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NATS 101-05 Lecture 16 Air Masses

This reference provides an overview of air masses, including their formation and characteristics. It explores different source regions and their impact on weather patterns. The article also discusses the modification of air masses and the creation of distinct types.

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NATS 101-05 Lecture 16 Air Masses

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  1. NATS 101-05Lecture 16Air Masses

  2. Supplemental References for Today’s Lecture Lutgens, F. K. and E. J. Tarbuck, 2001: The Atmosphere, An Introduction to the Atmosphere, 8th Ed. 484 pp. Prentice Hall. (ISBN 0-13-087957-6)

  3. Ocean Currents of World Ahrens Fig. 7.24

  4. Ekman Spiral Ahrens, Older Ed. Surface water moves 45 to the right of prevailing wind. Subsurface water moves at angles greater than 45. Net transport of surface layer is 90 to the right. Coriolis force is responsible for the rightward rotation.

  5. Upwelling from Alongshore Winds Ahrens Fig 7.25 Wind pushes surface water southward. Coriolis force deflects water to the right. Cold water from below rises to surface. Fog persists over the cold water.

  6. El Nino 3.4 Upwelling Regions weather.unisys.com

  7. El Nino-Southern Oscillation (ENSO) An important atmospheric-ocean feedback Normal conditions in tropical Pacific: -Warm SST, low SLP, and T-storms in W Pacific -Strong subtropical highs in E Pacific -Easterly winds and cool upwelling water along equator in East Pacific -Prevailing southerly winds off of Peru produce cold upwelling and excellent fishing

  8. El Niño-Southern Oscillation (ENSO) Every few years (4-5 years): -Equatorial Central Pacific warms -Low SLP, T-storms shift to Central and East Pacific (the Southern Oscillation) -Trades and southerly winds off Peru weaken -Upwelling ceases off Peru, warming leads to massive kill off of fish. Typically occurs around Christmas (an El Niño event) Alters global patterns of wind, temp and rain

  9. Walker Circulation Pushes water westward Darwin Tahiti Aguado & Burt, p230 Walker Circulation oscillates with a quasi-period of every few years. Oscillation is very evident in SLP records for Darwin and Tahiti.

  10. Southern Oscillation Index (SOI) SST SLP

  11. See current conditions

  12. El Nino Precipitation Extremes

  13. La Nina Precipitation Extremes

  14. El Nino Precipitation Extremes

  15. La Nina Precipitation Extremes

  16. ENSO-Atmosphere Coupling Ocean temperature pattern Ocean currents, upwelling SLP, winds, storms, etc. By observing SST’s and surface winds in equatorial Pacific, we are able to forecast ENSO events with considerable skill (much betteronce they have started to form). ENSO forecasts lead to skillful seasonal forecasts for the US several months in advance (e.g. 1997-1998 winter).

  17. Ocean and ENSO Summary • Major Ocean Currents Driven by prevailing wind • Upwelling Regions Occurs along west coasts of continents Cold water rises from below to surface Nutrient rich, excellent fishing regions

  18. Summary • El Nino-Southern Oscillation Occurs every few years Central equatorial Pacific warms Low SLP, T-storms move with warm water Upwelling weakens along Peru coast Can be predicted up to one-year in advance Modulates global patterns of wind, temp, rain

  19. What is an Air Mass? • Air Mass Large area (>1600 km by 1600 km) of air that contains relatively uniform, horizontal distributions of temperature and moisture.

  20. How Air Masses Form • If surface air resides in a region for a few days, it acquires the thermal and moisture characteristics of the underlying surface. • Source regions for Air Masses are: Big in area [ >>(1600 km)2 ] Dominated by persistent high pressure and light winds

  21. Air Mass Source Regions • Contrasting source regions are Continents versus Oceans Tropics versus Poles • An Air Mass is designated in terms of itsSource Region

  22. Air Mass Characteristics Ahrens Table 8.1

  23. Air Mass Source Regions for NA Ahrens Fig 8.2

  24. Creation of cP Air Mass Williams p22

  25. Creation of cP Air Mass Williams p23

  26. Creation of mP Air Mass Lutgens & Tarbuck, p 230

  27. Lake Effect Snows Lutgens & Tarbuck, p 230 As cP air flows over the warmer, open Great Lakes, it is warmed and moistened. When the modified cP air flows onshore, prodigious snows of several feet can result.

  28. Creation of mT and cT Air Masses Williams p24

  29. Contrasting Air Masses 17 Apr 1976 Ahrens Fig 8.9

  30. Paths of cP Air Masses Ahrens Fig 8.3

  31. cP Air Mass 24 Dec 1983 Ahrens Fig 3 p203

  32. Modification of cP Air Mass cP cP warm ocean mP warm ocean mP Ahrens Fig 8.4

  33. mP Air Masses Air mass modified further as it crosses several mountain ranges of West U.S. Ahrens Fig 8.5 Ahrens Fig 8.7

  34. cT Air Mass 29-30 Jun 1990 Ahrens Fig 8.10

  35. Winter mT Pacific Air Masses mP mT “Pineapple Express” Ahrens Fig 8.8

  36. Weather Map with Air Masses Ahrens Fig 8.11

  37. Summary • Air Masses Large (>1000 miles) regions with “uniform” temperature and moisture characteristics • Classified by Source Region Continental (c) or Maritime (m) Polar (P) or Tropical (T) • Source Regions Big in area (>>1600 km by 1600 km) Dominated by light winds (long resident times)

  38. Assignment for Next Lecture • Topic -Fronts • Reading -Ahrens pg 214-231 • Problems -8.12, 8.13

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