20.1 Air Masses Key Concepts

· An air mass is an immense body of air that is characterized by similar temperatures and amounts of moisture at any given altitude.

· As an air mass moves, its characteristics can change and so does the weather in the area over which the air mass moves.

· Air masses are classified according to their source region, the place where they form.

· Much of the weather in North America is influenced by continental polar (cP) and maritime tropical (mT) air masses.

· Polar (P) or tropical (T) indicates the temperature of an air mass. Continental (c) or maritime (m) indicates whether the air mass is dry or humid.

Vocabulary

· Air mass - a large body of air that is characterized by similar temperatures and amounts of moisture at any given altitude

20.2 Fronts Key Concepts

· When two air masses meet, they form a front, which is a boundary that separates two contrasting air masses.

· A warm front forms when warm air moves into an area formerly covered by cooler air.

· A cold front forms when cold, dense air moves into a region occupied by warmer air.

· A stationary front forms when the surface position between two air masses does not move.

· An occluded front forms when a cold front overtakes a warm front, producing a complex weather pattern.

· A middle-latitude cyclone is a large center of low pressure that generally travels from west to east and causes stormy weather.

Vocabulary

Front - the boundary between two adjoining air masses having contrasting characteristics

Warm front - a front along which a warm air mass overrides a retreating mass of cooler air

Cold front - a front along which a cold air mass thrusts beneath a warmer air mass

stationary front - a situation in which the surface position of a front does not move; The flow on either side of such a boundary is nearly parallel to the position of the front

occluded front - a front formed when a cold front overtakes a warm front; It marks the beginning of the end of a middle-latitude cyclone.

20.3 Severe Storms Key Concepts

· A thunderstorm generates thunder and lightning and frequently produces gusty winds, heavy rain, and hail. Thunderstorms form when warm, humid air rises in an unstable environment.

· Tornadoes are violent windstorms that take the form of a rotating column of air called a vortex, which extends downward from a cumulonimbus cloud. Most tornadoes are associated with severe thunderstorms.

· Hurricanes are whirling tropical cyclones with high winds that sometimes develop over the ocean when water temperatures are warm enough to provide the necessary heat and moisture to fuel the storms.

Vocabulary

· Thunderstorm - a storm produced by a cumulonimbus cloud and always accompanied by lightning and thunder; It is of relatively short duration and usually accompanied by strong wind gusts, heavy rain, and sometimes hail.

· Tornado - a small, very intense cyclonic storm with exceedingly high winds, most often produced along cold fronts in conjunction with severe thunderstorms

· Hurricane - a tropical cyclonic storm having winds in excess of 119 kilometers per hour

· Eye wall - the doughnut-shaped area of intense cumulonimbus development and very strong winds that surrounds the eye of a hurricane

· Eye - a zone of scattered clouds and calm averaging about 20 kilometers in diameter at the center of a hurricane

· storm surge - the abnormal rise of the sea along a shore as a result of strong winds

Diagrams

Practice Assessment

1. If an area is experiencing consecutive days of constant weather, this weather is called

A. air-mass weather.

B. warm-front weather.

C. cold-front weather.

D. occluded-front weather.

2. An air mass that forms over the Gulf of Mexico is a(n)

A. cP air mass.

B. mP air mass.

C. cT air mass.

D. mT air mass.

3. Air masses that have the greatest influence on weather in the midwestern United States are

A. mT and cT air masses.

B. cP and mT air masses.

C. mP and cP air masses.

D. cT and cP air masses.

4. Lake-effect snow is associated with a(n)

A. mP air mass.

B. cP air mass.

C. mT air mass.

D. cT air mass.

5. “Rain long foretold, long last; short notice, soon past.” The first five words of this weather proverb refer to a(n)

A. cold front.

B. warm front.

C. anticyclone.

D. tornado.

6. Which front often produces hours of moderate-to-light precipitation over a large area?

A. polar

B. maritime

C. cold

D. warm

7. A thunderstorm is most intense during its

A. cumulus stage.

B. wave stage.

C. mature stage.

D. dissipating stage.

8. When a hurricane reaches land, its intensity decreases as the result of

A. increase in pressure and temperature.

B. lack of cold, dry air to fuel the storm.

C. successive updrafts into the eye wall.

D. friction and the lack of warm, moist air.

9. The eye of a hurricane

A. has the greatest wind speeds.

B. is warmer than the rest of the storm.

C. experiences high pressures.

D. is responsible for heavy precipitation.

10. An air mass that forms over northern Canada is a

A. maritime tropical air mass.

B. maritime polar air mass.

C. continental polar air mass.

D. continental tropical air mass.

11. Which air mass would be characterized by warm and dry air?

A. maritime tropical air mass

B. maritime polar air mass

C. continental polar air mass

D. continental tropical air mass

12. Lake-effect snow forms in the northeastern United States and southeastern Canada

A. directly over the Great Lakes.

B. on the leeward sides of the Great Lakes.

C. on the windward sides of the Great Lakes.

D. along the Atlantic coast.

13. Indian summer in New York in the autumn is the result of what type of air mass?

A. maritime tropical air mass

B. maritime polar air mass

C. continental polar air mass

D. continental tropical air mass

14. What type of front forms when warm air moves into an area with cooler air?

A. occluded front

B. stationary front

C. warm front

D. cold front

15. In the midwestern United States, a middle-latitude cyclone is a

A. tropical hurricane.

B. exceptionally large tornado.

C. large center of high pressure.

D. large center of low pressure.

16. In what direction do most weather systems move across the continental United States?

A. from west to east

B. from east to west

C. from north to south

D. from south to north

17. What conditions are necessary for the formation of a thunderstorm?

A. cold, dry unstable air

B. warm, dry stable air

C. warm, humid unstable air

D. cold, humid stable air

18. In a hurricane, the highest wind speeds and heaviest rainfall occur

A. inside the eye.

B. in the eye wall.

C. along the hurricane’s leading edge.

D. along the hurricane’s trailing edge.

19. Tornadoes form

A. in all thunderstorms.

B. in association with anticyclones.

C. in association with high-pressure centers.

D. in some severe thunderstorms.

Answers

1. A

2. D

3. B

4. B

5. B

6. D

7. C

8. D

9. B

10. C

11. D

12. B

13. D

14. C

15. D

16. A

17. C

18. B

19. D

Note on Earth Space Science Study Guides, created by spencer_mees on 31/03/2014.

Earth Space Science Study Guides