15.4 air movement

1. 15.4 air movement The Water Cycle Continues

2. Learning Targets • List the properties of the air currents within a convection cell • 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

3. Air Movement • Caused by convection within Troposphere • Hot air rises • Less dense • Cold air sinks • More dense

4. Pressure • High pressure H • Sinking air • Cold • Dry • Low pressure L • Rising air • Hot • Wet

5. Low Pressure • Warmer air holds more moisture than colder air • When warm air rises and cools in low pressure zone, cannot hold all water it contains as vapor. • Excess water forms clouds and precipitation

6. High Pressure • When cool air descends, it warms. Since it can then hold more moisture, the descending air will evaporate water on the ground

7. Wind • Rules of wind • Moves from H to L • Moves from cold to hot • Named for direction it comes from • Local winds result from air moving between small H and L pressure systems • Global winds result from large H and L pressure systems

8. Sea Breezes & Land Breezes • Local wind • Created by high specific heat of water and low specific heat of land • From sea to land in summer–Sea Breeze • Cool water; hot land • From land to sea in winter – Land Breeze • Warm water; cold land • Moderates coastal climates

10. Global Wind Belts • 3 enormous convection cells • Control global climate zones • Hadley Cells 00 to 300 • Hot air rises at equator L • Ferrel Cells 300 to 500 • Separates Hadley and polar • Polar Cells 500 to 600 • Cold air falls at the poles H

11. Global Wind Belts • Circulation cells determine amount of precipitation region receives • Low pressure regions: • air is rising • rain is common • High pressure regions: • Sinking air causes evaporation • Usually dry