1. 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

2. 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

3. CLASSIFICATION OF AIR MASSES
1. Latitudinal position
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
2. Type of surface
Maritime m oceans
Continental c continents

4. 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

5. TYPICAL AIR MASSES
See Figure 6.2 Page 155

6. NORTH AMERICAN AIR MASSES
Strong influence on North American weather
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
See Fig 6.3, page 156

7. 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 rise
If warm air is unstable: thunderstorms

8. PRECIPITATION IN A COLD FRONT (ANIMATION)

9. 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 rise
If warm air is stable:
Steady precipitation
If warm air is unstable:
thunderstorms

10. PRECIPITATION IN A WARM FRONT (ANIMATION)

11. OCCLUDED FRONT
When a cold front overtakes a warm front (cold fronts move at a faster rate than warm fronts)

12. 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

16. THE PRESIDENT SNOW STORM (Feb 16-17 2003)
Stationary front

17. WEATHER
The condition of atmosphere at any particular time and place. It’s always changing
Weather surface map, July
CLIMATE
The synthesis of weather, the average weather of a region over a period of time
Annual average precipitation

18. WEATHER SYSTEMS
Some patterns of wind circulation present recurring patterns of weather
Weather systems:
Few kilometers (tornado)
Thousands kilometers (a large traveling cyclone)

19. CYCLONES
ANTICYCLONES
Air spirals inward and upward
Air spirals outward and downward
condensation, precipitation
condensation cannot occur

20. 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:
Wave cyclones (middle and high latitudes, ~1000km or 600miles)
Tropical cyclones (hurricanes, typhoons)
Tornado

21. 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.

22. WAVE CYCLONE FORMATION
See Fig 6.8 page 161, 162
Early stage:
There is a wave formation in the polar front
Cold 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

23. HOW DOES A WAVE CYCLONE AFFECT WEATHER?
See page 162

24. MARCH 21,

25. JUNE 12, 2004

26. JUNE

27. JUNE

28. JUNE