air masses a large body of air with uniform temperature and moisture characteristics. they acquire...
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AIR MASSES
A large body of air with uniform temperature and moisture characteristics.
They acquire their characteristics in source regions, because they move slowly when passing these regions
Ex: A very cold air mass with low water vapor is generated over cold , snow-covered surface in artic region
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AIR MASSES
• Air masses move from one region to another (pressure gradient, upper level winds, jet stream)
•When moving, the properties are influenced by the new environment
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CLASSIFICATION OF AIR MASSES
1. Latitudinal position
2. Type of surface
Air Mass Symbol Source region
Artic A Artic region
Antartic AA Antartica
Polar P Continents and oceans (50-60°)
Tropical T Continents and oceans (20-35°)
Equatorial E Oceans close to equator
Maritime m oceansContinental c continents
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TYPICAL AIR MASSES
Air mass Symbol
Source region Properties
Maritime equatorial
mE warm oceans in equatorial region
warm, very moist
Maritime Tropical mT warm oceans in tropical region
Warm, moist
Continental tropical
cT Subtropical deserts Warm, dry
Maritime polar mP Midlatitude oceans Cool, moist(winter)
Continental polar cP Northern continental interiors
Cold, dry (winter)
Continental artic cA Regions near north pole
Very cold and dry
Continental antartic
cAA Regions near south pole
Very cold and dry
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TYPICAL AIR MASSES
See Figure 6.2 Page 155
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NORTH AMERICAN AIR MASSES
See Fig 6.3, page 156
Strong influence on North American weather
1. Continental Polar (cP) Tongues of cold dry air; periodically
extend S,E producing cold temperatures and clear skies
2. Continental Artic (cA) When moving southward: severe cold
wave
3. Maritime Polar (mP)Unstable in winter: heavy precipitation over
coastal ranges
4. Maritime Tropical (mT)Moves northward bringing moist unstable air:
thunderstorms
5. Continental Tropical (cT) Does not move widely, influence weather conditions over source region
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FRONTS
Transition zone between two air masses of different characteristics
COLD FRONT
Transition zone where a cold air mass invades a warmer air mass
Colder air mass remains in contact with ground (because is denser)
It forces warm air mass to riseIf warm air is unstable: thunderstorms
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PRECIPITATION IN A COLD FRONT (ANIMATION)
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FRONTS
WARM FRONT
Transition zone where a warm air moves into a region of colder air
Cold air remains in contact with ground (denser)
It forces warm air mass to riseIf warm air is stable:Steady precipitationIf warm air is unstable:thunderstorms
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PRECIPITATION IN A WARM FRONT (ANIMATION)
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OCCLUDED FRONT
When a cold front overtakes a warm front (cold fronts move at a faster rate than warm fronts)
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STATIONARY FRONT
A front that is not moving. Masses are not strong enough to replace each other
There is a noticeable temperature change and shift in wind direction between two sides of front
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THE PRESIDENT SNOW STORM (Feb 16-17 2003)
Stationary front
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WEATHER
CLIMATE
The condition of atmosphere at any particular time and place. It’s always changing
The synthesis of weather, the average weather of a region over a period of time
Weather surface map, July 02 2008
Annual average precipitation
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WEATHER SYSTEMS
Some patterns of wind circulation present recurring patterns of weather
Weather systems:
Few kilometers (tornado)
Thousands kilometers (a large traveling cyclone)
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CYCLONES ANTICYCLONES
Air spirals inward and upward
condensation, precipitation
Air spirals outward and downward
condensation cannot occur
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TRAVELING CYCLONES AND ANTICYCLONES
CYCLONES AND ANTICYCLONES: masses of air moving in a spiraling motion
Most of them are large features moving slowly across Earth’s surface and bringing changes to weather.
TRAVELLING CYCLONES AND ANTICYCLONES
TYPES OF CYCLONES:
1. Wave cyclones (middle and high latitudes, ~1000km or 600miles)
2. Tropical cyclones (hurricanes, typhoons)3. Tornado
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WAVE CYCLONES
The wave cyclone forms, intensify and dissolves along the polar front
Conditions to form: two anticyclones, one with warm air, and the other with cold polar air are in contact in the polar front.
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WAVE CYCLONE FORMATION
See Fig 6.8 page 161, 162
A. Early stage:There is a wave formation in the polar
frontCold air is going southward and warm air is moving northward
B. Open stage:Wave is deepened and
intensified
C. Occluded stage:Cold front overtakes warm front
(occluded front)Precipitation is intensified
D. Dissolving stage:The cold front is reestablished
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HOW DOES A WAVE CYCLONE AFFECT WEATHER? See page 162
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MARCH 21, 22 2005
http://www.hpc.ncep.noaa.gov/dailywxmap/index.html
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JUNE 12, 2004
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JUNE 27 2008
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JUNE 28 2008
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JUNE 29 2008
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