Date post: | 21-Dec-2015 |
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What is an Air Mass?
• Air Mass
Large area (>1600 km by 1600 km) of air that contains relatively uniform, horizontal distributions of temperature and moisture.
How Air Masses Form
• If surface air resides in a region for a few days, it acquires the thermal and moisture characteristics of the underlying surface.
• Source regions for Air Masses are:
Big in area [ >>(1600 km)2 ]
Dominated by persistent high pressure and light winds
Air Mass Source Regions
• Contrasting source regions are
Continents versus Oceans
Tropics versus Poles
• An Air Mass is designated in terms of its Source Region
Lake Effect Snows
As cP air flows over the warmer, open Great Lakes, it is warmed and moistened. When the modified cP air flows onshore, prodigious snows of several feet can result.
Lutgens & Tarbuck, p 230
Modification of cP Air Mass
Ahrens Fig 8.4Ahrens Fig 8.4
cPcP
cPcP
mPmP
mPmP
warm oceanwarm ocean
warm oceanwarm ocean
mP Air Masses
Ahrens Fig 8.7Ahrens Fig 8.5
Air mass modified Air mass modified further as it crosses further as it crosses several mountain several mountain ranges of West U.S.ranges of West U.S.
Summary
• Air Masses
Large (>1000 miles) regions with “uniform” temperature and moisture characteristics
• Classified by Source Region Continental (c) or Maritime (m)Polar (P) or Tropical (T)
• Source Regions
Big in area (>>1600 km by 1600 km)
Dominated by light winds (long resident times)