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Not Only Have Scientists Perfected Techniques To SWATI SAXENA Story Cover Not only have scientists perfected China has played with creating artificial rain for a long time. In the United techniques to create Arab Emirates too artificial cloud seeding clouds to bring on has created rainstorms in the Dubai and Abu Dhabi deserts. In fact, faced with hard rain or snowfall, and extreme weather conditions, humans N the year 2008, the opening ceremony have often resorted to weather modification they have now even Iof the 29th Olympic Games to be held in various parts of the world. Common developed techniques in Beijing, China was threatened with rain. examples of weather modification include The observatory had given a rainy weather producing rain or snow in drought stricken that allow them to forecast, monitoring 90% of humidity rate. areas, suppressing hail that can ruin crops, prevent rainfall! How But Beijing fired over 1,000 rain dispersal or weakening hurricanes and tornados that rockets an evening before to blow away might cause great loss of lives and property. have they achieved this the rain clouds paving the way for a Weather modification can also grand opening ceremony and a four-hour be used as a tactic in war to enhance feat? extravaganza that dazzled the world! damaging weather in the enemy territory. SCIENCE REPORTER, JULY 2013 8 Cover Story From left: James Espy; Bernard Vonnegut in his lab; John Aiken; and Vince Schaefer (right) who discovered cloud seeding using a cold chamber, a deep freezer lined with black velvet In fact, Sydney Sheldon, in his 2004 thriller In 1875, the Frenchman Coulier box several times until the air was saturated novel, Are You Afraid of the Dark?, talks showed that particles floating in air served with the moisture from his lungs. The moisture of an egotistical maniac who develops as nuclei around which condensation in the box got condensed and formed fog a technology to control the weather and of water vapour occurs with little or no particles which are like cloud particles. But is now out to exercise that power to extort super saturation. Scottish physicist John no ice particles were formed. Schaefer then riches from vulnerable countries. That there Aitken using his portable expansion found an 8-inch piece of dry ice (frozen was a real possibility of nations working chamber known as Aitken nuclei counter carbon dioxide) with a temperature at on weather control technology to target demonstrated that there were two types of minus 79 degrees Centigrade) and thrust it enemy countries is borne out by the fact nuclei. Those with an affinity for water vapour into the supercooled box. In an instant the that in 1977, a convention was signed by on which condensation occurs before water air was full of ice crystals. The tiny crystals the United Nations to ban the use of weather saturation occurs are called hygroscopic quickly transformed into snowflakes, grew modification for military or any other hostile particles and others are non-hygroscopic rapidly larger as they sucked the remaining purposes. nuclei which require some degree of moisture in the freezer box and then fell to supersaturation in order to serve as centres the bottom. Making Rain of condensation. In 1919, A. Wigan used balloon flights and measured Aitken nuclei Perhaps for the first time, in the 5th April up to about 6 km height. 1839 issue of the National Gazette and An interesting experiment was Literary Register of Philadelphia, James P. performed by Vincent J. Schaefer, a Espy proposed that large fires could create laboratory assistant to Dr. Irwing Langmuir, a a good updraft in a humid atmosphere to Nobel laureate. Schaefer obtained a home generate cumulus clouds that cause rain refrigerator unit used for food storage and fall. Almost a hundred years later, in 1939, modified it. After bringing the temperature in Gorog and Rovo of Hungary examined the box below freezing, he breathed into the Espy’s suggestion that convective rains could be induced by burning large fires. Rockets being prepared, mounted and shot into the sky in By observing the fires on the lakes of oil, China to seed clouds Gorog and Rovo made calculations and concluded that the method was practical for producing rain artificially under certain conditions. 9 SCIENCE REPORTER, JULY 2013 Cover Story A pilot standing beside his aircraft laden with a cylinder containing silver iodide 2. Silver Iodide causes cloud 1. Silver Iodide (mixed moisture to freeze and create with acetone or Ice crystals propane) vaporized or sprayed to reach the clouds 3. Ice Crystals become The release of silver iodide was large enough to fall as rain or snow discontinued in July 1951 after the great floods in Kansas and adjacent states. It was one of the Seeding Generator most devastating floods in the area killing seventeen people. How Cloud Seeding Works Seeding Clouds Schaefer published an article on artificial weather modification have been Cloud seeding only works to the extent that these experiments in the 15 November cloud seeding to increase the rain or snow there is already water vapour present in the 1946 issue of Science magazine with the fall and hurricane seeding to mitigate its air. It has been used in several countries statement: “It is planned to attempt in the effects or turning its course. The methods to including United States of America, China, near future a large scale conversion of achieve these have been developed over India and Russia. super cooled clouds in the atmosphere the years and researchers continue to look The release of silver iodide into to ice crystal clouds, by scattering small for more efficient and reliable methods to an existing super-cooled cloud (i.e., air fragments of dry ice into the cloud from a perform these phenomenon. temperature between -39 and -5 Celsius) plane.” One of the main challenges in can convert water vapour to ice crystals, In November 1946, Dr. Bernard performing weather modifications is to which is called sublimation. The ice crystals Vonnegut discovered that microscopic minimize any long-term effects on the nucleated by the silver iodide will grow, and crystals of Silver Iodide (AgI) — commonly global climate. The scientific community local water droplets will shrink. The latent used in silver-based photography – has long sought safer ways to achieve heat released by converting water vapour nucleate water vapour to form ice crystals. weather modification successfully and with to ice will increase vertical air motion inside Vonnegut chose silver iodide crystals minimal uncertainty. the cloud and aid the convective growth of because there is nearly the same distance between molecules in the crystal lattice for USA conducted a cloud seeding operation called Operation both ice and AgI, making AgI the optimum material to nucleate ice. Popeye between 1967 and 1972 during the Vietnam War to Vonnegut also invented a practical extend the monsoon season over Laos. way of generating tiny silver iodide particles to serve as nuclei for ice crystals. He dissolved a mixture of AgI 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 SCIENCE REPORTER, JULY 2013 10 Cover Story clouds that are generally responsible for HURRICANE HALTING producing rain. Fleet of transport aircraft at 50,000 ft drop SOOT At the time of this discovery, soot in the path of and at targeted areas of CLOUD Dr. Vonnegut worked in the research the hurricane laboratory at General Electric Company in Schenectady, New York, which funded the initial work on cloud seeding. General SOOT Electric rented an airplane and released CONDENSED AIR dry ice into clouds on four days during November and December 1946. The last Soot is warmed by the Sun, day of seeding coincided with the heaviest heating the cool air around snowfall of the winter in the upstate New it at the very top of the York area, which made the company hurricane. This reduces the flow of air within the hurricane management concerned about the EYE and slows it down possibility of cloud seeding experiments causing harmful weather. MOOFED STORM Later, a General Electric and U.S. TRACK government research project released ACTUAL STORM silver iodide and dry ice in the vicinity of UPFLOW TRACK Albuquerque, New Mexico in 1948 and Depending on where 1949. Dr. Langmuir claimed that this release and when the soot caused rain all over the state of New Mexico. is dropped the now Langmuir’s group continued to release silver WARM AIR weakend hurricane will RAIN CONVERGING AIR COLD AIR change course iodide in New Mexico between November 1949 and July 1951. He claimed that the The smaller the radius of the Eye, the more intense the wind speed. release of silver iodide modified the weather, not only in the state of New Mexico but also more than thousand kilometres downwind. the cloud. Raindrops or snowflakes will grow Silver Iodide is the most common It is hard to make precise causal claims on larger by falling through a taller cloud. Also, ice nucleus used in cloud seeding, but it the reasons behind the weather at a large moist air from evaporated moisture in the is not the only material used. Dry ice was scale like this one, and hence Langmuir’s soil will be sucked into the base of the cloud widely used in experiments in the USA in claim was rejected by the meteorological by convection, thus increasing the total the 1950s and early 60s.
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