(Premium) Gist of Science Reporter Magazine: October 2013

Premium - Gist of Science Reporter: October 2013

HOW CLOUD SEEDING WORKS (Full Material Available Only For Premium Members)
HOW DO BEES HEAT THEIR HOMES? (Full Material Available Only For Premium Members)
NATIONAL BIODIVERSITY INFORMATION OUTLOOK (Full Material Available Only For Premium Members)

HOW CLOUD SEEDING WORKS

Schoaefer published an article on these experiments in the 1 5 November 1946 issue of Science magazine with the statement: “It is planned to attempt in the near future a large scale conversion of super cooled clouds in the atmosphere to ice crystal clouds, by scattering small fragments of dry ice into the cloud from a plane,”

In November 1946, Dr. Bernard Vonnegut discovered that microscopic crystals of Silver Iodide (Agl) - commonly used in silver-based photography - nucleate water vapour to form ice crystals, Vonnegut chose silver iodide crystals because there is nearly the same distance between molecules in the crystal lattice for both ice and Agl, making Agl the optimum material to nucleate ice, Vonnegut also invented a practical way of generating tiny silver iodide particles to serve as nuclei for ice crystals, He dissolved a mixture of Agl and another iodide in acetone, sprayed the solution through a nozzle to make droplets, and then burned the droplets, In this way, one gram of Silver Iodide can produce 1016 nuclei for ice crystals, Till now, Vonnegut’s method continues to be the most common way to seed clouds, Apart from dry ice (solid carbon dioxide), liquid propane and recently hygroscopic materials such as salt are also being used, Liquid propane can produce ice crystals at higher temperatures than silver iodide.

Some of the popular applications of artificial weather modification have been cloud seeding to increase the rain or snow fall and hurricane seeding to mitigate its effects or turning its course, The methods to achieve these have been developed over the years and researchers continue to look for more efficient and reliable methods to perform these phenomenon, One of the main Challenges in performing weather modifications is to minimize any longterm effects on the global climate, The scientific community has long sought safer ways to achieve weather modification successfully and with minimal uncertainty.

Seeding Clouds

Cloud seeding only works to the extent that there is already water vapour present in the air. It has been used in several countries including United States of America, China, India and Russia, The release of silver iodide into an existing super-cooled cloud (i.e., air temperature between -39 and ·5 Celsius) can convert water vapour to ice crystals, which is called sublimation, The ice crystals nucleated by the silver iodide will grow, and local water droplets will shrink, The latent heat released by converting water vapour to ice will increase vertical air motion inside the cloud and aid the convective growth of the cloud. Raindrops or snowflakes will grow larger by
falling through a taller cloud. Also, moist air from evaporated moisture in the soil will be sucked into the base of the cloud by convection, thus increasing the total amount of water in the cloud.

About thirty minutes after the silver iodide release, snow may fall below the cloud. Depending on the temperature and humidity below the cloud, the snow may Change to rain, or even evaporate, before reaching the ground. Silver Iodide is the most common ice nucleus used in cloud seeding, but it is not the only material used. Dry ice was widely used in experiments in the USA in the 1950s and early 60s. Substances with temperatures less than -40 Celsius (e.g., solid carbon dioxide pellets, liquid carbon dioxide, liquid propane, liquid nitrogen, etc.) can be dropped from airplanes into the tops of clouds to induce formation of ice crystals. Commonly, cloud seeding is performed over cumulus clouds that are generally responsible for producing rain.