Cloud seeding 449660 226051722 2008-07-16T16:44:33Z 70.91.51.10 '''Cloud seeding''', a form of [[weather control|weather modification]], is the attempt to change the amount or type of [[Precipitation (meteorology)|precipitation]] that falls from [[cloud]]s, by dispersing substances into the [[air]] that serve as [[Cloud condensation nuclei|cloud condensation]] or [[ice nucleus|ice nuclei]], 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. ==How cloud seeding works== [[Image:Ground Based Silver Iodide Generator.jpg|thumb|A ground-based Silver Iodide generator]] The most common [[Chemical substance|chemicals]] used for cloud seeding include [[silver iodide]] and [[dry ice]] (frozen [[carbon dioxide]]). The expansion of liquid propane into a gas has also been used and can produce ice crystals at warmer temperatures than silver iodide. The use of [[Hygroscopy|hygroscopic]] materials, such as salt, is increasing in popularity because of some promising research results. Seeding of clouds requires that they contain [[Supercooling|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. 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. Seeding of warm-season or tropical [[Cumulus cloud|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. 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 gun]]s or rockets). For release by aircraft, silver iodide [[Flare (pyrotechnic)|flare]]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]]s after release. ==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 [http://www.weathermodification.org 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 [http://www.ametsoc.org/policy/wxmod98.html]. 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]]. 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.<ref>"Beijing to keep skies clear on Games' opening day", BOCOG, 2007-04-26. Retrieved on 2007-04-27.</ref> The Chinese weather modification office rarely publishes in the open scientific literature and therefore their claims of success are widely [http://www.impactlab.com/2008/04/24/controlling-the-weather/ disputed]. 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. However, there have been several detailed ecological studies that showed negligible environmental and health impacts. <ref>Bureau of Reclamation, 1977: Project Skywater, A program of Research in Precipitation Management. Final Environmental Statement (INT FES 77-39). </ref><ref>Harris, Edward R., 1981: Sierra Cooperative Pilot Project - Environmental Assessment and Finding of No Significant Impact. U.S. Department of the Interior, Bureau of Reclamation, Denver, CO, 208 pp. </ref><ref>Howell, Wallace E., 1977: Environmental Impacts of Precipitation Management: Results and Inferences from Project Skywater. Bull. American Meteorological Society, 58, 488–501</ref>. The toxicity of silver and silver compounds (from silver iodide) was shown to be of low order. 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<ref>Donald A. Klein , 1978: Environmental Impacts of Artificial Ice Nucleating Agents, Dowden, Hutchinson & Ross, Inc., Stroudsburg, 256 pp. </ref>. A 1995 environmental assessment in the Sierra Nevada of California<ref>Parsons Engineering Science, Inc., 1995: Environmental Assessment for the Pacific Gas and Electric Company and the U.S. Forest Service, Stanislaus National Forest. </ref> and a 2004 [http://www.snowyhydro.com.au/files/SPET.pdf independent panel of experts] in Australia confirmed these earlier findings. ==History== [[Image:Cessna 210 Hagelflieger Detail.jpg|thumb|300px|Cessna 210 with cloud seeding equipment]] [[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 an 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 (Fahrenheit?) 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 13 November 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.<ref>Ted Steinberg. Oxford University Press, 2000.</ref> 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. 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.[http://www.acig.org/artman/publish/article_348.shtml] The 54th Weather Reconnaissance Squadron carried out the operation to "make mud, not war". [http://www.willthomas.net/Chemtrails/Articles/Weather_Warfare.htm] 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 [[Hippie]] movement at the time. 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]] [[Drainage basin|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 [[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 [[hurricane]]s 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. 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 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 [http://www.naiwmc.org/NAIWMC/wdmp.html], 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 [http://ams.confex.com/ams/Annual2005/techprogram/paper_82476.htm Weather Damage Modification Program]. A 2003 [http://newton.nap.edu/catalog/10829.html 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. In [[Australia]], [[CSIRO]] conducted major trials between 1947 and the early 1960s: * 1947 &ndash; 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 &ndash; 1956: CSIRO carried out similar trials [[South Australia]], [[Queensland]] and other States. Experiments used both ground-based and airborne [[silver iodide]] generators. * Late 1950s and early 1960s: Cloud seeding in the [[Snowy Mountains]], on the [[Cape York Peninsula]] in Queensland, in the [[New England (Australia)|New England]] district of [[New South Wales]], and in the [[Warragamba]] catchment area west of [[Sydney]]. Only the trial conducted in the Snowy Mountains produced statistically significant rainfall increases over the entire experiment. An Austrian study<ref>[http://www.hagelabwehr.com/links/studie.pdf Hagelabwehr in Niederösterreich], Zentralanstalt für Meteorologie und Geodynamik</ref> to use silver iodine seeding for hail prevention ran during 1981–2000, and the technique is still actively deployed there.<ref>[http://www.hagelabwehr.com/]</ref> ==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 [[rocket]]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[http://www.msnbc.msn.com/id/13107271/site/newsweek/page/2/]. 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. Again, see above for disputes regarding the Chinese claims. [http://www.boston.com/news/science/articles/2007/04/25/china_to_force_rain_ahead_of_olympics/] 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 [[airport]]s. Cloud seeding is also occasionally used by major [[ski resort]]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]] to examine the effects of cloud seeding on snowfall over Wyoming's [[Medicine Bow]], [[Sierra Madre]], and [[Wind River]] mountain ranges. [http://www.eurekalert.org/pub_releases/2006-01/ncfa-wcs012606.php] 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 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{{Fact|date=July 2008}}. Seeding over the [[Hydro Tasmania|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. Russian military pilots seeded clouds over [[Belarus]] after the [[Chernobyl disaster]] to remove radioactive particles from clouds heading toward [[Moscow]].[http://www.telegraph.co.uk/news/main.jhtml;jsessionid=O02BNM1IOZOVHQFIQMGCFGGAVCBQUIV0?xml=/news/2007/04/22/wrain22.xml] 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 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. 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.[http://news.bbc.co.uk/1/hi/uk_politics/5189048.stm] 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. 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]].[http://media01.couriermail.com.au/multimedia/2007/03/070300-water/story6-1.html] Outcomes of the study are hoped to ease continuing drought conditions in the states [[South East Queensland|South East]] region. In Moscow, the Russian Airforce tried seeding clouds with bags of cement on Jun 17, 2008. One of the bags did not pulverize and went through the roof of a house.[http://www.reuters.com/article/oddlyEnoughNews/idUSHAR75844520080617?feedType=RSS&feedName=oddlyEnoughNews] In India, Cloud seeding operations were conducted during the years 2003 and 2004 through U.S. based Weather Modification Inc. in state of Maharashtra [http://dst.gov.in/admin_finance/un-sq1207.htm]. In 2008, there are plans for 12 districts of state of Andhra Pradesh [http://deccan.com/City/Citynews.asp#State%20to%20seed%20clouds%20again]. ==See also== *[[Bioprecipitation]] *[[Artificial cloud]] *[[Chemtrail conspiracy theory]] ==References== <references/> ==External links== *[http://www.thingsasian.com/goto_article/article.2843.html Rainmaking in China] *[http://www.naiwmc.org/ North American Interstate Weather Modification Council] *[http://weathermodification.org/ Weather Modification Association] *[http://www.ametsoc.org/policy/wxmod98.html American Meteorological Society Policy Statement] *[http://www.wmo.int/web/arep/wmp/STATEMENTS/statwme.pdf World Meteorological Organization Policy Statement] *[http://www.wmo.int/web/arep/wmp/wmp_homepage.shtml World Meteorological Organization Weather Modification Programme] *[http://cloudseeding.dri.edu/ Nevada State Cloud Seeding Program] *"[http://commerce.senate.gov/public/index.cfm?FuseAction=PressReleases.Detail&PressRelease_Id=248556 The Weather Modification Operations and Research Board (passed Oct.2005) - in corporate cooperation with BAE Systems (HAARP apparatus & facility owner, as well as current company name for the Tesla-funding Marconi Company) and Raytheon Corporation (HAARP patent owner, as well as UAV manufacturer, distributor, and operations contractor)] *"[[Weather Modification Operations and Research Board|the Weather Modification Operations and Research Board on Wiki]]" *"[http://www.raytheonaircraft.com/government/multi_jets.shtml#main Raytheon Aircraft Company (Owner of HAARP patents, and, NOAA-funded aerosol weather modification/AESA radar weather weapons)]" *"[http://www.na.baesystems.com/releasesDetail.cfm?a=477 BAE Systems - APTI/ARCO program and apparatus-owner of the HAARP facility, railgun technology, electromagnetic armor, and, a sub-corporation partner with Raytheon via British Aerospace Corporation, as well as owner of Nicola Tesla's "Wardenclyffe Tower" (first EM long-range weapon) funding company, the Marconi Company]" *"[http://uncletaz.com/library/scimath/tesla/weapon.html Tesla's Wardenclyffe Tower (ionospheric heater) atmospheric/plasma research history, construction, utilization, & association w/ Marconi Company / GE who is now currently BAE Systems in conjunction with the current HAARP array]" *[http://www.boston.com/news/science/articles/2007/04/25/china_to_force_rain_ahead_of_olympics/ China to force rain ahead of Olympics] *Brendan Bombaci, [http://web.mac.com/kairologic/iWeb/h%26e/prophesies/C1203471-D06D-4848-848B-3751FDDD826F.html "Weather Modification Exposed; media journals and notes for the independent film documentary"] "Heaven & Earth," ongoing internet-based production as of 2007. *[http://www.artificialclouds.com/ Artificial Clouds] [[Category:Weather modification]] [[de:Hagelflieger]] [[fr:Ensemencement des nuages]] [[he:זריעת עננים]] [[io:Seminizado di nubi]] [[lt:Debesų sėja]] [[nl:Regen maken]] [[pl:Zasiewanie chmur]] [[pt:Semeadura de nuvens]] [[ro:Însămânţarea norilor]] [[fi:Sadepilvien kylväminen]] [[zh:人工降雨]]