1. Air Masses, Fronts and Global Wind Patterns
Meteorology
CGS – Earth Science

2. Air Masses

3. Definition:
Air mass - a large dome of air which has similar horizontal temperature and moisture characteristics throughout.
Very similar to a balloon.

4. Continental Arctic (cA):
Frigid – record low temperatures
Dry - very low dew points
Dense - very high barometric pressure
Usually originate north of the Arctic Circle
Siberian Express
Usually once or twice a winter
very rarely form during the summer
because the sun warms the Arctic.

5. Continental polar (cP):
Cold and dry - stable
Usually originates in NW Territory of Canada
Influences mainly the northern USA
Responsible for clear and pleasant weather during the summer
Usually in winter
Creates troughs in the polar jet stream
Lake effect snow in Great Lakes areas

6. Maritime polar (mP): Cool and moist - unstable
Originate over N. Atlantic and N. Pacific
Main Influence - the Pacific Northwest and the Northeast.
can form any time of the year
Generally not as cold as cP air masses

7. Maritime tropical (mT):
Warm and very moist – unstable
Originate in the Gulf of Mexico and the Southern Atlantic Ocean
Influences the eastern USA
Most prevalent during summer
Responsible for hot, humid summer days across the South and the East.

8. Continental Tropical (cT):
Very Hot and very dry – stable aloft
Originates in Desert Southwest and northern Mexico
Occurs in the summer, rarely in winter
Usually keeps the Desert Southwest scorching above 100oF during summer
Generally clear skies, hot, low humidity

9. Source Regions

11. Reasoning for Tornadoes
Orographic Perfection
Meeting of
Moist - mT
Hot - cT
Cool – cP
Rocky Mtn.

12. Tornado Alley

13. Fujita Scale
(NationalAtlas.com)

14. Fronts and their symbols

15. Fronts: Cold Warm Stationary Occluded Boundary between two air masses
Characterized by shift in weather
Cold
Warm
Stationary
Occluded

16. 5 Characteristics of a Front
Sharp temperature changes over a relatively short distance.
Changes in air moisture content
Shifts in wind direction
Pressure changes
Clouds and precipitation

18. Cold Fronts Temperature – drops rapidly Pressure – rises steadily
Clouds – Vertical building
Precipitation – Heavy along front
Winds – Strong and shifting
Typically move faster than warm front

19. Cold Front

20. Cold Front
(Fozzy)

21. Cold Front

22. In the summer, cold fronts can trigger:
thunderstorms
large hail
dangerous winds
tornadoes

23. Graphic Depiction!

24. Warm Fronts Temperature – rises slowly
Pressure – slight rise, then fall
Clouds – strato- and cirro-
Precipitation – long, steady
Winds – variable and light
Typically will have affect for days

25. Warm Front

26. Warm Front

27. Warm Front

28. Effects of warm fronts
Slow-moving warm front can mean days of wet weather before warm air
Sometimes water vapor in warm fronts condense to produce
rain
snow
sleet
freezing rain

29. Stationary Front

30. Stationary Fronts Temperature – stagnent
Pressure – slightly fluctuates
Clouds – altocumulus
Precipitation – none
Winds – variable and light
Can last for days weeks

31. Occluded Front

32. Occluded Fronts Temperature – Pressure – Clouds – cumulus
Warm – gets milder
Cold – gets colder
Pressure –
Warm - slight drop
Cold – slight rise
Clouds – cumulus
Precipitation – steady and light
Winds – variable and light

33. Occluded Front

35. Different Temperatures - Different Pressures
Less
Dense
Pressure
Cool
Air
Denser
More
Pressure
Warm
Air

36. Pressure and Air Movement

37. Pressure Gradient Force
Difference in pressure over a given distance---between isobars
Close together = step pressure gradient
STRONG winds
Far apart = gentle pressure gradient
Light winds
Just like contour lines

38. Pressure Gradient Force

39. Isobaric Maps

40. Coriolis Effect
Apparent force due to the rotation of the Earth (Think Merry-go-round)
N. Hemisphere  wind turns right
S. Hemisphere  wind turns left
Strength depends on latitude and wind speed

41. Coriolis Effect

44. Coriolis Effect

45. Centripetal Force In-ward directed force
Allows an object to remain in circular motion
Winds moving around high and low pressure areas
Clockwise around Highs.
Counter-clockwise around Lows.

46. Friction (What a Drag) The resistance to movement
Surface winds are affected by friction
Why? Ground resistance:
trees, mountains, houses, buildings, etc.
This drag causes winds to blow across pressure gradient at the surface.

47. Pressures All Together

48. General Planetary Circulation

50. Winds Horizontal movements at surface
Names from WHERE it came from…not where it is going!!!

51. Around Pressure Cells

52. Pressure Cells High – In and Up Low – Down and Out Converge at surface
Ascend in center
Diverge Aloft
Low – Down and Out
Converge aloft
Descend in center
Diverge at surface

53. X-section of Planetary Circulation

54. January Global Pressure Map

55. July Global Pressure Map

56. Summer Highs

58. Quiz Questions:
Where would you expect there to be the strongest winds? Why?
Where would you expect there to be the calmest winds?
Where would you expect clear, cool skies?
Where would you expect cloudy skies with the greatest potential for precipitation?

59. Work Cited (Incomplete)
seen 1/03/06