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CHAPTER 9 AIR MASSES AND FRONTS

CHAPTER 9 AIR MASSES AND FRONTS. Air masses. What’s an air mass? A large body of air with similar temperature and humidity characteristics Where do these air masses come from? (Source Regions) P = polar T = tropical A = Arctic m = maritime c = continental. Temperature. Moisture.

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CHAPTER 9 AIR MASSES AND FRONTS

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  1. CHAPTER 9 AIR MASSES AND FRONTS

  2. Air masses • What’s an air mass? • A large body of air with similar temperature and humidity characteristics • Where do these air masses come from? (Source Regions) • P = polar • T = tropical • A = Arctic • m = maritime • c = continental Temperature Moisture

  3. Continental Polar (cP) air masses • cP: cold, dry, stable • Extreme case: cA - Cold air rushes down into central U.S. from Canada: “arctic high” • Impacts: • Citrus crop damage in southeast • Lake-effect snows near Great Lakes when cold air moves over warmer water

  4. Maritime Polar (mP) air masses • mP: cool, moist, somewhat unstable • Air from Pacific is lifted by mountains on west coast, producing rain and snow

  5. Continental Tropical (cT) air masses • Hot and dry, stable aloft but unstable near surface • Only really occurs in U.S. in summer in southwest • Few clouds and minimal precipitation • Impacts: • drought if a cT air mass remains in place for a long time July 2005 heat wave

  6. Maritime Tropical (mT) air masses • Warm, moist, unstable • Flow northward from Gulf of Mexico provides fuel for thunderstorms in the eastern U.S. • Flow from Pacific into California • Impacts: • Severe weather in the central and eastern U.S. • Flooding in California The “Pineapple Express”

  7. Atmospheric Rivers http://www.atmos.albany.edu/student/cordeira/WEB/PWAT/global_loop.html

  8. Maritime Tropical air ahead of a tropical cyclone 6 9 0000 UTC 16 Aug 2007

  9. 250 hPa h (dam), 700 hPa  (105 s1), precipitable water (mm) 850–500 hPa mean wind (kt) 6 9 0000 UTC 17 Aug 2007

  10. 6 9 250 hPa h (dam), 700 hPa  (105 s1), precipitable water (mm) 850–500 hPa mean wind (kt) 0000 UTC 18 Aug 2007

  11. 6 9 250 hPa h (dam), 700 hPa  (105 s1), precipitable water (mm) 850–500 hPa mean wind (kt) 0000 UTC 19 Aug 2007

  12. 6 9 250 hPa h (dam), 700 hPa  (105 s1), precipitable water (mm) 850–500 hPa mean wind (kt) 1200 UTC 19 Aug 2007

  13. Rainfall Totals (in)

  14. Identifying air masses

  15. Identifying air masses

  16. Identifying air masses mP cP mT

  17. Fronts A Front - is the boundary between air masses; normally refers to where this interface intersects the ground (in all cases except stationary fronts, the symbols are placed pointing to the direction of movement) Warm Front Cold Front Stationary Front Occluded Front

  18. Fig. 9.16, p. 252

  19. Other Boundaries Dryline - Separation of warm, moist air (from Gulf) and warm, dry air (from SW United States) (common over west Texas in spring/summer) Dryline

  20. Cloud cover and surface dew point

  21. How to find a front • Sharp change in temperature • Sometimes, though… • Sharp change in dew point • Shift in wind direction • “Kink” in isobars • Weather/Clouds

  22. Fronts – Real World http://www.hpc.ncep.noaa.gov/sfc/namussfcwbg.gif

  23. Fronts – Real World **(Amanda) Fanning is one of my former students!

  24. Air mass change on Wednesday, 7 March 2012

  25. Fronts – Real World

  26. Fronts – Real World

  27. Cold fronts • “Dome” of dense cold air is replacing warm air • Steep leading edge – may have strong upward motion • Clouds and precip. usually ahead of fast-moving cold front, lagging behind if slow-moving

  28. What happens when a cold front passes?

  29. Fig. 9.15, p. 251

  30. Warm fronts • Warm air replacing cool air • Relatively gentle slope – leads to broad area of upward motion • Warm fronts usually move slower than cold fronts

  31. What happens when a warm front passes?

  32. Stationary fronts • Name is self-explanatory: doesn’t move much • In some cases where air is moist on both sides, stationary fronts can lead to flooding – rain forms along front and persists for many days

  33. Fig. 9.9, p. 246

  34. Extra Credit Quiz • In 1-2 sentences, explain why there is no such thing as a “maritime Arctic” (mA) air mass. • BE SURE TO WRITE YOUR NAME ON YOUR PAPER • Have a great spring break and be safe!

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