Types common cloud classifications

Clouds are classified into a system that uses Latin words to describe the appearance of as seen by an observer on the ground. The table below summarizes the four principal components of this classification system (Ahrens, 1994).

LLaattiin RRoooott TTrraannssllaattiioonn EExxaammppllee fair weather cumulus cumulus heap stratus layer altostratus cirrus curl of hair cirrus nimbus cumulonimbus

Further classification identifies clouds by height of cloud base. For example, cloud names containing the prefix "cirr-", as in cirrus clouds, are located at high levels while cloud names with the prefix "alto-", as in altostratus, are found at middle levels. This module introduces several cloud groups. The first three groups are identified based upon their height above the ground. The fourth group consists of vertically developed clouds, while the final group consists of a collection of miscellaneous cloud types.

High-Level Clouds High-level clouds form above 20,000 feet (6,000 meters) and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals. High-level clouds are typically thin and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon.

Photograph by: Knupp Mid-Level Clouds The bases of mid-level clouds typically appear between 6,500 to 20,000 feet (2,000 to 6,000 meters). Because of their lower altitudes, they are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough.

Photograph by: Holle

Low-level Clouds Low clouds are of mostly composed of water droplets since their bases generally lie below 6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may also contain ice particles and .

Photograph by: Holle

Vertically Developed Clouds Probably the most familiar of the classified clouds is the . Generated most commonly through either thermal convection or or frontal lifting, these clouds can grow to heights in excess of 39,000 feet (12,000 meters), releasing incredible amounts of energy through the condensation of water vapor within the cloud itself. Photograph by: Holle

Other Cloud Types Finally, we will introduce a collection of miscellaneous cloud types which do not fit into the previous four groups.

Classifications High-Level Clouds Last Update: 07/09/97 Cloud types include: cirrus and cirrostratus..

Mid-Level Clouds Cloud types include: altocumulus,, altostratus.

Low-Level Clouds Cloud types include: nimbostratus and stratocumulus..

Clouds with Vertical Development Cloud types include: fair weather cumulus and cumulonimbus..

Other Cloud Types Cloud types include: ,, billow clouds,, mammatus,, orographic and clouds.. Cloud Classification The classification of clouds was first conceptualized by French naturalist Jean Lamarck in 1801. Two years later, in 1803, the English scientist Luke Howard created a classification which was later adopted by the International Meteorological Commission in 1929.

The first scientific study of clouds began in 1803, when a method of cloud classification was devised by the British meteorologist Luke Howard. The next development was the publication in 1887 of a classification system that later formed the basis for the noted International (1896). This atlas, considerably revised and modified through the years (most recently in 1956), is now used throughout the world. Cloud types

Clouds are generally classified according to genera in which Latin words are used to describe the appearance of clouds as seen by an observer on the ground. The table below summarizes the four principal components of this classification system. Latin Root ccuummuulluuss ssttrraattuuss cciirrrruuss nniimmbbuuss

Translation hheeaapp llaayyeerr ccuurrl oof hhaaiirr rraaiinn

Cloud altitude

Clouds are further categorized according to their height above the ground (etages). These are:

•• High-Level Clouds Forms above 20,000 feet (6,000 meters) and are primarily composed of ice crystals. Denoted by the prefix cirro- or or cirrus and includes cirrus, cirrocumulus, and cirrostratus. •• Mid-Level Clouds Their bases appear between 6,500 to 20,000 feet (2,000 to 6,000 meters). Composed primarily of water droplets although they can also be composed of ice crystals when temperatures are cold enough. Denoted by the prefix alto- and includes altostratus, altocumulus and nimbostratus.

•• Low-level Clouds Their bases generally lie below 6,500 feet (2,000 meters). Mostly composed of water droplets but may also contain ice particles and snow. Includes stratus, stratocumulus, cumulus and cumulonimbus.

When cloud particles become too heavy to remain suspended in the air, they fall to the earth as . Precipitation occurs in a variety of forms; , rain, freezing rain, sleet or snow. This portion of the Clouds and Precipitation module focuses on precipitation and has been organized into the following sections.

Sections Rain and Hail Latest Update: 07/21/97 Atmospheric conditions that lead to the development of rain and hail.

Freezing Rain A detailed look at freezing rain, associated dangers and the conditions that lead to its development.

Sleet Atmospheric conditions that lead to the development of sleet.

Snow Atmospheric conditions that lead to the development of snow.

Acknowledgments Those who contributed to the Precipitation sections of the Clouds and Precipitation module.

The navigation menu (left) for this section is called "Precipitation" and the menu items are arranged in a recommended sequence, beginning with this introduction. In addition, this entire web server is accessible in both "graphics" and "text"-based modes, a feature controlled from the blue "User Interface" menu (located beneath the black navigation menus). More information about the user interface options, the navigation system,, or WW2010 in general is accessible from About This Server ..

InIn 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 is pulled down by gravity and deposited on the Earth's surface.[1] The main forms of precipitation include rain,, snow,, ice pellets,, and . It occurs when the atmosphere, a large gaseous solution, becomes saturated with water vapour and the water condenses, falling out of solution (i.e., precipitates).).[2] Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapour to the air. is precipitation that begins falling to the earth but evaporates before reaching the surface; it is one of the ways air can become saturated. Precipitation forms via collision with other rain drops or ice crystals within a cloud..

Moisture overriding associated with weather fronts is an overall major method of precipitation production. If enough moisture and upward motion is present, precipitation falls from convective clouds such as cumulonimbus and can organize into narrow rainbands.. Where relatively warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones. Lake-effect snowfall can be locally heavy. Thundersnow isis possible within a cyclone's comma head and within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation. On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. The movement of themonsoon trough,, or or intertropical convergence zone, brings rainy seasons toto savannah climes..

Rain drops range in size from oblate, pancake-like shapes for larger drops, to small spheres for smaller drops. Precipitation that reaches the surface of the earth can occur in many different forms, including rain,, freezing rain,, drizzle,, ice needles,, snow,, ice pellets or sleet, graupel and hail. Hail is formed within cumulonimbus clouds when strong updrafts of air cause the stones to cycle back and forth through the cloud, causing the hailstone to form in layers until it becomes heavy enough to fall from the cloud. Unlike raindrops, snowflakes grow in a variety of different shapes and patterns, determined by the temperature and humidity characteristics of the air the snowflake moves through on its way to the ground. While snow and ice pellets require temperatures close to the ground to be near or below freezing, hail can occur during much warmer temperature regimes due to the process of its formation. Precipitation may occur on other celestial bodies, e.g. when it gets cold, Mars has precipitation which most likely takes the form of ice needles, rather than rain or snow.[3]

The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities. Global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. Precipitation is a major component of the water cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 cubic kilometres (121,000 cu mi) of water falls as precipitation each year; 398,000 cubic kilometres (95,000 cu mi) of it over the oceans.[4] Given the Earth's surface area, that means the globally-averaged annual precipitation is 990 millimetres (39 in). Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes.

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Contents [hide]

• 1 Hydrometeor • 2 Types • 3 How the air becomes saturated o 3.1 Cooling air to its dew point o 3.2 Adding moisture to the air • 4 Formation o 4.1 Raindrops o 4.2 Ice pellets o 4.3 Hail o 4.4 Snowflakes o 4.5 Diamond dust • 5 Causes o 5.1 Frontal activity o 5.2 Convection o 5.3 Orographic effects o 5.4 Snow o 5.5 Within the tropics • 6 Measurement • 7 Return period • 8 Role in Köppen climate classification • 9 Effect on agriculture • 10 Changes due to global warming • 11 Changes due to urban heat island • 12 Forecasting • 13 See also • 14 References

• 15 External links [edit] Hydrometeor This anvil-shaped Cumulonimbus incus cloud is composed of hydrometeors.

The term meteor describes an object from outer space which has entered the Earth's atmosphere and produces a light phenomenon.[5] In contrast, any phenomenon which was at some point produced due to condensation or precipitation of moisture within the Earth's atmosphere is known as a hydrometeor. Particles composed of fallen precipitation which fell onto the Earth's surface can become hydrometeors if blown off the landscape by . Formations due to condensation such as clouds, haze, , and mist are composed of hydrometeors. All precipitation types are hydrometeors by definition, including virga, which is precipitation which evaporates before reaching the ground. Particles removed from the Earth's surface by wind such as blowing snow and blowing sea spray are also hydrometeors.[6]

[edit] Types See also: Precipitation types (meteorology)

A with heavy precipitation

Precipitation is a major component of the water cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 km3 (121,000 cu mi) of water falls as precipitation each year, 398,000 km3 (95,000 cu mi) of it over the oceans.[4] Given the Earth's surface area, that means the globally-averaged annual precipitation is 990 millimetres (39 in).

Mechanisms of producing precipitation include convective, stratiform,[7] and orographic rainfall. [8] Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation,[9] while stratiform processes involve weaker upward motions and less intense precipitation. Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice. Mixtures of different types of precipitation, including types in different categories, can fall simultaneously. Liquid forms of precipitation include rain and drizzle. Rain or drizzle that freezes on contact within a subfreezing air mass is called "freezing rain" or "freezing drizzle". Frozen forms of precipitation include snow, ice needles, ice pellets, hail, and graupel.[10] forming due to mountains over Wyoming

[edit] Adding moisture to the air

The main ways water vapour is added to the air are: wind convergence into areas of upward motion,[9] precipitation or virga falling from above,[18] daytime heating evaporating water from the surface of oceans, water bodies or wet land,[19] transpiration from plants,[20] cool or dry air moving over warmer water,[21] and lifting air over mountains.[22]

[edit] Formation Main article: Water cycle

Condensation and coalescence are important parts of the water cycle.

[edit] Raindrops

Coalescence occurs when water droplets fuse to create larger water droplets, or when water droplets freeze onto an ice crystal, which is known as the Bergeron process. Air resistance typically causes the water droplets in a cloud to remain stationary. When air turbulence occurs, water droplets collide, producing larger droplets. As these larger water droplets descend, coalescence continues, so that drops become heavy enough to overcome air resistance and fall as rain. Coalescence generally happens most often in clouds above freezing. In clouds below freezing, when ice crystals gain enough mass they begin to fall. This generally requires more mass than coalescence when occurring between the crystal and neighboring water droplets. This process is temperature dependent, as supercooled water droplets only exist in a cloud that is below freezing. In addition, because of the great temperature difference between cloud and ground level, these ice crystals may melt as they fall and become rain.[23]

Raindrops have sizes ranging from 0.1 millimetres (0.0039 in) to 9 millimetres (0.35 in) mean diameter, above which they tend to break up. Smaller drops are called cloud droplets, and their shape is spherical. As a raindrop increases in size, its shape becomes more oblate, with its largest cross-section facing the oncoming airflow. Contrary to the cartoon pictures of raindrops, their shape does not resemble a teardrop.[24] Intensity and duration of rainfall are usually inversely related, i.e., high intensity storms are likely to be of short duration and low intensity storms can have a long duration.[25][26] Rain drops associated with melting hail tend to be larger than other rain drops.[27] The METAR code for rain is RA, while the coding for rain showers is SHRA.[28]

[edit] Ice pellets

See also: Ice pellets

An accumulation of ice pellets

Ice pellets are a form of precipitation consisting of small, translucent balls of ice. This form of precipitation is also known as sleet in the United States.[29] Ice pellets are usually (but not always) smaller than hailstones.[30] They often bounce when they hit the ground, and generally do not freeze into a solid mass unless mixed with freezing rain. The METAR code for ice pellets is PL.[28]

Ice pellets form when a layer of above-freezing air is located between 1,500 metres (4,900 ft) and 3,000 metres (9,800 ft) above the ground, with sub-freezing air both above and below it. This causes the partial or complete melting of any snowflakes falling through the warm layer. As they fall back into the sub-freezing layer closer to the surface, they re-freeze into ice pellets. However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze, and freezing rain will be the result at the surface. A temperature profile showing a warm layer above the ground is most likely to be found in advance of awarm front during the cold season [31], but can occasionally be found behind a passing .

[edit] Hail See also: Hail

A large hailstone, about 6 cm (2.36 in) in diameter

Like other precipitation, hail forms in storm clouds when supercooled water droplets freeze on contact with condensation nuclei, such as dust or dirt. The storm's updraft blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of 5 millimetres (0.20 in) or more.[32] Within METAR code, GR is used to indicate larger hail, of a diameter of at least 6.4 millimetres (0.25 in). GR is derived from the French word grêle. Smaller-sized hail, as well as snow pellets, use the coding of GS, which is short for the French word grésil.[28] Stones just larger than golf ball- sized are one of the most frequently reported hail sizes.[33] Hailstones can grow to 15 centimetres (6 in) and weigh more than .5 kilograms (1.1 lb).[34] In large hailstones, latent heat released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.[35] The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.[36]

Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F).[32] Hail-producing clouds are often identifiable by their green coloration.[37][38] The growth rate is maximized at about −13 °C (9 °F), and becomes vanishingly small much below −30 °C (−22 °F) as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m).[39] Entrainment of dry air into strong over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid- latitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.[40]

[edit] Snowflakes

Main article: Snowflake A cloud is a visible mass of droplets of water or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. A cloud is also a visible mass attracted by gravity, such as masses of material in space called interstellar clouds and nebulae. Clouds are studied in the nephology or cloud physics branch of meteorology.

On Earth the condensing substance is typically water vapor , which forms small droplets or ice crystals, typically 0.01 mm (0.00039 in) in diameter. When surrounded by billions of other droplets or crystals they become visible as clouds. Dense deep clouds exhibit a high reflectance (70% to 95%) throughout the visible range of wavelengths. They thus appear white, at least from the top. Cloud droplets tend to scatter light efficiently, so that the intensity of the solar radiation decreases with depth into the gases, hence the gray or even sometimes dark appearance at the cloud base. Thin clouds may appear to have acquired the color of their environment or background and clouds illuminated by non-white light, such as during sunrise or sunset, may appear colored accordingly. Clouds look darker in the near-infrared because water absorbs solar radiation at those wavelengths. Contents [hide]

• 1 Classification o 1.1 High clouds (Family A) o 1.2 Middle clouds (Family B) o 1.3 Low clouds (Family C1) o 1.4 Low to middle clouds (Family C2) o 1.5 Vertical clouds (Family D) o 1.6 Other clouds o 1.7 Cloud fields • 2 Colors • 3 Clouds and climate o 3.1 Global brightening o 3.2 Bacteria in clouds • 4 Other planets • 5 Gallery • 6 See also • 7 References • 8 Bibliography

• 9 External links [edit] Classification

A cumulus cloudscape over Swifts Creek, Victoria, Australia

Cloud types or genera are grouped into three general categories: cirriform (wispy), stratiform (layered in sheets) and convective or cumuliform (heaped, rolled and/or rippled). These designations distinguish a cloud's physical structure and process of formation. All weather- related cloud types form in the troposphere, the lowest major layer of the earth's atmosphere. The individual genus types result from the categories being cross-classified by height range within the troposphere. This is determined by the base height of the cloud, not the cloud top, and base height ranges may vary depending on the geographical zone. Each cloud genus is divided into species and/or varieties determined by more specific aspects of its structure and/or process of formation in any particular situation. All Cirrus clouds are classified as high and thus constitute a single genus. Cumulus and stratus clouds in the high altitude range carry the prefix 'cirro', while similar genera in the middle range are prefixed by 'alto'. Any cumuliform or stratiform genus in the low or low to middle range either has no prefix or carries one that refers to a characteristic other than altitude. A vertically developed cloud genus or species typically occupies all altitude ranges and therefore has no height related prefix. This system was proposed in 1802, when it was presented to the Askesian Society by Luke Howard.

A sky of cirrus clouds.

[edit] High clouds (Family A)

High clouds will form between 10,000 and 25,000 ft (3,000 and 8,000 m) in the polar regions, 16,500 and 40,000 ft (5,000 and 12,000 m) in the temperate regions and 20,000 and 60,000 ft (6,000 and 18,000 m) in the tropical region.[1]

Clouds in Family A include:

• Genus Cirrus (Ci) • Genus Cirrocumulus (Cc) • Genus Cirrostratus (Cs)

[edit] Middle clouds (Family B)

Middle clouds tend to form at 6,500 ft (2,000 m) but may form at heights up to 13,000 ft (4,000 m), 23,000 ft (7,000 m) or 25,000 ft (8,000 m) depending on the region. Generally the warmer the climate, the higher the cloud base. Nimbostratus clouds are sometimes included with the middle clouds.[1] The World Meterological Organization classifies Nimbostratus as a middle cloud that can thicken down into the low height range during precipitation.

Clouds in Family B include:

• Genus Altocumulus (Ac) • Genus Altostratus (As) degrees of grey shades, depending on how much light is being reflected or transmitted back to the observer.

Other colors occur naturally in clouds. Bluish-grey is the result of light scattering within the cloud. In the visible spectrum, blue and green are at the short end of light's visible wavelengths, while red and yellow are at the long end. The short rays are more easily scattered by water droplets, and the long rays are more likely to be absorbed. The bluish color is evidence that such scattering is being produced by rain-sized droplets in the cloud.

A greenish tinge to a cloud is produced when sunlight is scattered by ice. A emitting green is an imminent sign of heavy rain, hail, strong and possible tornadoes.

Yellowish clouds are rare but may occur in the late spring through early fall months during forest fire season. The yellow color is due to the presence of pollutants in the smoke.

Red, orange and pink clouds occur almost entirely at sunrise/sunset and are the result of the scattering of sunlight by the atmosphere. The clouds do not become that color; they are reflecting long and unscattered rays of sunlight, which are predominant at those hours. The effect is much like if one were to shine a red spotlight on a white sheet. In combination with large, mature thunderheads this can produce blood-red clouds.

[edit] Clouds and climate

Global cloud cover, averaged over the month of October, 2009. The outlines of the continents can often be traced through observations of clouds alone, with the sharpest outlines where very dry land is surrounded by ocean. NASA composite satellite image; larger image available here.

See also: Cloud cover and Cloud feedback

The role of clouds in regulating weather and climate remains a leading source of uncertainty in projections of global warming.[5] This uncertainty arises because of the delicate balance of processes related to clouds, spanning scales from millimeters to planetary. Hence interactions between the large scale (synoptic meteorology) and clouds becomes difficult to represent in global models. The complexity and diversity of clouds, as outlined above, adds to the problem. High clouds, such as cirrus, tend to have both shortwave and longwave (i.e., albedo and greenhouse) effects that nearly cancel, while low clouds like stratocumulus have a strong shortwave effect but almost no longwave effect. As such, much research has focused on the response of low clouds to a changing climate. Leading global models can produce quite different results, though, with some showing increasing low-level clouds and other showing decreases.[6][7]

[edit] Global brightening

New research indicates a global brightening trend.[8] The details are not fully understood, but much of the global dimming (and subsequent reversal) is thought to be a consequence of changes in aerosol loading in the atmosphere, especially sulfur-based aerosol associated with biomass burning and urban pollution. Changes in aerosol burden can have indirect effects on clouds by changing the droplet size distribution[9] or the lifetime and precipitation characteristics of clouds[10].

[edit] Bacteria in clouds

Bioprecipitation, the concept of rain-making bacteria, was proposed by David Sands from Montana State University. Such microbes - called ice nucleators - are found in rain, snow, and hail throughout the world, according to Brent Christner, a microbiologist at Louisiana State University. These bacteria may be part of a constant feedback between terrestrial ecosystems and clouds and may even have evolved the ability to promote rainstorms as a means of dispersal. They may rely on the rainfall to spread to new habitats, much as plants rely on windblown pollen grains, Christner said.[11][12]

[edit] Other planets Main article: Extraterrestrial atmospheres

Within our Solar System, any planet or moon with an atmosphere also has clouds. Venus's clouds are composed of sulfuric acid droplets. Mars has high, thin clouds of water ice. Both Jupiter and Saturn have an outer cloud deck composed of ammonia clouds, an intermediate deck of ammonium hydrosulfide clouds and an inner deck of water clouds. Uranus and Neptune have cloudy atmospheres dominated by methane gas.

Saturn's moon Titan has clouds believed to be composed largely of droplets of liquid methane. The Cassini–Huygens Saturn mission uncovered evidence of a fluid cycle on Titan, including lakes near the poles and fluvial channels on the surface of the moon.

[edit] Gallery

Wind From Wikipedia, the free encyclopedia Jump to: navigation, search

For other uses, see Wind (disambiguation).

Wind, from the Tacuinum Sanitatis

A breeze lifts a veil

Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space. Winds are commonly classified by their spatial scale, their speed, the types of forces that cause them, the regions in which they occur, and their effect. The strongest observed winds on a planet in our solar system occur on Neptune and Saturn. years between 2005 and 2008. In several countries it has achieved relatively high levels of penetration, accounting for approximately 19 percent of electricity production inDenmark , 10 percent in Spain and Portugal, and 7 percent in Germany and the Republic of Ireland in 2008. One study indicates that an entirely renewable energy supply based on 70 percent wind is attainable at today's power prices by linking wind farms with an HVDC supergrid.[52]

[edit] Shear

Hodograph plot of wind vectors at various heights in the troposphere, which is used to diagnose vertical wind shear

Main article: Wind shear

Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the Earth's atmosphere.[53] Wind shear can be broken down into vertical and horizontal components, with horizontal wind shear seen across weather fronts and near the coast,[54] and vertical shear typically near the surface,[55] though also at higher levels in the atmosphere near upper level jets and frontal zones aloft.[56]

Wind shear itself is a microscale meteorological phenomenon occurring over a very small distance, but it can be associated with mesoscale or synoptic scale weather features such as squall lines and cold fronts. It is commonly observed near microbursts and caused by thunderstorms,[57] weather fronts, areas of locally higher low level winds referred to as low level jets, near mountains,[58] radiation inversions that occur because of clear skies and calm winds, buildings,[59] wind turbines,[60] and sailboats.[61] Wind shear has a significant effect during take-off and landing of aircraft because of their effects on control of the aircraft,[62] and was a significant cause of aircraft accidents involving large loss of life within the United States.[57]

Sound movement through the atmosphere is affected by wind shear, which can bend the wave front, causing sounds to be heard where they normally would not, or vice versa.[63] Strong vertical wind shear within the troposphere also inhibits tropical cyclone development,[64] but helps to organize individual thunderstorms into living longer life cycles that can then produce severe weather .[65] The thermal wind concept explains how differences in wind speed with height are dependent on horizontal temperature differences, and explains the existence of the jet stream. [66]

[edit] Usage of wind

[edit] History

Winds according to Aristoteles.

As a natural force, the wind was often personified as one or more wind gods or as an expression of the supernatural in many cultures. Vayu is the Hindu God of Wind.[67][68] The Greek wind gods include Boreas, Notus, Eurus, and Zephyrus.[68] Aeolus, in varying interpretations the ruler or keeper of the four winds, has also been described as Astraeus, the god of dusk who fathered the four winds with Eos, goddess of dawn. The Ancient Greeks also observed the seasonal change of the winds, as evidenced by the Tower of the Winds in Athens.[68] Venti are the Roman gods of the winds.[69] Fūjin, the Japanese wind god and is one of the eldest Shinto gods. According to legend, he was present at the creation of the world and first let the winds out of his bag to clear the world of mist.[70] In Norse mythology, Njord is the god of the wind.[68] There are also four dvärgar ( Norse dwarves), named Norðri, Suðri, Austri and Vestri, and probably the four stags of Yggdrasil, personify the four winds, and parallel the four Greek wind gods.[71] Stribog is the name of the Slavic god of winds, sky and air. He is said to be the ancestor (grandfather) of the winds of the eight directions.[68]

Kamikaze (神風) is a Japanese word, usually translated as divine wind, believed to be a gift from the gods. The term is first known to have been used as the name of a pair or series of typhoons that are said to have saved Japan from two Mongol fleets under Kublai Khan that attacked Japan in 1274 and again in 1281.[72] Protestant Wind is a name for the storm that deterred the Spanish Armada from an invasion of England in 1588 where the wind played a pivotal role,[73] or the favorable winds that enabled William of Orange to invade England in 1688.[74] During Napoleon's Egyptian Campaign, the French soldiers had a hard time with the khamsin wind: when the storm appeared "as a blood-stint in the distant sky", the natives went to take cover, while the French "did not react until it was too late, then choked and fainted in the blinding, suffocating walls of dust."[75] During the North African Campaign of the World War II, "allied and German troops were several times forced to halt in mid-battle because of sandstorms caused by khamsin ... Grains of sand whirled by the wind blinded the soldiers and created electrical disturbances that rendered compasses useless."[76]

[edit] Transportation

RAF Exeter airfield on 20 May 1944, showing the layout of the runways that allow aircraft to take off and land into the wind

There are many different forms of sailing ships, but they all have certain basic things in common. Except for rotor ships using the Magnus effect, every sailing ship has a hull, rigging and at least one mast to hold up the sails that use the wind to power the ship.[77] Ocean journeys by sailing ship can take many months,[78] and a common hazard is becoming becalmed because of lack of wind,[79] or being blown off course by severe storms or winds that do not allow progress in the desired direction.[80] A severe storm could lead to shipwreck , and the loss of all hands.[81] Sailing ships can only carry a certain quantity of supplies in their hold, so they have to plan long voyages carefully to include appropriate provisions, including fresh water .[82]

While aircraft usually travel under an internal power source, tail winds affect groundspeed,[83] and in the case of hot air balloons and other lighter-than-air vehicles, wind may play a significant role in their movement and ground track.[84] In addition, the direction of wind plays a role in the takeoff and landing of fixed-wing aircraft and airfield runways are usually aligned to take the direction of wind into account. Of all factors affecting the direction of flight operations at an airport, wind direction is considered the primary governing factor. While taking off with a tailwind may be permissible under certain circumstances, it is generally considered the least desirable choice because of performance and safety considerations, with a headwind the desirable choice. A tailwind will increase takeoff distance and decrease climb gradient such that runway length and obstacle clearance may become limiting factors.[85] An airship, or dirigible, is a lighter-than-air aircraft that can be steered and propelled through the air using rudders and propellers or other thrust.[86] Unlike other aerodynamic aircraft such as fixed-wing aircraft and helicopters, which produce lift by moving a wing, or airfoil, through the air, aerostatic aircraft, such as airships and hot air balloons, stay aloft by filling a large cavity, such as a balloon, with a cold, continuously alternating the members on the outside of the assembled group, which reduces heat loss by 50%.[121] Flying insects, a subset of arthropods, are swept along by the prevailing winds,[122] while birds follow their own course taking advantage of wind conditions, in order to either fly or glide.[123] As such, fine line patterns within weather radar imagery, associated with converging winds, are dominated by insect returns.[124] Bird migration, which tends to occur overnight within the lowest 7,000 feet (2,100 m) of the Earth's atmosphere, contaminates wind profiles gathered by weather radar, particularly the WSR-88D, by increasing the environmental wind returns by 15 knots (28 km/h) to 30 knots (56 km/h).[125]

Pikas use a wall of pebbles to store dry plants and grasses for the winter in order to protect the food from being blown away.[126] Cockroaches use slight winds that precede the attacks of potential predators, such as toads, to survive their encounters. Their cerci are very sensitive to the wind, and help them survive half of their attacks.[127] Elk has a keen sense of smell that can detect potential upwind predators at a distance of 0.5 miles (800 m).[128] Increases in wind above 15 kilometers per hour (9.3 mph) signals glaucous gulls to increase their foraging and aerial attacks on thick-billed murres.[129]

[edit] Related damage See also: Severe weather

Damage from Hurricane Andrew

High winds are known to cause damage, depending upon their strength. Infrequent wind gusts can cause poorly designed suspension bridges to sway. When wind gusts are at a similar frequency to the swaying of the bridge, the bridge can be destroyed more easily, such as what occurred with the Tacoma Narrows Bridge in 1940.[130] Wind speeds as low as 23 knots (43 km/h) can lead to power outages due to tree branches disrupting the flow of energy through power lines.[131] While no species of tree is guaranteed to stand up to hurricane-force winds, those with shallow roots are more prone to uproot, and brittle trees such as eucalyptus, sea hibiscus, and avocado are more prone to damage.[132] Hurricane-force winds cause substantial damage to mobile homes, and begin to structurally damage homes with foundations. Winds of this strength due to downsloped winds off terrain have been known to shatter windows and sandblast paint from cars.[49] Once winds exceed 135 knots (250 km/h), homes completely collapse, and significant damage is done to larger buildings. Total destruction to man-made structures occurs when winds reach 175 knots (324 km/h). The Saffir-Simpson scale and Enhanced Fujita scale were designed to help estimate wind speed from the damage caused by high winds related to tropical cyclones and tornadoes, and vice versa.[133][134]

Australia's Barrow Island holds the record for the strongest wind gust, reaching 408 km/h (253 mph) during tropical cyclone Olivia on 10 April 1996, surpassing the previous record held by Mount Washington (New Hampshire) of 372 km/h (231 mph) on the afternoon of 12 April 1934.[135]

Wildfire intensity increases during daytime hours. For example, burn rates of smoldering logs are up to five times greater during the day because of lower humidity, increased temperatures, and increased wind speeds.[136] Sunlight warms the ground during the day and causes air currents to travel uphill, and downhill during the night as the land cools. Wildfires are fanned by these winds and often follow the air currents over hills and through valleys.[137] United States wildfire operations revolve around a 24-hour fire day that begins at 10:00 a.m. because of the predictable increase in intensity resulting from the daytime warmth.[138]

[edit] In outer space

The solar wind is quite different from a terrestrial wind, in that its origin is the sun, and it is composed of charged particles that have escaped the sun's atmosphere. Similar to the solar wind, the planetary wind is composed of light gases that escape planetary atmospheres. Over long periods of time, the planetary wind can radically change the composition of planetary atmospheres.

[edit] Planetary wind Main article: Atmospheric escape

Possible future for Earth due to the planetary wind: Venus

The hydrodynamic wind within the upper portion of a planet's atmosphere allows light chemical elements such as hydrogen to move up to the exobase, the lower limit of the exosphere, where the gases can then reach escape velocity, entering outer space without impacting other particles of gas. This type of gas loss from a planet into space is known as planetary wind.[139] Such a process over geologic time causes water-rich planets such as the Earth to evolve into planets such as Venus over billions of years.[140] Planets with hot lower atmospheres could result in humid upper atmospheres that accelerate the loss of hydrogen.[141]

[edit] Solar wind Main article: Solar wind

The plasma in the solar wind meeting the heliopause

Rather than air, the solar wind is a stream of charged particles —a plasma —ejected from the upper atmosphere of the sun at a rate of 400 kilometers per second (890,000 mph). It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time. These particles are able to escape the sun's gravity, in part because of the high temperature of the corona,[142] but also because of high kinetic energy that particles gain through a process that is not well-understood. The solar wind creates the Heliosphere, a vast bubble in the interstellar medium surrounding the solar system.[143] Planets require large magnetic fields in order to reduce the ionization of their upper atmosphere by the solar wind.[141] Other phenomena include geomagnetic storms that can knock out power grids on Earth,[144] the aurorae such as the Northern Lights,[145] and the plasma tails of comets that always point away from the sun.[146]

[edit] On other planets

Strong 300 kilometers per hour (190 mph) winds at Venus's cloud tops circle the planet every four to five earth days.[147] When the poles of Mars are exposed to sunlight after their winter , the

frozen CO2 sublimes, creating significant winds that sweep off the poles as fast as 400 kilometers per hour (250 mph), which subsequently transports large amounts of dust and water vapor over its landscape.[148] Other Martian winds have resulted in cleaning events and dust devils.[149][150] On Jupiter , wind speeds of 100 meters per second (220 mph) are common in zonal jet streams.[151] Saturn's winds are among the solar system's fastest. Cassini–Huygens data indicated peak easterly winds of 375 meters per second (840 mph).[152] On Uranus, northern hemisphere wind speeds reach as high as 240 meters per second (540 mph) near 50 degrees north latitude.[153][154] [155] At the cloud tops of Neptune, prevailing winds range in speed from 400 meters per second (890 mph) along the equator to 250 meters per second (560 mph) at the poles.[156] At 70° S latitude on Neptune, a high-speed jet stream travels at a speed of 300 meters per second (670 mph).[157]