles which grow via the riming process depend primarily on liquid water content and cloud depth, and not on the exact details of cloud temperature, crystalline shape, and graupel shape and size. Fall times for seeding at ?15°C at an altitude of 5 km could be as long as 55 min. Particle masses cannot be calculated very precisely, mostly because of uncertainties in specification of the graupel shape and size. It is still possible, however, to develop general rules regarding cloud depth required for seeding, the much-used rule that cloud depth should exceed half the cloud-base height being a reasonable one to adopt.