pg class26-air masses, fronts
TRANSCRIPT
Physical GeographyLecture 26
Air Masses and Fronts
Air Masses
Definition:◦ Large (diameter > 1600
km) body of air
◦ Similar characteristics throughout
◦ Recognizable entity; travel as one
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Figure 7-2
◦ Modifies area over which it moves
◦Is changed by area over which it moves
Classification based on Source Region
MOISTURE CONTENT c—continental, dry m—maritime, humid
Temperature P—polar source region T—tropical source region A—arctic source region E—equatorial source region
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North American Air Masses
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Figure 7-1
Southwestern Deserts – cT More moderate conditions in NW vs NE – mP vs. cP
Effects on North American Weather
Lake Effect Snows
Properties and Sources
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Fronts
“Front” of an air mass Midlatitude clashes Types of Fronts:
◦ Cold front: cold air advancing◦ Warm front: warm air advancing◦ Stationary front: no advance of air masses◦ Occluded front: cold front overtakes warm front
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Cold Front◦ Fast moving, Steep frontal interface, warm air rises
at front ◦ Tall clouds, severe weather, “Squall line”
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Warm Front◦ Gentle slope of warm air rising above cool air◦ Slow moving◦ Sequence of clouds precedes front◦ Steady precipitation
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Stalled warm and cold fronts
Can produce prolonged rain
Stationary Front
Cold front overtakes warm front
Occluded Front