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Cloud seeding

Cloud seeding

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Cloud seeding, a form of intentional weather modification
Weather control
Weather control is the act of manipulating or altering certain aspects of the environment to produce desirable changes in weather. Weather control can have the goal of preventing damaging weather, such as hurricanes or tornadoes, from occurring; of causing beneficial weather, such as rainfall in...

, is the attempt to change the amount or type of precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...

 that falls from cloud
Cloud
A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...

s, by dispersing substances into the air that serve as cloud condensation
Cloud condensation nuclei
Cloud condensation nuclei or CCNs are small particles typically 0.2 µm, or 1/100 th the size of a cloud droplet ) about which cloud droplets coalesce. Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny...

 or ice nuclei
Ice nucleus
An ice nucleus is a particle which acts as the nucleus for the formation of an ice crystal in the atmosphere.The presence of ice nuclei increase the temperature that ice will form in the atmosphere from around −42°C to about −10°C...

, which alter the microphysical processes within the cloud. The usual intent is to increase precipitation (rain or snow), but hail and fog suppression are also widely practiced in airports.
The most common chemicals
Chemical substance
In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases.Chemical substances are...

 used for cloud seeding include silver iodide
Silver iodide
Silver iodide is a yellow, inorganic, photosensitive iodide of silver used in photography, in medicine as an antiseptic, and in rainmaking for cloud seeding.-Crystal structure:...

 and dry ice
Dry ice
Dry ice, sometimes referred to as "Cardice" or as "card ice" , is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue...

 (frozen carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

) rather than salt. Liquid propane, which expands into a gas, has also been used. This can produce ice crystals at higher temperatures than silver iodide. The use of hygroscopic
Hygroscopy
Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing material becoming physically 'changed,' somewhat, by an increase in volume, stickiness, or other...

 materials, such as salt, is becoming more popular after promising research .

Seeding of clouds requires that they contain supercooled
Supercooling
Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid....

 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
Freezing
Freezing or solidification is a phase change in which a liquid turns into a solid when its temperature is lowered below its freezing point. The reverse process is melting....

 nucleation
Nucleation
Nucleation is the extremely localized budding of a distinct thermodynamic phase. Some examples of phases that may form by way of nucleation in liquids are gaseous bubbles, crystals or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation...

. Dry ice or propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...

 expansion cools the air to such an extent that ice crystals can nucleate spontaneously from the vapor
Vapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....

 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.

In mid-latitude clouds, the usual seeding strategy has been based on the fact that the equilibrium vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...

 is lower over ice than over water. When The formation of ice particles in supercooled clouds allows those particles to grow at the expense of liquid droplets. If sufficient growth takes place, the particles become heavy enough to fall as precipitation from clouds that otherwise would produce no precipitation. This process is known as "static" seeding.

Seeding of warm-season or tropical cumulonimbus (convective) clouds seeks to exploit the latent heat
Latent heat
Latent heat is the heat released or absorbed by a chemical substance or a thermodynamic system during a process that occurs without a change in temperature. A typical example is a change of state of matter, meaning a phase transition such as the melting of ice or the boiling of water. The term was...

 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.

Cloud seeding chemicals may be dispersed by aircraft (as in the second figure) or by dispersion devices located on the ground (generators, as in first figure, or canisters fired from anti-aircraft guns or rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...

s). For release by aircraft, silver iodide flare
Flare (pyrotechnic)
A flare, also sometimes called a fusee, is a type of pyrotechnic that produces a brilliant light or intense heat without an explosion. Flares are used for signalling, illumination, or defensive countermeasures in civilian and military applications...

s are ignited and dispersed as an aircraft flies through the inflow of a cloud. When released by devices on the ground, the fine particles are carried downwind and upwards by air current
Air current
Air currents may be caused by differences in temperature, pressure, or impurity concentration. Temperature differences can cause air currents because warmer air is less dense than cooler air, causing the warmer air to appear "lighter." Thus, if the warm air is under the cool air, air currents will...

s after release.

An electronic mechanism was tested in 2010, when infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 pulses were directed to the air above Berlin
Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...

 by researchers from the University of Geneva
University of Geneva
The University of Geneva is a public research university located in Geneva, Switzerland.It was founded in 1559 by John Calvin, as a theological seminary and law school. It remained focused on theology until the 17th century, when it became a center for Enlightenment scholarship. In 1873, it...

. The experimenters posited that the pulses would encourage atmospheric sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 and nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...

 to form particles that would then act as seeds.

Effectiveness


Referring to the 1903, 1915, 1919 and 1944 and 1947 weather modification experiments, the Australian Federation of Meteorology discounted "rain making." By the 1950s the CSIRO
Commonwealth Scientific and Industrial Research Organisation
The Commonwealth Scientific and Industrial Research Organisation is the national government body for scientific research in Australia...

 Division of Radiophysics switched to investigating the physics of clouds and had hoped by 1957 to better understand these processes. By the 1960s the dreams of weather making had faded only to be re-ignited post-corporatisation of the Snowy Mountains Scheme
Snowy Mountains Scheme
The Snowy Mountains scheme is a hydroelectricity and irrigation complex in south-east Australia. It consists of sixteen major dams; seven power stations; a pumping station; and 225 kilometres of tunnels, pipelines and aqueducts and was constructed between 1949 and 1974. The Chief engineer was Sir...

 in order to achieve "above target" water. This would provide enhanced energy generation and profits to the public agencies who are the principal owners.
Cloud seeding has been shown to be effective in altering cloud structure and size and in converting supercooled liquid water to ice particles. The amount of precipitation due to seeding is difficult to quantify. Cloud seeding may also suppress precipitation.

A key challenge is in discerning how much precipitation would have occurred had clouds not been seeded. Overall, there is general expectation that winter cloud seeding over mountains will produce snow, expressed by professional organizations. There is statistical evidence for seasonal precipitation increases of about 10% with winter seeding.

The US government through its National Center for Atmospheric Research
National Center for Atmospheric Research
The National Center for Atmospheric Research has multiple facilities, including the I. M. Pei-designed Mesa Laboratory headquarters in Boulder, Colorado. NCAR is managed by the nonprofit University Corporation for Atmospheric Research and sponsored by the National Science Foundation...

 has analyzed seeded and unseeded clouds to understand the differences between them, and has conducted seeding research in other countries.

Clouds were seeded during the 2008 Summer Olympics
2008 Summer Olympics
The 2008 Summer Olympics, officially known as the Games of the XXIX Olympiad, was a major international multi-sport event that took place in Beijing, China, from August 8 to August 24, 2008. A total of 11,028 athletes from 204 National Olympic Committees competed in 28 sports and 302 events...

 in Beijing using rockets, so that there would be no rain during the opening
2008 Summer Olympics opening ceremony
The 2008 Summer Olympics opening ceremony was held at the Beijing National Stadium, also known as the Bird's Nest. It began at 8:00 pm China Standard Time on August 8, 2008, as 8 is considered to be a lucky number. The number 8 is associated with prosperity and confidence in Chinese culture...

 and closing
2008 Summer Olympics closing ceremony
The 2008 Summer Olympics closing ceremony was held at the Beijing National Stadium, also known as the Bird's Nest. It was directed by Chinese filmmaker Zhang Yimou and began at 8:00 pm China Standard Time on August 24, 2008...

 ceremonies. although others dispute their claims of success.

Impact on environment and health


With an NFPA 704 rating of Blue 2, silver iodide
Silver iodide
Silver iodide is a yellow, inorganic, photosensitive iodide of silver used in photography, in medicine as an antiseptic, and in rainmaking for cloud seeding.-Crystal structure:...

 can cause temporary incapacitation or possible residual injury to humans and mammals with intense or continued but not chronic exposure. However, there have been several detailed ecological studies that showed negligible environmental and health impacts. The toxicity of silver and silver compounds (from silver iodide) was shown to be of low order in some studies. These findings likely result from the minute amounts of silver generated by cloud seeding, which are 100 times less than industry emissions into the atmosphere in many parts of the world, or individual exposure from tooth fillings.

Accumulations in the soil, vegetation, and surface runoff have not been large enough to measure above natural background. A 1995 environmental assessment in the Sierra Nevada of California and a 2004 independent panel of experts (an overview only is presented in the executive summary of the research) in Australia confirmed these earlier findings.

Cloud seeding over Kosciuszko National Park
Kosciuszko National Park
Kosciuszko National Park covers 690,000 hectares and contains mainland Australia's highest peak, Mount Kosciuszko for which it is named, and Cabramurra the highest town in Australia...

 - a Biosphere Reserve - is problematic in that several rapid changes of environmental legislation were made to enable the "trial." Environmentalists are concerned about the uptake of elemental silver in a highly sensitive environment affecting the pygmy possum amongst other species as well as recent high level algal blooms in once pristine glacial lakes. The ABC program Earthbeat on July 14, 2004 heard that not every cloud has a silver lining where concerns for the health of the pygmy possums was raised. Research 50 years ago and analysis by the former Snowy Mountains Authority led to the cessation of the cloud seeding program in the 1950s with non-definitive results. Formerly, cloud seeding was rejected in Australia on environmental grounds because of concerns about the protected species, the pygmy possum. Since silver iodide and not elemental silver is the cloud seeding material, the claims of negative environmental impact are disputed by peer-reviewed research as summarized by the international weather modification association.

History



Vincent Schaefer
Vincent Schaefer
Vincent Joseph Schaefer was an American chemist and meteorologist who developed cloud seeding. On November 13, 1946, while a researcher at the General Electric Research Laboratory, Schaefer modified clouds in the Berkshire Mountains by seeding them with dry ice...

 (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
Irving Langmuir
Irving Langmuir was an American chemist and physicist. His most noted publication was the famous 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his...

 while climbing Mt. Washington in New Hampshire, Schaefer, Langmuir's research associate, created a way of experimenting with supercooled clouds using a deep freeze unit 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 14, 1946, he wanted to try a few experiments at General Electric's Schenectady
Schenectady, New York
Schenectady is a city in Schenectady County, New York, United States, of which it is the county seat. As of the 2010 census, the city had a population of 66,135...

 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
Dry ice
Dry ice, sometimes referred to as "Cardice" or as "card ice" , is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue...

 just to lower the temperature of his experimental chamber. To his astonishment, as soon as he breathed into the deep freezer, a bluish haze was noted, followed by an eye-popping display of millions of microscopic ice crystals, reflecting the strong light rays from the lamp 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˚C limit for liquid water.

Within the month, Schaefer's colleague, the noted atmospheric scientist Dr. Bernard Vonnegut
Bernard Vonnegut
Bernard Vonnegut was an American atmospheric scientist credited with discovering that silver iodide could be used effectively in cloud seeding to produce snow and rain...

 (brother of novelist Kurt Vonnegut
Kurt Vonnegut
Kurt Vonnegut, Jr. was a 20th century American writer. His works such as Cat's Cradle , Slaughterhouse-Five and Breakfast of Champions blend satire, gallows humor and science fiction. He was known for his humanist beliefs and was honorary president of the American Humanist Association.-Early...

) 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
Silver iodide
Silver iodide is a yellow, inorganic, photosensitive iodide of silver used in photography, in medicine as an antiseptic, and in rainmaking for cloud seeding.-Crystal structure:...

. Together with Dr. Vonnegut and Professor Henry Chessin, SUNY Albany, a crystallographer, co-authored a publication in Science Magazine and received a patent in 1975. 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
Lattice constant
The lattice constant [or lattice parameter] refers to the constant distance between unit cells in a crystal lattice. Lattices in three dimensions generally have three lattice constants, referred to as a, b, and c. However, in the special case of cubic crystal structures, all of the constants are...

 between the two types of crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

. (The crystallography
Crystallography
Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...

 of ice later played a role in Kurt Vonnegut's novel Cat's Cradle
Cat's Cradle
Cat's Cradle is the fourth novel by American writer Kurt Vonnegut, first published in 1963. It explores issues of science, technology, and religion, satirizing the arms race and many other targets along the way...

.) The first attempt to modify natural clouds in the field through "cloud seeding" began during a flight that began in upstate New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

 on 13 November 1946. Schaefer was able to cause snow to fall near Mount Greylock
Mount Greylock
Mount Greylock is the highest natural point in Massachusetts at . Its peak is located in the northwest corner of the state in the western part of the town of Adams in Berkshire County. Although geologically part of the Taconic Mountains, Mount Greylock is commonly associated with the abutting...

 in western Massachusetts, after he dumped six pounds of dry ice
Dry ice
Dry ice, sometimes referred to as "Cardice" or as "card ice" , is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue...

 into the target cloud from a plane after a 60-mile easterly chase from the Schenectady County Airport.

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, and lightning and hail
Hail
Hail is a form of solid precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hail stone. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms...

 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. From March 1967 until July 1972, the U.S. military's Operation Popeye
Operation Popeye
Operation Popeye was a US military cloud seeding operation during the Vietnam war to extend the monsoon season over Laos, specifically areas of the Ho Chi Minh Trail...

 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. The 54th Weather Reconnaissance Squadron carried out the operation to "make mud, not war".

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
Palm Springs, California
Palm Springs is a desert city in Riverside County, California, within the Coachella Valley. It is located approximately 37 miles east of San Bernardino, 111 miles east of Los Angeles and 136 miles northeast of San Diego...

. 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
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

. That lake was, at that time (1972–73), the primary water supply for Stillwater
Stillwater, Oklahoma
Stillwater is a city in north-central Oklahoma at the intersection of U.S. 177 and State Highway 51. It is the county seat of Payne County, Oklahoma, United States. As of the 2010 census, the city population was 45,688. Stillwater is the principal city of the Stillwater Micropolitan Statistical...

, Oklahoma
Oklahoma
Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...

 and was dangerously low. The project did not operate for a long enough time to show statistically any change from natural variation
Variation
- Physics :* Magnetic variation, difference between magnetic north and true north, measured as an angle* Variation , any perturbation of the mean motion or orbit of a planet or satellite, particularly of the moon- Mathematics :* Bounded variation...

s. However, at the same time, seeding operations have been ongoing in California since 1948.

An attempt by the United States military to modify hurricanes in the Atlantic basin
Atlantic Basin
The Atlantic Basin is the Atlantic Ocean.Atlantic Basin may also refer to:* Atlantic Basin Iron Works, an ironworks that operated in Brooklyn, New York, in the early to mid-20th century...

 using cloud seeding in the 1960s was called Project Stormfury
Project Stormfury
Project Stormfury was an attempt to weaken tropical cyclones by flying aircraft into them and seeding with silver iodide. The project was run by the United States Government from 1962 to 1983....

. 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.

Two federal agencies have supported various weather modification research projects, which began in the early 1960s: The United States Bureau of Reclamation
United States Bureau of Reclamation
The United States Bureau of Reclamation , and formerly the United States Reclamation Service , is an agency under the U.S...

 (Reclamation; Department of the Interior) and the National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

 (NOAA; Department of Commerce). Reclamation sponsored several cloud seeding research projects under the umbrella of Project Skywater from 1964 to 1988, and NOAA conducted the Atmospheric Modification Program from 1979 to 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, from 2002–2006.

Funding for research in the United States has declined in the last two decades. The Bureau of Reclamation sponsored a six-state research program from 2002–2006, however, called the "Weather Damage Modification Program". A 2003 study by the United States National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...

 urges a national research program to clear up remaining questions about weather modification's efficacy and practice.

In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, CSIRO conducted major trials between 1947 and the early 1960s:
  • 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.

  • 1953 – 1956: CSIRO carried out similar trials South Australia
    South Australia
    South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...

    , Queensland
    Queensland
    Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

     and other States. Experiments used both ground-based and airborne silver iodide
    Silver iodide
    Silver iodide is a yellow, inorganic, photosensitive iodide of silver used in photography, in medicine as an antiseptic, and in rainmaking for cloud seeding.-Crystal structure:...

     generators.

  • Late 1950s and early 1960s: Cloud seeding in the Snowy Mountains
    Snowy Mountains
    The Snowy Mountains, known informally as "The Snowies", are the highest Australian mountain range and contain the Australian mainland's highest mountain, Mount Kosciuszko, which reaches 2,228 metres AHD, approximately 7310 feet....

    , on the Cape York Peninsula
    Cape York Peninsula
    Cape York Peninsula is a large remote peninsula located in Far North Queensland at the tip of the state of Queensland, Australia, the largest unspoilt wilderness in northern Australia and one of the last remaining wilderness areas on Earth...

     in Queensland, in the New England
    New England (Australia)
    New England or New England North West is the name given to a generally undefined region about 60 kilometres inland, that includes the Northern Tablelands and the North West Slopes regions in the north of the state of New South Wales, Australia.-History:The region has been occupied by Indigenous...

     district of New South Wales
    New South Wales
    New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...

    , and in the Warragamba catchment area west of Sydney
    Sydney
    Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...

    .


Only the trial conducted in the Snowy Mountains produced statistically significant rainfall increases over the entire experiment.

An Austrian study to use silver iodine seeding for hail prevention ran during 1981–2000, and the technique is still actively deployed there.

Asia


The largest cloud seeding system in the world is that of the People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

, which believes that it increases the amount of rain over several increasingly arid
Arid
A 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...

 regions, including its capital city, Beijing
Beijing
Beijing , also known as Peking , is the capital of the People's Republic of China and one of the most populous cities in the world, with a population of 19,612,368 as of 2010. The city is the country's political, cultural, and educational center, and home to the headquarters for most of China's...

, by firing silver iodide rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...

s 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. About 24 countries currently practice weather modification operationally. China used cloud seeding in Beijing
Beijing
Beijing , also known as Peking , is the capital of the People's Republic of China and one of the most populous cities in the world, with a population of 19,612,368 as of 2010. The city is the country's political, cultural, and educational center, and home to the headquarters for most of China's...

 just before the 2008 Olympic Games in order to clear the air of pollution, but there are disputes regarding the Chinese claims. In February 2009, China also blasted iodide sticks over Beijing to artificially induce snowfall after four months of drought, and blasted iodide sticks over other areas of northern China to increase snowfall. The snowfall in Beijing lasted for approximately three days and led to the closure of 12 main roads around Beijing. At the end of October 2009 Beijing claimed it had its earliest snowfall since 1987 due to cloud seeding.

In Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

, open burning produces haze
Haze
Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic...

 that pollutes the regional environment. Cloud-seeding has been used to improve the air quality by encouraging rainfall. In India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, cloud seeding operations were conducted during the years 2003 and 2004 through U.S. based Weather Modification Inc. in the state of Maharashtra
Maharashtra
Maharashtra is a state located in India. It is the second most populous after Uttar Pradesh and third largest state by area in India...

. In 2008, there are plans for 12 districts of state of Andhra Pradesh.

North America


In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, cloud seeding is used to increase precipitation in areas experiencing drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...

, to reduce the size of hailstones that form in thunderstorms, and to reduce the amount of fog
Fog
Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...

 in and around airport
Airport
An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...

s. Cloud seeding is also occasionally used by major ski resort
Ski resort
A ski resort is a resort developed for skiing and other winter sports. In Europe a ski resort is a town or village in a ski area - a mountainous area, where there are ski trails and supporting services such as hotels and other accommodation, restaurants, equipment rental and a ski lift system...

s to induce snowfall. Eleven western states and one Canadian province (Alberta) have ongoing weather modification operational programs http://www.naiwmc.org. In January 2006, an $8.8 million cloud seeding project began in Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

 to examine the effects of cloud seeding on snowfall over Wyoming's Medicine Bow
Medicine Bow Mountains
The Medicine Bow Mountains are a mountain range in the Rocky Mountains that extend for from northern Colorado into southern Wyoming. The northern extent of this range is the sub-range the Snowy Range...

, Sierra Madre
Sierra Madre Range (Wyoming)
The Sierra Madre Range is located in south-central Wyoming. Geologically, it may be considered an extension of the Park Range or Front Range of Colorado. Its terrain lies within the US Continental Divide. Its western basins drain into the Colorado River and its eastern into the North Platte River...

, and Wind River
Wind River Range
The Wind River Range , is a mountain range of the Rocky Mountains in western Wyoming in the United States. The range runs roughly NW-SE for approximately 100 miles . The Continental Divide follows the crest of the range and includes Gannett Peak, which at 13,804 feet , is the highest peak...

 mountain ranges.

A number of commercial companies, such as Aero Systems Incorporated http://www.asicolorado.com/weathermod.htm, Atmospherics Incorporated http://www.atmos-inc.com/, North American Weather Consultants http://www.nawcinc.com/, Weather Modification Incorporated http://www.weathermod.com/, Weather Enhancement Technologies International http://www.WET-Intl.com, Seeding Operations and Atmospheric Research (SOAR) http://www.just-clouds.com, offer weather modification services centered on cloud seeding. The U.S. signed an international treaty in 1978 banning the use of weather modification for hostile purposes.http://www.un-documents.net/enmod.htm
During the sixties, Irving P. Krick & Associates operated a successful cloud seeding operation in the area around Calgary, Alberta. This utilized both aircraft and ground-based generators that pumped silver iodide into the atmosphere in an attempt to reduce the threat of hail damage. Ralph Langeman, Lynn Garrison
Lynn Garrison
Lynn Garrison is a Canadian pilot and political adviser. He was an RCAF fighter pilot from the 403 City of Calgary Squadron, commercial pilot, film producer, director and mercenary...

, and Stan McLeod, all ex-members of the RCAF's 403 Squadron, attending the University of Alberta, spent their summers flying hail suppression. A number of surplus Harvard aircraft were fitted with racks under each wing containing 32 railroad fuzees that were impregnated with silver iodide. These could be ignited individually or all at once, depending upon the threat. In coordination with ground units, the aircraft would lay a plume of silver iodide in front of approaching cumulo-nimbus clouds with noticeable effect. Large, active CBs were reduced to nothing. Heavy hail storms were reduced in intensity.
This effective program was funded by farmer contributions and government grants.

Europe


Cloud seeding was begun in France during the 1950s with the intent of reducing hail damage to crops. The ANELFA project consists of local agencies acting within a non-profit organization. A similar project in Spain is managed by the Consorcio por la Lucha Antigranizo de Aragon. The success of the French program was supported by insurance data; that of the Spanish program in studies conducted by the Spanish Agricultural Ministry.

Soviet military pilots seeded clouds over the Byelorussian SSR
Byelorussian SSR
The Byelorussian Soviet Socialist Republic was one of fifteen constituent republics of the Soviet Union. It was one of the four original founding members of the Soviet Union in 1922, together with the Ukrainian SSR, the Transcaucasian SFSR and the Russian Soviet Federative Socialist Republic...

 after the Chernobyl disaster
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...

 to remove radioactive particles from clouds heading toward Moscow
Moscow
Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...

. At the July 2006 G8
G8
The Group of Eight is a forum, created by France in 1975, for the governments of seven major economies: Canada, France, Germany, Italy, Japan, the United Kingdom, and the United States. In 1997, the group added Russia, thus becoming the 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. In Moscow, the Russian Airforce tried seeding clouds with bags of cement on June 17, 2008. One of the bags did not pulverize and went through the roof of a house. In October 2009, the Mayor of Moscow promised a "winter without snow" for the city after revealing efforts by the Russian Air Force to seed the clouds upwind from Moscow throughout the winter.

Australia


In Australia, CSIRO’s activities in Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...

 in the 1960s were successful. Seeding over the Hydro-Electricity Commission
Hydro Tasmania
Hydro Tasmania, known for most of its history as The HEC, is the government owned enterprise which is the predominant electricity generator in the state of Tasmania, Australia...

 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.

In 2004, Snowy Hydro Limited
Snowy Hydro Limited
Snowy Hydro Limited, previously known as the Snowy Mountains Hydro-electric Authority, is a corporation in Australia jointly owned by the Commonwealth , New South Wales and Victorian Governments....

 began a trial of cloud seeding to assess the feasibility of increasing snow precipitation in the Snowy Mountains
Snowy Mountains
The Snowy Mountains, known informally as "The Snowies", are the highest Australian mountain range and contain the Australian mainland's highest mountain, Mount Kosciuszko, which reaches 2,228 metres AHD, approximately 7310 feet....

 in Australia. The test period, originally scheduled to end in 2009, was later extended to 2014. The New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...

 (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 1 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 however does not make reference to former cloud seeding experiments by the then Snowy Mountains Authority which rejected weather modification. The trial required changes to NSW environmental legislation in order to facilitate placement of the cloud seeding apparatus. The modern experiment is not supported for the Australian Alps.

In December 2006, the Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

 government of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 announced A$
Australian dollar
The Australian dollar is the currency of the Commonwealth of Australia, including Christmas Island, Cocos Islands, and Norfolk Island, as well as the independent Pacific Island states of Kiribati, Nauru and Tuvalu...

7.6 million in funding for "warm cloud" seeding research to be conducted jointly by the Australian Bureau of Meteorology
Bureau of Meteorology
The Bureau of Meteorology is an Executive Agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together the state meteorological services that existed before then...

 and the United States National Center for Atmospheric Research
National Center for Atmospheric Research
The National Center for Atmospheric Research has multiple facilities, including the I. M. Pei-designed Mesa Laboratory headquarters in Boulder, Colorado. NCAR is managed by the nonprofit University Corporation for Atmospheric Research and sponsored by the National Science Foundation...

. Outcomes of the study are hoped to ease continuing drought conditions in the states South East
South East Queensland
South East Queensland is a region of the state of Queensland in Australia, which contains approximately two-thirds of the state population...

 region.

See also

  • Atmospheric moisture extraction
    Atmospheric moisture extraction
    Atmospheric moisture extraction removes water vapor from air for drinking, cleaning, and other uses.Some foggy neighborhoods in Lima, Peru are using "fog nets" to harvest moisture as an alternative to scarce natural rainfall....

  • Bioprecipitation
    Bioprecipitation
    Bioprecipitation is the concept of rain-making bacteria and was proposed by David Sands from Montana State University before 1983. The formation of ice in clouds is required for snow and most rainfall. Dust and soot particles can serve as ice nuclei, but biological ice nuclei are capable of...

  • Chemtrail conspiracy theory
  • Project Cumulus
    Project Cumulus
    Operation Cumulus was a project of the UK government in the 1950s which was investigating weather manipulation, in particular through cloud seeding experiments...


External links