Wind

Wind is the natural movement of air or other gases near a planet's surface. It happens in many ways, from small flows during thunderstorms that last minutes, to breezes caused by the heating of land that last a few hours, to huge global winds created by differences in solar energy absorbed in different climate zones on Earth. The study of wind is called anemology.

Large-scale winds are mainly caused by the difference in heating between the equator and the poles, and by the rotation of the planet, known as the Coriolis effect. Local winds like sea breeze and land breeze or mountain and valley breezes can also be important. Winds can be grouped by their size, speed, direction, the forces that create them, where they occur, and what effects they have.

Wind has been important for humans throughout history and in daily life. It has powered sailing ships to travel across oceans, helped hot air balloons to fly, and is used to generate electricity. Strong winds can sometimes be dangerous, damaging trees, buildings, and affecting flights. Wind also shapes the land through erosion and helps spread seeds, affecting plants and animals.

Causes

See also: Atmospheric pressure

Wind happens because air pressure changes. Air moves from places with higher pressure to places with lower pressure. On Earth, moving air gets pushed to the side by something called the Coriolis effect, except right at the equator.

Big wind patterns are mostly caused by two things: the sun heating the equator more than the poles, and the Earth's rotation. Near the ground, friction slows the wind down and makes it blow toward lower pressure areas.

Measurement

Wind direction tells us where the wind is coming from. For example, a north wind blows from the north to the south. Weather vanes and windsocks at airports show the wind direction. Wind speed is measured by instruments called anemometers. These instruments often have rotating cups or propellers.

Different places measure wind speeds in different ways. In the United States, wind speeds are sometimes measured over a 1-minute average. A quick burst of strong wind is called a wind gust, and a longer period of stronger wind is called a squall.

Models

Models help us learn about how air moves. We can study air movement side to side by using data from different places. We can also study movement up and down using special patterns.

Scientists use math to figure out how wind changes over time. This helps them predict the weather and learn about the Earth's climate. Things like sunlight, the Earth's spin, and friction affect wind. Computers are now helping scientists understand wind more quickly.

Wind force scale

See also: Tropical cyclone intensity scales and Surface weather analysis

Long ago, a system called the Beaufort wind force scale was made to describe wind speed by looking at how the sea looked. It has many levels, and we use words like breeze, gale, storm, or hurricane to talk about different wind speeds.

The Enhanced Fujita Scale is used to measure how strong tornadoes are by looking at the damage they cause. It has six levels. This scale is used in the United States and some other places like Canada and France.

Enhanced Fujita scale

The station model is a way to show wind on weather maps using a special symbol called a wind barb. The wind barb shows wind direction and speed. Small parts of the barb, called flags and pennants, tell us how fast the wind is blowing. Once these symbols are drawn on a map, we can learn about areas with the same wind speed.

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 (9.3 km/h; 5.8 mph) of wind.
• Each full flag depicts 10 knots (19 km/h; 12 mph) of wind.
• Each pennant (filled triangle) depicts 50 knots (93 km/h; 58 mph) of wind.

Winds are shown as blowing from the direction the barb is facing. Once plotted on a map, an analysis of isotachs (lines of equal wind speeds) can be done. Isotachs help us find the jet Stream on weather charts.

Global climatology

Main article: Prevailing winds

Winds on Earth move in different patterns depending on where you are. Near the poles, winds usually blow from east to west. In areas farther from the poles but not too close to the equator, called the mid-latitudes, winds blow from west to east. Near the equator, winds also blow from east to west.

Tropics

See also: Trade winds and Monsoon

In the tropics, close to the equator, there are steady winds called trade winds. In the north, these winds blow mostly from the northeast, and in the south, from the southeast. These winds help guide big storms that form over oceans.

A monsoon is a big seasonal wind that blows for several months in tropical areas. It was first named in places like India and Bangladesh. These winds bring a lot of rain when they blow from the Indian Ocean and the Arabian Sea.

Westerlies and their impact

Main article: Westerlies

The westerlies are strong winds that blow from west to east in the mid-latitudes, between 35 and 65 degrees from the equator. In the north, they mostly come from the southwest, and in the south, from the northwest. They are strongest in winter and help move weather systems across the oceans. These winds also help create ocean currents that carry warm water toward the poles.

Polar easterlies

Main article: Polar easterlies

Near the poles, there are dry and cold winds called polar easterlies. These winds blow from east to west, from high-pressure areas at the poles toward lower pressure areas farther away. They are usually weak and can change direction because of the Earth's rotation.

Local considerations

Sea and land breezes

Main article: Sea breeze

Near the coast, the land and sea heat up differently, which affects the wind. During the day, land warms up faster than the sea. Warm air rises over the land, and cooler air from the sea moves in to replace it, creating a breeze that brings cooler air to the land. At night, the land cools down faster than the sea, sometimes causing a breeze that moves from the land back to the sea.

Near mountains

Mountains change how the wind blows. When air moves over mountains, it can speed up, slow down, or change direction. This can make flying near mountains tricky for airplanes. Some places have special names for these fast mountain winds, like the Papagayo wind in Central America or the Mistral in Europe. These winds can affect the ocean, bringing up deep, cool water that helps sea creatures grow.

In places with lots of mountains, the wind can twist and turn in unpredictable ways. When moist air moves up a mountain, it cools and drops its water as rain on the windward side. The air then becomes dry as it moves down the other side, often creating dry, warm winds known as downslope winds. These winds have different names in different places, like the foehn in Europe or the chinook in the United States. In California, downslope winds like the Santa Ana can become very strong.

Shear

Wind shear is when the wind speed or direction changes over a short distance in the air. This can happen up, down, and side to side. You can see wind shear near weather fronts, close to the coast, or near the ground. It is often noticed near thunderstorms, mountains, big buildings, wind turbines, and sailboats.

Wind shear matters for airplanes when they take off and land. It can also change how we hear sounds and affect the weather.

In civilization

Religion

Wind has been important in many cultures. It is often seen as a god or powerful spirit. In Hindu beliefs, Vayu is the God of Wind. The ancient Greeks had wind gods like Boreas, Notus, Eurus, and Zephyrus. The Japanese god Fūjin is linked to wind. In Norse stories, Njörðr is the god of wind. Many other cultures have their own wind gods and spirits.

History

Wind has had big effects on history. In Japan, strong winds called "kamikaze" helped protect the country from invaders. In 1588, a storm helped stop a fleet trying to attack England. Wind has also caused problems in wars, like sandstorms making it hard for soldiers to fight.

Transportation

Sailing ships use wind to travel across oceans. They need wind to move, and strong storms can make their journeys dangerous. Today, airplanes also feel the effects of wind, which can change how fast they travel and where they go.

Power source

People have used wind for a long time to power machines. Ancient people used wind to heat furnaces, and later built windmills to grind grain and pump water. Today, wind is a big source of clean energy, helping to power many places around the world.

Metallurgy

Wind has been used for metalworking for a very long time, helping to heat furnaces for melting metals.

Recreation

Wind is important in many fun activities, like hang gliding, hot air ballooning, kite flying, sailing, and windsurfing. Wind can change how these sports feel and work, making them exciting and challenging.

In the natural world

See also: Aeolian processes

Wind is very important in dry areas because it can move dirt and dust over long distances. This moving of dirt is called deflation. Wind can also help plants spread their seeds and pollen far away from where they grew. Even though wind isn't the main way plants spread their seeds, it helps many plants share their seeds, spores, and pollen.

Erosion

Wind can move small bits of dirt and sand from one place to another. This moving is called deflation. When these bits hit other things, they can wear them down, which is called abrasion. Wind erosion usually happens where there isn't much plants to hold the soil down, like in deserts. One example is the formation of sand dunes. Loess is a type of windblown dirt that can form thick layers and is important for farming, but it can also erode easily. Farmers often plant trees and bushes, called windbreaks, to help stop this erosion.

Desert dust migration

In the summer, winds can carry dust from places like the Sahara Desert in Africa to faraway places, even all the way to the United States. This dust can change the color of the sky and affect air quality. It can also hurt coral reefs in places like Florida and the Caribbean. Dust from other places, like the Gobi Desert in Asia, can also travel very far.

There are special names for winds that carry dust in different parts of the world. For example, the Calima brings dust to the Canary Islands, the Harmattan brings dust to the Gulf of Guinea, and the Sirocco brings dust from North Africa to southern Europe.

Effect on plants

See also: Seed dispersal

Wind helps some plants spread their seeds by carrying them through the air. For example, dandelions have tiny, feathery parts on their seeds that let the wind carry them far away. Maples have seeds with wings that flutter to the ground. Wind can also carry pollen between plants, which helps them make new plants.

Wind can also affect how trees grow. Strong winds can prevent trees from growing very tall, especially near coasts or on mountains. Wind can also damage plants by throwing sand at them, which can hurt young plants.

Effect on animals

Cattle and sheep can feel very cold when it is windy and chilly, because the wind takes away their body heat. Penguins in cold places like Antarctica huddle together to stay warm. Small flying insects are carried by the wind, while birds use the wind to help them fly during migration.

Small animals like pikas build walls of pebbles to keep their food from being blown away. Cockroaches can feel tiny changes in the wind that warn them when danger is coming. Elk can smell predators that are upwind from them. And some birds, like glaucous gulls, hunt more when the wind is strong.

Related damage

See also: Severe weather

Strong winds can cause damage. They can push on buildings and bridges, making them sway or break apart. Even light winds can knock down tree branches, which can knock out power lines. Some trees, like eucalyptus, hibiscus, and avocado, are more easily damaged by wind.

Very powerful winds can damage homes, especially those without strong foundations. They can break windows or scratch car paint. Extremely strong winds can destroy buildings completely. Scientists use special scales like the Saffir–Simpson scale and Enhanced Fujita scale to estimate how strong winds were based on the damage they caused, especially during big storms like tornadoes.

Australia's Barrow Island holds a record for the strongest wind ever measured, during a big storm in 1996. Wildfires can also grow much faster when winds are stronger, helping the fire spread quickly.

In outer space

Main article: Stellar wind

The solar wind is very different from wind on Earth. It comes from the Sun and is made of tiny charged particles that have left the Sun's atmosphere. Planetary wind is made of light gases that escape from planets' atmospheres over time. This can change what a planet's atmosphere is like.

The fastest wind ever found came from around a black hole called IGR J17091-3624. It moves at an amazing 20,000,000 miles per hour.

Planetary wind

Main article: Atmospheric escape

In the upper parts of a planet’s atmosphere, light gases like hydrogen can rise to a special level called the exobase. From there, they can escape into space. This slow loss of gas is called planetary wind. Over very long times, this can change planets. For example, Earth, which has water, might end up like Venus if this kept happening. Hotter planets can lose their gases even faster.

Solar wind

Main article: Solar wind

The solar wind isn’t air—it’s a flow of charged particles, called a plasma, coming from the Sun’s upper atmosphere. It’s mostly made of tiny particles called electrons and protons. These particles can escape the Sun because of the Sun’s high heat and energy. The solar wind makes a big bubble called the Heliopshere around our Solar System. Earth’s magnetic field helps protect our atmosphere from this wind. The solar wind can also create beautiful lights in the sky, like the Northern Lights, and can affect things like power grids on Earth. It also makes the tails of comets point away from the Sun.

On other planets

On Venus, strong winds circle the planet every few days. On Mars, when it gets warmer near the poles, frozen carbon dioxide turns into gas and makes fast winds that move dust and water. Jupiter and Saturn also have very fast winds. Uranus and Neptune have strong winds, especially near their poles. The fastest wind ever found is on a planet far away from us, blowing at over 11,000 miles per hour.