Seeding clouds to produce precipitation

Description

Dr. Vincent Schaefer undertook the first weather modification experiments for General Electric in 1946. Cloud seeding companies use aircraft or ground generators to release silver iodide particles into clouds when temperature and moisture are ripe for rain. Attracting clumps of moisture, the silver iodide particles trigger formation of ice crystals which then fall as additional rain or snow.

Cloud seeding requires that cloud contain enough moisture for the silver iodide crystals to tip near-saturation into rain or snow.

Context

Experiments in seeding clouds to increase precipitation emerged in the United States during the 1940s, after researchers observed that supercooled clouds could be influenced by introduced particles. Early enthusiasm encouraged programmes across water-scarce regions, but results proved variable and difficult to verify. By the late twentieth century, international initiatives had expanded the practice’s profile, while improved atmospheric science shifted attention toward rigorous evaluation, environmental safeguards, and the limits imposed by suitable cloud conditions.

Implementation

Estimates of increases in precipitation resulting from weather modification programmes range from 10 to 15 percent over normal rainfall in the wintertime northern hemisphere areas to as much as 25 percent in tropical regions.

Claim

A U.S. Air Force research study, "Weather as a Force Multiplier" outlines how powerful "ionospheric heaters" and clouds generated by chemical condensation trails - contrails - spread behind airborne tankers could allow U.S. aerospace forces to "own the weather" by the year 2025.