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. 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 cPGenerally not as cold as cP air masses

6. Source Regions

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

9. Tornado Alley http://www.britannica.com/thunderstorms _tornadoes/video/ocliwea124v4.mov http://www.britannica.com/thunderstorms _tornadoes/video/ocliwea124v4.mov

10. Fujita Scale (NationalAtlas.com)

11. Fronts and their symbols

12. Air Gun How do air molecules create air pressure?

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

14. 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

16. 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

17. Cold Front

18. (Fozzy) Cold Front

19. Stratus Clouds

20. Cold Front

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

22. Graphic Depiction!

23. 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

24. Warm Front

27. 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

28. Stationary Front

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

30. Occluded Front

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

32. Occluded Front

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

35. Pressure and Air Movement

38. 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

39. Pressure Gradient Force

40. Isobaric Maps

41. 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

42. Coriolis Effect

46. 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.

47. 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.

48. General Planetary Circulation

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

51. Around Pressure Cells

52. Pressure Cells High – In and Up  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 January

55. July Global Pressure Map July

56. Summer Highs

58. Quiz Questions: 1. Where would you expect there to be the strongest winds? Why? 2. Where would you expect there to be the calmest winds? 3. Where would you expect clear, cool skies? 4. Where would you expect cloudy skies with the greatest potential for precipitation?

59. Work Cited (Incomplete) http://www.usatoday.com/weather/tg/wamsorce/wamsorce.htm seen 1/03/06 http://www.srh.weather.gov/srh/jetstream/synoptic/airmass.htm