Wind is the natural movement of air or other relative to a planet's surface. Winds occur 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 on Earth. The study of wind is called anemology.["Anemology."
]
Accessed 23 Nov. 2024.
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, which is called the Coriolis effect. Within the tropics and subtropics, 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 prevail.
Winds are commonly classified by their spatial scale, their speed and direction, the forces that cause them, the regions in which they occur, and their effect. Winds have various defining aspects such as velocity (wind speed), the density of the gases involved, and energy content or wind energy. In meteorology, winds are often referred to according to their strength, and the direction from which the wind is blowing. The convention for directions refer to where the wind comes from; therefore, a 'western' or 'westerly' wind blows from the west to the east, a 'northern' wind blows south, and so on. This is sometimes counter-intuitive.
Short bursts of high speed wind are termed Wind gust. Strong winds of intermediate duration (around one minute) are termed . Long-duration winds have various names associated with their average strength, such as , gale, storm, and hurricane.
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 from a planet's atmosphere into space. The strongest observed winds on a planet in the Solar System occur on Neptune and Saturn.
In human civilization, the concept of wind has been explored in mythology, influenced the events of history, expanded the range of transport and warfare, and provided a wind power for mechanical work, electricity, and recreation. Wind powers the voyages of across Earth's oceans. Hot air balloons 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 human-made structures can be damaged or destroyed.
Winds can shape landforms, via a variety of aeolian processes such as the formation of fertile soils, for example loess, and by erosion. Dust from large deserts 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 also affects the spread of wildfires. Winds can disperse seeds from various plants, enabling the survival and dispersal of those plant species, as well as flying insect and bird populations. When combined with cold temperatures, the wind has a negative impact on livestock. Wind affects animals' food stores, as well as their hunting and defensive strategies.
Causes
Wind is caused by differences in atmospheric pressure, which are primarily due to temperature differences. When a difference in atmospheric pressure exists, air moves from the higher to the lower pressure area, resulting in winds of various speeds. On a rotating planet, air will also be deflected by the
Coriolis effect, except exactly on the equator. Globally, the two major driving factors of large-scale wind patterns (the atmospheric circulation) are the differential heating between the equator and the poles (difference in absorption of
solar energy leading to
) and the
Coriolis effect. 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 horizontal 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.
Measurement
Wind direction is usually expressed in terms of the direction from which it originates. For example, a
northerly wind blows from the north to the south.
pivot to indicate the direction of the wind.
At airports,
indicate wind direction, and can also be used to estimate wind speed by the angle of hang.
Wind speed is measured by
, 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
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 height and are averaged over a 10‑minute time frame. The United States reports winds over a 1‑minute average for tropical cyclones,[Office of the Federal Coordinator for Meteorology. Federal Meteorological Handbook No. 1 – Surface Weather Observations and Reports September 2005 Appendix A: Glossary. Retrieved 2008-04-06.] India typically reports winds over a 3‑minute average.
To determine winds aloft, radiosondes determine wind speed by GPS, LORAN, or radar tracking of the probe.
Models
Models can provide spatial and temporal information about airflow. Spatial information can be obtained through the interpolation of data from various measurement stations, allowing for horizontal data calculation. Alternatively, profiles, such as the logarithmic wind profile, can be utilized to derive vertical information.
Temporal information is typically computed by solving the Navier-Stokes equations within numerical weather prediction models, generating global data for General Circulation Models or specific regional data. The calculation of wind fields is influenced by factors such as radiation differentials, Earth's rotation, and friction, among others.
Numerical weather prediction models have significantly advanced our understanding of atmospheric dynamics and have become indispensable tools in weather forecasting and climate research. By leveraging both spatial and temporal data, these models enable scientists to analyze and predict global and regional wind patterns, contributing to our comprehension of the Earth's complex atmospheric system.
Wind force scale
Historically, the
Beaufort scale, created by
Francis Beaufort, provides an empirical description of wind speed based on observed sea conditions. Originally it was a 13-level scale (012), but during the 1940s, the scale was expanded to 18 levels (017).
There are general terms that differentiate winds of different average speeds such as a breeze, a gale, a storm, or a hurricane. Within the Beaufort scale, gale-force winds lie between and 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 to .
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:
|
|
|
|
| 0 | <1 | <2 | Calm | Low Pressure Area | Tropical disturbance | Tropical low
Tropical Depression | Tropical depression | Tropical depression | Tropical depression |
| 1 | 1–3 | 2–6 | Light air |
| 2 | 4–6 | 7–11 | Light breeze |
| 3 | 7–10 | 13–19 | Gentle breeze |
| 4 | 11–16 | 20–30 | Moderate breeze |
| 5 | 17–21 | 31–39 | Fresh breeze | Depression |
| 6 | 22–27 | 41–50 | Strong breeze |
| 7 | 28–29 | 52–54 | Moderate gale | Deep depression | Tropical depression |
| 30–33 | 56–61 |
| 8 | 34–40 | 63–74 | Fresh gale | Cyclonic storm | Moderate tropical storm | Tropical cyclone (1) | Tropical storm | Tropical storm | Tropical storm |
| 9 | 41–47 | 76–87 | Strong gale |
| 10 | 48–55 | 89–102 | Whole gale | Severe cyclonic storm | Severe tropical storm | Tropical cyclone (2) | Severe tropical storm |
| 11 | 56–63 | 104–117 | Storm |
| 12 | 64–72 | 119–133 | Hurricane | Very severe cyclonic storm | Tropical cyclone | Severe tropical cyclone (3) | Typhoon | Typhoon | Hurricane (1) |
| 13 | 73–85 | 135–157 | Hurricane (2) |
| 14 | 86–89 | 159–165 | Severe tropical cyclone (4) | Major hurricane (3) |
| 15 | 90–99 | 167–183 | Intense tropical cyclone |
| 16 | 100–106 | 185–196 | Major hurricane (4) |
| 17 | 107–114 | 198–211 | Severe tropical cyclone (5) |
| 115–119 | 213–220 | Very intense tropical cyclone | Super typhoon |
| >120 | >222 | Super cyclonic storm | Major hurricane (5) |
Enhanced Fujita scale
The Enhanced Fujita Scale (EF Scale) rates the strength of tornadoes by using damage to estimate wind speed. It has six levels, from visible damage to complete destruction. It is used in the United States and in some other countries, including Canada and France, with small modifications.
Station model
The
station model plotted on surface
uses a wind barb to show both wind direction and speed. The wind barb shows the speed using "flags" on the end.
-
Each half of a flag depicts of wind.
-
Each full flag depicts of wind.
-
Each pennant (filled triangle) depicts 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.
Global climatology
Easterly winds, on average, dominate the flow pattern across the poles, westerly winds blow across the
mid-latitudes of the Earth, polewards 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.
Tropics
The trade winds (also called trades) are the prevailing pattern of
easterlies 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 the world's oceans.
Trade winds also steer African dust westward across the Atlantic Ocean into the Caribbean, 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.
Westerlies and their impact
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,
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 , 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.
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
at the
North Pole and
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 westward 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 sea 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.
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. A background along-shore wind either strengthens or weakens the sea breeze, depending on its orientation with respect to the Coriolis force.
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
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 mountain 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 .
In mountainous areas, local distortion of the airflow becomes severe. Jagged terrain combines to produce unpredictable flow patterns and turbulence, such as lee waves, which can be topped by . Strong , 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 down sloped 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.
Shear
Wind shear, sometimes referred to as
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 and . It is commonly observed near and caused by ,
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.
In civilization
Religion
As a natural force, the wind was often personified as one or more
or as an expression of the
supernatural in many cultures.
Vayu is the Vedic and Hindu God of Wind.
The Greek wind gods include Boreas,
Greek Goddess,
Eurus, and
Zephyrus.
, 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 is 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, Njörðr 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.
is the name of the
Slavic Mythology of winds, sky and air. He is said to be the ancestor (grandfather) of the winds of the eight directions.
History
Kamikaze 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.
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 Ottomans 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."
Transportation
There are many different forms of sailing ships, but they all have certain basic things in common. Except for
using the
Magnus effect, every sailing ship has a hull,
rigging and at least one mast to hold up the
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
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
Maritime history carefully to include appropriate provisions, including fresh water.
For aerodynamic aircraft which operate relative to the air, winds affect groundspeed,
Power source
The ancient
Sinhalese people of
Anuradhapura and in other cities around
Sri Lanka used the monsoon winds to power furnaces as early as 300
Common Era. The furnaces were constructed on the path of the monsoon winds to bring the temperatures inside up to .
A rudimentary
windmill was used to power an organ in the first century CE.
Windmills were later built in
Sistan,
Afghanistan, from the 7th century CE. These were vertical-axle windmills,
with
Windmill sail covered in reed matting or cloth material. These windmills were used to grind corn and draw up water, and were used in the
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.
Wind power is now one of the main sources of renewable energy, and its use is growing rapidly, driven by innovation and falling prices.[ The Physics of Wind Turbines. Kira Grogg Carleton College (2005) p. 8. (PDF). Retrieved 2011-11-03.]
Metallurgy
In Pre-Hispanic times and historically wind has been used in the
Andean world to drive the combustion used in metal smelting.
Recreation
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 aircraft. Wind gradient can have a noticeable effect on
, 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.
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,
, 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,
(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 in the northern hemisphere), the westward-moving trade winds south of the northward-moving subtropical ridge expand northwestward from the Caribbean 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
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.
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
(
Taraxacum spp.,
Asteraceae), which have a feathery pappus attached to their seeds and can be dispersed long distances, and
(
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 islands 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
or
ruderal species. Unusual mechanisms of wind dispersal include
. 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 coasts 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 through erosion,
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 to . 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.[ ARS Studies Effect of Wind Sandblasting on Cotton Plants / January 26, 2010 / News from the USDA Agricultural Research Service. Ars.usda.gov. Retrieved 2011-11-03.] 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.
Besides plant gametes (seeds) wind also helps plants' enemies: and other of are even lighter and able to travel long distances.
Effect on animals
Cattle and
sheep are prone to
wind chill caused by a combination of wind and cold temperatures, when winds exceed , rendering their hair and wool coverings ineffective.
Although
use both a layer of
fat and
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,
use
kleptothermy 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
, 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 of the Earth's atmosphere, contaminates wind profiles gathered by weather radar, particularly the WSR-88D, by increasing the environmental wind returns by to .
use a wall of pebbles to store dry plants and grasses for the winter in order to protect the food from being blown away.
Related damage
High winds are known to cause damage, depending upon the magnitude of their velocity and pressure differential. Wind pressures are positive on the windward side of a structure and negative on the leeward side. Infrequent wind gusts can cause poorly designed suspension bridges to sway. When wind gusts are at a similar frequency to the swaying of the bridge, the bridge can be destroyed more easily, such as what occurred with the Tacoma Narrows Bridge in 1940.
Wind speeds as low as 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 , homes completely collapse, and significant damage is done to larger buildings. Total destruction to artificial structures occurs when winds reach . 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
, 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.
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.
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.
The fastest wind ever recorded came from the accretion disc of the IGR J17091-3624 black hole. Its speed is , which is 3% of the speed of light.
Planetary wind
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.
Solar wind
Rather than air, the solar wind is a stream of charged particles—a plasma—ejected from the upper atmosphere of the Sun at a rate of .
It consists mostly of
electrons and
with energies of about 1
electron volt. 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
solar 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 caused by the solar wind include geomagnetic storms that can knock out power grids on Earth,
the aurorae such as the Northern Lights,
and the plasma tails of
that always point away from the Sun.
On other planets
Strong winds at Venus's cloud tops circle the planet every four to five Earth days.
When the poles of
Mars are exposed to sunlight after their winter, the frozen CO
2 sublimates, creating significant winds that sweep off the poles as fast as , which subsequently transports large amounts of dust and water vapor over its
landscape.
Other Martian winds have resulted in
and dust devils.
[ NASA – NASA Mars Rover Churns Up Questions With Sulfur-Rich Soil. Nasa.gov. Retrieved 2011-11-03.] On
Jupiter, wind speeds of are common in zonal jet streams.
Saturn's winds are among the Solar System's fastest. Cassini–Huygens data indicated peak easterly winds of .
On
Uranus, northern hemisphere wind speeds reach as high as near 50 degrees north latitude.
At the cloud tops of
Neptune, prevailing winds range in speed from along the equator to at the poles.
At 70° S latitude on Neptune, a high-speed jet stream travels at a speed of .
The fastest wind on any known planet is on HD 80606 b located 190
away, where it blows at more than 11,000 mph or 5 km/s.
See also
External links
