- What Causes Wind?
- How Wind Is Measured
- Using Winds to Forecast Weather
- Wind and Climate Change
Wind is defined as the horizontal movement of air from one place to another. While low winds are less noticeable, forceful winds during inclement weather are hard to ignore.
What causes a lot of wind some days and nearly no wind on others? And how is it predicted and measured? Here, we explore the answers, as well as how climate change is impacting the wind’s power.
What Causes Wind?
Wind exists because of differences in air pressure, which begins with the sun. As sunlight strikes the Earth, it doesn’t emit heat equally. It strikes different places at different angles, which creates unique degrees of warming.
In the places that warm more quickly, heat energy is transferred to the air molecules, causing them to excite, spread out, and rise. This transfer 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 known as centers of high pressure.
Air molecules from these regions of high pressure always move to the regions of low pressure, filling the space that 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.
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.
What Are Prevailing Winds?
Prevailing winds are global wind belts that blow from the same direction over the same sections of the Earth throughout the year. Prevailing winds blow continuously because the heat imbalances that create them always exist.
The direction wind blows is determined by how the high and low pressure are positioned, and also by the Coriolis force.
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.
What Are Coriolis Force?
The Coriolis force is the tendency of air to veer slightly to the right of its path of motion in the Northern Hemisphere. This is often called an “apparent” force, because there’s no actual push involved. Rather, it is a perceived motion due to Earth’s eastward rotation.
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—any force that opposes motion—increases and the 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
Wind blows at all levels of the atmosphere, and changes in wind speed and direction at increasing heights produce wind shear. These violent changes in wind speed or direction produce churning motions and turbulence that can contribute to severe weather—including thunderstorm mesocyclones, which spawn tornadoes.
Wind shear 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
Because air is an invisible gas, wind can’t be measured in the same way as rain and show. Rather, it must be measured by the force it applies to objects.
An anemometer is a wind-measuring instrument 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 meter per second (m/s) or miles per hour (mph).
A different weather instrument called a wind vane is used for measuring wind direction. Vanes consist of a propeller with a pointer and a tail and a directional marker. 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. These also signal relative wind speed and can tell whether winds are calm, light, or strong.
Using Winds to Forecast Weather
Winds are also a forecasting tool in themselves. If winds are blowing from the north, for example, it can be an indication that colder, drier air is 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.
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.
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.
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 how climate change will affect large-scale circulations and local winds.
In theory, as global temperatures rise, winds should weaken. 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 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.
