The Coriolis effect is an apparent deflection in
the paths of moving objects caused by Earth's faster speed near
the equator than near the poles. In the solar system, the greatest
expression of this effect occurs in planetary atmospheres. On Earth,
for example, the air around us moves freely above the ground. Low-pressure
centers draw air in; high-pressure centers push air away. As illustrated
here, Earth's differential rotation bends the paths of moving air
just enough to create a consistent circulating pattern.
Unlike spinning bicycle wheels and other kinds of rotation we see
all around us, Earth's rotational rate is very small--only one rotation
a day. Water swirling down a drain, by contrast, may take only a
few seconds to make one rotation, a very fast rate. Thus, contrary
to popular belief, the Coriolis effect doesn't influence the direction
of draining water one way or the other.
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The Coriolis Effect
Because Earth rotates faster near the equator than
near the poles (indicated by the varying lengths of the yellow arrows),
moving air drawn to low-pressure areas at midlatitudes travels east
either faster or slower than the low itself. As the low draws air
in (white arrows), the difference in speeds causes the air to curve--counterclockwise
in the Northern Hemisphere and clockwise in the Southern Hemisphere
(purple arrows).
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On Earth
As shown in this photograph of the 1997 Pacific
storm named Hurricane Linda, air moving from all directions toward
a low-pressure area rotates counterclockwise in the Northern Hemisphere.
By contrast, air being pushed away from high-pressure areas circulates
clockwise north of the equator and counterclockwise south of the
equator.
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In the Solar System
Jupiter's Great Red Spot, a huge storm bigger than
Earth itself, exemplifies the
Coriolis effect at work on other planets. Observed for more than
300 years, the Great Red Spot rotates counterclockwise in Jupiter's
Southern Hemisphere--a dead giveaway that it is a high-pressure
system.
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