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Weather modification is the act of intentionally manipulating or altering the weather. The most common form of weather modification is cloud seeding, which increases rainfall or snowfall, usually for the purpose of increasing the local water supply.^[1] Weather modification can also have the goal of preventing damaging weather, such as hail or hurricanes, from occurring; or of provoking damaging weather against an enemy, as a tactic of military or economic warfare like Operation Popeye, where clouds were seeded to prolong the monsoon in Vietnam. Weather modification in warfare has been banned by the United Nations under the Environmental Modification Convention.

History

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A popular belief in Northern Europe was that shooting prevents hail, which thus caused many agricultural towns to fire cannons without ammunition. Veterans of the Seven Years’ War, Napoleonic wars, and the American Civil War reported that rain fell after every large battle. After their stories were collected in War and Weather, the United States Department of War in the late 19th century purchased $9,000 of gunpowder and explosives to detonate them in Texas, in hopes of condensing water vapor into rain. The results of the test, supervised by Robert Dyrenforth, were inconclusive.^[2]

Wilhelm Reich performed cloudbusting experiments in the 1950s, the results of which are controversial and were not widely accepted by mainstream science.

In November 1954 the Thailand Royal Rainmaking Project (Thai: โครงการฝนหลวง) was initiated by King Bhumibol Adulyadej. He discovered that many areas faced the problem of drought. Over 82 percent of Thai agricultural land relied on rainfall. Thai farmers were not able to grow crops for lack of water. The royal rainmaking project debuted on 20 July 1969 at his behest, when the first rainmaking attempt was made at Khao Yai National Park. Dry ice flakes were scattered over clouds. Reportedly, some rainfall resulted. In 1971, the government established the Artificial Rainmaking Research and Development Project within the Thai Ministry of Agriculture and Cooperatives.^{[3][circular reference]}

In January 2011, several newspapers and magazines, including the UK’s Sunday Times and Arabian Business, reported that scientists backed by the government of Abu Dhabi, the capital of the United Arab Emirates, had created over 50 artificial rainstorms between July and August 2010 near Al Ain, a city which lies close to the country’s border with Oman and is the second-largest city in the Abu Dhabi Emirate. The artificial rainstorms were said to have sometimes caused hail, gales and thunderstorms, baffling local residents.^[4]

In the run up to the 2008 Beijing Olympic Games, the Chinese Government said they could control precipitation to some extent and that the Games would not be hampered by bad weather conditions. For this purpose they established a government office called the Beijing Weather Modification Office, which is under the national weather control office.^[5][6]

Cloud seeding

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Main article: Cloud seeding

Cloud seeding is a common technique to enhance precipitation. Cloud seeding entails spraying small particles, such as silver iodide, onto clouds to attempt to affect their development, usually with the goal of increasing precipitation. Cloud seeding only works to the extent that there is already water vapor present in the air. Critics generally contend that claimed successes occur in conditions which were going to lead to rain anyway. It is used in a variety of drought-prone countries, including the United States, China, India, and Russia. In China, there is a perceived dependency upon it in dry regions, and there is a strong suspicion it is used to “wash the air” in dry and heavily polluted places, such as Beijing.^[7] In mountainous areas of the United States such as the Rocky Mountains and Sierra Nevada,^[8] cloud seeding has been employed since the 1950s.

Project Cirrus was an attempt by General Electric to modify the weather which ran from 1947-1952. During that time, under the supervision of the United States Air Force, attempts were made to create snowstorms and seed hurricanes by using silver iodide. While General Electric reported positive results, they also acknowledged that their experiments were controversial.^[9]

The United Arab Emirates has been cloud seeding since the 2000s and aims to increase rainfall by 15-30% per year. The materials used are potassium chloride, sodium chloride, magnesium, and other materials.^[10][11]

Consequences

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Societal

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Not having adequate systems to handle weather modification may have disastrous consequences. “In the city of Jeddah in Western Saudi Arabia was damaged by floods in 2009 that reportedly killed more than 100 people; igniting questions of why the country doesn’t have effective drainage systems in place.”^[11]

Human

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The U.S. National Library of Medicine notes that the silver iodide has no known “ill effects” on people, although people’s “hands may have remained yellowed for weeks” after being exposed to it.^[12]

Storm prevention

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Project Stormfury was an attempt to weaken tropical cyclones by flying aircraft into storms and seeding the eyewall with silver iodide. The project was run by the United States Government from 1962 to 1983. A similar project using soot was run in 1958, with inconclusive results.^[13] Various methods have been proposed to reduce the harmful effects of hurricanes. Moshe Alamaro of the Massachusetts Institute of Technology^[14] proposed using barges with upward-pointing jet engines to trigger smaller storms to disrupt the progress of an incoming hurricane; critics doubt the jets would be powerful enough to make any noticeable difference.^[13]

Alexandre Chorin of the University of California, Berkeley, proposed dropping large amounts of environmentally friendly oils on the sea surface to prevent droplet formation.^[15] Experiments by Kerry Emanuel^[16] of MIT in 2002 suggested that hurricane-force winds would disrupt the oil slick, making it ineffective.^[13] Other scientists disputed the factual basis of the theoretical mechanism assumed by this approach.^[15]

The Florida company Dyn-O-Mat and its CEO, Peter Cordani, proposed the use of a patented product it developed, called Dyn-O-Gel, to reduce the strength of hurricanes. The substance is a polymer in powder form (a polyacrylic acid derivative) which reportedly has the ability to absorb 1,500 times its own weight in water. The theory is that the polymer is dropped into clouds to remove their moisture and force the storm to use more energy to move the heavier water drops, thus helping to dissipate the storm. When the gel reaches the ocean surface, it is reportedly dissolved. Peter Cordani teamed up with Mark Daniels and Victor Miller, the owners of a government contracting aviation firm AeroGroup which operated ex-military aircraft commercially. Using a high altitude B-57 Bomber, AeroGroup tested the substance dropping 9,000 pounds from the B-57 aircraft’s large bomb bay and dispersing it into a large thunderstorm cell just off the east coast of Florida. The tests were documented on film and made international news showing the storms were successfully removed on monitored Doppler radar. In 2003, the program was shut down because of political pressure through NOAA.^[17] Numerical simulations performed by NOAA showed however that it would not be a practical solution for large systems like a tropical cyclone.^[18]

Hail cannons have been used by some farmers since the 19th century in an attempt to ward off hail, but there is no reliable scientific evidence to confirm their effectiveness. Another new anti-hurricane technology^[19] is a method for the reduction of tropical cyclones’ destructive force – pumping sea water into and diffusing it in the wind at the bottom of such tropical cyclones in its eye wall.

Hurricane modification

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See also: Wind shear, Deep ocean water, and Saharan Air Layer

NOAA published a page addressing various ideas in regard to tropical cyclone manipulation.

In 2007, “How to stop a hurricane”^[20] explored various ideas such as:

• Using lasers to discharge lightning in storms which are likely to become hurricanes
• Pouring liquid nitrogen onto the sea to deprive the hurricane of heat energy.
• Creating soot to absorb sunlight and change air temperature and create convection currents in the outer wall.

Researchers from NOAA’s hurricane research division addressed hurricane control based ideas.^[21]

Later ideas (2017) include laser inversion along the same lines as laser cooling (normally used at cryogenic temperatures) but intended to cool the top 1mm of water. If enough power were to be used then it may be enough, combined with computer modelling, to form an interference pattern able to inhibit a hurricane or significantly reduce its strength by depriving it of heat energy.^[22][23]

Other proposals for hurricane modification include the construction of a large array of offshore wind turbines along the East Coast of the United States. Such turbines would have the dual purpose of generating plentiful energy whilst also reducing the power of oncoming hurricanes before they make landfall.^[24]

Pumping up deep ocean waters to cool the surface

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See also: Thermocline, Sea surface temperature, and Coast Guard

Pumping up colder deep ocean water in front of a tropical storm to cool the sea surface skin temperature could be a technique used to fight hurricanes in the Atlantic before they develop into major hurricanes.^[25][26]

It is purely speculative and difficult to realize since placing such pumps in the path of a hurricane would be difficult. Furthermore, any such project would need a large number of them to upwell enough water to cool a large enough sea surface area to have any effectiveness. That is without counting the large amount of energy needed to power those pumps and its effects on marine life.^[27][28]

In military

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Main article: Weather warfare

Operation Popeye was a highly classified operation run by the US military from 1967-1972.^[29] The purpose was to prolong the monsoon in Southeast Asia. The overwhelming precipitation successfully disrupted the tactical logistics of the Vietnamese army. Operation Popeye is believed as the first successful practice of weather modification technology in warfare. After it was unveiled, weather modification in warfare was banned by the Environmental Modification Convention (ENMOD).^[30]

In “Benign Weather Modification” published in March 1997, Air Force Major Barry B. Coble superficially documents the existence of weather modification science where he traces the developments that have occurred, notably, in the hands of the Pentagon and CIA’s staunchest ideological enemies.

• The first scientifically controlled and monitored effort generally recognized by the meteorological community as constituting weather modification occurred in 1948. When Dr. Irving Langmuir first experimented with artificially seeding clouds to produce rain in New Mexico, his experiments showed positive results – sparking tremendous interest in the field nearly overnight.^[31]
• Many countries throughout the world practice weather modification. The Russians have long been interested in using weather modification as a way to control hail.^[32]

In the 1990s a directive from the chief of staff of the Air Force Ronald R. Fogleman was issued to examine the concepts, capabilities, and technologies the United States would require to remain the dominant air and space force in the future.

In law

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US and Canada agreement

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In 1975, the US and Canada entered into an agreement under the auspices of the United Nations for the exchange of information on weather modification activity.^[33]

1977 UN Environmental Modification Convention

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Main article: Environmental Modification Convention

Weather modification, particularly hostile weather warfare, was addressed by the “United Nations General Assembly Resolution 31/72, TIAS 9614 Convention^[34] on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques.” The Convention was signed in Geneva on May 18, 1977; entered into force on October 5, 1978; ratified by U.S. President Jimmy Carter on December 13, 1979; and the U.S. ratification deposited in New York on January 17, 1980.^[35]

US National Oceanic and Atmospheric Administration

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In the US, the National Oceanic and Atmospheric Administration keeps records of weather modification projects on behalf of the Secretary of Commerce, under the authority of Public Law 92-205, 15 USC § 330B, enacted in 1971.^[36]

Proposed US legislation

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U.S. Senate Bill 517^[37] and U.S. House Bill 2995^[38] were two bills proposed in 2005 that would have expanded experimental weather modification, to establish a Weather Modification Operations and Research Board, and implemented a national weather modification policy. Neither was made into law.

Senate Bill 1807 and House Bill 3445, identical bills introduced July 17, 2007, proposed to established a Weather Mitigation Advisory and Research Board to fund weather modification research^[39][40]

Passed Tennessee legislation

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Tennessee bill HB 2063/SB 2691 was signed into law on April 11, 2024. This bill bans the “intentional injection, release, or dispersion” of chemicals within Tennessee “with the express purpose of affecting temperature, weather, or the intensity of the sunlight.”^[41][42]

The text of the bill doesn’t explicitly reference the chemtrail conspiracy theory, but the sponsor of the bill, Sen. Steve Southerland said that it is one of the intended targets of the bill.^[43]

In religion and mythology

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See also: Mythopoeic thought and Rainmaking (ritual)

Magical and religious practices to control the weather are attested in a variety of cultures. In ancient India, it is said that yajna or Vedic rituals of chanting mantras and offerings were performed by rishis to bring sudden bursts of rainfall in rain starved regions. Some Indigenous Americans, like some Europeans, had rituals which they believed could induce rain.

The early modern era saw people observe that during battles the firing of cannons and other firearms often initiated precipitation.

In Greek mythology, Iphigenia was offered as a human sacrifice to appease the wrath of the goddess Artemis, who had becalmed the Achaean fleet at Aulis at the beginning of the Trojan War. In Homer‘s Odyssey, Aeolus, keeper of the winds, bestowed Odysseus and his crew with a gift of the four winds in a bag. However, the sailors opened the bag while Odysseus slept, looking for booty (money), and as a result, were blown off course by the resulting gale.^[44] In ancient Rome, the lapis manalis was a sacred stone kept outside the walls of Rome in a temple of Mars. When Rome suffered from drought, the stone was dragged into the city.^[45] The Berwick witches of Scotland were found guilty of using black magic to summon storms to murder King James VI of Scotland by seeking to sink the ship upon which he travelled.^[46] Scandinavian witches allegedly claimed to sell the wind in bags or magically confined into wooden staves; they sold the bags to seamen who could release them when becalmed.^[47] In various towns of Navarre, prayers petitioned Saint Peter to grant rain in times of drought. If the rain was not forthcoming, the statue of St Peter was removed from the church and tossed into a river.

In the Hebrew Bible, it is recorded that Elijah in the way of judgement, told King Ahab that neither dew nor rain would fall until Elijah called for it.^[48] It is further recorded that the ensuing drought lasted for a period of 3.5 years at which time Elijah called the rains to come again and the land was restored.^[49] The New Testament records Jesus Christ controlling a storm by speaking to it.^[50]

In Islam, Salat Al-Istisqa’ (Prayer for Rain) is taken as a recourse when seeking rain from God during times of drought.^[51]

Conspiracy theories

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See also: List of conspiracy theories § Weather and earthquake control projects

Weather modification, along with climate engineering, is a recurring theme in conspiracy theories. The chemtrail conspiracy theory supposes that jet contrails are chemically altered to modify the weather and other phenomena. Other theories attempt to implicate scientific infrastructure such as the High-frequency Active Auroral Research Program (HAARP).^[52]

Popular Culture

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Frank Herbert‘s Dune series features weather control technology, mainly on two planets: Arrakis, where the technology is used by the Fremen to assure privacy from observation and hide their true population and their plans to terraform the planet from the Imperium; and, Chapterhouse, where the Bene Gesserit intend to turn the planet into a desert.

The ability to manipulate the weather has become a common superpower in superhero fiction. A notable example is the Marvel Comics character Storm.

In the children’s book Cloudy with a Chance of Meatballs, the fictional town of Chewandswallow has weather that rains down food instead of actual rain or snow, which becomes so extreme it forces its citizens to move to a different town. This was adapted into a movie where Flint Lockwood, the town’s outcast and scientist, has created a machine that converts water from the clouds into food.

In the Star Trek franchise, the United Federation of Planets has weather modification technology, in addition to terraforming capabilities.

Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy.^[1] On Earth, most weather phenomena occur in the lowest layer of the planet’s atmosphere, the troposphere,^[2][3] just below the stratosphere. Weather refers to day-to-day temperature, precipitation, and other atmospheric conditions, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time.^[4] When used without qualification, “weather” is generally understood to mean the weather of Earth.

Weather is driven by air pressure, temperature, and moisture differences between one place and another. These differences can occur due to the Sun’s angle at any particular spot, which varies with latitude. The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations: the Hadley cell, the Ferrel cell, the polar cell, and the jet stream. Weather systems in the middle latitudes, such as extratropical cyclones, are caused by instabilities of the jet streamflow. Because Earth’s axis is tilted relative to its orbital plane (called the ecliptic), sunlight is incident at different angles at different times of the year. On Earth’s surface, temperatures usually range ±40 °C (−40 °F to 104 °F) annually. Over thousands of years, changes in Earth’s orbit can affect the amount and distribution of solar energy received by Earth, thus influencing long-term climate and global climate change.

Surface temperature differences in turn cause pressure differences. Higher altitudes are cooler than lower altitudes, as most atmospheric heating is due to contact with the Earth’s surface while radiative losses to space are mostly constant. Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Earth’s weather system is a chaotic system; as a result, small changes to one part of the system can grow to have large effects on the system as a whole. Human attempts to control the weather have occurred throughout history, and there is evidence that human activities such as agriculture and industry have modified weather patterns.

Studying how the weather works on other planets has been helpful in understanding how weather works on Earth. A famous landmark in the Solar System, Jupiter’s Great Red Spot, is an anticyclonic storm known to have existed for at least 300 years. However, the weather is not limited to planetary bodies. A star’s corona is constantly being lost to space, creating what is essentially a very thin atmosphere throughout the Solar System. The movement of mass ejected from the Sun is known as the solar wind.

Causes

On Earth, common weather phenomena include wind, cloud, rain, snow, fog and dust storms. Some more common events include natural disasters such as tornadoes, hurricanes, typhoons and ice storms. Almost all familiar weather phenomena occur in the troposphere (the lower part of the atmosphere).^[3] Weather does occur in the stratosphere and can affect weather lower down in the troposphere, but the exact mechanisms are poorly understood.^[5]

Weather occurs primarily due to air pressure, temperature and moisture differences from one place to another. These differences can occur due to the sun angle at any particular spot, which varies by latitude in the tropics. In other words, the farther from the tropics one lies, the lower the sun angle is, which causes those locations to be cooler due to the spread of the sunlight over a greater surface.^[6] The strong temperature contrast between polar and tropical air gives rise to the large scale atmospheric circulation cells and the jet stream.^[7] Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow (see baroclinity).^[8] Weather systems in the tropics, such as monsoons or organized thunderstorm systems, are caused by different processes.

Because the Earth’s axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. In June the Northern Hemisphere is tilted towards the Sun, so at any given Northern Hemisphere latitude sunlight falls more directly on that spot than in December (see Effect of sun angle on climate).^[10] This effect causes seasons. Over thousands to hundreds of thousands of years, changes in Earth’s orbital parameters affect the amount and distribution of solar energy received by the Earth and influence long-term climate. (See Milankovitch cycles).^[11]

The uneven solar heating (the formation of zones of temperature and moisture gradients, or frontogenesis) can also be due to the weather itself in the form of cloudiness and precipitation.^[12] Higher altitudes are typically cooler than lower altitudes, which is the result of higher surface temperature and radiational heating, which produces the adiabatic lapse rate.^[13][14] In some situations, the temperature actually increases with height. This phenomenon is known as an inversion and can cause mountaintops to be warmer than the valleys below. Inversions can lead to the formation of fog and often act as a cap that suppresses thunderstorm development. On local scales, temperature differences can occur because different surfaces (such as oceans, forests, ice sheets, or human-made objects) have differing physical characteristics such as reflectivity, roughness, or moisture content.

Surface temperature differences in turn cause pressure differences. A hot surface warms the air above it causing it to expand and lower the density and the resulting surface air pressure.^[15] The resulting horizontal pressure gradient moves the air from higher to lower pressure regions, creating a wind, and the Earth’s rotation then causes deflection of this airflow due to the Coriolis effect.^[16] The simple systems thus formed can then display emergent behaviour to produce more complex systems and thus other weather phenomena. Large scale examples include the Hadley cell while a smaller scale example would be coastal breezes.

The atmosphere is a chaotic system. As a result, small changes to one part of the system can accumulate and magnify to cause large effects on the system as a whole.^[17] This atmospheric instability makes weather forecasting less predictable than tidal waves or eclipses.^[18] Although it is difficult to accurately predict weather more than a few days in advance, weather forecasters are continually working to extend this limit through meteorological research and refining current methodologies in weather prediction. However, it is theoretically impossible to make useful day-to-day predictions more than about two weeks ahead, imposing an upper limit to potential for improved prediction skill.^[19]

Shaping the planet Earth

Main article: Weathering

Weather is one of the fundamental processes that shape the Earth. The process of weathering breaks down the rocks and soils into smaller fragments and then into their constituent substances.^[20] During rains precipitation, the water droplets absorb and dissolve carbon dioxide from the surrounding air. This causes the rainwater to be slightly acidic, which aids the erosive properties of water. The released sediment and chemicals are then free to take part in chemical reactions that can affect the surface further (such as acid rain), and sodium and chloride ions (salt) deposited in the seas/oceans. The sediment may reform in time and by geological forces into other rocks and soils. In this way, weather plays a major role in erosion of the surface.^[21]

Effect on humans

Further information: Biometeorology

Weather, seen from an anthropological perspective, is something all humans in the world constantly experience through their senses, at least while being outside. There are socially and scientifically constructed understandings of what weather is, what makes it change, the effect the weather, and especially inclement weather, has on humans in different situations, etc.^[22] Therefore, weather is something people often communicate about.

In the United States, the National Weather Service has an annual report for fatalities, injury, and total damage costs which include crop and property. They gather this data via National Weather Service offices located throughout the 50 states in the United States as well as Puerto Rico, Guam, and the Virgin Islands. As of 2019, tornadoes have had the greatest impact on humans with 42 fatalities while costing crop and property damage over 3 billion dollars.^[23]

Effects on populations

The weather has played a large and sometimes direct part in human history. Aside from climatic changes that have caused the gradual drift of populations (for example the desertification of the Middle East, and the formation of land bridges during glacial periods), extreme weather events have caused smaller scale population movements and intruded directly in historical events. One such event is the saving of Japan from invasion by the Mongol fleet of Kublai Khan by the Kamikaze winds in 1281.^[24] French claims to Florida came to an end in 1565 when a hurricane destroyed the French fleet, allowing Spain to conquer Fort Caroline.^[25] More recently, Hurricane Katrina redistributed over one million people from the central Gulf coast elsewhere across the United States, becoming the largest diaspora in the history of the United States.^[26]

The Little Ice Age caused crop failures and famines in Europe. During the period known as the Grindelwald Fluctuation (1560–1630), volcanic forcing events^[27] seem to have led to more extreme weather events.^[28] These included droughts, storms and unseasonal blizzards, as well as causing the Swiss Grindelwald Glacier to expand. The 1690s saw the worst famine in France since the Middle Ages. Finland suffered a severe famine in 1696–1697, during which about one-third of the Finnish population died.^[29]

Forecasting

Main article: Weather forecasting

Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Human beings have attempted to predict the weather informally for millennia, and formally since at least the nineteenth century.^[30] Weather forecasts are made by collecting quantitative data about the current state of the atmosphere and using scientific understanding of atmospheric processes to project how the atmosphere will evolve.^[31]

Once an all-human endeavor based mainly upon changes in barometric pressure, current weather conditions, and sky condition,^[32][33] forecast models are now used to determine future conditions. On the other hand, human input is still required to pick the best possible forecast model to base the forecast upon, which involves many disciplines such as pattern recognition skills, teleconnections, knowledge of model performance, and knowledge of model biases.

The chaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, the error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes mean that forecasts become less accurate as of the difference in current time and the time for which the forecast is being made (the range of the forecast) increases. The use of ensembles and model consensus helps to narrow the error and pick the most likely outcome.^[34][35][36]

There are a variety of end users to weather forecasts. Weather warnings are important forecasts because they are used to protect life and property.^[37][38] Forecasts based on temperature and precipitation are important to agriculture,^{[39][40][41][42]} and therefore to commodity traders within stock markets. Temperature forecasts are used by utility companies to estimate demand over coming days.^[43][44][45]

In some areas, people use weather forecasts to determine what to wear on a given day. Since outdoor activities are severely curtailed by heavy rain, snow and the wind chill, forecasts can be used to plan activities around these events and to plan ahead to survive through them.

Tropical weather forecasting is different from that at higher latitudes. The sun shines more directly on the tropics than on higher latitudes (at least on average over a year), which makes the tropics warm (Stevens 2011). And, the vertical direction (up, as one stands on the Earth’s surface) is perpendicular to the Earth’s axis of rotation at the equator, while the axis of rotation and the vertical are the same at the pole; this causes the Earth’s rotation to influence the atmospheric circulation more strongly at high latitudes than low latitudes. Because of these two factors, clouds and rainstorms in the tropics can occur more spontaneously compared to those at higher latitudes, where they are more tightly controlled by larger-scale forces in the atmosphere. Because of these differences, clouds and rain are more difficult to forecast in the tropics than at higher latitudes. On the other hand, the temperature is easily forecast in the tropics, because it does not change much.^[46]

Modification

The aspiration to control the weather is evident throughout human history: from ancient rituals intended to bring rain for crops to the U.S. Military Operation Popeye, an attempt to disrupt supply lines by lengthening the North Vietnamese monsoon. The most successful attempts at influencing weather involve cloud seeding; they include the fog– and low stratus dispersion techniques employed by major airports, techniques used to increase winter precipitation over mountains, and techniques to suppress hail.^[47] A recent example of weather control was China’s preparation for the 2008 Summer Olympic Games. China shot 1,104 rain dispersal rockets from 21 sites in the city of Beijing in an effort to keep rain away from the opening ceremony of the games on 8 August 2008. Guo Hu, head of the Beijing Municipal Meteorological Bureau (BMB), confirmed the success of the operation with 100 millimeters falling in Baoding City of Hebei Province, to the southwest and Beijing’s Fangshan District recording a rainfall of 25 millimeters.^[48]

Whereas there is inconclusive evidence for these techniques’ efficacy, there is extensive evidence that human activity such as agriculture and industry results in inadvertent weather modification:^[47]

• Acid rain, caused by industrial emission of sulfur dioxide and nitrogen oxides into the atmosphere, adversely affects freshwater lakes, vegetation, and structures.
• Anthropogenic pollutants reduce air quality and visibility.
• Climate change caused by human activities that emit greenhouse gases into the air is expected to affect the frequency of extreme weather events such as drought, extreme temperatures, flooding, high winds, and severe storms.^[49]
• Heat, generated by large metropolitan areas have been shown to minutely affect nearby weather, even at distances as far as 1,600 kilometres (990 mi).^[50]

The effects of inadvertent weather modification may pose serious threats to many aspects of civilization, including ecosystems, natural resources, food and fiber production, economic development, and human health.^[51]

Microscale meteorology

Microscale meteorology is the study of short-lived atmospheric phenomena smaller than mesoscale, about 1 km or less. These two branches of meteorology are sometimes grouped together as “mesoscale and microscale meteorology” (MMM) and together study all phenomena smaller than synoptic scale; that is they study features generally too small to be depicted on a weather map. These include small and generally fleeting cloud “puffs” and other small cloud features.^[52]

Extremes on Earth

Main articles: Extremes on Earth and List of weather records

On Earth, temperatures usually range ±40 °C (100 °F to −40 °F) annually. The range of climates and latitudes across the planet can offer extremes of temperature outside this range. The coldest air temperature ever recorded on Earth is −89.2 °C (−128.6 °F), at Vostok Station, Antarctica on 21 July 1983. The hottest air temperature ever recorded was 57.7 °C (135.9 °F) at ‘Aziziya, Libya, on 13 September 1922,^[54] but that reading is queried. The highest recorded average annual temperature was 34.4 °C (93.9 °F) at Dallol, Ethiopia.^[55] The coldest recorded average annual temperature was −55.1 °C (−67.2 °F) at Vostok Station, Antarctica.^[56]

The coldest average annual temperature in a permanently inhabited location is at Eureka, Nunavut, in Canada, where the annual average temperature is −19.7 °C (−3.5 °F).^[57]

The windiest place ever recorded is in Antarctica, Commonwealth Bay (George V Coast). Here the gales reach 199 mph (320 km/h).^[58] Furthermore, the greatest snowfall in a period of twelve months occurred in Mount Rainier, Washington, US. It was recorded as 31,102 mm (102.04 ft) of snow.^[59]

Extraterrestrial weather

Studying how the weather works on other planets has been seen as helpful in understanding how it works on Earth.^[60] Weather on other planets follows many of the same physical principles as weather on Earth, but occurs on different scales and in atmospheres having different chemical composition. The Cassini–Huygens mission to Titan discovered clouds formed from methane or ethane which deposit rain composed of liquid methane and other organic compounds.^[61] Earth’s atmosphere includes six latitudinal circulation zones, three in each hemisphere.^[62] In contrast, Jupiter’s banded appearance shows many such zones,^[63] Titan has a single jet stream near the 50th parallel north latitude,^[64] and Venus has a single jet near the equator.^[65]

One of the most famous landmarks in the Solar System, Jupiter’s Great Red Spot, is an anticyclonic storm known to have existed for at least 300 years.^[66] On other giant planets, the lack of a surface allows the wind to reach enormous speeds: gusts of up to 600 metres per second (about 2,100 km/h or 1,300 mph) have been measured on the planet Neptune.^[67] This has created a puzzle for planetary scientists. The weather is ultimately created by solar energy and the amount of energy received by Neptune is only about ¹⁄₉₀₀ of that received by Earth, yet the intensity of weather phenomena on Neptune is far greater than on Earth.^[68] As of 2007, the strongest planetary winds discovered are on the extrasolar planet HD 189733 b, which is thought to have easterly winds moving at more than 9,600 kilometres per hour (6,000 mph).^[69]

Space weather

Main article: Space weather

Weather is not limited to planetary bodies. Like all stars, the Sun’s corona is constantly being lost to space, creating what is essentially a very thin atmosphere throughout the Solar System. The movement of mass ejected from the Sun is known as the solar wind. Inconsistencies in this wind and larger events on the surface of the star, such as coronal mass ejections, form a system that has features analogous to conventional weather systems (such as pressure and wind) and is generally known as space weather. Coronal mass ejections have been tracked as far out in the Solar System as Saturn.^[70] The activity of this system can affect planetary atmospheres and occasionally surfaces. The interaction of the solar wind with the terrestrial atmosphere can produce spectacular aurorae,^[71] and can play havoc with electrically sensitive systems such as electricity grids and radio signals.^[72]