If this skater extended her arms as far away from her body as she could, she would spin more slowly. Similarly, the Earth would spin more slowly if the molecules of the atmosphere were clustered in high pressure systems near the equator.
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Windows to the Universe

Can Earth’s Spin Be Changed by Wind?
News story originally written on March 19, 2003

Earth’s atmosphere is changing all the time. Winds and pressure patterns change over days, weeks, and years. Not only do those changes affect the weather, they affect the rotation of the Earth as well, causing changes to the length of days.

How does the air around us affect the spin of our planet? Earth is spinning like a skater spins on the ice. When a skater moves his or her arms out, mass is moved far from the axis of rotation (the skater’s body) and the skater spins more slowly. The spinning Earth works in the same way! When atmospheric pressure is high at the equator, mass is moved far away from Earth’s axis of rotation, and the planet spins more slowly.

There are other ways the atmosphere can affect Earth’s rotation too. For instance, strong winds in the atmosphere cause Earth to slow its spin because the total amount of movement must stay they same. “If the atmosphere speeds up then the solid Earth must slow down,” says David A. Salstein, the scientist who led the recent study to understand Earth’s rotation.

The research team compared wind and pressure measurements with measurements of Earth’s rotation. They found evidence that Earth’s spin is affected by the movements of air and can cause the length of days to change up to a small fraction of a second. (So if you feel like it’s been a very long day, you may be right!)

Last modified July 31, 2003 by Jennifer Bergman.

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