TOI once again introduced this new technology to me. Seeding was a term that was familiar only when used in context of agriculture and farming. To manipulate the constituents of clouds to enable more precipitation sounded bizarre! Research on this topic revealed that cloud seeding is an old technique that is currently being exacted. Cloud Seeding efforts were initiated by Dr. Vincent J. Schaefer at NY in 1946; when he was attempting to create clouds in a lab experiment. The experiment was carried out in a chilled chamber that was further cooled by dry ice. Dry ice was the accidental catalyst as the ice crystals ultimately provided a nucleus around which droplets of water coalesced that would produce rain.
Static Method/Cold Rain Process:
Presence of clouds is indispensable for producing rainfall. Cloud seeding merely increases the potential of causing greater precipitation. Ice crystals required for ‘Natural Rain’ (ensuing from unseeded cloud), are formed when cold water comes in contact with dust particles in the atmosphere. These ice crystals act as a nucleus that attracts formation of water droplets around it. Water droplets coalescence around these ice crystals and increase in size until they are large enough to detach causing rain!
Cloud seeding is expected to provide substitutes of such ice crystals which ultimately exploits greater proportion of water vapor in the cloud. The seeding effort done using silver iodide (it is similar to ice crystals in structure)is expected to achieve maximum coalescence of water vapor engendering more rainfall.
Warm Rain Process: For cloud formation in tropical climate that do not reach freezing point
In tropical climates, water droplets form around a “hygroscopic particle” such as dust which acts a nucleus around which droplets coalescence until they are large enough to detach and cause rain. Calcium chloride is used as a substitute to attract more water droplets achieve greater precipitation.
1. Seeding is a controversial method because it is a relatively new technology which is still evolving and is therefore not popular among some scientists. Others insist of its credibility and quote that “Absence of evidence is not evidence of absence; sometimes it can just take a long time for clear evidence to accumulate.”
2. Cloud seeding is used in Russia to clear the skies to prevent rainfall on special occasions. The Russians apparently crave for clear weather and hence attempt to “empty” their skies by inducing premature rainfall. They use a mixture of silver iodide, cement and liquid nitrogen to seed their clouds. However, last year, cement dislodged for seeding purposes failed to fragment and fell through the atmosphere to the ground in a solid form destroying private property!
For additional information please refer the SOAR (Seeding Operations & Atmospheric Research ) website that specializes in weather modification services and details atmospheric research technologies.