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~ 'I I I I I , I I I I I I I I , I I I the solution was changed to contain AgI, sodium iodide (NaCl), paradichlorobenzene (CJ14Cl~ and acetone, Cloud chamber test results indicated the number of ice crystals produced by the new solution at -1 OC were nearly equivalent to the old solution containing the perchlorates. Also, these new particles initially acted as hygroscopic CCN which continued to that ensure the vast numbers of water droplets formed would have a strong tendency to contain IN particles, Contact nucleation occurs when ice nuclei initially are not trapped in water droplets, but eventually are captured by other droplets through random collisions within the cloud, then become ice crystals, The entire process of hygroscopic condensation, followed by freezing and contact nucleation, forms greater numbers of ice crystals at relatively warmer temperatures within a cloud than by simple contact nucleation, Within supercooled convective clouds there are regions in which the ice crystals that form from water droplets tend to grow into characteristic shapes. This refers to "crystal habits." These shapes depend upon the actual temperature of the water when it converts from water droplet to ice crystal. The study of the physical characteristics of ice crystals is complicated, however, there have been some generalized findings which the scientific community appears to accept as repeatable observations: Near the freezing level, around -3C, supercooled water droplets tend to form into "plate" type crystals which transition into "columns" from -5C to -9C, then back into plates again between -11 C and -21 C. There are other types of ice crystals within these ranges, but these tend to be the dominant crystal types found. Growth rates of ice crystal mass show a peak at -15C and a smaller one near -7C. Once larger ice crystals are formed they able to grow in mass much faster than those with smaller crystal shapes, such as needles and columns, and will increase ice crystal formation quickly. Therefore, in order to obtain the desired cloud seeding effects each cloud must be treated within a proper time interval, or window of opportunity, to produce the optimum ice crystal concentrations in clouds naturally deficient in them. A cloud growing to - maturity must be treated with enough time allowed so that the generated ice nuclei can be lifted by natural updraft action into, and through, the appropriate temperature and moisture regime and reside there for a sufficient time to interact with the supercooled cloud water. If this opportunity window is missed when attempting rainfall stimulation, for instance, clouds can collapse prematurely resulting in wasted effort and resources. Therefore, supercooled cloud volume "residence time" is critical to the success of both rain stimulation and hail reduction efforts. Under certain atmospheric conditions, clouds may be stimulated to grow larger and rain longer than would be the case, if otherwise left unseeded. Weakly and moderately growing cumuliform cloud behavior can be altered through what is called the "dynamic effect" theory. The theory runs like this: A sufficiently large amount of seeding agent is inserted quickly into the supercooled portion of a cloud to promote a conversion from water droplets to ice crystals causing a rapid release of the latent heat of fusion from large quantities the droplets thus making the cloud slightly warmer and more buoyant, invigorating cloud updrafts and causing more moisture to enter the cloud to be "processed" into rainfall, eventually raining more, and longer, than ifleft unseeded. 7