WeatherMod Cloud Seeding Guidelines

Home Browse Search

Laureate Irving Langmuir at the General Electric Laboratories in Schenectady. A strong stimulus was the 1946 seeding field test by Vincent Schaefer in which dry ice was dropped into a stratocumulus cloud over Massachusetts. Very quickly the cloud, consisting of supercooled water droplets, was transformed into a swarm of ice crystals that grew and fell from its base, leaving a distinct hole in the cloud. Had natural ice forming nuclei been of sufficient concentration in this cloud, they would have transformed its supercooled liquid droplets into ice crystals themselves. The dry ice pellets dropped into the cloud counteracted the dearth in natural nuclei by creating artificial ice embryos through Chilling the air in their vicinity to _40oC or lower, a critical tempera ture helow wh ich cloud droplets no longer remain supercooled, but freeze. These new frozen particles then mixed through the cloud, growing at the expense of the supercooled cloud droplets, thus converting a non-precipitating cloud into a precipitating one. Later, Vonnegut of the G E Laboratories discovered how to produce ice embroys by introducing a swarm,of minute silver iodide smoke particles into a supercooled cloud. Their structure is similar to that of ice, and water was deposited on them in the form of ice. Subsequently, other investigators discovered other nucleating agents. At present, silver iodide remains the chief agent in use, although dry ice, and some organics are occasionally used. Scientific studies of nucleation led to questions about the details of how nature produces precipitation. The field data had indicated that natural precipitation efficiencies were often low. Many supercooled cloud droplets are formed in updraft regions that occur in cumulus clouds or on the upwind slopes of mountain ranges, that are not completely 5