1. Air Masses
Chapter 21 Section 1

2. Global Wind Patterns
Uneven heating by the Sun and Earth’s rotation cause differences in air pressure.
These differences cause wind patterns.
Fluids flow from high to low pressure.

3. Air Mass A large body of air with similar temperature and humidity.
Forms when that mass of air moves slowly or remains stationary.

4. Air Masses Source Region Type of Air Symbol Continental Dry c Maritime
 Moist m 
Tropical
 Warm T 
Polar
 Cold P 

5. North American Air Masses come from six locations:
Source Location
Movement
Weather cP
(1)Polar regions of Canada
south-southeast
Cold and dry mP
(2) Polar Pacific
(3) Polar Atlantic
southeast;
southwest-south
Cold and moist cT
(4) U.S. southwest
north-northeast
Warm and dry mT
(5)Tropical Pacific;
(6)Tropical Atlantic
northeast;
North-northwest
Warm and moist

6. North American Air Masses come from six locations:

7. An air mass brings the weather of its source region but can change as it travels.
Cold, dry air can travel over a warm ocean, pick up humidity and warm…rise, expand, cool, …forming clouds.

8. How is the air over a continent different from the air over an ocean?

9. Air moves from cold weather to hot.
Air near the poles is colder. It sinks, and creates a high pressure area.
Air near the equator is warm. It rises, creating a low pressure area.
Air moves from high pressure to low pressure, or from cold weather to hot weather.

10. Global Wind Patterns
Air generally flows from the poles to the equator.
Remember the Coriolis effect. It bends winds to the right in the Northern Hemisphere.

11. Air Masses