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I I I I I I I I I I I SBC'l'ION II. PRECIPITATION CHEMISTRY AND STABLE ISOTOPB PROGRAM The goals of this program relate to the processes of ]~emoval of water substance from clouds passing across the Central Sierra Nevada in the winter. Evidence accrued over several years and presented in journals, oJnferences and workshops by numerous researchers, shows that supercooled lil~uid water is frequently located in the lower elevations from the surface ('7,000 - 8,000 ft) to 12,000 ft mal. ~ The majority of the precipitation which falls in the central Sierra Nevada during the winter months comes from storms, moving WE!st to east. The river catchment areas which comprise the central Sierra Ne,rada rl!gion yield spring runoff water to supply 'irrigation areas and hydroelectric power sys- tems. The winter snows also are used by a very large numbE~r of :9ki resort areas representing a $100 million component of the economy of thl! region. Because of these economic issues, there are several cloud-seedin~:J programs being conducted in this region of the Sierra Nevada, attempting to augment precipitation on both the western and eastern slopes. I I I I I I I I The use of trace chemistry and the stable isotopic composition of the precipitation falling in the area yields valuable infol'1llatioltl on the dispersion of seeding agents and the capture of cloud wate]~ substance by precipitating particulates. (a) The Program Goals & By measuring the trace chemical composition of seeded Sierr.! snowfall and r~lating this to the stable oxygen isotopic composition of the snow, the ice' crystal habits and their structure, estimates can be madle of: 1'. the elevation range over which supercooled liquid water is captured by falling ice crystals~ 2. the extent to which seeding agents (AgI) and special tracers (e.g., In203) released from seeding locations, are captured by warmer and colder habit ice crystals~ and '