Wind
Encyclopedia
Wind is the flow
of gas
es 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 element
s 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
.
In meteorology
, winds are often referred to according to their strength, and the direction from which the wind is blowing. Short bursts of high speed wind are termed gusts. Strong winds of intermediate duration (around one minute) are termed squall
s. Long-duration winds have various names associated with their average strength, such as breeze, gale
, storm, hurricane
, and typhoon. Wind occurs on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hours, to global
winds resulting from the difference in absorption of solar energy between the climate zones on Earth. The two main causes of large-scale atmospheric circulation
are the differential heating between the equator and the poles, and the rotation of the planet (Coriolis effect
). Within the tropics, thermal low
circulations over terrain and high plateaus can drive monsoon
circulations. In coastal areas the sea breeze
/land breeze cycle can define local winds; in areas that have variable terrain, mountain and valley breezes can dominate local winds.
In human
civilization
, wind has inspired mythology
, influenced the events of history
, expanded the range of transport
and warfare, and provided a power source
for mechanical work
, electricity
and recreation
. Wind powers the voyages of sailing ship
s across Earth's oceans. Hot air balloon
s use the wind to take short trips, and powered flight uses it to increase lift and reduce fuel consumption. Areas of wind shear
caused by various weather
phenomena can lead to dangerous situations for aircraft
. When winds become strong, trees and man-made structures are damaged or destroyed.
Winds can shape landforms, via a variety of aeolian processes such as the formation of fertile soils, such as loess
, and by erosion
. Dust
from large desert
s can be moved great distances from its source region by the prevailing winds
; winds that are accelerated by rough topography and associated with dust outbreaks have been assigned regional names in various parts of the world because of their significant effects on those regions. Wind affects the spread of wildfire
s. Winds disperse seeds from various plants, enabling the survival and dispersal of those plant species, as well as flying insect populations. When combined with cold temperatures, wind has a negative impact on livestock
. Wind affects animals' food stores, as well as their hunting and defensive strategies.
exists, the air is accelerated from higher to lower pressure. On a rotating planet, the air will be deflected by the Coriolis effect
, except exactly on the equator. Globally, the two major driving factors of large-scale winds (the atmospheric circulation
) are the differential heating between the equator and the poles (difference in absorption of solar energy leading to buoyancy forces) and the rotation of the planet
. Outside the tropics and aloft from frictional effects of the surface, the large-scale winds tend to approach geostrophic balance. Near the Earth's surface, friction
causes the wind to be slower than it would be otherwise. Surface friction also causes winds to blow more inward into low pressure areas.
Winds defined by an equilibrium of physical forces are used in the decomposition and analysis of wind profiles. They are useful for simplifying the atmospheric equations of motion and for making qualitative arguments about the horizontal and vertical distribution of winds. The geostrophic wind
component is the result of the balance between Coriolis force and pressure gradient force. It flows parallel to isobars and approximates the flow above the atmospheric boundary layer in the midlatitudes. The thermal wind
is the difference in the geostrophic wind between two levels in the atmosphere. It exists only in an atmosphere with horizontal temperature gradient
s. The ageostrophic wind
component is the difference between actual and geostrophic wind, which is responsible for air "filling up" cyclones over time. The gradient wind is similar to the geostrophic wind but also includes centrifugal force
(or centripetal acceleration).
is reported by the direction from which it originates. For example, a northerly wind blows from the north to the south. Weather vane
s pivot to indicate the direction of the wind. At airports, windsock
s are primarily used to indicate wind direction, but can also be used to estimate wind speed by its angle of hang. Wind speed is measured by anemometer
s, most commonly using rotating cups or propellers. When a high measurement frequency is needed (such as in research applications), wind can be measured by the propagation speed of ultrasound
signals or by the effect of ventilation on the resistance of a heated wire. Another type of anemometer uses pitot tube
s that take advantage of the pressure differential between an inner tube and an outer tube that is exposed to the wind to determine the dynamic pressure, which is then used to compute the wind speed.
Sustained wind speeds are reported globally at a sp=us 10 height and are averaged over a 10 minute time frame. The United States
reports winds over a 1 minute average for tropical cyclones, and a 2 minute average within weather observations. India
typically reports winds over a 3 minute average. Knowing the wind sampling average is important, as the value of a one-minute sustained wind is typically 14% greater than a ten-minute sustained wind. A short burst of high speed wind is termed a wind gust, one technical definition of a wind gust is: the maxima that exceed the lowest wind speed measured during a ten minute time interval by sp=us 10. A squall
is a doubling of the wind speed above a certain threshold, which lasts for a minute or more.
To determine winds aloft, rawinsondes determine wind speed by GPS, radio navigation
, or radar
tracking of the probe. Alternatively, movement of the parent weather balloon
position can be tracked from the ground visually using theodolite
s. Remote sensing
techniques for wind include SODAR
, Doppler
LIDAR
s and RADAR
s, which can measure the Doppler shift of electromagnetic radiation
scattered or reflected off suspended aerosol
s or molecule
s, and radiometer
s and radars can be used to measure the surface roughness of the ocean from space or airplanes. Ocean roughness can be used to estimate wind velocity close to the sea surface over oceans. Geostationary satellite imagery can be used to estimate the winds throughout the atmosphere based upon how far clouds move from one image to the next. Wind Engineering
describes the study of the effects of the wind on the built environment, including buildings, bridges and other man-made objects.
provides an empirical description of wind speed based on observed sea conditions. Originally it was a 13-level scale, but during the 1940s, the scale was expanded to 17 levels. There are general terms that differentiate winds of different average speeds such as a breeze, a gale, a storm, tornado, or a hurricane. Within the Beaufort scale, gale-force winds lie between sp=us 28 and sp=us 55 with preceding adjectives such as moderate, fresh, strong, and whole used to differentiate the wind's strength within the gale category. A storm has winds of sp=us 56 to sp=us 63. The terminology for tropical cyclones differs from one region to another globally. Most ocean basins use the average wind speed to determine the tropical cyclone's category. Below is a summary of the classifications used by Regional Specialized Meteorological Centers
worldwide:
(EF Scale) rates the strength of tornadoes in the United States based on the damage they cause. Below is that scale.
The station model
plotted on surface weather map
s uses a wind barb to show both wind direction
and speed. The wind barb shows the speed using "flags" on the end.
Winds are depicted as blowing from the direction the barb is facing. Therefore, a northeast wind will be depicted with a line extending from the cloud circle to the northeast, with flags indicating wind speed on the northeast end of this line. Once plotted on a map, an analysis of isotachs (lines of equal wind speeds) can be accomplished. Isotachs are particularly useful in diagnosing the location of the jet stream on upper level constant pressure charts, and are usually located at or above the 300 hPa level.
of the air in motion. Total wind energy flowing through an imaginary area A during the time t is:
where v is the wind velocity
and ρ is the air density
. The formula presented is structured in two parts: (A·v·t) is the volume of air passing through A, which is considered perpendicular to the wind velocity; (ρ·½ v2) is the kinetic energy of the moving air per unit volume.
Total wind power is:
Wind power is thus proportional to the third power of the wind velocity.
).
and drag
, gearbox losses, generator and converter losses, reduce the power delivered by a wind turbine. The basic relation that the turbine power is (approximately) proportional to the third power of velocity remains.
Easterly winds, on average, dominate the flow pattern across the poles, westerly winds blow across the mid-latitudes
of the earth, to the north of the subtropical ridge
, while easterlies again dominate the tropics
.
Directly under the subtropical ridge
are the doldrums, or horse latitudes, where winds are lighter. Many of the Earth's deserts lie near the average latitude of the subtropical ridge, where descent reduces the relative humidity
of the air mass. The strongest winds are in the mid-latitudes where cold Arctic air meets warm air from the tropics.
surface winds found in the tropics
towards the Earth's equator
. The trade winds blow predominantly from the northeast in the Northern Hemisphere
and from the southeast in the Southern Hemisphere
. The trade winds act as the steering flow for tropical cyclones that form over world's oceans. Trade winds also steer African dust westward across the Atlantic Ocean
into the Caribbean Sea
, as well as portions of southeast North America
.
A monsoon
is a seasonal prevailing wind that lasts for several months within tropical regions. The term was first used in English in India
, Bangladesh
, Pakistan
, and neighboring countries to refer to the big seasonal winds blowing from the Indian Ocean
and Arabian Sea
in the southwest bringing heavy rainfall to the area. Its poleward progression is accelerated by the development off a heat low over the Asian, African, and North American continents during May through July, and over Australia in December.
The Westerlies or the Prevailing Westerlies are the prevailing winds
in the middle latitudes
between 35 and 65 degrees latitude
. These prevailing winds blow from the west
to the east
to the north of the subtropical ridge, and steer extratropical cyclones in this general manner. The winds are predominantly from the southwest in the Northern Hemisphere
and from the northwest in the Southern Hemisphere
. They are strongest in the winter when the pressure is lower over the poles, and weakest during the summer and when pressures are higher over the poles.
Together with the trade wind
s, the westerlies enabled a round-trip trade route for sailing ships crossing the Atlantic and Pacific Oceans, as the westerlies lead to the development of strong ocean currents on the western sides of oceans in both hemispheres through the process of western intensification. These western ocean currents transport warm, sub tropical water polewards toward the polar region
s. The westerlies can be particularly strong, especially in the southern hemisphere, where there is less land in the middle latitudes to cause the flow pattern to amplify, which slows the winds down. The strongest westerly winds in the middle latitudes are within a band known as the Roaring Forties
, between 40 and 50 degrees latitude south of the equator. The Westerlies play an important role in carrying the warm, equatorial waters and winds to the western coasts of continents, especially in the southern hemisphere because of its vast oceanic expanse.
s at the north
and south pole
s towards the low-pressure areas within the Westerlies at high latitudes. Unlike the Westerlies, these prevailing winds blow from the east
to the west
, and are often weak and irregular. Because of the low sun angle, cold
air builds up and subsides
at the pole creating surface high-pressure areas, forcing an equatorward outflow of air; that outflow is deflected eastward by the Coriolis effect.
is warmed by the sun more slowly because of water's greater specific heat compared to land. As the temperature of the surface of the land
rises, the land heats the air above it by conduction. The warm air is less dense than the surrounding environment and so it rises. This causes a pressure gradient of about 2 millibars from the ocean to the land. The cooler air above the sea, now with higher sea level pressure, flows inland into the lower pressure, creating a cooler breeze near the coast. When large-scale winds are calm, the strength of the sea breeze is directly proportional to the temperature difference between the land mass and the sea. If an offshore wind of sp=us 8 exists, the sea breeze is not likely to develop.
At night, the land cools off more quickly than the ocean because of differences in their specific heat values. This temperature change causes the daytime sea breeze to dissipate. When the temperature onshore cools below the temperature offshore, the pressure over the water will be lower than that of the land, establishing a land breeze, as long as an onshore wind is not strong enough to oppose it.
Over elevated surfaces, heating of the ground exceeds the heating of the surrounding air at the same altitude above sea level
, creating an associated thermal low over the terrain and enhancing any thermal lows that would have otherwise existed, and changing the wind circulation of the region. In areas where there is rugged topography
that significantly interrupts the environmental wind flow, the wind circulation between mountains and valleys is the most important contributor to the prevailing winds. Hills and valleys substantially distort the airflow by increasing friction between the atmosphere and landmass by acting as a physical block to the flow, deflecting the wind parallel to the range just upstream of the topography, which is known as a barrier jet. This barrier jet can increase the low level wind by 45%. Wind direction also changes because of the contour of the land.
If there is a pass
in the mountain range, winds will rush through the pass with considerable speed because of the Bernoulli principle that describes an inverse relationship between speed and pressure. The airflow can remain turbulent and erratic for some distance downwind into the flatter countryside. These conditions are dangerous to ascending and descending airplanes. Cool winds accelerating through mountain gaps have been given regional names. In Central America
, examples include the Papagayo wind
, the Panama
wind, and the Tehuano wind
. In Europe
, similar winds are known as the Bora
, Tramontane
, and Mistral
. When these winds blow over open waters, they increase mixing of the upper layers of the ocean that elevates cool, nutrient rich waters to the surface, which leads to increased marine life.
In mountainous areas, local distortion of the airflow becomes severe. Jagged terrain combines to produce unpredictable flow patterns and turbulence, such as rotors
, which can be topped by lenticular cloud
s. Strong updrafts, downdrafts and eddies develop as the air flows over hills and down valleys. Orographic precipitation
occurs on the windward side of mountains and is caused by the rising air motion of a large-scale flow of moist air across the mountain ridge, also known as upslope flow, resulting in adiabatic cooling and condensation. In mountainous parts of the world subjected to relatively consistent winds (for example, the trade winds), a more moist climate usually prevails on the windward side of a mountain than on the leeward or downwind side. Moisture is removed by orographic lift, leaving drier air on the descending and generally warming, leeward side where a rain shadow
is observed. Winds that flow over mountains down into lower elevations are known as downslope winds. These winds are warm and dry. In Europe downwind of the Alps
, they are known as foehn. In Poland
, an example is the halny wiatr. In Argentina, the local name for downsloped winds is zonda. In Java, the local name for such winds is koembang. In New Zealand
, they are known as the Nor'west arch
, and are accompanied by the cloud formation they are named after that has inspired artwork over the years. In the Great Plains of the United States, the winds are known as a chinook
. In California, downsloped winds are funneled through mountain passes, which intensify their effect, and examples into Santa Ana
and sundowner
winds. Wind speeds during downslope wind effect can exceed sp=us 160.
of wind-powered generators was 120.8 gigawatts. Although wind produces only about 1.5% of worldwide electricity use, it is growing rapidly, having doubled in the three years between 2005 and 2008. In several countries it has achieved relatively high levels of penetration, accounting for approximately 19% of electricity production in Denmark
, 10% in Spain
and Portugal
, and 7% in Germany
and the Republic of Ireland in 2008. One study indicates that an entirely renewable energy supply based on 70% wind is attainable at today's power prices by linking wind farm
s with an HVDC
supergrid.
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. Wind shear can be broken down into vertical and horizontal components, with horizontal wind shear seen across weather fronts and near the coast, and vertical shear typically near the surface, though also at higher levels in the atmosphere near upper level jets and frontal zones aloft.
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 line
s and cold front
s. It is commonly observed near microburst
s and downburst
s caused by thunderstorm
s, weather fronts, areas of locally higher low level winds referred to as low level jets, near mountain
s, radiation inversions that occur because of clear skies and calm winds, buildings, wind turbine
s, and sailboat
s. Wind shear has a significant effect during take-off and landing of aircraft because of their effects on control of the aircraft, and was a significant cause of aircraft accidents involving large loss of life within the United States
.
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. Strong vertical wind shear within the troposphere also inhibits tropical cyclone
development, but helps to organize individual thunderstorms into living longer life cycles that can then produce severe weather
. 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.
s or as an expression of the supernatural
in many cultures. Vayu
is the Hindu God of Wind. The Greek wind gods include Boreas, Notus, Eurus, and Zephyrus. 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
. Venti are the Roman gods of the winds. 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. In Norse mythology
, Njord
is the god of the wind. 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. 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.
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. 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, or the favorable winds that enabled William of Orange
to invade England in 1688. 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." 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."
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 sail
s that use the wind to power the ship. Ocean journeys by sailing ship can take many months, and a common hazard is becoming becalmed because of lack of wind, or being blown off course by severe storm
s or winds that do not allow progress in the desired direction. A severe storm could lead to shipwreck
, and the loss of all hands. 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
.
For aerodynamic aircraft
which operate relative to the air, winds affect groundspeed, and in the case of lighter-than-air vehicles, wind may play a significant or solitary role in their movement and ground track. The velocity
of surface wind is generally the primary factor governing the direction of flight operations at an airport, and airfield runways are aligned to account for the common wind direction(s) of the local area. While taking off with a tailwind
may be necessary under certain circumstances, a headwind is generally desirable. A tailwind increases takeoff distance required and decreases the climb gradient.
Historically, the ancient Sinhalese of Anuradhapura
and in other cities around Sri Lanka
used the monsoon winds to power furnaces as early as 300 BCE
. The furnaces were constructed on the path of the monsoon winds to exploit the wind power, to bring the temperatures inside up to sp=us 1200. An early historical reference to a rudimentary windmill
was used to power an organ
in the first century CE. The first practical windmill
s were later built in Sistan
, Afghanistan
, from the 7th century CE. These were vertical-axle windmills, which had long vertical driveshaft
s with rectangle shaped blades. Made of six to twelve sails
covered in reed matting
or cloth material, these windmills were used to grind corn and draw up water, and were used in the gristmill
ing and sugarcane industries. Horizontal-axle windmills were later used extensively in Northwestern Europe to grind flour beginning in the 1180s, and many Dutch windmills still exist. High altitude wind power is the focus of over 30 companies worldwide using tethered technology rather than ground-hugging compressive-towers. Oil is being saved by using wind for powering cargo ships by use of the mechanical energy converted from the wind's kinetic energy using very large kites.
Wind figures prominently in several popular sports, including recreational hang gliding
, hot air ballooning
, kite flying
, snowkiting
, kite landboarding
, kite surfing, paragliding
, sailing
, and windsurfing
. In gliding, wind gradients just above the surface affect the takeoff and landing phases of flight of a glider
. Wind gradient can have a noticeable effect on ground launches, also known as winch launches or wire launches. If the wind gradient is significant or sudden, or both, and the pilot maintains the same pitch attitude, the indicated airspeed will increase, possibly exceeding the maximum ground launch tow speed. The pilot must adjust the airspeed to deal with the effect of the gradient. When landing, wind shear is also a hazard, particularly when the winds are strong. As the glider descends through the wind gradient on final approach to landing, airspeed decreases while sink rate increases, and there is insufficient time to accelerate prior to ground contact. The pilot must anticipate the wind gradient and use a higher approach speed to compensate for it.
Erosion can be the result of material movement by the wind. There are two main effects. First, wind causes small particles to be lifted and therefore moved to another region. This is called deflation. Second, these suspended particles may impact on solid objects causing erosion by abrasion (ecological succession). Wind erosion generally occurs in areas with little or no vegetation, often in areas where there is insufficient rainfall to support vegetation. An example is the formation of sand dunes, on a beach or in a desert. Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, silt
y, pale yellow or buff, windblown (Aeolian) sediment
. It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces. Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world. Loess deposits are geologically unstable by nature, and will erode very readily. Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess.
into southeastern North America. When dust from the Sahara
moving around the southern periphery of the ridge within the belt of trade winds moves over land, rainfall is suppressed and the sky changes from a blue to a white appearance, which leads to an increase in red sunsets. Its presence negatively impacts air quality by adding to the count of airborne particulates. Over 50% of the African dust that reaches the United States affects Florida. Since 1970, dust outbreaks have worsened because of periods of drought in Africa. There is a large variability in the dust transport to the Caribbean and Florida from year to year. Dust events have been linked to a decline in the health of coral reef
s across the Caribbean and Florida, primarily since the 1970s. Similar dust plumes originate in the Gobi desert
, which combined with pollutants, spread large distances downwind, or eastward, into North America.
There are local names for winds associated with sand and dust storms. The Calima carries dust on southeast winds into the Canary islands
. The Harmattan
carries dust during the winter into the Gulf of Guinea
. The Sirocco
brings dust from north Africa into southern Europe because of the movement of extratropical cyclones through the Mediterranean Sea
. Spring storm systems moving across the eastern Mediterranean Sea cause dust to carry across Egypt
and the Arabian peninsula
, which are locally known as Khamsin
. The Shamal
is caused by cold fronts lifting dust into the atmosphere for days at a time across the Persian Gulf
states.
Wind dispersal of seeds, or anemochory, is one of the more primitive means of dispersal. Wind dispersal can take on one of two primary forms: seeds can float on the breeze or alternatively, they can flutter to the ground. The classic examples of these dispersal mechanisms include dandelions (Taraxacum
spp., Asteraceae
), which have a feathery pappus
attached to their seeds and can be dispersed long distances, and maple
s (Acer (genus) spp., Sapindaceae
), which have winged seeds and flutter to the ground. An important constraint on wind dispersal is the need for abundant seed production to maximize the likelihood of a seed landing in a site suitable for germination
. There are also strong evolutionary constraints on this dispersal mechanism. For instance, species in the Asteraceae on island
s tended to have reduced dispersal capabilities (i.e., larger seed mass and smaller pappus) relative to the same species on the mainland. Reliance upon wind dispersal is common among many weed
y or ruderal species. Unusual mechanisms of wind dispersal include tumbleweed
s. A related process to anemochory is anemophily
, which is the process where pollen is distributed by wind. Large families of plants are pollinated in this manner, which is favored when individuals of the dominant plant species are spaced closely together.
Wind also limits tree growth. On coast
s and isolated mountains, the tree line is often much lower than in corresponding altitudes inland and in larger, more complex mountain systems, because strong winds reduce tree growth. High winds scour away thin soil
s through erosion, as well as damage limbs and twigs. When high winds knock down or uproot trees, the process is known as windthrow
. This is most likely on windward slopes of mountains, with severe cases generally occurring to tree stand
s that are 75 years or older. Plant varieties near the coast, such as the Sitka spruce
and sea grape
, are pruned
back by wind and salt spray near the coastline.
Wind can also cause plants damage through sand abrasion. Strong winds will pick up loose sand and topsoil
and hurl it through the air at speeds ranging from 25–40 miles per hour. Such windblown sand causes extensive damage to plant seedlings because it ruptures plant cells, making them vulnerable to evaporation and drought. Using a mechanical sandblaster in a laboratory setting, scientists affiliated with the Agricultural Research Service
studied the effects of windblown sand abrasion on cotton seedlings. The study showed that the seedlings responded to the damage created by the windblown sand abrasion by shifting energy from stem and root growth to the growth and repair of the damaged stems. After a period of four weeks the growth of the seedling once again became uniform throughout the plant, as it was before the windblown sand abrasion occurred.
and sheep are prone to wind chill
caused by a combination of wind and cold temperatures, when winds exceed sp=us 40, rendering their hair and wool coverings ineffective. Although penguin
s use both a layer of fat
and feather
s to help guard against coldness in both water and air, their flippers
and feet are less immune to the cold. In the coldest climates such as Antarctica, emperor penguin
s use huddling
behavior to survive the wind and cold, continuously alternating the members on the outside of the assembled group, which reduces heat loss by 50%. Flying insect
s, a subset of arthropods, are swept along by the prevailing winds, while birds follow their own course taking advantage of wind conditions, in order to either fly or glide. As such, fine line patterns within weather radar
imagery, associated with converging winds, are dominated by insect returns. Bird migration, which tends to occur overnight within the lowest sp=us 7000 of the Earth's atmosphere
, contaminates wind profiles gathered by weather radar, particularly the WSR-88D, by increasing the environmental wind returns by sp=us 15 to sp=us 30.
Pika
s use a wall of pebbles to store dry plants and grasses for the winter in order to protect the food from being blown away. Cockroach
es use slight winds that precede the attacks of potential predators, such as toad
s, to survive their encounters. Their cerci
are very sensitive to the wind, and help them survive half of their attacks. Elk
has a keen sense of smell that can detect potential upwind predators at a distance of sp=us 0.5. Increases in wind above sp=us 15 signals glaucous gull
s to increase their foraging and aerial attacks on thick-billed murres.
High winds are known to cause damage, depending upon their strength. Infrequent wind gusts can cause poorly designed suspension bridge
s 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. Wind speeds as low as sp=us 23 can lead to power outages due to tree branches disrupting the flow of energy through power lines. 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. 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. Once winds exceed sp=us 135, homes completely collapse, and significant damage is done to larger buildings. Total destruction to man-made structures occurs when winds reach sp=us 175. 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 tornado
es, and vice versa.
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 of 372 km/h (231 mph) set on Mount Washington (New Hampshire)
on the afternoon of 12 April 1934. The most powerful gusts of wind on Earth were created by nuclear detonations. The blast wave is similar to a strong wind gust over the ground. The largest nuclear explosion (50–58 megatons at an altitude of about 13,000 ft) generated a 20 bar blast pressure at ground zero, which is similar to a wind gust of 3,100 miles per hour.
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. 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. 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.
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. Such a process over geologic time causes water-rich planets such as the Earth to evolve into planets like Venus
. Additionally, planets with hotter lower atmospheres could accelerate the loss rate of hydrogen.
—a plasma
—ejected from the upper atmosphere
of the sun at a rate of sp=us 400. It consists mostly of electrons and proton
s 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
, 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. Planets require large magnetic fields in order to reduce the ionization of their upper atmosphere by the solar wind. Other phenomena include geomagnetic storm
s that can knock out power grids on Earth, the aurorae such as the Northern Lights
, and the plasma tails of comet
s that always point away from the sun.
are exposed to sunlight after their winter
, the frozen CO2 sublimes
, creating significant winds that sweep off the poles as fast as sp=us 400, which subsequently transports large amounts of dust and water vapor over its landscape
. Other Martian winds have resulted in cleaning event
s and dust devils. On Jupiter
, wind speeds of sp=us 100 are common in zonal jet streams. Saturn's winds are among the solar system's fastest. Cassini–Huygens data indicated peak easterly winds of sp=us 375. On Uranus
, northern hemisphere wind speeds reach as high as sp=us 240 near 50 degrees north latitude. At the cloud tops of Neptune
, prevailing winds range in speed from sp=us 400 along the equator to sp=us 250 at the poles. At 70° S latitude on Neptune, a high-speed jet stream travels at a speed of sp=us 300.
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
of gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
es on a large scale. On Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, wind consists of the bulk movement of air. In outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
, solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
is the movement of gases or charged particles from the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
through space, while planetary wind is the outgassing
Outgassing
Outgassing is the release of a gas that was dissolved, trapped, frozen or absorbed in some material. As an example, research has shown how the concentration of carbon dioxide in the Earth's atmosphere has sometimes been linked to ocean outgassing...
of light chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
s from a planet's atmosphere into space. Winds are commonly classified by their spatial scale
Scale (spatial)
Spatial scale provides a "shorthand" form for discussing relative lengths, areas, distances and sizes. A microclimate, for instance, is one which might occur in a mountain valley or near a lakeshore, whereas a megatrend is one which involves the whole planet....
, their speed
Speed
In kinematics, the speed of an object is the magnitude of its velocity ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as...
, 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
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
occur on Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
and Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
.
In meteorology
Meteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...
, winds are often referred to according to their strength, and the direction from which the wind is blowing. Short bursts of high speed wind are termed gusts. Strong winds of intermediate duration (around one minute) are termed squall
Squall
A squall is a sudden, sharp increase in wind speed which is usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. Squalls refer to an increase in the sustained winds over a short time interval, as there may be higher gusts during a squall event...
s. Long-duration winds have various names associated with their average strength, such as breeze, gale
Gale
A gale is a very strong wind. There are conflicting definitions of how strong a wind must be to be considered a gale. The U.S. government's National Weather Service defines a gale as 34–47 knots of sustained surface winds. Forecasters typically issue gale warnings when winds of this strength are...
, storm, hurricane
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
, and typhoon. Wind occurs on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hours, to global
World
World is a common name for the whole of human civilization, specifically human experience, history, or the human condition in general, worldwide, i.e. anywhere on Earth....
winds resulting from the difference in absorption of solar energy between the climate zones on Earth. The two main causes of large-scale atmospheric circulation
Atmospheric circulation
Atmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....
are the differential heating between the equator and the poles, and the rotation of the planet (Coriolis effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...
). Within the tropics, thermal low
Thermal low
Thermal lows, or heat lows, are non-frontal low-pressure areas that occur over the continents in the subtropics such as near the Sonoran Desert, the Mexican plateau, Sahara, South America over northwest Argentina, Australia, the Iberian peninsula, and Tibetan plateau during the warm season as the...
circulations over terrain and high plateaus can drive monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
circulations. In coastal areas the sea breeze
Sea breeze
A sea-breeze is a wind from the sea that develops over land near coasts. It is formed by increasing temperature differences between the land and water; these create a pressure minimum over the land due to its relative warmth, and forces higher pressure, cooler air from the sea to move inland...
/land breeze cycle can define local winds; in areas that have variable terrain, mountain and valley breezes can dominate local winds.
In human
Human
Humans are the only living species in the Homo genus...
civilization
Civilization
Civilization is a sometimes controversial term that has been used in several related ways. Primarily, the term has been used to refer to the material and instrumental side of human cultures that are complex in terms of technology, science, and division of labor. Such civilizations are generally...
, wind has inspired mythology
Mythology
The term mythology can refer either to the study of myths, or to a body or collection of myths. As examples, comparative mythology is the study of connections between myths from different cultures, whereas Greek mythology is the body of myths from ancient Greece...
, influenced the events of history
History
History is the discovery, collection, organization, and presentation of information about past events. History can also mean the period of time after writing was invented. Scholars who write about history are called historians...
, expanded the range of transport
Transport
Transport or transportation is the movement of people, cattle, animals and goods from one location to another. Modes of transport include air, rail, road, water, cable, pipeline, and space. The field can be divided into infrastructure, vehicles, and operations...
and warfare, and provided a power source
Wind power
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....
for mechanical work
Mechanical work
In physics, work is a scalar quantity that can be described as the product of a force times the distance through which it acts, and it is called the work of the force. Only the component of a force in the direction of the movement of its point of application does work...
, electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
and recreation
Recreation
Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasure and are considered to be "fun"...
. Wind powers the voyages of sailing ship
Sailing ship
The term sailing ship is now used to refer to any large wind-powered vessel. In technical terms, a ship was a sailing vessel with a specific rig of at least three masts, square rigged on all of them, making the sailing adjective redundant. In popular usage "ship" became associated with all large...
s across Earth's oceans. Hot air balloon
Hot air balloon
The hot air balloon is the oldest successful human-carrying flight technology. It is in a class of aircraft known as balloon aircraft. On November 21, 1783, in Paris, France, the first untethered manned flight was made by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes in a hot air...
s use the wind to take short trips, and powered flight uses it to increase lift and reduce fuel consumption. Areas of wind shear
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 atmosphere...
caused by various weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
phenomena can lead to dangerous situations for aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
. When winds become strong, trees and man-made structures are damaged or destroyed.
Winds can shape landforms, via a variety of aeolian processes such as the formation of fertile soils, such as loess
Loess
Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometre size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate...
, and by erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
. Dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
from large desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
s can be moved great distances from its source region by the prevailing winds
Prevailing winds
Prevailing winds are winds that blow predominantly from a single general direction over a particular point on Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant winds...
; winds that are accelerated by rough topography and associated with dust outbreaks have been assigned regional names in various parts of the world because of their significant effects on those regions. Wind affects the spread of wildfire
Wildfire
A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, desert fire, grass fire, hill fire, squirrel fire, vegetation fire, veldfire, and wilkjjofire may be used to describe the same...
s. Winds disperse seeds from various plants, enabling the survival and dispersal of those plant species, as well as flying insect populations. When combined with cold temperatures, wind has a negative impact on livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
. Wind affects animals' food stores, as well as their hunting and defensive strategies.
Cause
Wind is caused by differences in pressure. When a difference in pressurePressure gradient force
The pressure gradient force is not actually a 'force' but the acceleration of air due to pressure difference . It is usually responsible for accelerating a parcel of air from a high atmospheric pressure region to a low pressure region, resulting in wind...
exists, the air is accelerated from higher to lower pressure. On a rotating planet, the air will be deflected by the Coriolis effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...
, except exactly on the equator. Globally, the two major driving factors of large-scale winds (the atmospheric circulation
Atmospheric circulation
Atmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....
) are the differential heating between the equator and the poles (difference in absorption of solar energy leading to buoyancy forces) and the rotation of the planet
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...
. Outside the tropics and aloft from frictional effects of the surface, the large-scale winds tend to approach geostrophic balance. Near the Earth's surface, friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
causes the wind to be slower than it would be otherwise. Surface friction also causes winds to blow more inward into low pressure areas.
Winds defined by an equilibrium of physical forces are used in the decomposition and analysis of wind profiles. They are useful for simplifying the atmospheric equations of motion and for making qualitative arguments about the horizontal and vertical distribution of winds. The geostrophic wind
Geostrophic wind
The geostrophic wind is the theoretical wind that would result from an exact balance between the Coriolis effect and the pressure gradient force. This condition is called geostrophic balance. The geostrophic wind is directed parallel to isobars . This balance seldom holds exactly in nature...
component is the result of the balance between Coriolis force and pressure gradient force. It flows parallel to isobars and approximates the flow above the atmospheric boundary layer in the midlatitudes. The thermal wind
Thermal wind
The thermal wind is a vertical shear in the geostrophic wind caused by a horizontal temperature gradient. Its name is a misnomer, because the thermal wind is not actually a wind, but rather a wind shear.- Physical Intuition :...
is the difference in the geostrophic wind between two levels in the atmosphere. It exists only in an atmosphere with horizontal temperature gradient
Temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degrees per unit length...
s. The ageostrophic wind
Ageostrophy
Ageostrophy is the real condition that works against geostrophic wind or geostrophic currents in the ocean, and works against an exact balance between the Coriolis force and the pressure gradient force...
component is the difference between actual and geostrophic wind, which is responsible for air "filling up" cyclones over time. The gradient wind is similar to the geostrophic wind but also includes centrifugal force
Centrifugal force
Centrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
(or centripetal acceleration).
Measurement
Wind directionWind direction
Wind direction is reported by the direction from which it originates. For example, a northerly wind blows from the north to the south. Wind direction is usually reported in cardinal directions or in azimuth degrees...
is reported by the direction from which it originates. For example, a northerly wind blows from the north to the south. Weather vane
Weather vane
A weather vane is an instrument for showing the direction of the wind. They are typically used as an architectural ornament to the highest point of a building....
s pivot to indicate the direction of the wind. At airports, windsock
Windsock
A windsock is a conical textile tube designed to indicate wind direction and relative wind speed. Windsocks typically are used at airports and at chemical plants where there is risk of gaseous leakage...
s are primarily used to indicate wind direction, but can also be used to estimate wind speed by its angle of hang. Wind speed is measured by anemometer
Anemometer
An anemometer is a device for measuring wind speed, and is a common weather station instrument. The term is derived from the Greek word anemos, meaning wind, and is used to describe any airspeed measurement instrument used in meteorology or aerodynamics...
s, most commonly using rotating cups or propellers. When a high measurement frequency is needed (such as in research applications), wind can be measured by the propagation speed of ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
signals or by the effect of ventilation on the resistance of a heated wire. Another type of anemometer uses pitot tube
Pitot tube
A pitot tube is a pressure measurement instrument used to measure fluid flow velocity. The pitot tube was invented by the French engineer Henri Pitot Ulo in the early 18th century and was modified to its modern form in the mid-19th century by French scientist Henry Darcy...
s that take advantage of the pressure differential between an inner tube and an outer tube that is exposed to the wind to determine the dynamic pressure, which is then used to compute the wind speed.
Sustained wind speeds are reported globally at a sp=us 10 height and are averaged over a 10 minute time frame. The United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
reports winds over a 1 minute average for tropical cyclones, and a 2 minute average within weather observations. India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
typically reports winds over a 3 minute average. Knowing the wind sampling average is important, as the value of a one-minute sustained wind is typically 14% greater than a ten-minute sustained wind. A short burst of high speed wind is termed a wind gust, one technical definition of a wind gust is: the maxima that exceed the lowest wind speed measured during a ten minute time interval by sp=us 10. A squall
Squall
A squall is a sudden, sharp increase in wind speed which is usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. Squalls refer to an increase in the sustained winds over a short time interval, as there may be higher gusts during a squall event...
is a doubling of the wind speed above a certain threshold, which lasts for a minute or more.
To determine winds aloft, rawinsondes determine wind speed by GPS, radio navigation
LORAN
LORAN is a terrestrial radio navigation system using low frequency radio transmitters in multiple deployment to determine the location and speed of the receiver....
, or radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
tracking of the probe. Alternatively, movement of the parent weather balloon
Weather balloon
A weather or sounding balloon is a balloon which carries instruments aloft to send back information on atmospheric pressure, temperature, humidity and wind speed by means of a small, expendable measuring device called a radiosonde...
position can be tracked from the ground visually using theodolite
Theodolite
A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...
s. Remote sensing
Remote sensing
Remote sensing is the acquisition of information about an object or phenomenon, without making physical contact with the object. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth by means of propagated signals Remote sensing...
techniques for wind include SODAR
SODAR
SODAR , also written as sodar, is a meteorological instrument used as a wind profiler to measure the scattering of sound waves by atmospheric turbulence...
, Doppler
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
LIDAR
LIDAR
LIDAR is an optical remote sensing technology that can measure the distance to, or other properties of a target by illuminating the target with light, often using pulses from a laser...
s and RADAR
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
s, which can measure the Doppler shift of electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
scattered or reflected off suspended aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
s or molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s, and radiometer
Radiometer
A radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....
s and radars can be used to measure the surface roughness of the ocean from space or airplanes. Ocean roughness can be used to estimate wind velocity close to the sea surface over oceans. Geostationary satellite imagery can be used to estimate the winds throughout the atmosphere based upon how far clouds move from one image to the next. Wind Engineering
Wind engineering
Wind engineering analyzes effects of wind in the natural and the built environment and studies the possible damage, inconvenience or benefits which may result from wind. In the field of structural engineering it includes strong winds, which may cause discomfort, as well as extreme winds, such as in...
describes the study of the effects of the wind on the built environment, including buildings, bridges and other man-made objects.
Wind force scale
Historically, the Beaufort wind force scaleBeaufort scale
The Beaufort Scale is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort Wind Force Scale.-History:...
provides an empirical description of wind speed based on observed sea conditions. Originally it was a 13-level scale, but during the 1940s, the scale was expanded to 17 levels. There are general terms that differentiate winds of different average speeds such as a breeze, a gale, a storm, tornado, or a hurricane. Within the Beaufort scale, gale-force winds lie between sp=us 28 and sp=us 55 with preceding adjectives such as moderate, fresh, strong, and whole used to differentiate the wind's strength within the gale category. A storm has winds of sp=us 56 to sp=us 63. The terminology for tropical cyclones differs from one region to another globally. Most ocean basins use the average wind speed to determine the tropical cyclone's category. Below is a summary of the classifications used by Regional Specialized Meteorological Centers
Regional Specialized Meteorological Centre
A Regional Specialized Meteorological Centre is responsible for the distribution of information, advisories, and warnings regarding the specific program they have a part of, agreed by consensus at the World Meteorological Organization as part of the World Weather Watch.-Tropical...
worldwide:
| General wind classifications | Tropical cyclone classifications (all winds are 10-minute averages) | |||||||
|---|---|---|---|---|---|---|---|---|
| 0 | <1 | Calm | Low Pressure Area | Tropical disturbance | Tropical low Tropical Depression |
Tropical depression | Tropical depression | Tropical depression |
| 1 | 1–3 | Light air | ||||||
| 2 | 4–6 | Light breeze | ||||||
| 3 | 7–10 | Gentle breeze | ||||||
| 4 | 11–16 | Moderate breeze | ||||||
| 5 | 17–21 | Fresh breeze | Depression | |||||
| 6 | 22–27 | Strong breeze | ||||||
| 7 | 28–29 | Moderate gale | Deep depression | Tropical depression | ||||
| 30–33 | ||||||||
| 8 | 34–40 | Fresh gale | Cyclonic storm | Moderate tropical storm | Tropical cyclone (1) | Tropical storm | Tropical storm | Tropical storm |
| 9 | 41–47 | Strong gale | ||||||
| 10 | 48–55 | Whole gale | Severe cyclonic storm | Severe tropical storm | Tropical cyclone (2) | Severe tropical storm | ||
| 11 | 56–63 | Storm | ||||||
| 12 | 64–72 | Hurricane | Very severe cyclonic storm | Tropical cyclone | Severe tropical cyclone (3) | Typhoon | Typhoon | Hurricane (1) |
| 13 | 73–85 | Hurricane (2) | ||||||
| 14 | 86–89 | Severe tropical cyclone (4) | Major hurricane (3) | |||||
| 15 | 90–99 | Intense tropical cyclone | ||||||
| 16 | 100–106 | Major hurricane (4) | ||||||
| 17 | 107–114 | Severe tropical cyclone (5) | ||||||
| 115–119 | Very intense tropical cyclone | Super typhoon | ||||||
| >120 | Super cyclonic storm | Major hurricane (5) | ||||||
Fujita scale
The Enhanced Fujita ScaleEnhanced Fujita Scale
The Enhanced Fujita Scale rates the strength of tornadoes in the United States based on the damage they cause.Implemented in place of the Fujita scale introduced in 1971 by Ted Fujita, it began operational use on February 1, 2007. The scale has the same basic design as the original Fujita scale:...
(EF Scale) rates the strength of tornadoes in the United States based on the damage they cause. Below is that scale.
| Scale | Wind speed | Relative frequency | Potential damage | ||
| mph | km/h | ||||
| EF0 | 65–85 | 105–137 | 53.5% | Minor or no damage. Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over. Confirmed tornadoes with no reported damage (i.e., those that remain in open fields) are always rated EF0. |
|
| EF1 | 86–110 | 138–178 | 31.6% | Moderate damage. Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken. |
 |
| EF2 | 111–135 | 179–218 | 10.7% | Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground. |
|
| EF3 | 136–165 | 219–266 | 3.4% | Severe damage. Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations are badly damaged. |
 |
| EF4 | 166–200 | 267–322 | 0.7% | Extreme damage. Well-constructed and whole frame houses completely leveled; cars and other large objects thrown and small missiles generated. |
 |
| EF5 | >200 | >322 | <0.1% | Total Destruction. Strong-framed, well-built houses leveled off and foundations swept away; steel-reinforced concrete structures are critically damaged; tall buildings collapse or have severe structural deformations. |
|
Station model
Station model
A station model is a symbolic illustration showing the weather occurring at a given reporting station. Meteorologists created the station model to plot a number of weather elements in a small space on weather maps...
plotted on surface weather map
Weather map
A weather map displays various meteorological features across a particular area at a particular point in time. Such maps have been in use since the mid-19th century and are used for research and weather forecasting purposes. Maps using isotherms show temperature gradients, which can help locate...
s uses a wind barb to show both wind direction
Wind direction
Wind direction is reported by the direction from which it originates. For example, a northerly wind blows from the north to the south. Wind direction is usually reported in cardinal directions or in azimuth degrees...
and speed. The wind barb shows the speed using "flags" on the end.
- Each half of a flag depicts sp=us 5 of wind.
- Each full flag depicts sp=us 10 of wind.
- Each pennantPennant (commissioning)The commissioning pennant is a pennant flown from the masthead of a warship. The history of flying a commissioning pennant dates back to the days of chivalry with their trail pendants being flown from the mastheads of ships they commanded...
(filled triangle) depicts sp=us 50 of wind.
Winds are depicted as blowing from the direction the barb is facing. Therefore, a northeast wind will be depicted with a line extending from the cloud circle to the northeast, with flags indicating wind speed on the northeast end of this line. Once plotted on a map, an analysis of isotachs (lines of equal wind speeds) can be accomplished. Isotachs are particularly useful in diagnosing the location of the jet stream on upper level constant pressure charts, and are usually located at or above the 300 hPa level.
Wind energy
Wind energy is the kinetic energyKinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
of the air in motion. Total wind energy flowing through an imaginary area A during the time t is:
- E = A·v·t·ρ·½ v2,
where v is the wind velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
and ρ is the air density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
. The formula presented is structured in two parts: (A·v·t) is the volume of air passing through A, which is considered perpendicular to the wind velocity; (ρ·½ v2) is the kinetic energy of the moving air per unit volume.
Total wind power is:
- P = E/t = A·ρ·½ v3
Wind power is thus proportional to the third power of the wind velocity.
Theoretical power captured by a wind turbine
Total wind power could be captured only if the wind velocity is reduced to zero. In a realistic wind turbine this is impossible, as the captured air must also leave the turbine. A relation between the input and output wind velocity must be considered. Using the concept of stream tube, the maximal achievable extraction of wind power by a wind turbine is 59% of the total theoretical wind power (see: Betz' lawBetz' law
Betz's law is a theory about the maximum possible energy to be derived from a "hydraulic wind engine", or a wind turbine such as the Éolienne Bollée , the Eclipse Windmill , and the Aermotor...
).
Practical wind turbine power
Further insufficiencies, such as rotor blade frictionFriction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
and drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
, gearbox losses, generator and converter losses, reduce the power delivered by a wind turbine. The basic relation that the turbine power is (approximately) proportional to the third power of velocity remains.
Global climatology
Mid-latitudes
The mid-latitudes are the areas on earth between the tropics and the polar regions, approximately 30° to 60° north or south of the equator. The mid-latitudes are an important region in meteorology, having weather patterns which are generally distinct from weather in the tropics and the polar...
of the earth, to the north of the subtropical ridge
Subtropical ridge
The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...
, while easterlies again dominate the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
.
Directly under the subtropical ridge
Subtropical ridge
The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...
are the doldrums, or horse latitudes, where winds are lighter. Many of the Earth's deserts lie near the average latitude of the subtropical ridge, where descent reduces the relative humidity
Relative humidity
Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
of the air mass. The strongest winds are in the mid-latitudes where cold Arctic air meets warm air from the tropics.
Tropics
The trade winds (also called trades) are the prevailing pattern of easterlyEasterlies
The easterlies commonly refer to the low latitude trade winds near the equator . These winds carry tropical waves and cyclones from east to west in lower latitudes...
surface winds found in the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
towards the Earth's equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
. The trade winds blow predominantly from the northeast in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
and from the southeast in the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
. The trade winds act as the steering flow for tropical cyclones that form over world's oceans. Trade winds also steer African dust westward across the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
into the Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
, as well as portions of southeast North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
A monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
is a seasonal prevailing wind that lasts for several months within tropical regions. The term was first used in English in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Bangladesh
Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...
, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, and neighboring countries to refer to the big seasonal winds blowing from the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and Arabian Sea
Arabian Sea
The Arabian Sea is a region of the Indian Ocean bounded on the east by India, on the north by Pakistan and Iran, on the west by the Arabian Peninsula, on the south, approximately, by a line between Cape Guardafui in northeastern Somalia and Kanyakumari in India...
in the southwest bringing heavy rainfall to the area. Its poleward progression is accelerated by the development off a heat low over the Asian, African, and North American continents during May through July, and over Australia in December.
Westerlies and their impact
The Westerlies or the Prevailing Westerlies are the prevailing winds
Prevailing winds
Prevailing winds are winds that blow predominantly from a single general direction over a particular point on Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant winds...
in the middle latitudes
Middle latitudes
The middle latitudes are between 23°26'22" North and 66°33'39" North, and between 23°26'22" South and 66°33'39" South latitude, or, the Earth's temperate zones between the tropics and the Arctic and Antarctic. The prevailing winds in the middle latitudes are often very strong...
between 35 and 65 degrees latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
. These prevailing winds blow from the west
West
West is a noun, adjective, or adverb indicating direction or geography.West is one of the four cardinal directions or compass points. It is the opposite of east and is perpendicular to north and south.By convention, the left side of a map is west....
to the east
East
East is a noun, adjective, or adverb indicating direction or geography.East is one of the four cardinal directions or compass points. It is the opposite of west and is perpendicular to north and south.By convention, the right side of a map is east....
to the north of the subtropical ridge, and steer extratropical cyclones in this general manner. The winds are predominantly from the southwest in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
and from the northwest in the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
. They are strongest in the winter when the pressure is lower over the poles, and weakest during the summer and when pressures are higher over the poles.
Together with the trade wind
Trade wind
The trade winds are the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth's atmosphere, in the lower section of the troposphere near the Earth's equator...
s, the westerlies enabled a round-trip trade route for sailing ships crossing the Atlantic and Pacific Oceans, as the westerlies lead to the development of strong ocean currents on the western sides of oceans in both hemispheres through the process of western intensification. These western ocean currents transport warm, sub tropical water polewards toward the polar region
Polar region
Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...
s. The westerlies can be particularly strong, especially in the southern hemisphere, where there is less land in the middle latitudes to cause the flow pattern to amplify, which slows the winds down. The strongest westerly winds in the middle latitudes are within a band known as the Roaring Forties
Roaring Forties
The Roaring Forties is the name given to strong westerly winds found in the Southern Hemisphere, generally between the latitudes of 40 and 49 degrees. Air displaced from the Equator towards the South Pole, which travels close to the surface between the latitudes of 30 and 60 degrees south, combines...
, between 40 and 50 degrees latitude south of the equator. The Westerlies play an important role in carrying the warm, equatorial waters and winds to the western coasts of continents, especially in the southern hemisphere because of its vast oceanic expanse.
Polar easterlies
The polar easterlies, also known as Polar Hadley cells, are dry, cold prevailing winds that blow from the high-pressure areas of the polar highPolar high
The polar highs are areas of high atmospheric pressure around the north and south poles, south polar high being the stronger one because land gains and loses heat more effectively than sea...
s at the north
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...
and south pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...
s towards the low-pressure areas within the Westerlies at high latitudes. Unlike the Westerlies, these prevailing winds blow from the east
East
East is a noun, adjective, or adverb indicating direction or geography.East is one of the four cardinal directions or compass points. It is the opposite of west and is perpendicular to north and south.By convention, the right side of a map is east....
to the west
West
West is a noun, adjective, or adverb indicating direction or geography.West is one of the four cardinal directions or compass points. It is the opposite of east and is perpendicular to north and south.By convention, the left side of a map is west....
, and are often weak and irregular. Because of the low sun angle, cold
Cold
Cold describes the condition of low temperature.Cold may also refer to:*Common cold, a contagious viral infectious disease of the upper respiratory system*Chronic obstructive pulmonary disease...
air builds up and subsides
Subsidence (atmosphere)
Subsidence in the Earth's atmosphere is most commonly caused by low temperatures: as air cools, it becomes denser and moves towards the ground, just as warm air becomes less dense and moves upwards...
at the pole creating surface high-pressure areas, forcing an equatorward outflow of air; that outflow is deflected eastward by the Coriolis effect.
Local considerations
Sea and land breezes
In coastal regions, sea breezes and land breezes can be important factors in a location's prevailing winds. The seaOcean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
is warmed by the sun more slowly because of water's greater specific heat compared to land. As the temperature of the surface of the land
Landform
A landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...
rises, the land heats the air above it by conduction. The warm air is less dense than the surrounding environment and so it rises. This causes a pressure gradient of about 2 millibars from the ocean to the land. The cooler air above the sea, now with higher sea level pressure, flows inland into the lower pressure, creating a cooler breeze near the coast. When large-scale winds are calm, the strength of the sea breeze is directly proportional to the temperature difference between the land mass and the sea. If an offshore wind of sp=us 8 exists, the sea breeze is not likely to develop.
At night, the land cools off more quickly than the ocean because of differences in their specific heat values. This temperature change causes the daytime sea breeze to dissipate. When the temperature onshore cools below the temperature offshore, the pressure over the water will be lower than that of the land, establishing a land breeze, as long as an onshore wind is not strong enough to oppose it.
Near mountains
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, creating an associated thermal low over the terrain and enhancing any thermal lows that would have otherwise existed, and changing the wind circulation of the region. In areas where there is rugged topography
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
that significantly interrupts the environmental wind flow, the wind circulation between mountains and valleys is the most important contributor to the prevailing winds. Hills and valleys substantially distort the airflow by increasing friction between the atmosphere and landmass by acting as a physical block to the flow, deflecting the wind parallel to the range just upstream of the topography, which is known as a barrier jet. This barrier jet can increase the low level wind by 45%. Wind direction also changes because of the contour of the land.
If there is a pass
Mountain pass
A mountain pass is a route through a mountain range or over a ridge. If following the lowest possible route, a pass is locally the highest point on that route...
in the mountain range, winds will rush through the pass with considerable speed because of the Bernoulli principle that describes an inverse relationship between speed and pressure. The airflow can remain turbulent and erratic for some distance downwind into the flatter countryside. These conditions are dangerous to ascending and descending airplanes. Cool winds accelerating through mountain gaps have been given regional names. In Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
, examples include the Papagayo wind
Papagayo wind
The Papagayo wind is a north to northeasterly wind which periodically blows through the gap in the mountain ranges of Central America in which Lake Nicaragua is located. It is named for the Gulf of Papagayo on the Pacific coast in this region. The wind is stronger than the trade winds which...
, the Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
wind, and the Tehuano wind
Tehuano wind
The Tehuano wind is a north to northeasterly wind which periodically blows across the Isthmus of Tehuantepec in southern Mexico. The wind is stronger than the trade winds which normally blow here. It is notable for causing a pronounced increase in upwelling of cooler, nutrient-rich waters in the...
. In Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, similar winds are known as the Bora
Bora (wind)
Bora or Bura is a northern to north-eastern katabatic wind in the Adriatic, Bosnia and Herzegovina, Croatia, Montenegro, Italy, Greece, Slovenia, and Turkey....
, Tramontane
Tramontane
Tramontane is a classical name for a northern wind. The exact form of the name and precise direction varies from country to country. The word came to English from Italian tramontana, which developed from Latin trānsmontānus , "beyond the mountains/across the mountains", referring to the alps in...
, and Mistral
Mistral (wind)
The mistral is a strong, cold and usually dry regional wind in France, coming from the north or northwest, which accelerates when it passes through the valleys of the Rhone and the Durance Rivers to the coast of the Mediterranean around the Camargue region. It affects the northeast of the plain...
. When these winds blow over open waters, they increase mixing of the upper layers of the ocean that elevates cool, nutrient rich waters to the surface, which leads to increased marine life.
In mountainous areas, local distortion of the airflow becomes severe. Jagged terrain combines to produce unpredictable flow patterns and turbulence, such as rotors
Lee waves
In meteorology, lee waves are atmospheric standing waves. The most common form is mountain waves, which are atmospheric internal gravity waves...
, which can be topped by lenticular cloud
Lenticular cloud
Lenticular clouds are stationary lens-shaped clouds that form at high altitudes, normally aligned perpendicular to the wind direction. Lenticular clouds can be separated into altocumulus standing lenticularis , stratocumulus standing lenticular , and cirrocumulus standing lenticular...
s. Strong updrafts, downdrafts and eddies develop as the air flows over hills and down valleys. Orographic precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
occurs on the windward side of mountains and is caused by the rising air motion of a large-scale flow of moist air across the mountain ridge, also known as upslope flow, resulting in adiabatic cooling and condensation. In mountainous parts of the world subjected to relatively consistent winds (for example, the trade winds), a more moist climate usually prevails on the windward side of a mountain than on the leeward or downwind side. Moisture is removed by orographic lift, leaving drier air on the descending and generally warming, leeward side where a rain shadow
Rain shadow
A rain shadow is a dry area on the lee side of a mountainous area. The mountains block the passage of rain-producing weather systems, casting a "shadow" of dryness behind them. As shown by the diagram to the right, the warm moist air is "pulled" by the prevailing winds over a mountain...
is observed. Winds that flow over mountains down into lower elevations are known as downslope winds. These winds are warm and dry. In Europe downwind of the Alps
Alps
The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....
, they are known as foehn. In Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
, an example is the halny wiatr. In Argentina, the local name for downsloped winds is zonda. In Java, the local name for such winds is koembang. In New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, they are known as the Nor'west arch
Nor'west arch
The Nor'west arch is a weather pattern peculiar to the east coast of New Zealand's South Island. For this reason, it is also often referred to as the Canterbury arch. It is shown in an apparent arch of high white cloud in an otherwise clear blue sky over the Southern Alps, and is accompanied by a...
, and are accompanied by the cloud formation they are named after that has inspired artwork over the years. In the Great Plains of the United States, the winds are known as a chinook
Chinook wind
Chinook winds , often called chinooks, commonly refers to foehn winds in the interior West of North America, where the Canadian Prairies and Great Plains meet various mountain ranges, although the original usage is in reference to wet, warm coastal winds in the Pacific Northwest.Chinook is claimed...
. In California, downsloped winds are funneled through mountain passes, which intensify their effect, and examples into Santa Ana
Santa Ana wind
The Santa Ana winds are strong, extremely dry offshore winds that characteristically sweep through Southern California and northern Baja California in late fall and winter. They can range from hot to cold, depending on the prevailing temperatures in the source regions, the Great Basin and upper...
and sundowner
Sundowner (wind)
A sundowner is an offshore northerly Foehn wind in Santa Barbara, California. It occurs when a region of high pressure is directly north of the area, whose coast trends east–west. This contrasts with the more typical onshore flow...
winds. Wind speeds during downslope wind effect can exceed sp=us 160.
Average wind speeds
As described earlier, prevailing and local winds are not spread evenly across the earth, which means that wind speeds also differ by region. In addition, the wind speed also increases with the altitude.Wind power density
Nowadays, a yardstick used to determine the best locations for wind energy development is referred to as wind power density (WPD). It is a calculation relating to the effective force of the wind at a particular location, frequently expressed in terms of the elevation above ground level over a period of time. It takes into account wind velocity and mass. Color coded maps are prepared for a particular area are described as, for example, "mean annual power density at 50 meters." The results of the above calculation are included in an index developed by the National Renewable Energy Lab and referred to as "NREL CLASS." The larger the WPD calculation, the higher it is rated by class. At the end of 2008, worldwide nameplate capacityNameplate capacity
Nameplate capacity, also known as the rated capacity, nominal capacity, installed capacity or maximum effect, refers to the intended technical full–load sustained output of a facility such as a power plant, a chemical plant, fuel plant, metal refinery, mine, and many others.For dispatchable power,...
of wind-powered generators was 120.8 gigawatts. Although wind produces only about 1.5% of worldwide electricity use, it is growing rapidly, having doubled in the three years between 2005 and 2008. In several countries it has achieved relatively high levels of penetration, accounting for approximately 19% of electricity production in Denmark
Wind power in Denmark
Wind power provided 18.9% of electricity production and 24.1% of generation capacity in Denmark in 2008, Denmark was a pioneer in developing commercial wind power during the 1970s, and today almost half of the wind turbines around the world are produced by Danish manufacturers such as Vestas and...
, 10% in Spain
Wind power in Spain
Spain is the world's fourth biggest producer of wind power, after China, the United States and Germany, with an installed capacity of 19,959 megawatts at the end of 2010, a rise of 1,609 MW for the year...
and Portugal
Wind power in Portugal
In December 2010, there was 3,937 MW of wind power nameplate capacity installed in Portugal. The major wind turbine manufacturers in the Portuguese market are Enercon, Vestas and Gamesa...
, and 7% in Germany
Wind power in Germany
In 2010, the installed capacity of wind power in Germany was 27.2 GW. Wind power currently produces about seven percent of Germany’s total electrical power. More than 21,607 wind turbines are located in the German federal area and the country has plans to build more wind turbines...
and the Republic of Ireland in 2008. One study indicates that an entirely renewable energy supply based on 70% wind is attainable at today's power prices by linking wind farm
Wind farm
A wind farm is a group of wind turbines in the same location used to produce electric power. A large wind farm may consist of several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other...
s with an HVDC
High-voltage direct current
A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses...
supergrid.
Shear
Wind shear, sometimes referred to as windshear or wind gradient
Wind gradient
In common usage, wind gradient, more specifically wind speed gradientor wind velocity gradient,or alternatively shear wind,...
, is a difference in wind speed and direction over a relatively short distance in the Earth's atmosphere. Wind shear can be broken down into vertical and horizontal components, with horizontal wind shear seen across weather fronts and near the coast, and vertical shear typically near the surface, though also at higher levels in the atmosphere near upper level jets and frontal zones aloft.
Wind shear itself is a microscale meteorological
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" and together study all phenomena smaller than synoptic scale; that is they...
phenomenon occurring over a very small distance, but it can be associated with mesoscale
Mesoscale meteorology
Mesoscale meteorology is the study of weather systems smaller than synoptic scale systems but larger than microscale and storm-scale cumulus systems. Horizontal dimensions generally range from around 5 kilometers to several hundred kilometers...
or synoptic scale weather features such as squall line
Squall line
A squall line is a line of severe thunderstorms that can form along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts....
s and cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
s. It is commonly observed near microburst
Microburst
A microburst is a very localized column of sinking air, producing damaging divergent and straight-line winds at the surface that are similar to, but distinguishable from, tornadoes, which generally have convergent damage. There are two types of microbursts: wet microbursts and dry microbursts...
s and downburst
Downburst
A downburst is created by an area of significantly rain-cooled air that, after reaching ground level, spreads out in all directions producing strong winds. Unlike winds in a tornado, winds in a downburst are directed outwards from the point where it hits land or water...
s caused by thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
s, weather fronts, areas of locally higher low level winds referred to as low level jets, near mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
s, radiation inversions that occur because of clear skies and calm winds, buildings, wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
s, and sailboat
Sailboat
A sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in the size are not strictly defined and what constitutes a sailing ship, sailboat, or a...
s. Wind shear has a significant effect during take-off and landing of aircraft because of their effects on control of the aircraft, and was a significant cause of aircraft accidents involving large loss of life within the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
.
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. Strong vertical wind shear within the troposphere also inhibits tropical cyclone
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
development, but helps to organize individual thunderstorms into living longer life cycles that can then produce severe weather
Severe weather
Severe weather phenomena are weather conditions that are hazardous to human life and property.- Examples Include :Severe weather can occur under a variety of situations, but three characteristics are generally needed: a temperature or moisture boundary, moisture, and , instability in the...
. The thermal wind
Thermal wind
The thermal wind is a vertical shear in the geostrophic wind caused by a horizontal temperature gradient. Its name is a misnomer, because the thermal wind is not actually a wind, but rather a wind shear.- Physical Intuition :...
concept explains how differences in wind speed with height are dependent on horizontal temperature differences, and explains the existence of the jet stream.
History
As a natural force, the wind was often personified as one or more wind godWind god
There are many different gods of wind in different religions:*Aeolus, the ruler of the winds in Greek mythology*Amun, Egyptian god of creation and the wind*Anemoi, the Greek wind gods Boreas, Notus, Eurus, and Zephyrus...
s or as an expression of the supernatural
Supernatural
The supernatural or is that which is not subject to the laws of nature, or more figuratively, that which is said to exist above and beyond nature...
in many cultures. Vayu
Vayu
Vāyu is a primary Hindu deity, the Lord of the winds, the father of Bhima and the spiritual father of Lord Hanuman...
is the Hindu God of Wind. The Greek wind gods include Boreas, Notus, Eurus, and Zephyrus. Aeolus
Aeolus
Aeolus was the ruler of the winds in Greek mythology. In fact this name was shared by three mythic characters. These three personages are often difficult to tell apart, and even the ancient mythographers appear to have been perplexed about which Aeolus was which...
, in varying interpretations the ruler or keeper of the four winds, has also been described as Astraeus
Astraeus
In Greek mythology, Astraeus or Astraeos was an astrological deity and the Titan-god of the dusk. In Hesiod's Theogony and in the Bibliotheca, Astraeus is a second-generation Titan, descended from Crius and Eurybia. However, Hyginus wrote that he was descended directly from Tartarus and Gaia, and...
, the god of dusk who fathered the four winds with Eos
Eos
In Greek mythology, Eos is the Titan goddess of the dawn, who rose from her home at the edge of Oceanus, the ocean that surrounds the world, to herald her brother Helios, the Sun.- Greek literature :...
, goddess of dawn. The Ancient Greeks also observed the seasonal change of the winds, as evidenced by the Tower of the Winds
Tower of the Winds
The Tower of the Winds, also called horologion , is an octagonal Pentelic marble clocktower on the Roman agora in Athens. The structure features a combination of sundials, a water clock and a wind vane...
in Athens
Athens
Athens , is the capital and largest city of Greece. Athens dominates the Attica region and is one of the world's oldest cities, as its recorded history spans around 3,400 years. Classical Athens was a powerful city-state...
. Venti are the Roman gods of the winds. Fūjin
Fujin
is the Japanese god of the wind and one of the eldest Shinto gods.He is portrayed as a terrifying dark demon, resembling a red headed black humanoid wearing a leopard skin, carrying a large bag of winds on his shoulders....
, the Japanese wind god and is one of the eldest Shinto
Shinto
or Shintoism, also kami-no-michi, is the indigenous spirituality of Japan and the Japanese people. It is a set of practices, to be carried out diligently, to establish a connection between present day Japan and its ancient past. Shinto practices were first recorded and codified in the written...
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. In Norse mythology
Norse mythology
Norse mythology, a subset of Germanic mythology, is the overall term for the myths, legends and beliefs about supernatural beings of Norse pagans. It flourished prior to the Christianization of Scandinavia, during the Early Middle Ages, and passed into Nordic folklore, with some aspects surviving...
, Njord
Njord
In Norse mythology, Njörðr is a god among the Vanir. Njörðr is father of the deities Freyr and Freyja by his unnamed Van sister, was in an ill-fated marriage with the goddess Skaði, lives in Nóatún and is associated with sea, seafaring, wind, fishing, wealth, and crop fertility.Njörðr is attested...
is the god of the wind. There are also four dvärgar (Norse dwarves), named Norðri, Suðri, Austri and Vestri
Norðri, Suðri, Austri and Vestri
In Norse mythology, Norðri, Suðri, Austri and Vestri are four dwarves in the Prose Edda book Gylfaginning who each support one of the four cardinal points. Together, they uphold the heavenly dome, created from the skull of the jötunn Ymir...
, and probably the four stags of Yggdrasil, personify the four winds, and parallel the four Greek wind gods. Stribog
Stribog
Stribog in the Slavic pantheon, is the god and spirit of the winds, sky and air; he is said to be the ancestor of the winds of the eight directions. The etymology of the name is disputed, see ....
is the name of the Slavic god
Slavic mythology
Slavic mythology is the mythological aspect of the polytheistic religion that was practised by the Slavs before Christianisation.The religion possesses many common traits with other religions descended from the Proto-Indo-European religion....
of winds, sky and air. He is said to be the ancestor (grandfather) of the winds of the eight directions.
Kamikaze
Kamikaze (typhoon)
The Kamikaze , were two winds or storms that are said to have saved Japan from two Mongol fleets under Kublai Khan. These fleets attacked Japan in 1274 and again in 1281...
(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. Protestant Wind
Protestant Wind
The phrase Protestant Wind has been used in more than one context, notably:#The storm that lashed the Spanish Armada. According to Protestant propaganda, the wind wrecked the Spanish fleet and thus saved England from invasion by the army of Philip II of Spain...
is a name for the storm that deterred the Spanish Armada
Spanish Armada
This article refers to the Battle of Gravelines, for the modern navy of Spain, see Spanish NavyThe Spanish Armada was the Spanish fleet that sailed against England under the command of the Duke of Medina Sidonia in 1588, with the intention of overthrowing Elizabeth I of England to stop English...
from an invasion of England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
in 1588 where the wind played a pivotal role, or the favorable winds that enabled William of Orange
William III of England
William III & II was a sovereign Prince of Orange of the House of Orange-Nassau by birth. From 1672 he governed as Stadtholder William III of Orange over Holland, Zeeland, Utrecht, Guelders, and Overijssel of the Dutch Republic. From 1689 he reigned as William III over England and Ireland...
to invade England in 1688. During Napoleon
Napoleon I of France
Napoleon Bonaparte was a French military and political leader during the latter stages of the French Revolution.As Napoleon I, he was Emperor of the French from 1804 to 1815...
's Egyptian Campaign, the French soldiers had a hard time with the khamsin
Khamsin
Khamsin, khamseen, chamsin or hamsin , also known as khamaseen refers to a dry, hot and dusty local wind blowing in North Africa and the Arabian Peninsula. Similar winds in the area are sirocco and simoom...
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." During the North African Campaign
North African campaign
During the Second World War, the North African Campaign took place in North Africa from 10 June 1940 to 13 May 1943. It included campaigns fought in the Libyan and Egyptian deserts and in Morocco and Algeria and Tunisia .The campaign was fought between the Allies and Axis powers, many of whom had...
of the World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, "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."
Transportation
Magnus effect
The Magnus effect is the phenomenon whereby a spinning object flying in a fluid creates a whirlpool of fluid around itself, and experiences a force perpendicular to the line of motion...
, every sailing ship has a hull, rigging
Rigging
Rigging is the apparatus through which the force of the wind is used to propel sailboats and sailing ships forward. This includes masts, yards, sails, and cordage.-Terms and classifications:...
and at least one mast
Mast (sailing)
The mast of a sailing vessel is a tall, vertical, or near vertical, spar, or arrangement of spars, which supports the sails. Large ships have several masts, with the size and configuration depending on the style of ship...
to hold up the sail
Sail
A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...
s that use the wind to power the ship. Ocean journeys by sailing ship can take many months, and a common hazard is becoming becalmed because of lack of wind, or being blown off course by severe storm
Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...
s or winds that do not allow progress in the desired direction. A severe storm could lead to shipwreck
Shipwreck
A shipwreck is what remains of a ship that has wrecked, either sunk or beached. Whatever the cause, a sunken ship or a wrecked ship is a physical example of the event: this explains why the two concepts are often overlapping in English....
, and the loss of all hands. Sailing ships can only carry a certain quantity of supplies in their hold
Hold (ship)
thumb|right|120px|View of the hold of a container shipA ship's hold is a space for carrying cargo. Cargo in holds may be either packaged in crates, bales, etc., or unpackaged . Access to holds is by a large hatch at the top...
, so they have to plan long voyages
Maritime history
Maritime history is the study of human activity at sea. It covers a broad thematic element of history that often uses a global approach, although national and regional histories remain predominant...
carefully to include appropriate provisions, including fresh water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
.
For aerodynamic aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
which operate relative to the air, winds affect groundspeed, and in the case of lighter-than-air vehicles, wind may play a significant or solitary role in their movement and ground track. The velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
of surface wind is generally the primary factor governing the direction of flight operations at an airport, and airfield runways are aligned to account for the common wind direction(s) of the local area. While taking off with a tailwind
Tailwind
A tailwind is a wind that blows in the direction of travel of an object, while a headwind blows against the direction of travel. A tailwind increases the object's speed and reduces the time required to reach its destination, while a headwind has the opposite effect...
may be necessary under certain circumstances, a headwind is generally desirable. A tailwind increases takeoff distance required and decreases the climb gradient.
Power source
Anuradhapura
Anuradhapura, , is one of the ancient capitals of Sri Lanka, famous for its well-preserved ruins of ancient Lankan civilization.The city, now a UNESCO World Heritage Site, lies 205 km north of the current capital Colombo in Sri Lanka's North Central Province, on the banks of the historic...
and in other cities around Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
used the monsoon winds to power furnaces as early as 300 BCE
Common Era
Common Era ,abbreviated as CE, is an alternative designation for the calendar era originally introduced by Dionysius Exiguus in the 6th century, traditionally identified with Anno Domini .Dates before the year 1 CE are indicated by the usage of BCE, short for Before the Common Era Common Era...
. The furnaces were constructed on the path of the monsoon winds to exploit the wind power, to bring the temperatures inside up to sp=us 1200. An early historical reference to a rudimentary windmill
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
was used to power an organ
Organ (music)
The organ , is a keyboard instrument of one or more divisions, each played with its own keyboard operated either with the hands or with the feet. The organ is a relatively old musical instrument in the Western musical tradition, dating from the time of Ctesibius of Alexandria who is credited with...
in the first century CE. The first practical windmill
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
s were later built in Sistan
Sistan
Sīstān is a border region in eastern Iran , southwestern Afghanistan and northern tip of Southwestern Pakistan .-Etymology:...
, Afghanistan
Afghanistan
Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...
, from the 7th century CE. These were vertical-axle windmills, which had long vertical driveshaft
Driveshaft
A drive shaft, driveshaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical component for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement...
s with rectangle shaped blades. Made of six to twelve sails
Windmill sail
Windmills are powered by their sails. Sails are found in different designs, from primitive common sails to the advanced patent sails.-Jib sails:...
covered in reed matting
Reed mat (craft)
Reed mats are handmade mats of plaited reed, made throughout most of India and Thailand.The mats are produced by plaiting reeds, strips of palm leaf, or some other easily available local plant. The supple mats made by this process of weaving without a loom are widely used in Thai homes...
or cloth material, these windmills were used to grind corn and draw up water, and were used in the gristmill
Gristmill
The terms gristmill or grist mill can refer either to a building in which grain is ground into flour, or to the grinding mechanism itself.- Early history :...
ing and sugarcane industries. Horizontal-axle windmills were later used extensively in Northwestern Europe to grind flour beginning in the 1180s, and many Dutch windmills still exist. High altitude wind power is the focus of over 30 companies worldwide using tethered technology rather than ground-hugging compressive-towers. Oil is being saved by using wind for powering cargo ships by use of the mechanical energy converted from the wind's kinetic energy using very large kites.
Recreation
Hang gliding
Hang gliding is an air sport in which a pilot flies a light and unmotorized foot-launchable aircraft called a hang glider ....
, hot air ballooning
Hot air ballooning
Hot air ballooning is the activity of flying hot air balloons. Attractive aspects of ballooning include the exceptional quiet , the lack of a feeling of movement, and the bird's-eye view...
, kite flying
Kite
A kite is a tethered aircraft. The necessary lift that makes the kite wing fly is generated when air flows over and under the kite's wing, producing low pressure above the wing and high pressure below it. This deflection also generates horizontal drag along the direction of the wind...
, snowkiting
Snowkiting
Snowkiting is an outdoor winter sport where people use kite power to glide on snow or ice. The sport is similar to kitesurfing, but with the footwear used in snowboarding or skiing. In the early days of snowkiting, foil kites were the most common type; nowadays some kitesurfers use their water gear...
, kite landboarding
Kite landboarding
Kite landboarding also known as Land kiteboarding or flyboarding, is based on the ever-growing sport of Kitesurfing, where a rider on a surf-style board is pulled over water by a kite. Kite landboarding involves the use of a mountain board or landboard, which is essentially an oversized skateboard...
, kite surfing, paragliding
Paragliding
Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure...
, sailing
Sailing
Sailing is the propulsion of a vehicle and the control of its movement with large foils called sails. By changing the rigging, rudder, and sometimes the keel or centre board, a sailor manages the force of the wind on the sails in order to move the boat relative to its surrounding medium and...
, and windsurfing
Windsurfing
Windsurfing or sailboarding is a surface water sport that combines elements of surfing and sailing. It consists of a board usually two to four metres long, powered by the orthogonal effect of the wind on a sail. The rig is connected to the board by a free-rotating universal joint and comprises a...
. In gliding, wind gradients just above the surface affect the takeoff and landing phases of flight of a glider
Glider aircraft
Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...
. Wind gradient can have a noticeable effect on ground launches, also known as winch launches or wire launches. If the wind gradient is significant or sudden, or both, and the pilot maintains the same pitch attitude, the indicated airspeed will increase, possibly exceeding the maximum ground launch tow speed. The pilot must adjust the airspeed to deal with the effect of the gradient. When landing, wind shear is also a hazard, particularly when the winds are strong. As the glider descends through the wind gradient on final approach to landing, airspeed decreases while sink rate increases, and there is insufficient time to accelerate prior to ground contact. The pilot must anticipate the wind gradient and use a higher approach speed to compensate for it.
Role in the natural world
In arid climates, the main source of erosion is wind. The general wind circulation moves small particulates such as dust across wide oceans thousands of kilometers downwind of their point of origin, which is known as deflation. Westerly winds in the mid-latitudes of the planet drive the movement of ocean currents from west to east across the world's oceans. Wind has a very important role in aiding plants and other immobile organisms in dispersal of seeds, spores, pollen, etc. Although wind is not the primary form of seed dispersal in plants, it provides dispersal for a large percentage of the biomass of land plants.Erosion
Erosion can be the result of material movement by the wind. There are two main effects. First, wind causes small particles to be lifted and therefore moved to another region. This is called deflation. Second, these suspended particles may impact on solid objects causing erosion by abrasion (ecological succession). Wind erosion generally occurs in areas with little or no vegetation, often in areas where there is insufficient rainfall to support vegetation. An example is the formation of sand dunes, on a beach or in a desert. Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
y, pale yellow or buff, windblown (Aeolian) sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
. It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces. Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world. Loess deposits are geologically unstable by nature, and will erode very readily. Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess.
Desert dust migration
During mid-summer (July), the westward-moving trade winds south of the northward-moving subtropical ridge expand northwestward from the Caribbean SeaCaribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
into southeastern North America. When dust from the Sahara
Sahara
The Sahara is the world's second largest desert, after Antarctica. At over , it covers most of Northern Africa, making it almost as large as Europe or the United States. The Sahara stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean...
moving around the southern periphery of the ridge within the belt of trade winds moves over land, rainfall is suppressed and the sky changes from a blue to a white appearance, which leads to an increase in red sunsets. Its presence negatively impacts air quality by adding to the count of airborne particulates. Over 50% of the African dust that reaches the United States affects Florida. Since 1970, dust outbreaks have worsened because of periods of drought in Africa. There is a large variability in the dust transport to the Caribbean and Florida from year to year. Dust events have been linked to a decline in the health of coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s across the Caribbean and Florida, primarily since the 1970s. Similar dust plumes originate in the Gobi desert
Gobi Desert
The Gobi is a large desert region in Asia. It covers parts of northern and northwestern China, and of southern Mongolia. The desert basins of the Gobi are bounded by the Altai Mountains and the grasslands and steppes of Mongolia on the north, by the Hexi Corridor and Tibetan Plateau to the...
, which combined with pollutants, spread large distances downwind, or eastward, into North America.
There are local names for winds associated with sand and dust storms. The Calima carries dust on southeast winds into the Canary islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
. The Harmattan
Harmattan
The Harmattan is a dry and dusty West African trade wind. It blows south from the Sahara into the Gulf of Guinea between the end of November and the middle of March...
carries dust during the winter into the Gulf of Guinea
Gulf of Guinea
The Gulf of Guinea is the northeasternmost part of the tropical Atlantic Ocean between Cape Lopez in Gabon, north and west to Cape Palmas in Liberia. The intersection of the Equator and Prime Meridian is in the gulf....
. The Sirocco
Sirocco
Sirocco, scirocco, , jugo or, rarely, siroc is a Mediterranean wind that comes from the Sahara and reaches hurricane speeds in North Africa and Southern Europe. It is known in North Africa by the Arabic word qibli or ghibli Sirocco, scirocco, , jugo or, rarely, siroc is a Mediterranean wind...
brings dust from north Africa into southern Europe because of the movement of extratropical cyclones through the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
. Spring storm systems moving across the eastern Mediterranean Sea cause dust to carry across Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
and the Arabian peninsula
Arabian Peninsula
The Arabian Peninsula is a land mass situated north-east of Africa. Also known as Arabia or the Arabian subcontinent, it is the world's largest peninsula and covers 3,237,500 km2...
, which are locally known as Khamsin
Khamsin
Khamsin, khamseen, chamsin or hamsin , also known as khamaseen refers to a dry, hot and dusty local wind blowing in North Africa and the Arabian Peninsula. Similar winds in the area are sirocco and simoom...
. The Shamal
Shamal (wind)
A shamal is a northwesterly wind blowing over Iraq and the Persian Gulf states , often strong during the day, but decreasing at night. This weather effect occurs anywhere from once to several times a year, mostly in summer but sometimes in winter...
is caused by cold fronts lifting dust into the atmosphere for days at a time across the Persian Gulf
Persian Gulf
The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...
states.
Effect on plants
Wind dispersal of seeds, or anemochory, is one of the more primitive means of dispersal. Wind dispersal can take on one of two primary forms: seeds can float on the breeze or alternatively, they can flutter to the ground. The classic examples of these dispersal mechanisms include dandelions (Taraxacum
Taraxacum
Taraxacum is a large genus of flowering plants in the family Asteraceae. They are native to Eurasia and North America, and two species, T. officinale and T. erythrospermum, are found as weeds worldwide. Both species are edible in their entirety...
spp., Asteraceae
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
), which have a feathery pappus
Pappus (flower structure)
The pappus is the modified calyx, the part of an individual disk, ray or ligule floret surrounding the base of the corolla, in flower heads of the plant family Asteraceae. The pappus may be composed of bristles , awns, scales, or may be absent. In some species, the pappus is too small to see...
attached to their seeds and can be dispersed long distances, and maple
Maple
Acer is a genus of trees or shrubs commonly known as maple.Maples are variously classified in a family of their own, the Aceraceae, or together with the Hippocastanaceae included in the family Sapindaceae. Modern classifications, including the Angiosperm Phylogeny Group system, favour inclusion in...
s (Acer (genus) spp., Sapindaceae
Sapindaceae
Sapindaceae, also known as the soapberry family, is a family of flowering plants in the order Sapindales. There are about 140-150 genera with 1400-2000 species, including maple, horse chestnut and lychee....
), which have winged seeds and flutter to the ground. An important constraint on wind dispersal is the need for abundant seed production to maximize the likelihood of a seed landing in a site suitable for germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
. There are also strong evolutionary constraints on this dispersal mechanism. For instance, species in the Asteraceae on island
Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...
s tended to have reduced dispersal capabilities (i.e., larger seed mass and smaller pappus) relative to the same species on the mainland. Reliance upon wind dispersal is common among many weed
Weed
A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...
y or ruderal species. Unusual mechanisms of wind dispersal include tumbleweed
Tumbleweed
A tumbleweed is the above-ground part of a plant that, once mature and dry, disengages from the root and tumbles away in the wind. Usually, the tumbleweed is the entire plant apart from the roots, but in a few species it is a flower cluster. The tumbleweed habit is most common in steppe and desert...
s. A related process to anemochory is anemophily
Anemophily
Anemophily or wind pollination is a form of pollination whereby pollen is distributed by wind. Anemophilous plants may be either gymnosperms or angiosperms ....
, which is the process where pollen is distributed by wind. Large families of plants are pollinated in this manner, which is favored when individuals of the dominant plant species are spaced closely together.
Wind also limits tree growth. On coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
s and isolated mountains, the tree line is often much lower than in corresponding altitudes inland and in larger, more complex mountain systems, because strong winds reduce tree growth. High winds scour away thin soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s through erosion, as well as damage limbs and twigs. When high winds knock down or uproot trees, the process is known as windthrow
Windthrow
In forestry, windthrow refers to trees uprooted or broken by wind. Breakage of the tree bole instead of uprooting is sometimes called windsnap.- Causes :...
. This is most likely on windward slopes of mountains, with severe cases generally occurring to tree stand
Tree stand
Tree stands are open or enclosed platforms used by hunters. The platforms are secured to trees in order to elevate the hunter and give him or her a better vantage point. Many people also know tree stands as deer stands...
s that are 75 years or older. Plant varieties near the coast, such as the Sitka spruce
Sitka Spruce
Picea sitchensis, the Sitka Spruce, is a large coniferous evergreen tree growing to 50–70 m tall, exceptionally to 95 m tall, and with a trunk diameter of up to 5 m, exceptionally to 6–7 m diameter...
and sea grape
Coccoloba uvifera
Coccoloba uvifera is a species of flowering plant in the buckwheat family, Polygonaceae, that is native to coastal beaches throughout tropical America and the Caribbean, including southern Florida, the Bahamas, Barbados and Bermuda...
, are pruned
Pruning
Pruning is a horticultural practice involving the selective removal of parts of a plant, such as branches, buds, or roots. Reasons to prune plants include deadwood removal, shaping , improving or maintaining health, reducing risk from falling branches, preparing nursery specimens for...
back by wind and salt spray near the coastline.
Wind can also cause plants damage through sand abrasion. Strong winds will pick up loose sand and topsoil
Topsoil
Topsoil is the upper, outermost layer of soil, usually the top to . It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs.-Importance:...
and hurl it through the air at speeds ranging from 25–40 miles per hour. Such windblown sand causes extensive damage to plant seedlings because it ruptures plant cells, making them vulnerable to evaporation and drought. Using a mechanical sandblaster in a laboratory setting, scientists affiliated with the Agricultural Research Service
Agricultural Research Service
The Agricultural Research Service is the principal in-house research agency of the United States Department of Agriculture . ARS is one of four agencies in USDA's Research, Education and Economics mission area...
studied the effects of windblown sand abrasion on cotton seedlings. The study showed that the seedlings responded to the damage created by the windblown sand abrasion by shifting energy from stem and root growth to the growth and repair of the damaged stems. After a period of four weeks the growth of the seedling once again became uniform throughout the plant, as it was before the windblown sand abrasion occurred.
Effect on animals
CattleCattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
and sheep are prone to wind chill
Wind chill
Wind chill is the felt air temperature on exposed skin due to wind. The wind chill temperature is always lower than the air temperature, and the windchill is undefined at the higher temps...
caused by a combination of wind and cold temperatures, when winds exceed sp=us 40, rendering their hair and wool coverings ineffective. Although penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
s use both a layer of fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
and feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s to help guard against coldness in both water and air, their flippers
Flipper (anatomy)
A flipper is a typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example penguins , cetaceans A flipper is a typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example penguins (also called...
and feet are less immune to the cold. In the coldest climates such as Antarctica, emperor penguin
Emperor Penguin
The Emperor Penguin is the tallest and heaviest of all living penguin species and is endemic to Antarctica. The male and female are similar in plumage and size, reaching in height and weighing anywhere from . The dorsal side and head are black and sharply delineated from the white belly,...
s use huddling
Huddle
In sport, a huddle is when a team gathers together, usually in a tight circle, to strategise, motivate or celebrate. It is a popular strategy for keeping opponents insulated from sensitive information, and acts as a form of insulation when the level of noise in the venue is such that normal...
behavior to survive the wind and cold, continuously alternating the members on the outside of the assembled group, which reduces heat loss by 50%. Flying insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, a subset of arthropods, are swept along by the prevailing winds, while birds follow their own course taking advantage of wind conditions, in order to either fly or glide. As such, fine line patterns within weather radar
Weather radar
Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...
imagery, associated with converging winds, are dominated by insect returns. Bird migration, which tends to occur overnight within the lowest sp=us 7000 of the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
, contaminates wind profiles gathered by weather radar, particularly the WSR-88D, by increasing the environmental wind returns by sp=us 15 to sp=us 30.
Pika
Pika
The pika is a small mammal, with short limbs, rounded ears, and short tail. The name pika is used for any member of the Ochotonidae, a family within the order of lagomorphs, which also includes the Leporidae . One genus, Ochotona, is recognised within the family, and it includes 30 species...
s use a wall of pebbles to store dry plants and grasses for the winter in order to protect the food from being blown away. Cockroach
Cockroach
Cockroaches are insects of the order Blattaria or Blattodea, of which about 30 species out of 4,500 total are associated with human habitations...
es use slight winds that precede the attacks of potential predators, such as toad
Toad
A toad is any of a number of species of amphibians in the order Anura characterized by dry, leathery skin , short legs, and snoat-like parotoid glands...
s, to survive their encounters. Their cerci
Cercus
Cerci are paired appendages on the rear-most segments of many arthropods, including insects and arachnids but not crustaceans. Cerci often serve as sensory organs, but they may also be used as weapons or copulation aids, or they may simply be vestigial structures.Typical cerci may appear to be...
are very sensitive to the wind, and help them survive half of their attacks. Elk
Elk
The Elk is the large deer, also called Cervus canadensis or wapiti, of North America and eastern Asia.Elk may also refer to:Other antlered mammals:...
has a keen sense of smell that can detect potential upwind predators at a distance of sp=us 0.5. Increases in wind above sp=us 15 signals glaucous gull
Glaucous Gull
The Glaucous Gull is a large gull which breeds in the Arctic regions of the northern hemisphere and the Atlantic coasts of Europe. It is migratory, wintering from in the North Atlantic and North Pacific oceans as far south as the British Isles and northernmost states of the USA, also on the Great...
s to increase their foraging and aerial attacks on thick-billed murres.
Related damage
Suspension bridge
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. Outside Tibet and Bhutan, where the first examples of this type of bridge were built in the 15th century, this type of bridge dates from the early 19th century...
s 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
Tacoma Narrows Bridge (1940)
The 1940 Tacoma Narrows Bridge was the first incarnation of the Tacoma Narrows Bridge, a suspension bridge in the U.S. state of Washington that spanned the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula. It opened to traffic on July 1, 1940, and dramatically collapsed...
in 1940. Wind speeds as low as sp=us 23 can lead to power outages due to tree branches disrupting the flow of energy through power lines. 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
Eucalyptus
Eucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia...
, sea hibiscus
Hibiscus
Hibiscus is a genus of flowering plants in the mallow family, Malvaceae. It is quite large, containing several hundred species that are native to warm-temperate, subtropical and tropical regions throughout the world...
, and avocado
Avocado
The avocado is a tree native to Central Mexico, classified in the flowering plant family Lauraceae along with cinnamon, camphor and bay laurel...
are more prone to damage. 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. Once winds exceed sp=us 135, homes completely collapse, and significant damage is done to larger buildings. Total destruction to man-made structures occurs when winds reach sp=us 175. The Saffir-Simpson scale and Enhanced Fujita scale
Enhanced Fujita Scale
The Enhanced Fujita Scale rates the strength of tornadoes in the United States based on the damage they cause.Implemented in place of the Fujita scale introduced in 1971 by Ted Fujita, it began operational use on February 1, 2007. The scale has the same basic design as the original Fujita scale:...
were designed to help estimate wind speed from the damage caused by high winds related to tropical cyclones and tornado
Tornado
A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...
es, and vice versa.
Australia's Barrow Island
Barrow Island (Western Australia)
Barrow Island is a island located northwest off the coast of Western Australia. The island is the second largest in Western Australia after Dirk Hartog Island.-Discovery and early history:...
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 of 372 km/h (231 mph) set on Mount Washington (New Hampshire)
Mount Washington (New Hampshire)
Mount Washington is the highest peak in the Northeastern United States at , famous for dangerously erratic weather. For 76 years, a weather observatory on the summit held the record for the highest wind gust directly measured at the Earth's surface, , on the afternoon of April 12, 1934...
on the afternoon of 12 April 1934. The most powerful gusts of wind on Earth were created by nuclear detonations. The blast wave is similar to a strong wind gust over the ground. The largest nuclear explosion (50–58 megatons at an altitude of about 13,000 ft) generated a 20 bar blast pressure at ground zero, which is similar to a wind gust of 3,100 miles per hour.
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. 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. 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.
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.Planetary wind
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
to move up to the exobase, the lower limit of the exosphere
Exosphere
The exosphere is the uppermost layer of Earth's atmosphere. In the exosphere, an upward travelling molecule moving fast enough to attain escape velocity can escape to space with a low chance of collisions; if it is moving below escape velocity it will be prevented from escaping from the celestial...
, where the gases can then reach escape velocity
Escape velocity
In physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
, entering outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
without impacting other particles of gas. This type of gas loss from a planet into space is known as planetary wind. Such a process over geologic time causes water-rich planets such as the Earth to evolve into planets like Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
. Additionally, planets with hotter lower atmospheres could accelerate the loss rate of hydrogen.
Solar wind
Rather than air, the solar wind is a stream of charged particlesElectric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
—a plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
—ejected from the upper atmosphere
Stellar atmosphere
The stellar atmosphere is the outer region of the volume of a star, lying above the stellar core, radiation zone and convection zone. It is divided into several regions of distinct character:...
of the sun at a rate of sp=us 400. It consists mostly of electrons and proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s 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
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
of the corona
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
, but also because of high kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
that particles gain through a process that is not well-understood. The solar wind creates the Heliosphere
Heliosphere
The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...
, a vast bubble in the interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
surrounding the solar system. Planets require large magnetic fields in order to reduce the ionization of their upper atmosphere by the solar wind. Other phenomena include geomagnetic storm
Geomagnetic storm
A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in the interplanetary medium. A geomagnetic storm is a major component of space weather and provides the input for many other components of space weather...
s that can knock out power grids on Earth, the aurorae such as the Northern Lights
Aurora (astronomy)
An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...
, and the plasma tails of comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s that always point away from the sun.
On other planets
Strong sp=us 300 winds at Venus's cloud tops circle the planet every four to five earth days. When the poles of MarsMars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
are exposed to sunlight after their winter
Winter
Winter is the coldest season of the year in temperate climates, between autumn and spring. At the winter solstice, the days are shortest and the nights are longest, with days lengthening as the season progresses after the solstice.-Meteorology:...
, the frozen CO2 sublimes
Sublimation (physics)
Sublimation is the process of transition of a substance from the solid phase to the gas phase without passing through an intermediate liquid phase...
, creating significant winds that sweep off the poles as fast as sp=us 400, which subsequently transports large amounts of dust and water vapor over its landscape
Landscape
Landscape comprises the visible features of an area of land, including the physical elements of landforms such as mountains, hills, water bodies such as rivers, lakes, ponds and the sea, living elements of land cover including indigenous vegetation, human elements including different forms of...
. Other Martian winds have resulted in cleaning event
Cleaning event
A cleaning event is a phenomenon whereby dust is removed from solar panels, particularly ones on Mars, by the action of wind. The term cleaning event is used on several NASA webpages; generally the term is used in reference to the fact that Martian winds have blown dust clear of the solar panels of...
s and dust devils. On Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, wind speeds of sp=us 100 are common in zonal jet streams. Saturn's winds are among the solar system's fastest. Cassini–Huygens data indicated peak easterly winds of sp=us 375. On Uranus
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
, northern hemisphere wind speeds reach as high as sp=us 240 near 50 degrees north latitude. At the cloud tops of Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
, prevailing winds range in speed from sp=us 400 along the equator to sp=us 250 at the poles. At 70° S latitude on Neptune, a high-speed jet stream travels at a speed of sp=us 300.
See also
- ClimatologyClimatologyClimatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...
- Küssner effect
- Wind advisoryGale warningA gale warning is a warning issued by weather services in maritime locations about the existence of winds of gale force or above or the imminent occurrence of gales at sea...
- Wind engineeringWind engineeringWind engineering analyzes effects of wind in the natural and the built environment and studies the possible damage, inconvenience or benefits which may result from wind. In the field of structural engineering it includes strong winds, which may cause discomfort, as well as extreme winds, such as in...
- Wind wave
- List of local winds
- North windNorth windA north wind is a wind that originates in the north and blows south. The north wind has had historical and literal significance, since it often signals cold weather and seasonal change in the Northern hemisphere.-Mythology:...
- South windSouth windFor other uses, see South wind .A south wind is a wind that originates in the south and blows north.Words used in English to describe the south wind are auster, buster , föhn/foehn , gibli , friagem , khamsin For other uses, see South wind (disambiguation).A south wind is a wind that originates in...
- West windWest windA west wind is a wind that blows from the west, in an eastward direction. In Western tradition, it has usually been considered the mildest and most favorable of the directional winds....
- East windEast windAn east wind is a wind that originates in the east and blows west. In Greek mythology, Eurus, the east wind, was the only wind not associated with any of the three Greek seasons, and is the only one of these four Anemoi not mentioned in Hesiod's Theogony or in the Orphic Hymns.-Biblical...
External links
- Meteorology Guides: Forces and Winds – Instructional module from the University of Illinois
- Names of Winds – A list from Golden Gate Weather Services
- Wind Atlases of the World – Lists of wind atlases and wind surveys from all over the world
- Winds of Mars: Aeolian Activity and Landforms – Paper with slides that illustrate the wind activity on the planet Mars
- Classification of Wind Speeds
- Wind-speed chart
- The Bibliography of Aeolian Research