1. 21.1 Air Masses
CHAPTER 21
EARTH SCIENCE

2. Vocabulary Terms
Air mass – a large body of air with the same amount of temperature and moisture (humidity) of the region where it exists
Forms due to small pressure differences causing the mass to move slow or stay stationary

3. What Causes Air Pressure
Earth’s Rotation causes air pressure differences
Which creates wind patterns
Fluids (Also AIR) flow from high to low pressure

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

5. N. American Air Masses come from 6 locations…
Source Location
Movement
Weather cP
(1) Polar Regions of Canada
south – southeast
Cold & Dry mP
(2) Polar Pacific
(3) Polar Atlantic
southeast; southwest-south
Cold & Moist cT
(4) US southwest
north-northeast
Warm & dry mT
(5) Tropical Pacific
(6) Tropical Atlantic
northeast;
north-northwest
Warm & moist

6. As it travels… Air mass brings weather from it’s source (origin)
BUT can change as it travels
EX: Cold, dry air travels over a warm ocean… Picks up humidity & warmth… rises, expands, & cools… forms clouds!

7. What weather do the four air masses bring?
1. cP (Continental Polar) brings cool/dry air in summer, cold air in North during winter.
2. mP (Maritime Polar) brings rain/snow in Pac coast during winter and cool/foggy weather in summer mPA tl-move eastward toward Europe or westward over New England and Canada (cold, cloudy)
3. cT (Continental Tropical) brings hot/dry weather during summer
4. mT (Maritime Tropical) (mT Atl) brings hot, humid weather with thunderstorms in summer and mild/cloudy weather in winter. (mT Pac)-brings moderate precipitation