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GEOG 100 Lecture 8--Precipitation, Air Masses and Storms
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GEOG 100 Lecture 8--Precipitation, Air Masses and Storms

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Transcript

  • 1. Air Masses, Storms and other scary stuff and other scary stuff
  • 2. Formation of Precipitation: The Bergeron Process
  • 3. The Collision-coalescence process
  • 4. Some Different Forms of Precipitation • Rain – Drizzle vs. showers
  • 5. Some Different Forms of Precipitation • Snow • Sleet • Glaze (ice storm) 6
  • 6. Hail
  • 7. The Formation of Hail
  • 8. Global Precipitation
  • 9. Global Precipitation: The ITCZ Connection
  • 10. Precipitation in the U.S.
  • 11. What Is An Air Mass? A large parcel of air with characteristics which distinguish it from surrounding air 1000 mi (1600 km) across, several miles deep Conditions of temp., humidity, stability consistent horizontally at any altitude Moves as a coherent whole, not easily torn apart by local turbulence  Source region: Where an air mass originates 12
  • 12. Source Regions  Extensive, physically uniform surface area  High or low latitude Not found in the midlatitudes (too much atmospheric activity)  High pressure zones are common source regions (because air sinks, stays close to the ground, where it picks up surface characteristics)
  • 13. Air Mass Movement & Modification  Once an air mass moves, it influences the regions it enters  It is also influenced by those regions, especially in its lower section, closest to the ground
  • 14. Lake-effect snow: cP air crossing warmer water cP air crossing warmer water Areas commonly affected around the Great Lakes Buffalo, NY (Dec., 2001)--Nearly seven feet of lake effect snow fell in 5 days 16
  • 15. Air Mass Classification  Latitude A = arctic/antarctic P = polar T = tropical E = equatorial  Surface Conditions m = maritime c = continental
  • 16. Major Air Mass Source Regions  (c)A  mP  cP  mT  cT  (m)E
  • 17. Air Masses of North America
  • 18. So what happens when these air masses meet??? They start frontin’.
  • 19. Frontal lifting
  • 20. Movement of a Warm Front
  • 21. Warm Front: Development
  • 22. Movement of a Cold Front
  • 23. Cold Front: Development
  • 24. Comparison: Note the shape of the frontal boundary
  • 25. Stationary Front
  • 26. Occluded Front
  • 27. Fronts on a Weather Map
  • 28. Putting it together: Note line A – A’
  • 29. A cross section along line A – A’ (from the map on the previous slide)
  • 30. Real-World Application: An Atlantic Storm
  • 31. Life-cycle of a Midlatitude Cyclone
  • 32. A Hypothetical Weather Map (note the alternating Highs and Lows…)
  • 33. How do the Upper-level Winds Move?
  • 34. Major Midlatitude Disturbances  Midlatitudes Where are the most dynamic weather region polar and tropical air masses meet and mix  Midlatitude cyclones (a.k.a. depressions, lows, wave cyclones) Large low pressure systems (1000+ miles across) moving from west to east in the region of the Westerlies (35º to 70º N and S latitude)
  • 35. Characteristic weather changes with the passage of a cold front:  Sharp temp. drop as the front approaches  As the front approaches, wind direction is southerly  After the front passes, wind shifts to more northerly (opposite for the Southern Hemisphere)  Air pressure drops as the front approaches, rises after it passes  Clear skies, followed by clouds and precip. along the edge of the front, then colder with clear skies again as the front passes
  • 36. Mapping it out:
  • 37. Midlatitude Anticyclones  High pressure systems moving west to east  No fronts  Subsidence  Clear, dry weather  Cold in winter  May stagnate, stalling other weather systems behind them
  • 38. Now on to the fun stuff!
  • 39. Lightning
  • 40. Thunder
  • 41. Tornadoes
  • 42. Tornado formation
  • 43. 46
  • 44. 48
  • 45. Tropical Disturbances  Tropical Depression - winds up to 38 mph  Tropical Storm - winds 39 - 73 mph  Hurricane - winds 74+ mph
  • 46. Hurricanes Four different names for the same event:     Hurricane Typhoon Cyclones, tropical cyclones Baguios
  • 47. Hurricane Origins          Form in tropical and subtropical zones approx. 8° to 15° N or S latitude Rarely form within 3° N or S of equator (no Coriolis force), rarely cross it Tend to form in or just poleward of the ITCZ Tend to form in late summer and fall (warmest sea sfc. temps.) Storm’s low pressure cell feeds off warm sea sfc. temps. (up to 81°F!) Gains energy from release of latent heat of condensation during intense precipitation Always form over oceans Do not / rarely form in the south Atlantic or southeast Pacific because the water is too cold and air pressure too high Storm intensity lessens as it gains latitude (into cooler waters) or moves over land
  • 48. Hurricanes
  • 49. Hurricane Tracking
  • 50. Pressure Signature of a Hurricane
  • 51. Hurricane Structure
  • 52. Hurricane Katrina making landfall
  • 53. Storm Surge
  • 54. Storm surge damage in Galveston, TX from Hurricane Ike (Category 2) 58