The modification of cloud processes to influence quantity and types of precipitation remains a scientific and technical challenge. Although many modification theories have been advanced, the complexity and variability of natural precipitation production has limited predictable application. It is unlikely that advances in weather modification can be made by field experimentation alone. Numerical models of precipitation processes are now of sufficient sophistication that they can contribute much to our understanding. The primary objective of the research is to gain further understanding of the effects of ice-phase seeding on the formation of rain and hail. Results from advanced, time dependent models in two and three spatial dimensions will be used in comparison with actual observations of seeded and unseeded convective clouds to ascertain important physical processes in cloud modification. Secondary objectives are to study the transport of seeding materials and to conduct tests using two-dimensional models as a forecast aid. The Principal Investigators will undertake this research as part of a joint NSF/NOAA experiment on the modification of convective clouds known as the North Dakota Thunderstorm Project.//
