If Earth were not rotating on its axis, global winds would move in roughly straight paths from the poles to the equator. However, because Earth rotates, global winds move in a curved path between the poles and the equator. Notice in Figure 13 that global winds curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The curving effect that Earth's rotation has on all freemoving objects, including global winds, is called the Coriolis effect. If Earth were not rotating, a rocket launched from the North Pole toward the equator would move in a straight line, as shown in Figure 15. However, because Earth is rotating underneath the rocket, the rocket would appear to an observer on Earth to curve to the right. Similary, Earth's rotation causes global winds to curve.
Monsoons
Seasonal changes in the heating of Earth's surface affect the circulation of the atmosphere. A monsoon is a wind system that is characterized by seasonal reversal of direction. Monsoons are similar to land and sea breezes except that they occur on a much wider scale and longer time frame. For example, the summer monsoon that occurs over much of South and Southeast Asia blows warm, humid air from the ocean onto land. As this air rises over land, it cools and brings heavy rainfall to parts of that region. In winter the monsoon reverses, blowing from land onto water and bringing drier weather.
Jet Stream
Global wind patterns are also affected by fast-moving streams of air at high altitudes. A belt of high-speed wind in the upper troposphere is called a jet stream. Jet streams are caused by great differences in air pressure that develop at high altitudes.
Figure 15 The Coriolis effect causes free-moving objects, such as rockets and global winds, to move in a curved path. A A rocket launched from the North Pole toward the equator would move in a straight line if Earth were not rotating. B The Coriolis effect causes such a rocket to appear to curve to the right. Similarly, the Coriolis effect causes global winds to curve to the right in the Northern Hemisphere.
ddSection 24.3 Assessment
Reviewing Concepts
What happens to solar energy when it reaches Earth's atmosphere?- Explain how energy is transferred within the troposphere.
- What causes the wind to blow?
- How are local winds and global winds similar? How are they different?
What are monsoons, and what causes them?
Critical Thinking
Relating Cause and Effects How does the Coriolis effect influence global wind patterns?
Applying Concepts You and your family vacation at a cabin on the shore of a large lake. At night, you notice that a breeze blows over your cabin toward the lake. Explain what causes the wind to blow in that direction.
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