Air Masses, Fronts and Global Wind Patterns

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 • http://www.britannica.com/thunderstorms_tornadoes/video/ocliwea124v4.mov

13. Fujita Scale (NationalAtlas.com)

14. Fronts and their symbols

15. Fronts: • 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 – • 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 Less 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 • STRONGwinds • 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!!!