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Coriolis Effect
Dana Desonie, Ph.D.
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Printed: April 24, 2013
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C ONCEPT
Concept 1. Coriolis Effect
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Coriolis Effect
• Explain the Coriolis effect.
Is this an example of the Coriolis effect?
Does Coriolis determine which direction water in a toilet will swirl? Unfortunately, no. Friction and the power of
the flush have too big an influence. But in the atmosphere and oceans, Coriolis affects flow direction.
Coriolis Effect
The Coriolis effect is not a force, even though that’s what it is sometimes called. Coriolis does not force anything
to happen! Coriolis is an effect. What does that mean?
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The Coriolis effect describes how Earth’s rotation steers winds and surface ocean currents. Unlike land, air and
water move freely (in the absence of obstacles). The Coriolis effect causes the path of a freely moving object to
appear to curve. This is because Earth is rotating beneath the object. So even though the object’s path is straight, it
appears to curve. The curve appears to be to the right in the Northern Hemisphere. It appears to be to the left in the
Southern Hemisphere.
Here is an example in the Northern Hemisphere. A plane takes off from City A . The pilot wants to land in City B,
which is 500 miles due north. But the plane will not arrive there without corrections. City B was due north of City
A when the plane took off. But during the time it takes for the airplane to fly 500 miles, City B moves east. This
happens because of Earth’s rotation. So if the airplane flies due north, it will arrive at a different city, City C. City C
is west of City B (in the Northern Hemisphere). To reach City B, the pilot should curve right while flying north. The
opposite happens in the Southern Hemisphere. In the flights between cities pictured below (Figure 1.1), the flight
paths look curved. Since a flight path must curve to the right in the Northern Hemisphere, can you tell which city
the plane took off from in each case?
FIGURE 1.1
The Coriolis effect is the reason that
airlines’ flight paths look curved, even
though they are the shortest possible
path.
Effect for Air or Water
As wind or an ocean current moves, the Earth spins underneath it. Wind or water that travels toward the poles from
the Equator curves to the east. Wind or water that travels toward the equator from the poles curves to the west. The
Coriolis effect bends the direction of surface currents to the right in the Northern Hemisphere. The currents curve
left in the Southern Hemisphere (Figure 1.2).
Vocabulary
• Coriolis effect: Apparent deflection of a freely moving object like water or air because of Earth’s rotation.
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Concept 1. Coriolis Effect
FIGURE 1.2
The Coriolis effect causes winds and currents to form circular patterns. The direction that they spin depends on the
hemisphere that they are in.
Summary
• Earth rotates beneath freely moving objects like water and air. Compared with a spot on the planet, the objects
appear to be moving.
• Freely moving objects appear to move right in the Northern Hemisphere. They appear to move left in the
Southern Hemisphere.
• Coriolis is an effect rather than a force. Coriolis does not force a motion. An object appears to have a change
of motion due to the Coriolis effect.
Practice
Use these resources to answer the questions that follow.
MEDIA
Click image to the left for more content.
1.
2.
3.
4.
What is the Coriolis effect?
What is subject to the Coriolis effect?
What is the direction of deflection in the Northern Hemisphere?
What is the direction of deflection in the Southern Hemisphere?
Test your skills on the Coriolis effect.
http://www.montereyinstitute.org/noaa/lesson08/l8ex1.htm
5. What happens if pilots do not correct for the Coriolis effect?
Review
1. What is the Coriolis effect?
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2. How does the Coriolis effect explain the curved flight paths in the image above (Figure 1.1)?
3. How does Coriolis affect wind and water?
References
1. Image copyright Santiago Cornejo, 2012. . Used under license from Shutterstock.com
2. Courtesy of US Navy Oceanographic Office. . Public Domain
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