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What causes wind?

You walk outside and feel a gentle breeze that blows through your hair. It can be pretty soothing — but sometimes you step out the door and Mother Nature practically blows you down the street with a gust of wind so strong that objects go flying and turn into projectiles. In the best-case scenario, it’s just a windy day. But if it’s truly bad weather like a hurricane or Nor’easter, those strong winds can be deadly. So, where does wind come from anyway?

What is wind?

Ground level view of tall grasses and reeds blowing in the wind on a clear day
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The answer might be simpler than you would imagine. It all comes down to temperature and how it affects gases that are naturally found in our atmosphere. Whether you know it or not, oxygen isn’t the only thing floating around in the Earth’s atmosphere. Even though oxygen is the dominant gas, our atmosphere is also composed of nitrogen, carbon dioxide, argon, and other trace gases.

How temperature impacts those gas molecules

Dandelion pappus separating from stem and blowing away in the wind
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When the temperature changes (say, from a frigid 40 degrees in the morning to a mild 65 in the afternoon), that can impact how those gas molecules interact with each other. At colder temperatures, the molecules move slower and tend to crowd together into dense packs. But when the air is warm, the molecules are more active and spread farther apart. The temperature doesn’t always change at an even rate in our atmosphere, and that can lead to uneven temperature pockets. Each type of gas will behave differently depending on the temperature. And that behavior can impact the weather by changing pressure.

Temperature and pressure

Brown autumn leaves getting picked up and blowing around on a windy day
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Since we’re talking about weather, you’ve probably heard a meteorologist talk about pressure moving into a region and impacting the weather forecast. That pressure is caused by the uneven heating or cooling of the Earth’s atmosphere. High pressure occurs when the air is colder while low pressure occurs when the air is warmer.

What does this have to do with wind, though?

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We’re getting there, we promise! These pressure systems — full of hot and cold gas molecules — will eventually meet, and that's when the fun part begins. When low and high pressures converge, molecules begin to pass between the two pressure systems and cause wind. Specifically, the wind strength is determined by the difference in temperature between pressure pockets. So, if the temperature difference is minimal, you might get a light breeze or no wind at all. But when the temperatures are more extreme, that’s when you get those intense gusts that blow you down the street.

However, temperature difference isn’t the only determinant for strong winds. The distance between a high and low pressure system can also impact wind strength. Two systems that are very far apart won’t produce strong winds. However, if two systems are in close proximity, some very forceful gusts can develop.

So, wind flows through pressure?

High aerial view of earth's curvature seen from above the clouds
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Actually, no — not at all. This is where it gets a little tricky. Officially, wind flows around pressure rather than through it. If you’re wondering why this is the case, it’s all because of the Earth’s rotation. In the Northern Hemisphere, the wind flows to the east while in the Southern Hemisphere, it flows to the west.

We know how to measure wind strength. Going back to that meteorologist’s forecast, if you’ve ever seen arrows flowing through a pressure system labeled “L” or “H,” those arrows represent wind. Officially, the term for the arrows is “isobar.” And if you were to look at a formal wind map, each isobar would be labeled with a specific pressure value measured in millibars. Isobars are critical indicators because even their direction and curvature around a pressure system can be used to predict exactly how strong the winds will be.

Does wind have a purpose?

Tropical trees blowing fiercely in the wind as storm clouds approach
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You ask that at just the right time. Wind isn’t just something designed to ruin your hair after a salon appointment. Wind is Mother Nature’s way of moving excess heat through the atmosphere. But winds can be slowed down when they come into contact with friction from the ground such as buildings or mountain ranges.

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