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Encyclopedia > Cloud seeding
Cessna 210 with cloud seeding equipment

Cloud seeding, a form of weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei. The usual intent is to increase precipitation, but hail suppression is also widely practiced. Silver iodide and dry ice are the most commonly used substances in cloud seeding. Image File history File links Download high-resolution version (2605x1954, 1006 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cloud seeding ... Image File history File links Download high-resolution version (2605x1954, 1006 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cloud seeding ... Cloud seeding is the attempt to change the amount or type of precipitation that falls out of clouds or the structure of clouds by dispersing substances into the air which allow water droplets or ice crystals to form more easily. ... For other uses, see Cloud (disambiguation). ... Look up air in Wiktionary, the free dictionary. ... Aerosol pollution over Northern India and Bangladesh - NASA Cloud condensation nuclei or CCNs (also known as cloud seeds) are small particles (typically 0. ... Ice nuclei are particles that act as nuclei for the formation of ice crystals in the atmosphere. ... Silver iodide (AgI) is a chemical compound used in photography, an antiseptic in medicine, rainmaking and cloud seeding. ... Small pellets of dry ice sublimating in air. ...

Contents

How cloud seeding works

The most common chemicals used for cloud seeding include silver iodide and dry ice (frozen carbon dioxide). The expansion of liquid propane into a gas is being used on a smaller scale. The use of hygroscopic materials, such as salt, is increasing in popularity because of some promising research results. Water and steam are two different forms of the same chemical substance A chemical substance is a material with a definite chemical composition. ... Carbon dioxide (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption. ...


Seeding of clouds requires that they contain supercooled liquid water—that is, liquid water colder than zero degrees Celsius. Introduction of a substance such as silver iodide, which has a crystalline structure similar to that of ice, will induce freezing (heterogeneous nucleation). Dry ice or propane expansion cools the air to such an extent that ice crystals can nucleate spontaneously from the vapor phase. Unlike seeding with silver iodide, this spontaneous nucleation does not require any existing droplets or particles because it produces extremely high vapor supersaturations near the seeding substance. However, the existing droplets are needed for the ice crystals to grow into large enough particles to precipitate out. Supercool redirects here. ... Crystal (disambiguation) Insulin crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... In physics and chemistry, freezing is the process whereby a liquid turns to a solid when cold enough. ... Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. ... This article is about the chemical use. ...


In mid-latitude clouds, the usual seeding strategy has been predicated upon the fact that the equilibrium vapor pressure is lower over ice than over water. When ice particles form in supercooled clouds, this fact allows the ice particles to grow at the expense of liquid droplets. If there is sufficient growth, the particles become heavy enough to fall as snow (or, if melting occurs, rain) from clouds that otherwise would produce no precipitation. This process is known as "static" seeding. Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. ...


Seeding of warm-season or tropical cumuliform (convective) clouds seeks to exploit the latent heat released by freezing. This strategy of "dynamic" seeding assumes that the additional latent heat adds buoyancy, strengthens updrafts, ensures more low-level convergence, and ultimately causes rapid growth of properly selected clouds. This article or section does not adequately cite its references or sources. ... In thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a substance during a change of phase (i. ...


Cloud seeding chemicals may be dispersed by aircraft or by dispersion devices located on the ground (generators or canisters fired from anti-aircraft guns or rockets). For release by aircraft, silver iodide flares are ignited and dispersed as an aircraft flies through a cloud. When released by devices on the ground, the fine particles are carried downwind and upwards by air currents after release. American troops man an anti-aircraft gun near the Algerian coastline in 1943 Anti-aircraft, or air defense, is any method of combating military aircraft from the ground. ... A World War I-era parachute flare dropped from aircraft for illumination. ... A current is the rate of fluid flow, especially water or air. ...


Controversy

While cloud seeding has shown to be effective in altering cloud structure and size, and converting cloud water to ice particles, it is more controversial whether cloud seeding increases the amount of precipitation at the ground. Part of the problem is that it is difficult to discern how much precipitation would have occurred had the cloud not been "seeded." In other words, it is hard to discern additional precipitation from seeding from the natural precipitation variability, which is frequently much greater in magnitude. Nevertheless, there is more credible scientific evidence for the effectiveness of winter cloud seeding over mountains (to produce snow) than there is for seeding warm-season cumuli form (convective) clouds. This statement is supported by the professional societies Weather Modification Association, World Meteorological Organization, and American Meteorological Society (AMS). The AMS further states that there is statistical evidence for seasonal precipitation increases of about 10% with winter seeding [1]. WMO flag The World Meteorological Organization (WMO, French: , OMM) is an intergovernmental organization with a membership of 188 Member States and Territories. ... The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. ...


The National Center for Atmospheric Research (NCAR), an institution in Boulder, Colorado, has made some statistical analysis of seeded and unseeded clouds in an attempt to understand the differences between them. They have conducted seeding research in several countries that include Mali, Saudi Arabia, Mexico, South Africa, Thailand, Italy, and Argentina. NCAR, Boulder, Colorado National Center for Atmospheric Research (NCAR) is a U.S.-based institute whose stated mission is: NCARs flagship Mesa Laboratory is located in the outskirts of Boulder, Colorado, in a dramatic complex of buildings designed by architect I.M. Pei. ... Official language(s) English Capital Denver Largest city Denver Largest metro area Denver-Aurora Metro Area Area  Ranked 8th  - Total 104,185 sq mi (269,837 km²)  - Width 280 miles (451 km)  - Length 380 miles (612 km)  - % water 0. ...


It has also been told that in the 2008 summer olympics in Beijing they will be seeding the clouds so that there will be no rain during the medal ceremonies.[1]


With an NFPA 704 rating of Blue 2, silver iodide can cause temporary incapacitation or possible residual injury (e.g., chloroform) with intense or continued but not chronic exposure. Silver iodide (AgI) is a chemical compound used in photography, an antiseptic in medicine, rainmaking and cloud seeding. ...


History

Vincent Schaefer (1906-1993) discovered the principle of cloud seeding in July 1946 through a series of serendipitous events. Following ideas generated between himself and Nobel Laureate Irving Langmuir while climbing Mt Washington in NH, Schaefer, Langmuir's Research Associate created a way of experimenting with supercooled clouds using a deep freeze unit lined with black velveteen. He tried hundreds of potential agents to stimulate ice crystal growth, i.e salt, talcum powder,soils, dust and various chemical agents with minor effect. Then one hot and humid July day he wanted to try a few experiments at Schenectady's GE Research Lab. He was dismayed to find that the deep freezer was not cold enough to produce a cloud using breath air. He decided to move the process along by adding a chunk of dry ice just to lower the temperature. To his astonishment as soon as he breathed into the chamber a bluish haze was noted followed by a eye-popping display of millions of tiny ice crystals reflecting the strong light rays illuminating a cross-section of the chamber. He instantly realized that he had discovered a way to change supercooled water into ice crystals. The experiment was easily replicated and he explored the temperature gradient to establish the -40 degree limit for liquid water. Within the month,Schaefer's colleague, the noted atmospheric scientist Dr. Bernard Vonnegut (brother of novelist Kurt Vonnegut) is credited with discovering another method for "seeding" supercooled cloud water. Vonnegut accomplished his discovery at the desk, looking up information in a basic chemistry text and then tinkering with silver and iodide chemicals to produce silver iodide. Both methods were adopted for use in cloud seeding during 1946 while working for the General Electric Corporation in the state of New York. Schaefer's altered a cloud's heat budget, Vonnegut's altered formative crystal structure -- an ingenious property related to a good match in lattice constant between the two types of crystal. (The crystallography of ice later played a role in Kurt Vonnegut's novel Cat's Cradle). The first attempt to modify natural clouds in the field through "cloud seeding" began during a flight that began in upstate New York on November 13 1946. Schaefer was able to cause snow to fall near Mt. Greylock in eastern Massachusetts, after he dumped six pounds of dry ice into the target cloud from a plane after a 60 mile easterly chase from the Schenectady County Airport. [2] Vincent Joseph Schaefer (July 4, 1906–July 25, 1993) was an American chemist and meteorologist who developed cloud seeding. ... Dr. Bernard Vonnegut (August 29, 1914 – April 25, 1997) was an atmospheric scientist credited with discovering that silver iodide could be used effectively in cloud seeding to produce snow and rain. ... Kurt Vonnegut, Jr. ... Lattice constant, or a, defines the distance between atoms in crystal lattice. ... For other uses, see Crystal (disambiguation). ... Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ... For the string game, see Cats cradle. ... This article is about the state. ... Year 1946 (MCMXLVI) was a common year starting on Tuesday (link will display full 1946 calendar) of the Gregorian calendar. ... Small pellets of dry ice sublimating in air. ...


Dry ice and silver iodide agents are effective in changing the physical chemistry of supercooled clouds, thus useful in augmentation of winter snowfall over mountains and under certain conditions, lightning and hail suppression. While not a new technique hygroscopic seeding for enhancement of rainfall in warm clouds is enjoying a revival, based on some positive indications from research in South Africa, Mexico, and elsewhere. The hygroscopic material most commonly used is salt. It is postulated that hygroscopic seeding causes the droplet size spectrum in clouds to become more maritime (bigger drops) and less continental, stimulating rainfall through coalescence. This article is about the precipitation. ... A hygroscopic substance is a substance that absorbs water readily from its surroundings. ...


From March 1967 until July 1972, the US military Operation Popeye cloud seeded silver iodide to extend the monsoon season over North Vietnam, specifically the Ho Chi Minh Trail. The operation resulted in the targeted areas seeing an extension of the monsoon period an average of 30 to 45 days.[2] The 54th Weather Reconnaissance Squadron carried out the operation to "make mud, not war." [3] Operation Popeye (Operation Intermediary / Operation Compatriot) was a US military cloud seeding project (running from March 20, 1967 until July 5, 1972) during the Vietnam war to extend the monsoon season over North Vietnam, specifically the Ho Chi Minh Trail. ...


In 1969 at the Woodstock Festival, various people claimed to have witnessed clouds being seeded by the US military. This was said to be the cause of the rain which lasted throughout most of the festival. This remains one of the many conspiracy theories put forth by members of the hippy movement at the time. The Woodstock Music and Art Fair was a historic event held at Max Yasgurs 600 acre (2. ...


One private organization which offered, during the 1970s, to conduct weather modification (cloud seeding from the ground using silver iodide flares) was Irving P. Krick and Associates of Palm Springs, California. They were contracted by the Oklahoma State University in 1972 to conduct such a seeding project to increase warm cloud rainfall in the Lake Carl Blackwell watershed. That lake was, at that time (1972-73), the primary water supply for Stillwater, Oklahoma and was dangerously low. The project did not operate for a long enough time to show statistically any change from natural variations. However, at the same time, seeding operations have been ongoing in California since 1948. The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ... Palm Springs is a famed Riverside County, California desert resort city, approximately 110 miles (177 km) east of Los Angeles and 140 miles (225 km) northeast of San Diego. ... Oklahoma State University Logo The Oklahoma State University System comprises of five educational instututes across Oklahoma. ... A drainage basin is the area within the drainage basin divide (blue outline), and drains the surface runoff and river discharge (green lines) of a contiguous area. ... For the song by James Blunt, see 1973 (song). ... Stillwater is the name of some places in the United States of America: Stillwater, Minnesota Stillwater, New York Stillwater, Oklahoma Stillwater is the name of several rivers, see Stillwater River. ... For other uses, see Oklahoma (disambiguation). ... In music, variation is a formal technique where material is altered during repetition; reiteration with changes. ... Year 1948 (MCMXLVIII) was a leap year starting on Thursday (link will display the 1948 calendar) of the Gregorian calendar. ...


An attempt by the United States military to modify hurricanes in the Atlantic basin using cloud seeding in the 1960s was called Project Stormfury. Only a few hurricanes were tested with cloud seeding because of the strict rules that were set by the scientists of the project. It was unclear whether the project was successful; hurricanes appeared to change in structure slightly, but only temporarily. The fear that cloud seeding could potentially change the course or power of hurricanes and negatively affect people in the storm's path stopped the project. This article is about weather phenomena. ... The Atlantic Basin includes the main body of the Atlantic Ocean, the Gulf of Mexico and the Caribbean Sea, but ommits other bodies of water considered to be a part of the Atlantic Ocean in the broad sense, such as the Mediteranean Sea. ... Project Stormfury was an attempt to weaken hurricanes by using cloud seeding in the eyewall of these storms. ...


Two Federal agencies have supported various weather modification research projects, which began in the early 1960s: The United States Bureau of Reclamation (Reclamation; Department of the Interior) and the National Oceanic and Atmospheric Administration (NOAA; Department of Commerce). Reclamation sponsored several cloud seeding research projects under the umbrella of Project Skywater from 1964-1988, and NOAA conducted the Atmospheric Modification Program from 1979-1993. The sponsored projects were carried out in several states and two countries (Thailand and Morocco), studying both winter and summer cloud seeding. More recently, Reclamation sponsored a small cooperative research program with six Western states called the Weather Damage Modification Program [4], from 2002-2006. The United States Bureau of Reclamation (Formerly the United States Reclamation Service) is a division of the U.S. Department of the Interior which oversees water development projects in the western United States. ... The National Oceanic and Atmospheric Administration (NOAA) is a scientific agency of the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. ...


Funding for research has declined in the last two decades. A 2003 study by the United States National Academy of Sciences urges a national research program to clear up remaining questions about weather modification's efficacy and practice. President Harding and the National Academy of Sciences at the White House, Washington, DC, April 1921 The National Academy of Sciences (NAS) is a corporation in the United States whose members serve pro bono as advisers to the nation on science, engineering, and medicine. ...


In Australia, CSIRO conducted major trials between 1947 and the early 1960s: The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is the national government body for scientific research in Australia. ...

  • 1947 – 1952: CSIRO scientists dropped dry ice into the tops of cumulus clouds. The method worked reliably with clouds that were very cold, producing rain that would not have otherwise fallen.

Only the trial conducted in the Snowy Mountains produced statistically significant rainfall increases over the entire experiment. For the song, see South Australia (song). ... Slogan or Nickname: Sunshine State, Smart State Motto(s): Audax at Fidelis (Bold but Faithful) Other Australian states and territories Capital Brisbane Government Constitutional monarchy Governor Quentin Bryce Premier Anna Bligh (ALP) Federal representation  - House seats 28  - Senate seats 12 Gross State Product (2004-05)  - Product ($m)  $158,506 (3rd... Silver iodide (AgI) is a chemical compound used in photography, an antiseptic in medicine, rainmaking and cloud seeding. ... Worldwind image of Snowy Mountains The Snowy Mountains (known for short as the Snowies) are the highest Australian mountain range and contain the Australian mainlands highest mountain, Mount Kosciuszko, which reaches 2228 metres AHD. They are located in southern New South Wales and are part of the larger Australian... This article is about the peninsula located in the Australian state of Queensland; it should not be confused with either Yorke Peninsula in South Australia, or Cape York, Greenland. ... The New England region of Australia, here showing Mt Duval Approximate location of New England within New South Wales; red a narrow definition, yellow a broader definition New England is the name given to a region in the north of the state of New South Wales, Australia. ... NSW redirects here. ... A town in New South Wales, Australia. ... This article is about the metropolitan area in Australia. ...


Modern uses

The largest cloud seeding system in the world is that of the People's Republic of China, which believes that it increases the amount of rain over several increasingly arid regions, including its capital city, Beijing, by firing silver iodide rockets into the sky where rain is desired. There is even political strife caused by neighboring regions which accuse each other of "stealing rain" using cloud seeding[5]. About 24 countries currently practice weather modification operationally. China also plans to use cloud seeding in Beijing just before the 2008 Olympic Games in order to clear the air of pollution. [6] In general terms, the climate of a locale or region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life. ... Peking redirects here. ... This article is about vehicles powered by rocket engines. ... Peking redirects here. ...


In the United States, cloud seeding is used to increase precipitation in areas experiencing drought, to reduce the size of hailstones that form in thunderstorms, and to reduce the amount of fog in and around airports. Cloud seeding is also occasionally used by major ski resorts to induce snowfall. Eleven western states and one Canadian province (Alberta) have ongoing weather modification operational programs [7]. In January 2006, an $8.8 million cloud seeding project began in Wyoming to examine the effects of cloud seeding on snowfall over Wyoming's Medicine Bow, Sierra Madre, and Wind River mountain ranges. [8] Fields outside Benambra, Victoria, Australia suffering from drought conditions A drought is an extended period of months or years when a region notes a deficiency in its water supply. ... Hailstone Hail is a type of graupel (a form of precipitation) composed of balls or irregular lumps of ice. ... A rolling thundercloud over Enschede, The Netherlands. ... For other uses, see Fog (disambiguation). ... St. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... Official language(s) English Capital Cheyenne Largest city Cheyenne Area  Ranked 10th  - Total 97,818 sq mi (253,348 km²)  - Width 280 miles (450 km)  - Length 360 miles (580 km)  - % water 0. ... Medicine Bow is a town in Carbon County, Wyoming, United States. ... This is a list of mountain ranges organized alphabetically by continent. ... The Wind River is the name of several rivers in the United States Wind River in Wyoming Wind River, a designated National Wild and Scenic River in northern Alaska Wind River in southern Alaska, called in Inuit, Gui-guok-lok Wind River in Colorado Wind River in Idaho Wind River...


A number of commercial companies, such as Aero Systems Incorporated [9], Atmospherics Incorporated [10], North American Weather Consultants [11], Weather Modification Incorporated [12], Weather Enhancement Technologies International [13] offer weather modification services centered on cloud seeding. The USAF proposed its use on the battlefield in 1996, although the U.S. signed an international treaty in 1978 banning the use of weather modification for hostile purposes.


In Australia, CSIRO’s activities in Tasmania in the 1960s were successful. Seeding over the Hydro-Electricity Commission catchment area on the Central Plateau achieved rainfall increases as high as 30% in autumn. The Tasmanian experiments were so successful that the Commission has regularly undertaken seeding ever since in mountainous parts of the State. Slogan or Nickname: Island of Inspiration; The Apple Isle; Holiday Isle Motto(s): Ubertas et Fidelitas (Fertility and Faithfulness) Other Australian states and territories Capital Hobart Government Constitutional monarchy Governor William Cox Premier Paul Lennon (ALP) Federal representation  - House seats 5  - Senate seats 12 Gross State Product (2004-05)  - Product... Hydro Tasmania, known for most of its history as The HEC, is the predominant electricity generator in the state of Tasmania, Australia. ...


Russian military pilots seeded clouds over Belarus after the Chernobyl disaster to remove radioactive particles from clouds heading toward Moscow.[14] Chernobyl reactor number four after the disaster, showing the extensive damage to the main reactor hall (image center) and turbine building (image lower left) The reactor accident at the Chernobyl nuclear power plant is the worst nuclear power plant accident in history, resulting in a severe nuclear meltdown. ... For other uses, see Moscow (disambiguation). ...


Beginning in Winter 2004, Snowy Hydro Limited is conducting a six-year research project of winter cloud seeding to assess the feasibility of increasing snow precipitation in the Snowy Mountains in Australia. The NSW Natural Resources Commission, responsible for supervising the cloud seeding operations, believes that the trial may have difficulty establishing statistically whether cloud seeding operations are increasing snowfall. This project was discussed at a summit in Narrabri, NSW on 1st December 2006. The summit met with the intention of outlining a proposal for a 5 year trial, focussing on Northern NSW. The various implications of such a widespread trial were discussed, drawing on the combined knowledge of several worldwide experts, including representatives from the Tasmanian Hydro Cloud Seeding Project. Snowy Hydro Limited, previously known as the Snowy Mountains Hydro-electric Authority, is a corporation in Australia jointly owned by the Commonwealth (13%), New South Wales (58%) and Victorian (29%) Governments. ... Worldwind image of Snowy Mountains The Snowy Mountains (known for short as the Snowies) are the highest Australian mountain range and contain the Australian mainlands highest mountain, Mount Kosciuszko, which reaches 2228 metres AHD. They are located in southern New South Wales and are part of the larger Australian... Narrabri is a town of approximately 8000 persons and a Local Government Area in north-central New South Wales. ...


At the July 2006 G8 Summit, President Putin commented that air force jets had been deployed to seed incoming clouds so they rained over Finland. Rain drenched the summit anyway.[15] Group of Eight redirects here. ...


In Southeast Asia, open burning produces haze that pollutes the regional environment. Cloud-seeding has been used to improve the air quality by encouraging rainfall. Location of Southeast Asia Southeast Asia is a subregion of Asia. ... Haze is an atmospheric phenomenon where dust, smoke and other pollutant particles obscure the normal clarity of the sky. ...


In December 2006, the Queensland government of Australia announced AUD$7.6 million in funding for "warm cloud" seeding research to be conducted jointly by the Australian Bureau of Meteorology and the United States National Center for Atmospheric Research.[16] Outcomes of the study are hoped to ease continuing drought conditions in the states South East region. Slogan or Nickname: Sunshine State, Smart State Motto(s): Audax at Fidelis (Bold but Faithful) Other Australian states and territories Capital Brisbane Government Constitutional monarchy Governor Quentin Bryce Premier Anna Bligh (ALP) Federal representation  - House seats 28  - Senate seats 12 Gross State Product (2004-05)  - Product ($m)  $158,506 (3rd... The Bureau of Meteorology is an Australian government organisation responsible for providing weather services to Australia and surrounding areas. ... NCAR, Boulder, Colorado National Center for Atmospheric Research (NCAR) is a U.S.-based institute whose stated mission is: NCARs flagship Mesa Laboratory is located in the outskirts of Boulder, Colorado, in a dramatic complex of buildings designed by architect I.M. Pei. ... The South East Queensland region. ...


See also

  • Bioprecipitation

References

  1. ^ "Beijing to keep skies clear on Games' opening day", BOCOG, 2007-04-26. Retrieved on 2007-04-27.
  2. ^ Ted Steinberg. Oxford University Press, 2000.

External links

  • Brendan Bombaci, "Weather Modification Exposed; media journals and notes for the independent film documentary" "Heaven & Earth," ongoing internet-based production as of 2007.
A bill to establish a Weather Modification Operations and Research Board, and for other purposes, was introduced on March 3, 2005, by Senator Kay Bailey Hutchison. ...

  Results from FactBites:
 
NCAR | RAL - Wyoming Weather Modification Pilot Project (391 words)
This program involves cloud seeding operations, to be implemented by Weather Modification, Incorporated (WMI) based in Fargo, North Dakota, and scientific evaluations, performed by the National Center for Atmospheric Research (NCAR) Research Applications Laboratory (RAL).
Cloud seeding technology will be used in the pilot program and evaluated as a long-term water management tool rather than as a tool to mitigate the effects of drought conditions.
Cloud seeding is most effective under normal or near-normal weather conditions.
Cloud seeding - Wikipedia, the free encyclopedia (1032 words)
Cloud seeding, also known as weather modification, is the attempt to change the amount or type of precipitation that falls out of clouds, or their structure, by dispersing substances into the air which allow water droplets or ice crystals to form more easily.
The largest cloud seeding system in the world is that of the People's Republic of China, which believes that it increases the amount of rain over several increasingly arid regions, including its capital city, Beijing, by firing silver iodide rockets into the sky where rain is desired.
In the United States, cloud seeding is used to increase precipitation in areas experiencing drought, to reduce the size of hailstones that form in thunderstorms, and to reduce the amount of fog in and around airports.
  More results at FactBites »

 
 

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