Why the atmosphere spins with the Earth

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Main Question or Discussion Point

The mantle of the earth spins at about 1000mph at the equator and at 0mph at the poles. The atmosphere spins in unison and I've never fully understood why.

I would be very grateful for a scientific explanation.
 

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  • #2
D H
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Friction.

Suppose the atmosphere wasn't rotating. Think of what a 1000 mph would do. It would rip the surface to shreds. That however would slow the wind down, at least at the surface. The slower winds at the surface would in turn interact with the faster moving air aloft. Over a relatively short period of time the atmosphere wind would eventually settle into a state where it is more or less rotating with the Earth.

In fact, the Earth hasn't always been rotating at one revolution per 23.9344696 hours (the current length of a sidereal day). The rotation rate has been decreasing over time. 380 million years ago a day was only 22 hours long. The atmosphere has kept pace with this decrease because the atmosphere interacts with the rotating Earth.
 
  • #3
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Also, the Earth is not smooth, so you get turbulence and density waves which transfer energy between surface and atmosphere.

One example is the way wind over water drives waves: The longer the 'fetch', the bigger the wave as it absorbs energy from the wind. This is then dissipated when the wave breaks on a reef or shore...
http://www.seafriends.org.nz/oceano/waves.htm
 
  • #4
DoggerDan
The air closest to the surface of any spinning object tends to stick with the object. That's as true for hard drives and gyroscopes as it is for the Earth. The difference between the former two and the Earth is that the Earth's atmosphere has no outer element of friction, so it rotates with the Earth throughout its altitude.
 
  • #5
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I think the question has been mostly answered, but yes, friction... there's no (very little?) friction between "space" and the atmosphere, but there is friction (drag) between the earth and the atmosphere...

Also, this is an interesting read... http://www.srh.noaa.gov/jetstream/global/jet.htm
 
  • #6
D H
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Actually, the upper atmosphere is rotating faster than is the Earth itself. This is due to the diurnal bulge and due to interactions between the Earth's magnetic field and the partially ionized upper atmosphere, which in turn interacts with the neutral atmosphere.
 
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Yeah, I guess it does spin faster, The jet stream would be proof... Right?
 
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D H
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Yeah, I guess it does spin faster, The jet stream would be proof... Right?
Not really. For one thing, the jet streams are rather small. For another, the jet streams are somewhat counterbalanced by the prevailing easterlies (the lower atmosphere under-rotates in the tropics). The super-rotation of the ionosphere encompasses much of the ionosphere and is a phenomenon quite distinct from the jet streams.
 

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