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 very complex and changes occur all the time. Winds and pressure patterns change over days, weeks, and years. Not only do those changes affect the weather, but also scientists have recently found evidence that they affect the rotation of the Earth as well, causing changes to the length of days. (So if you feel like today has been a very long day, you may be right!)

How does the air around us affect the spin of our planet? Concepts from physics, such as angular momentum, can help us understand how this happens. Angular momentum describes the spin of the Earth on its axis. Imagine that the spin of the Earth is like a skater spinning on the ice. When the skater moves his or her arms out, mass is moved far from the axis of rotation and the skater’s spin slows down. Similarly, when atmospheric pressure is high at the equator, increased mass is located far from Earth’s axis of rotation, and the spin slows.

Strong winds can also cause the Earth’s rotation to slow because, according to the laws of physics, the total amount of angular momentum must stay the same. “So if the atmosphere speeds up (stronger westerly winds) then the solid Earth must slow down (length-of-day increases),” says scientist David A. Salstein, who led the recent study to understand how the atmosphere affected Earth’s rotation.

Especially strong winds, like those related to El Nino, can cause small but measurable changes to Earth’s rotation. During El Nino, the rotation of the Earth may be slower because of the strong winds. Earth’s rotation does not slow very much, but it does make each day a fraction of a millisecond longer.

Salstein and his team looked at wind and pressure measurements from the National Weather Service. They used measurements of the Earth’s rotation from a variety of space-based observation systems such as GPS satellites and geodetic satellites. They compared the atmosphere data with the rotation data and found support for their hypothesis that the movements of air through our atmosphere affect Earth’s rotation!

Last modified July 31, 2003 by Jennifer Bergman.

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