AIR MASSES AND FRONTSWebQuest

Earth Science

AIR MASSES● Air Mass: A large volume of air defined by its

TEMPERATURE and WATER VAPOR.● c = Continental = Dry● m = Maritime = Moist● P = Polar = Cold● T = Tropical = Warm

● cP = Continental Polar air = ● mP = Maritime Polar air =● cT = Continental Tropical = ● mT = Maritime Tropical =

Cold, Dry air from CanadaCold, Moist air from N. Atlantic

Warm, Dry air from MexicoWarm, Moist air from Gulf of Mexico

Frontal Boundaries● Frontal Boundary = Where two different air masses

collide.● Cool, Dry air collides with Warm, Moist air.

Cold Front● Cold Front = Where a cP air mass collides with a mT air

mass.● cP air is doing the pushing.● mT air is rising UP creating vertical clouds.

● Cumulonimbus clouds● Thunderstorm

● What is the weather at A?● What is the weather at B?● What is the weather at C?

C B A

Warm Front● Warm Front = When a mT air mass collides with a cP air

mass.● mT air mass is doing the pushing.● As mT air pushes, it rises over the cP air creating low

horizontal clouds.● Stratus, nimbostratus, cirrus

● What is the weather at A?● What is the weather at B?● What is the weather at C?

C B A

Weather Map Symbols● Identify the weather map symbols to determine

weather in your area.● Cold Front =

● Warm Front =

cP mT

Air Pressure● Air Pressure: The weight of the air pushing down on the

surface of earth.Barometer:

•The tool that measures air pressure.

High and Low Pressure Systems● High pressure is caused by Cool, Dry air SINKING.● Low pressure is caused by Warm, Moist air RISING.

● Cool, Dry Air● = High Pressure● = Clear Skies

● Warm, Moist Air ● = Low Pressure● = Cloudy Skies

Global Winds● Global Winds: the global circulation of air from HIGH

pressure to LOW pressure. ● THE WINDS WILL BLOW FROM HIGH TO LOW

● The winds would go either North or South except for the Coriolis Effect causes the wind to curve to the

● What Global Winds affect North America?

Prevailing Westerlies

RIGHT

Coriolis Effect● The apparent curve of the wind to the right in the

Northern Hemisphere.● Caused by Earth’s Rotation● http://www.wiley.com/college/strahler/0471480533/animations/ch

07_animations/animation2.html

Pressure Systems● Surface winds:

● High = Move OUT of the center● Low = Move IN toward the center

● Add the Coriolis effect (curve to the right) ◻ Motion around a High = Clockwise◻ Motion around a Low = Counter Clockwise

AntiCyclone Cyclone

Pressure Centers● Isobars: Lines on a map connecting places with equal

pressure. This shows you the area of High and Low Pressure.

● Arrows show direction of wind.

Current U.S. Weather Map● May 24, 2011

Friday’s Weather Map

mP

mT

Weather Forecasting

cP

mT

NW

SW

Mid-Latitude Cyclone

Weather Station Model● Used to deliver a lot of information in a small space

Weather Map