Points to Consider
- How does the difference in solar radiation that reaches the lower and upper latitudes
explain the way the atmosphere circulates? - How does the atmosphere protect life on Earth from harmful radiation and from ex-
treme temperatures? - What would the consequences be if the Earth’s overall heat budget were not balanced?
15.4 Air Movement.
Lesson Objectives
- List the parts of an atmospheric convection cell and the properties of the air currents
within it. - Describe how high and low pressure cells create local winds and explain how several
types of local winds form. - Discuss how global convection cells lead to the global wind belts.
Preview Questions
- How do high and low pressure zones determine where winds blow?
- How are land and sea breezes related to monsoon winds?
- What determines the directions in which the global wind belts blow?
Introduction
Knowing a few basic principles can give a person a good understanding of how and why air
moves. Warm air rises, creating a low pressure region, and cool air sinks, creating a high
pressure zone. Air flowing from areas of high pressure to low pressure creates winds. Air
moving at the bases of the three major convection cells in each hemisphere north and south
of the equator creates the global wind belts.
Air Pressure and Winds
Think back to what you learned about convection cells in the previous lesson. Warm air
rises, creating an upward-flowing limb of a convection cell (Figure15.19). Upward flowing
air lowers the air pressure of the area, forming alow pressure zone. The rising air sucks
in air from the surrounding area, creating wind.