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Wind: the story on HearLore | HearLore
Wind
The strongest wind ever recorded on a planet in our solar system does not blow on Earth, but on Neptune, where jet streams race at speeds exceeding 2,000 kilometers per hour. This invisible engine drives the weather of our world, yet for most of human history, it remained a mysterious force that could save a nation or destroy a fleet. Wind is the natural movement of air or other gases relative to a planet's surface, a phenomenon that operates on scales ranging from the thunderstorm flows lasting tens of minutes to the global circulations that have shaped the climate of Earth for billions of years. The study of this movement, known as anemology, reveals that 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 creates the Coriolis effect. Within the tropics and subtropics, thermal low circulations over terrain and high plateaus drive monsoon circulations, while in coastal areas, the sea breeze and land breeze cycle define local winds. In areas that have variable terrain, mountain and valley breezes can prevail, creating a complex tapestry of air movement that affects everything from the spread of seeds to the formation of fertile soils like loess.
The Physics of Pressure
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 are the differential heating between the equator and the poles 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 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. 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 gradients. 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.
Common questions
What is the strongest wind ever recorded on a planet in our solar system?
The strongest wind ever recorded on a planet in our solar system occurs on Neptune, where jet streams race at speeds exceeding 2,000 kilometers per hour. This phenomenon operates on scales ranging from thunderstorm flows to global circulations that have shaped the climate of Earth for billions of years.
How is wind speed measured and what instruments are used?
Wind speed is measured by anemometers, most commonly using rotating cups or propellers. When a high measurement frequency is needed, wind can be measured by the propagation speed of ultrasound signals or by the effect of ventilation on the resistance of a heated wire.
When was the strongest wind gust on Earth recorded and where did it occur?
Australia's Barrow Island holds the record for the strongest wind gust, reaching 408 kilometers per hour or 253 miles per hour during tropical Cyclone Olivia on the 10th of April 1996. This event surpassed the previous record of 372 kilometers per hour or 231 miles per hour set on Mount Washington in New Hampshire on the afternoon of the 12th of April 1934.
Who created the Beaufort wind force scale and how many levels does it have?
The Beaufort wind force scale was created by Francis Beaufort and originally provided a 13-level scale from 0 to 12. During the 1940s, the scale was expanded to 18 levels from 0 to 17 to describe wind speed based on observed sea conditions.
Why does wind direction matter for sailing ships and aircraft?
For sailing ships, wind direction determines the ability to power the vessel and avoid hazards like being becalmed or blown off course. For aircraft, the velocity of surface wind is the primary factor governing flight operations, as airfield runways are aligned to account for the common wind direction of the local area.
How does wind affect plant growth and seed dispersal?
Wind disperses seeds, spores, and pollen through mechanisms like anemochory and anemophily, which are critical for plant reproduction and evolution. Strong winds can also limit tree growth by scouring away thin soils, damaging limbs, and causing windthrow, which is most likely on windward slopes of mountains.
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. Weather vanes pivot to indicate the direction of the wind. At airports, windsocks indicate wind direction, and can also be used to estimate wind speed by the angle of hang. Wind speed is measured by anemometers, 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 tubes 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, 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 10 meters per second for periods of seconds. A squall is an increase of the wind speed above a certain threshold, which lasts for a minute or more. To determine winds aloft, radiosondes 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 theodolites. Remote sensing techniques for wind include SODAR, Doppler lidars and radars, which can measure the Doppler shift of electromagnetic radiation scattered or reflected off suspended aerosols or molecules, and radiometers 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 at cloud top 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 artificial objects.
The Beaufort Scale
Historically, the Beaufort wind force scale, created by Francis Beaufort, provides an empirical description of wind speed based on observed sea conditions. Originally it was a 13-level scale from 0 to 12, but during the 1940s, the scale was expanded to 18 levels from 0 to 17. 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 34 and 47 knots 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 48 to 55 knots. 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. General wind classifications include Calm, Light air, Light breeze, Gentle breeze, Moderate breeze, Fresh breeze, Strong breeze, Moderate gale, Fresh gale, Strong gale, Whole gale, Storm, Hurricane, and beyond. Tropical cyclone classifications vary by region, with terms like Tropical disturbance, Tropical depression, Tropical storm, Severe tropical storm, Typhoon, and Super typhoon used to describe the intensity of these systems. The Enhanced Fujita 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. The station model plotted on surface weather maps 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 5 knots of wind. Each full flag depicts 10 knots of wind. Each pennant or filled triangle depicts 50 knots 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 or 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.
Gods and Armadas
As a natural force, the wind was often personified as one or more wind gods or as an expression of the supernatural in many cultures. Vayu is the Vedic and 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 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 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 or grandfather of the winds of the eight directions. In Māori mythology, Tāwhirimātea or Tāwhiri is the god of weather, including thunder and lightning, wind, clouds and storms. In the Yoruba pantheon, Ọya or Iansã is the orisha of winds, lightning, and storms. 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. 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 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.
Sails and Turbines
There are many different forms of sailing ships, but they all have certain basic things in common. Except for rotor ships using the Magnus effect, every sailing ship has a hull, rigging and at least one mast to hold up the sails that use the wind to power the ship. 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 storms 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 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. 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 bring the temperatures inside up to 1,000 degrees Celsius. 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 sails covered in reed matting or cloth material. These windmills were used to grind corn and draw up water, and were used in the gristmilling 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. Most of the installed capacity in wind power is onshore, but offshore wind power offers a large potential as wind speeds are typically higher and more constant away from the coast. Wind energy, the kinetic energy of the air, is proportional to the third power of wind velocity. Betz's law described the theoretical upper limit of what fraction of this energy wind turbines can extract, which is about 59%.
Erosion and Extremes
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. 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, which have a feathery pappus attached to their seeds and can be dispersed long distances, and maples, 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, meaning larger seed mass and smaller pappus, relative to the same species on the mainland. Reliance upon wind dispersal is common among many weedy or ruderal species. Unusual mechanisms of wind dispersal include tumbleweeds. 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 soils 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 stands 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 10 to 50 meters per second. 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. Besides plant gametes, wind also helps plants' enemies. Spores and other propagules of plant pathogens are even lighter and able to travel long distances. A few plant diseases are known to have been known to travel over marginal seas and even entire oceans. Humans are unable to prevent or even slow down wind dispersal of plant pathogens, requiring prediction and amelioration instead.
The Solar Wind
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 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. 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 10^12 particles per second. It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time. These particles are able to escape the Sun's gravity, in part because of the high temperature of the corona, 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 comets that always point away from the Sun. 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 CO2 sublimates, creating significant winds that sweep off the poles as fast as 100 meters per second, which subsequently transports large amounts of dust and water vapor over its landscape. Other Martian winds have resulted in cleaning events and dust devils. On Jupiter, wind speeds of 100 meters per second are common in zonal jet streams. Saturn's winds are among the Solar System's fastest. Cassini-Huygens data indicated peak easterly winds of 500 meters per second. On Uranus, northern hemisphere wind speeds reach as high as 250 meters per second near 50 degrees north latitude. At the cloud tops of Neptune, prevailing winds range in speed from 200 meters per second along the equator to 500 meters per second at the poles. At 70 degrees south latitude on Neptune, a high-speed jet stream travels at a speed of 1,000 meters per second. The fastest wind on any known planet is on HD 80606 b located 190 light years away, where it blows at more than 11,000 miles per hour or 5 kilometers per second. Australia's Barrow Island holds the record for the strongest wind gust, reaching 408 kilometers per hour or 253 miles per hour during tropical Cyclone Olivia on the 10th of April 1996, surpassing the previous record of 372 kilometers per hour or 231 miles per hour set on Mount Washington in New Hampshire on the afternoon of the 12th of April 1934.