What Causes Wind to Blow?

Discover how imbalances between high and low air pressure get things moving.

A young boy flies a kite in a field with wind turbines.

Erik Isakson / Getty Images

Wind, the horizontal movement of air from one place to another, is one of the basic elements of weather. Although its variable and, at times, calm nature can make it an afterthought to some (according to a survey on mobile weather app preferences, only 38% of people said it was an important part of weather forecasts), there's no forgetting its sheer force. It's what makes wind power an ideal renewable energy source, as well as one of the most damaging components of tornadoes, microbursts, hurricanes, and other severe storms.

What Causes Wind?

Wind exists because of differences in air pressure. As sunlight strikes the Earth, it doesn't heat it equally. It strikes different places at different angles; and some places, such as land, heat more quickly than others, such as oceans. In the places that warm more quickly, heat energy is transferred to the air molecules, causing them to excite, spread out, and rise; this is observed as a decrease in pressure, or the creation of a low pressure center. Meanwhile, molecules within cooler pockets of air are more tightly packed and sink downward, exerting a high amount of force onto the air below them; these are centers of high pressure.

Because Mother Nature doesn't like imbalance, air molecules from these regions of high pressure always move to the regions of low pressure, in an effort to "fill in" the space the warm, rising air leaves behind. (Meteorologists call the force that pushes air horizontally between high and low pressure regions the "pressure gradient force.") The resulting rush of air between these two locations is the wind we experience. It's also how winds aloft, including the prevailing winds that reside in the upper levels of the atmosphere, are born.

Prevailing Winds

True to their name, prevailing winds are global wind belts that blow from the same direction, over the same sections of earth, throughout the year. Examples include the westerlies, the easterlies, the trade winds, and the midlatitude and subtropical jet streams. Prevailing winds blow continuously because the heat imbalances that create them (for example, those between the equator and the North Pole) always exist.

Wind's speed is determined by how much of a pressure difference exists. The bigger the difference between the pressures, the faster the air rushes toward the low pressure.

The direction wind blows is determined by how the high and low pressure are positioned, and also by the Coriolis force — an apparent force that curves wind's path slightly to the right. Wind direction is always expressed in the direction the wind is blowing from. For example, if winds are blowing from the north to the south, they are "northerly winds," or winds from the north.

Coriolis Force

The Coriolis force is the tendency of air (and all other free-moving objects) to veer slightly to the right of its path of motion in the Northern Hemisphere. It's often called an "apparent" force, because there's no actual push involved, it's simply a perceived motion due to Earth's eastward rotation. In the Southern Hemisphere, the Coriolis force curves air in the opposite direction, or to the left.

Wind Gusts

As the wind blows, a number of things can interrupt air's motion and make its speed vary, such as trees, mountains, and buildings. Whenever air is obstructed in this way, friction (a force that opposes motion) increases and wind's speed slows. Once wind passes the object, it flows freely again, and its speed increases in a sudden, short burst known as a gust.

Wind Shear

View looking up at a highway interchange and blue sky.
Visualize wind shear as a highway interchange.

P_Wei / Getty Images

Wind doesn't just blow along Earth's surface; it blows at all levels of the atmosphere, too. In fact, winds can blow at different speeds and different directions as you travel vertically up into the atmosphere. These changes in wind speed, direction, or both, at increasing heights produce wind shear. Think of a cloverleaf or a highway interchange, with cars traveling at various speeds, in various directions, at multiple levels; wind shear behaves in a similar way.

These violent changes in wind speed or direction produce churning motions, turbulence, and roll a necessary ingredient for many kinds of severe weather, including thunderstorm mesocyclones which spawn tornadoes. On the other hand, it can create a hostile environment for hurricanes and tropical cyclones, since such winds can lop off the tops of these storms, allowing dry air to be drawn into their bellies.

How Wind Is Measured

A wind vane and anemometer against a blue sky.

Oliver Childs / Getty Images

Because air, and therefore wind, is an invisible gas, it can't be measured in the same way as say, rain and snow. Instead, it's measured by the force it applies on objects.

The sideways ferris-wheel-like instrument that measures wind is called an anemometer. It's made up of three conical or hemispherical cups mounted to a long rod. As the wind blows, air fills the mouths of the cups, pushing the wheel into a spin. As the cup-wheel rotates, it turns the rod, which is connected to a small generator inside the anemometer. By counting the number of rotations, the generator calculates the corresponding wind speed in either meters per second (m/s) or miles per hour (mph).

A different weather instrument — a wind vane — is used for measuring wind direction. Vanes, which consist of a propeller with a pointer and a tail, and a directional marker, lie parallel to the wind. The tail position indicates the direction where the wind is blowing from, while the pointer marks where it's blowing to. Windsocks are another type of wind vane; they also signal relative wind speed, that is, whether winds are calm, light, or strong.

Using Winds to Forecast Weather

In addition to being a component of weather forecasts, winds are also a forecasting tool. If winds are blowing from the north, for example, it can be an indication that colder, drier air may be moving into an area. Similarly, southerly winds can be indicative of the arrival of warm, moist air.

Meteorologists also use wind measurements to tell how fast weather systems are moving, which allows them to forecast how soon they'll arrive at a specific location. In fact, jet stream winds are responsible for steering storm systems across the United States and around the globe.

What Are Jet Streams?

Jet streams are ribbons of high-speed winds that flow from west to east above the Earth's surface. They occur at the boundary between hot and cold air masses, where hot air rises and cold air sinks down to replace it, creating an air current. Jet winds can reach speeds over 275 mph.

Winds not only drive the movement of weather systems and severe storms, they also carry air pollution from one part of the world to another. In June 2020, the trade winds swept a plume of Saharan dust from north Africa nearly 5,000 miles across the Atlantic Ocean into the Gulf of Mexico.

As evidenced by the Enhanced Fujita and Saffir-Simpson Scales, winds are also used to measure the intensity and damage potential of tornadoes and hurricanes.

Wind and Climate Change

Because winds are driven by unequal heating of the atmosphere, climate warming is expected to influence their occurrence. However, it is still unclear what the affects of climate change on large scale circulations and local winds will be. In theory, as global temperatures rise, winds should weaken, since the world's coldest locations are warming at faster rates than already-warm ones, shrinking temperature and, as a result, pressure differences. But research findings don't consistently support this. Previously, scientists believed that global winds had decreased slightly since the 1980s — a phenomenon known as "global stilling." But in 2019, a study in the journal Nature Climate Change revealed that this stilling reversed in 2010, and that since then, global average wind speed has increased from 7 mph to 7.4 mph.

Based on these findings, it's possible that natural climate cycles may be acting within the larger, long-term warming pattern to trigger the switch from slower to faster winds every few decades. And if this proves true, it could cause U.S. wind patterns to vary regionally and seasonally.

Determining where these variations could occur will be critical for renewable wind resources and the wind power industry's long-term planning, especially when it comes to erecting new wind farms. However, if the current pattern holds, the average global electricity generation from wind could increase 37% by 2024.

View Article Sources
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  2. Zeng, Zhenzhong et al. "A Reversal In Global Terrestrial Stilling And Its Implications For Wind Energy Production." Nature Climate Change, vol. 9, no. 12, 2019, pp. 979-985., doi:10.1038/s41558-019-0622-6