Chapter 8: section 3 Input
A huge body of air that has similar temperature, humidity, and air pressure at any given height is called
an air mass.
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4 major types of air masses influence the weather of North America:
1. Tropical- warm air mass, forms over the tropics, low air pressure
2. Polar- cold air mass, forms at 50’N and higher or 50” S or lower, high air pressure
3. Maritime- air masses that form over oceans
4. Continental- air masses that form over land
Maritime Tropical- warm, humid air mass that forms over oceans. These can form over the Gulf
of Mexico, over the Pacific, in the summer, usually bring hot, humid air
Maritime Polar- cool, humid air masses that form over the icy cold N Pacific and N Atlantic, even
in the summer, can bring fog, rain and cool temps
Continental Tropical- hot, dry air masses that form mostly over SW and N Mexico, brings hot,
dry weather to the S Great Plains
Continental Polar- large, cold air masses that form over central or northern Canada and Alaska
How Air Masses Move:
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In the US, air masses are mainly moved by prevailing westerlies and the jet stream
Prevailing westerlies- major wind belt pushing air masses from west to east
Jet Stream- embedded in the westerlies, high speed, moves west to east
Fronts- the boundaries where air masses meet, air masses don’t mix easily, density plays a major
role. The density is based on temperature and humidity.
Types of Air Masses:
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Cold Fronts
Warm Fronts
Stationary Fronts
Occluded Fronts
Cyclones vs Anticyclones
Cyclones- a swirling center of low air pressure, cause clouds, wind, precipitation, spins counter clockwise
Anticyclones- an area of high pressure with dry air, cause dry, clear weather, spins clockwise