Research on Snowfall Augmentation
Operational weather modification projects to augment snowfall have benefitted from the results of numerous research experiments that have been conducted since the 1950s and 1960s. Many of the experiments prior to 1970 relied primarily on statistical evaluation of precipitation data from seeded and nonseeded periods to determine if cloud seeding was having a positive impact on snowfall. As instrumentation evolved in the 1970s and 1980s, the various physical links in the chain of events in the cloud seeding process began to be documented. The chain of events begins with the release of seeding material by aircraft or ground-based units, followed by transport and dispersion of the seeding aerosols to clouds containing supercooled liquid water. The seeding material then interacts with cloud water to form an enhanced concentration of ice crystals which grow by vapor deposition and/or accretion of cloud drops. As ice particle mass increases the ice crystals (or snowflakes) begin to fall to the surface, and result in an increase in precipitation.
Wintertime cloud seeding for snowpack augmentation has historically involved a variety of techniques, seeding materials and dispensing methods. The research has been conducted in numerous mountainous areas of the western U.S., including the Rocky Mountains of Colorado, Montana and Utah; the Cascade Mountains of Washington, and the Sierra Nevada of California. A summary of results from many of the key winter snowfall augmentation research experiments can be found in the following document.
The Desert Research Institute has been involved in weather modification research since the early 1960s. Trace chemical methods for evaluating cloud seeding experiments evolved at DRI, and these methods are still being applied to current wintertime research and operational seeding projects. A summary of trace chemistry research by DRI is contained in the following presentation.
A review of the concepts of wintertime cloud seeding, a wintertime cloud seeding case study, and recent trace chemistry research results can be found in the presentation: