A light stir of leaves, a fresh breeze at the beach, ang gusts of arctic cold — these are all examples of wind, which is simply the movement of air from from high to low pressure. Let’s explore what causes wind on the Earth and the different types of wind you might encounter.
What Causes Wind?
The weather on Earth is driven by the sun. The sun’s light does not shine the same way on every surface, and this causes energy imbalances between dry and wet, tropical and arctic, sea and land, concrete and grass, and so many more. Wind is nature’s attempt to equalize the Earth’s weather systems. Take the sun away, and within a few weeks, our world would be just a big ball of ice with little wind.
In addition to the sun, here are some high-level factors that drive wind formation:
Imagine a sunny July day in the desert. The ground is scorching hot, and there’s no way you’re walking on it barefoot! The air above this sandy cauldron is strongly heated, so it gets lighter and rises. Cooler air surrounding the sandy area will then replace the hot, rising air, and the process repeats. This is a simple circulation of wind caused by changing temperatures. A sea breeze along the coast covers a much larger area but forms in a similar way. During a sea breeze, air rises over the hotter coastline, and cooler sea air replaces it.
In our desert example, the hot air moved upward, and the cool air flowed in to replace it. When air rises, the pressure beneath it drops — if this happens over a large enough area, then a low-pressure cell can take shape. The same process in reverse creates high pressure. For instance, high pressure forms over polar locations every winter because there’s much less sunlight, and the air loses its heat to space. This process is referred to as global circulation, which causes wind due to the creation of high- and low-pressure systems.
The snow-covered ground will make the air become even colder. Cold air is heavier than warm air, so voila: higher pressure at the surface. If you’re in such a weather pattern, your home barometer will show the pressure increasing. High-pressure zones are largely responsible for moving cold fronts around the Earth, helped along by the jet stream. Low-pressure areas such as hurricanes may have intense gradients, or differences, across them. The greater the pressure difference is between zones, the faster the wind will blow to even out the pressure gradient and balance the forces.
Air generally cools at night and warms in the daytime, and this cycle of cooling and warming can make for some crazy winds in mountain areas. Jumbled terrain like a canyon can focus a strong wind through one area, while 300 feet away, the breezes are very gentle. The wind typically blows up the mountain during the day as the warm air rises and down the mountain at night when the cool air is sinking.
The Jet Stream: A River of Wind
The jet stream moves large high- and low-pressure systems around the Earth in a constantly changing pattern. It is driven by temperature differences, just like all other winds, and is sometimes called a “river” of wind.
- The jet stream “river” resides between 20,000 and 50,000 feet above ground level.
- Kinks in the jet can be compared to a meandering river’s flow, and the air will move more quickly in the middle of the river than along the edges.
- There is typically a polar jet stream and a subtropical jet stream, which both change position as the seasons change. For instance, the polar jet stream is farther south in the winter and moves northward in the summer.
- Remember that temperature changes affect the jet stream: the greater the temperature contrast, the stronger it will be. This means the polar jet stream is usually stronger than the subtropical version.
- The jet stream helps to form and move large pressure cells around the Earth and increases the potential for severe weather in the spring.
Special Kinds of Wind Storms
- Microburst: A microburst is a sudden downburst of rain-cooled air that may reach speeds of 110 mph and cause significant damage. A microburst usually covers an area about 2 miles across, with a length of 5 to 10 miles.
- Tornado: A tornado is a violently rotating column of air produced by a thunderstorm and contact with the ground. Most twisters are less than a quarter-mile wide, but extreme ones can reach 2 miles wide. Wind speeds in tornadoes vary from less than 86 mph in the weakest versions to over 200 mph in the most intense ones. Tornadoes are influenced by the jet stream as well as temperatures and pressures.
- Hurricane: A hurricane converts heat energy from the ocean into wind energy. Hurricanes are usually several hundred miles wide, with most of the destructive winds existing within 50 miles of the center. Given their size, hurricanes have a much larger footprint of damage than tornadoes. Hurricane wind speeds may run from 74 mph on the low end to over 155 mph on the high end.
- Derecho: Derechos are severe wind storms that form from downbursts and microbursts in thunderstorms. As the storm develops, winds can exceed 100 mph and travel at least 250 miles, causing damage to trees, homes, and vehicles.
It’s All About the Sun
All wind starts with some influence from solar heating, or a lack thereof. Everything else — pressure changes, sea breezes, tornadoes, and the like — is linked to this starting point. It might be interesting to track wind, temperature, and pressure changes at your home with an easy-to-use weather station and see how they relate to one another. For instance, open your freezer door and notice how the cold air sinks. Let air out of a bicycle tire and note how it feels cooler than the surrounding air. These are both examples of temperature and pressure changes, which are always tied together. Give it a try!
Steve LaNore is a certified broadcast meteorologist with more than 30 years’ forecasting and technical experience. He has provided meteorological consulting for everything from insurance adjusters to court cases and is a nine-time award-winning author and broadcaster. LaNore has authored two books, available on Amazon. He resides in north Texas near beautiful Lake Texoma.