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K12 LibreTexts

10.18: Circulation in the Atmosphere

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    5495
  • Where can you go to experience wind?

    Wind is one of the most obviously dynamic features of our dynamic planet. For a long time Mt. Washington in New Hampshire was known as the windiest place on Earth. It no longer is called that, but it's still plenty windy. A wind speed of 231 miles per hour was recorded on the mountain in April 1934. In a 200 mph wind, you would not be able to stand up. Temperatures due to wind chill would be outrageously cold!

    Atmospheric Circulation

    Wind is just moving air. You can't really see it, but you can see its effects. Whether it’s a gentle breeze or strong wind, you are most aware of air when it moves (Figure below). You can feel its molecules press against you. You can see things, like dirt and leaves, moving in the wind. And you can see object moving, like flags and trees, as a result of the wind.

    Effects of the wind blowing

    How can you tell the wind is blowing in these photos?

    Why Air Moves

    Air movement takes place in the troposphere. This is the lowest layer of the atmosphere. Air moves because of differences in heating. These differences create convection currents and winds (Figure below).

    • Air in the troposphere is warmer near the ground. The warm air rises because it is light. The light, rising air creates an area of low air pressure at the surface.
    • The rising air cools as it reaches the top of the troposphere. The air gets denser, so it sinks to the surface. The sinking, heavy air creates an area of high air pressure near the ground.
    • Air always flows from an area of higher pressure to an area of lower pressure. Air flowing over Earth’s surface is called wind. The greater the difference in pressure, the stronger the wind blows.

    Diagram of a convection cell

    Differences in air temperature cause convection currents and wind.

    Summary

    • Warm air rises because it is less dense. This creates an area of low pressure.
    • Cool air sinks because it is denser. This creates an area of high pressure.
    • Wind blows from areas of high pressure to areas of low pressure.

    Review

    1. Diagram and label the parts of a convection cell in the troposphere.
    2. Why does warm air rise? Why does cool air sink?
    3. What creates wind?

    Explore More

    Use the resource below to answer the questions that follow.

    1. Where is insolation strongest?
    2. What type of pressure occurs at the Equator? Why?
    3. What type of pressure occurs at the poles? Why?
    4. What are Hadley cells?
    5. How do surface winds move?
    6. What happens at the polar front?
    7. How does air move differently at high altitudes?
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