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Study Guide Chapter 7
1. Define the following air mass symbols: mE, MT, cT, mP, cP,
and cA.
2. What are the 5 air masses that influence the weather of
North America. Describe characteristics of each air mass.
Know where each originates.
3. What is a front?
4. Draw the symbol for different fronts.
5. What is a stationary front and occluded front?
6. Describe the characteristics of cyclone and anticyclone.
7. What are thunderstorms?
8. What are tornadoes? Where is tornado alley?
9. Describe a hurricane. Where do hurricanes form?
Air Masses and Atmospheric
Disturbances
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An air mass is a large body of air homogeneous
in temperature and humidity.
A source region refers to where the air mass is
located geographically.
Source Regions
 E= Equatorial ( very warm)
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T= Tropical (warm)
P=Polar (cold)
A=Artic (very cold)
c= Continental (dry)
m=Maritime (wet)
Source Regions
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Combined to make various classifications
 mE
 mT
 cT
 mP
 cP
 cA
Fig. 7-1, p. 178
Air Masses
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cP continental polar
 Source region is Canada.
 Weather associated with this air mass is cold,
crisp, and clear weather.
 Rarely travels Western U.S.
cA continental artic
 Originates Artic Ocean it is extremely cold, dry,
and stable air. Rarely reaches the U.S.
Air Masses
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mP maritime polar
 Source region is Northern Pacific Ocean
 It is cold air, damp, and unstable. When this air
meets other cold air it usually results in cloudy
weather with precipitation. This is the source
of many MidWestern snowstorms.
Air Masses
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mT Maritime Tropical
 Source region Gulf of Mexico subtropical
region of Atlantic Ocean (Caribbean)
 When this air mass reaches cP air results in
significant precipitation.
 Responsible for thunderstorm activity.
cT continental Tropical
 Hot, dry, and clear skies.
 Sahara of North America. Where?
 Least important of air masses.
Cold Front and Warm Fronts
Weather symbols
Fig. 7-4, p. 181
Convergent or Cyclonic
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Low pressure
Air in the center is displaced upward
Diameter is approximately 600 miles
Counterclock wise movement
Divergent or anticyclonic
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High pressure air in center is subsiding
Usually associated with fair weather
Diameter about 900 miles
Clockwise movement
Cyclones and anticyclones tend to develop in
certain areas more frequently. These are known
as storm tracks.
Thunderstorms
•Thunderstorms are
uplift of moist air.
•Charges cause by friction
of air moving over ice
particles.
Thunderstorms
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When the lightning
discharge occurs the air is
heated to 45,0000 F. The air
expands explosively as
thunder.
Tornadoes
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Intense cyclonic/ low pressure storm
Tornado alley Oklahoma
and Kansas.
Natural funnel
Hurricanes
Diameters are 100-400 miles
Severe tropical cyclones that develop over warm oceans
Table 7-3, p. 197
Latent Heat of Condensation
Fig. 4-11, p. 96
Fig. 7-18, p. 195
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Weather symbols