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GEU 0027: Meteorology Lecture 10 Wind: Global Systems

GEU 0027: Meteorology Lecture 10 Wind: Global Systems. Global Circulation. In the absence of rotation , air would tend to flow from the equator toward the poles. Hot, less dense air rising at the equator, becomes denser as it cools and descends at the poles, traveling

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GEU 0027: Meteorology Lecture 10 Wind: Global Systems

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  1. GEU 0027: MeteorologyLecture 10Wind: Global Systems

  2. Global Circulation • In the absence of rotation, air would tend to flow from the equator toward the poles. Hot, less dense air rising at the equator, becomes denser as it cools and descends at the poles, traveling back to tropical areas to heat up again.

  3. Global Circulation • Because of earth’s rotation we have several circulation cells not just one per hemisphere

  4. Three-cell Model • With the 3 cell structure of wind circulation and the combination of PGF and Coriolis, semi-permanent circulation patterns are established.

  5. Semi-permanent Pressure and Winds Semi-permanent structures in the atmosphere provide consistent wind patterns and breeding grounds for air masses.

  6. Semi-Permanent Pressure (January)

  7. 500-mb streamline and isotherms in January

  8. Stronger Winter PGF

  9. Semi-Permanent Pressure (July)

  10. 500-mb streamline and isotherms in July

  11. Weaker Summer PGF

  12. Intertropical Convergence Zone • ITCZ • Hot equatorial air rises in convection. • Air moves away from the equator toward the poles. • Low Pressure results around the equator. • A band of convective thunderstorms circles the tropical areas of the globe.

  13. ITCZ • Equatorial Cumulus and Thunderstorms

  14. India Monsoon Precipitation

  15. Monsoons (dry)

  16. Monsoons (wet)

  17. Subtropical High and the ITCZ (Sahara)

  18. Sahara Desert and the Sahel of Africa

  19. Jet Locations Jet stream locations greatly affect local and global climate.

  20. Jet Formation Sharply varying pressure and temperature differences create the exaggerated situation shown. Tightly packed isobars create stronger winds aloft in the frontal region.

  21. Polar Jet Winds are Westerly and parallel to the frontal boundary. This creates the polar jet stream. It is strongest in the winter and weakest in the summer.

  22. Seasonal Polar Jet Changes • Location and Velocity variations

  23. What cause the jets? • L = m v r • r = distance from rotational axis • m = mass • v = velocity

  24. Fig. 4, p. 270

  25. Jupiter’s Bands • Higher Angular Momentum, Yields more zones?

  26. Wind Jets • Other jet formation mechanisms are less well known.

  27. The Dishpan Experiment • Uneven heating of the equator and poles of the earth. • Rotation. • Viscosity and turbulence.

  28. Rossby Waves Kinking in the jet stream occurs on a cyclic basis. Weather patterns are also somewhat cyclic.

  29. Rossby Cycle A complete Rossby cycle observed over ~ 6 weeks.

  30. Ocean Currents

  31. Gulf Stream

  32. Coastal Upwelling

  33. Ekman spiral, Ekman layer, and Ekman transport

  34. Normal South Pacific Condition • Easterly “trade-winds” usually prevail and upwelling occurs • When exceptionally strong this cooling is called a La Nina.

  35. El Nino • During an El Nino, pressure conditions (and winds) reverse. • Extremely warm water and wind reversal affects weather.

  36. Sea Surface Temperatures A warm water wave migrates eastward during and El Nino as upwelling and cooling is severely diminished along the western coast of S. America.

  37. Fig. 10-21b, p. 276

  38. El Nino and La Nina events, and ENSO Cycle • La Nina versus El Nino conditions over the past 60 years. • The Y-axis is a parameter calculated from a combination of: • air temperature • water temperature • air pressure (sea-level) • wind speed and direction • cloud cover

  39. Weather pattern changes during El Nino condition

  40. Weather pattern changes during La Nina condition

  41. Global hydrological impacts of El Nino

  42. Pacific Decadal Oscillation (PDO)

  43. North Atlantic Oscillation (NAO)

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