Lecture14 oct28-bb

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Lecture14 oct28-bb

  1. 1. Lecture  14 Air Mass Fronts 1
  2. 2. Air Masses
  3. 3. Weather map 11/02/2009 Weather strongly depends on where an air mass comes from!!!
  4. 4. What is an air mass? An air mass is a large body of air with similar temperature and humidity An air mass is named by its birthplace (source region) 4
  5. 5. Must be dominated by light wind (or non at all) Must have an extensive, uniform surface 5
  6. 6. air mass name By two letters with two properties
  7. 7. air mass name By two letters with two properties cA cP cT mP mT
  8. 8. 8
  9. 9. 9
  10. 10. Why cold cP passage causes clear weather?
  11. 11. The upper air flow on the map below would bring ____ air masses into the Pacific Northwest and ____ air masses into the eastern United States. a. b. c. d. mT, mP mP, cP mT, cP mP, cT 11
  12. 12. Air masses of North America mP/west coast 12
  13. 13. What would happen as cP passes over great lakes? 13
  14. 14. Lake-effect snow is produced in the winter when cold, arctic winds move across long warmer lake water, and is deposited on the lee shores. Figure 1, p. 207
  15. 15. What would happen as two air masses meet? 15
  16. 16. Fronts
  17. 17. Atmospheric Fronts Boundary, transition zone between two different air masses frontal boundary can be 1-100 km wide cP 17
  18. 18. Cold Fronts Cold air replaces warm Much steeper than warm fronts Advances faster than warm front More violent weather –cumulonimbus clouds Short, sharp showers mT cP 18
  19. 19. Weather associated with cold front passing Weather Before Passing While Passing After Passing Winds south-southwest gusty; shifting west-northwest Temp. warm sudden drop steadily dropping Dew Point high; remains steady sharp drop lowering Pressure falling steadily minimum, then sharp rise rising steadily Precip. short period of showers heavy rains, sometimes with hail, thunder and lightning showers then clearing
  20. 20. Warm Fronts Warm air replaces cold Gentle slope Covers a wide area with its weather Stratus clouds get lower as front approaches Drizzle or steady rain cP mT 20
  21. 21. mT cP
  22. 22. Weather associated with warm front passing Winds Temperature Dew Point Precipitation Before Passing south-southeast cool-cold, slow warming While Passing variable steady rise steady rise After Passing south-southwest warmer, then steady steady light-to-moderate rain, snow, sleet, or drizzle rise, then steady drizzle or none usually none, sometimes light rain or showers Why?
  23. 23. Warm Fronts Warm air replaces cold Gentle slope Covers a wide area with its weather Stratus clouds get lower as front approaches Drizzle or steady rain cP mT 23
  24. 24. Stationary Fronts  no moving weather: clear, partly cloudy, cloudy, light precipitation 24
  25. 25. Occluded Fronts  separate two cold air masses Lifts the warm air off the ground Weather is complex Cold occluded front– cold front lifted warm front Warm occluded front- cold front rises up and over warm front 25
  26. 26. Catches up 26
  27. 27. Catches up 27
  28. 28. Atmospheric Fronts Boundary, transition zone between two different air masses frontal boundary can be 1-100 km wide cP 28
  29. 29. The diagram below represents a side view of a ____ occluded front with the coldest air located at position ____. a. b. c. d. cold type, B warm type, B cold type, A warm type, A 29
  30. 30. Review Questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. What is an air mass? What and where are good source regions for air masses? How are air masses classified? What are the characteristics of the air masses that commonly affect weather over the U.S.? How can air masses be modified? What are the fundamental, physical processes involved with generating lake effect snows? What is a front? What are the types of fronts? How are they analyzed (what symbol) on a surface weather map? What are the characteristics of each kind of front? What is observed during frontal passage for each kind of front? Why is the weather at LA much drier than at Atlanta? What are the two jet streams and how are they created? What is the Walker circulation? What is El Nino? How often does it occur? How do pressure, precipitation, SSTs and ocean currents change in the equatorial pacific during an El Nino event? 30

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