Chapter 16.2

Air Masses

and

Fronts

Air Masses

• Large body of air where temperature and moisture content are similar throughout.

• Named for where they form:M- Maritime- over water- Wet

C- Continental- over land- Dry

P- Polar- over polar regions- Cold

T- Tropical- over tropical regions- Warm

Combine letters to describe air masses

• mP- Maritime Polar– Wet, Cold

• cP- Continental Polar– Dry, Cold

• mT- Maritime Tropical– Wet, Warm

• cT- Continental Tropical– Dry, Warm

Air Masses that affect weather in North America

http://www.physicalgeography.net/fundamentals/7r.html

Air Masses

Fronts

• The boundary between Air Masses

• Four types:

– Cold

– Warm

– Occluded

– Stationary

Cold Front• Cold, denser air moves under warm, less dense

air and pushes the warm air up.• Moves quickly and brings heavy precipitation,

followed by cooler, drier air.

http://www.physicalgeography.net/fundamentals/7r.html

Warm Front• Warm, less dense air moves over cold, denser air.• Brings drizzly rain, followed by clear, warm

weather.

http://www.physicalgeography.net/fundamentals/7r.html

Occluded Front• Warm air caught between two colder air masses.• Cold air pushes warm air up, bringing cool

temperatures and large amounts of precipitation.

http://www.physicalgeography.net/fundamentals/7r.html

Stationary Front• “Stalemate” between a cold air mass and a

warm air mass.• Brings many days of cloudy, wet weather.

http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/tstorm/stat_front.html

Fronts

Vertical Air Movement• Cyclone: the winds circulate counterclockwise around a low. The air

is warm at the surface so it rises in a column such that its winds spiral upward and cool. The cyclone is associated with rain-making conditions.

• Anticyclone: develops where cold air aloft, being heavier and having a higher pressure, descends in spiraling motions to reach the surface as a pressure high. Brings dry, clear weather.

http://rst.gsfc.nasa.gov/Sect14/Sect14_1c.html