1. The Water Cycle Continues
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
How does air temperature relate to the amount of water vapor the air can hold? Warm air can hold more water vapor.
Humidity is the amount of water vapor in the air.
What is created when the amount of water vapor is over 100%? Precipitation

4. Pressure High pressure H Low pressure L Sinking air Rising air Cold
Dry
Low pressure L
Rising air
Hot
Wet
A lot of pressure is exerted when air particles are compacted.
Tip: Students piled on top of each other creates what type of pressure? High
Students separated in the classroom creates what type of pressure? Low

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
High Air Pressure is associated with colder and drier places.
Low Air Pressure is associated with warmer and humid places.
Warm air rising creates low pressure zone at the ground. Air from the surrounding area is sucked into the space left by the rising air. Air flows horizontally at top of the troposphere; horizontal flow = advection. The air cools until it descends. Where it reaches the ground, it creates high pressure zone
How is wind created? When air moves from high pressure to low pressure.

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
The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. Water has a high specific heat meaning it takes the ocean longer to either get warmer or cooler. Land has a low specific heat, meaning it doesn’t take must heat to increase the temperature.

9. Sea breezes blow what type of air
Sea breezes blow what type of air? Cooler air from the ocean to the land and warmer air from the land out to sea.

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
If Earth did not rotate, there would only be 2 huge convection cells. One in the northern and the other in the southern hemisphere. Low pressure at the equator going to the high pressure in the poles. But the Earth does rotate causing the coriolus effect. Wind are deflected to the right.

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