2/14/2013 1 Chapter 20: Weather 20.1 Air Masses & Weather • Air mass : a large body of air in the lower troposphere that has similar characteristics throughout, such as temperature and humidity • Characteristics depend on origin Air Masses of North America www.fas.org Air Masses http://www.classzone.com/books/earth_science/terc/content/visualizations/e s2001/es2001page01.cfm?chapter_no=20 Chapter 20: Weather 20.2 Fronts and Lows • Front : the boundary that separates opposing air masses • Air masses may differ in –Temperature –Humidity –Both •Less dense air is forced to rise over more dense air •Forms a wedge as less dense air is uplifted. • The lifting force causes condensation (clouds), and if enough moisture, precipitation Kinds of fronts: • Cold : boundary between advancing cold air mass and the warm air mass it is displacing
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2/14/2013
1
Chapter 20: Weather
20.1 Air Masses & Weather
• Air mass: a large body of air in the lower troposphere that has similar characteristics throughout, such as temperature and humidity
• Characteristics depend on origin
Air Masses of North America
www.fas.org
Air Masseshttp://www.classzone.com/books/earth_science/terc/content/visualizations/e
s2001/es2001page01.cfm?chapter_no=20
Chapter 20: Weather
20.2 Fronts and Lows
• Front: the boundary that separates opposing air masses
• Air masses may differ in
–Temperature
–Humidity
–Both
•Less dense air is forced to rise over more dense air
•Forms a wedge as less dense air is uplifted.
• The lifting force causes condensation (clouds), and if enough moisture, precipitation
Kinds of fronts:
• Cold: boundary between advancing cold air mass and the warm air mass it is displacing
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•The greater the contrast between air masses, the more dramatic the weather.
•Occluded front: when a cold front “catches up” to a warm front
•Stationary front: when a front does not move (it’s simply an air mass boundary)
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