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MET 61 Introduction to Meteorology - Lecture 11

MET 61 Introduction to Meteorology - Lecture 11. Global Circulation Dr. Eugene Cordero Reading: W&H Pg. 297-298 Ahrens: Chapter 11: Wind: Global Systems Class Outline: Circulation models Jet stream El Nino. Review.

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MET 61 Introduction to Meteorology - Lecture 11

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  1. MET 61 Introduction to Meteorology

  2. MET 61 Introduction to Meteorology - Lecture 11 Global Circulation Dr. Eugene Cordero Reading: W&H Pg. 297-298 Ahrens: Chapter 11: Wind: Global Systems Class Outline: • Circulation models • Jet stream • El Nino MET 61 Introduction to Meteorology

  3. Review Answer the following question based on material covered in Chapter 11 of Ahrens. • Explain how and why the average surface pressure features shift from summer to winter • Why it is impossible on the earth for the Hadley cell to extend from the pole to the equator? • Why is the jet stream stronger in winter than in summer? • Explain physically what an El Nino event is. • Explain how the southern oscillation is related to El Nino. • Explain why the trade winds are NE and SE in the northern and southern hemispheres respectively. MET 61 Introduction to Meteorology

  4. Scale Time Scale Distance Scale Examples Macroscale -Planetary Weeks to years 1000-40,000km Westerlies, trade winds -Synoptic Days to weeks 100-5000km Cyclones, anticyclones and hurricanes Mesoscale Minutes to days 1-100km Land-sea breeze, thunderstorms and tornadoes Microscale Seconds to minutes <1km Turbulence, dust devils and gusts Atmospheric Scales of Motion MET 61 Introduction to Meteorology

  5. Large scale flow of the atmosphere Focus on both upper level and lower level winds Definitions: Zonal winds (East-West) Meridional winds (North-South). Westerly winds; comes from the west Southwest winds, comes from the south west General Circulation of the Atmosphere MET 61 Introduction to Meteorology

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  7. http://www.atmos.washington.edu/gfd_exp/exp_e/doc/bc/images/bc01.gifhttp://www.atmos.washington.edu/gfd_exp/exp_e/doc/bc/images/bc01.gif View of the atmosphere in motion MET 61 Introduction to Meteorology

  8. Early description of general circulation George Hadley (1685-1768) developed this model Assumptions: Earth is primarily heated in the tropics Thermally direct circulation results from heating differences Surface heat imbalance produces air movement to balance. Single Cell Model MET 61 Introduction to Meteorology

  9. MET 61 Introduction to Meteorology

  10. Proposed to explain how the Earth’s heat balance is maintained Good simple model of global circulation Terms: Hadley Cell: The tropical circulation ITCZ - intertropical convergence zone Horse Latitudes Trade Winds Three Cell Model MET 61 Introduction to Meteorology

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  13. Explains much of the observed surface pressure distributions Three Cell Model (2) MET 61 Introduction to Meteorology

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  29. What is El Niño? • El Niño is: • El Niño occurs: • The name, “El Niño” (means ‘boy child’ in Spanish) as it often occurs around Christmas time. a warming of the equatorial eastern Pacific Ocean about about once every 2 to 7 years MET 61 Introduction to Meteorology

  30. ‘Normal’ conditions (sea surface temps) MET 61 Introduction to Meteorology

  31. El Niño (sea surface temps) MET 61 Introduction to Meteorology

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  35. ENSO (El Niño-Southern Oscillation) • The Southern Oscillation: • is the atmospheric part of El Niño • The Southern Oscillation Index is the pressure difference between Tahiti and Darwin, Pressure(Tahiti) – Pressure(Darwin) • During El Niño, the pressure is _______ in the west and _______ in the east • During El Nino, the Southern Oscillation Index is (positive/negative). higher lower MET 61 Introduction to Meteorology

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  40. NAO Index is difference between the polar low and the subtropical high during the winter season (December through March) MET 61 Introduction to Meteorology

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  42. What is the NAO? • The North Atlantic Oscillation (NAO) represents • winter climate variability in the North Atlantic region • ranging from central North America to Europe and much into Northern Asia • The NAO is a large scale seesaw in atmospheric mass MET 61 Introduction to Meteorology

  43. Phases of the NAO • A positive index • stronger than usual subtropical high pressure • deeper than normal Icelandic low. • The increased pressure gradients produces: • stronger winter storms crossing the Atlantic Ocean • warm and wet winters in Europe • cold and dry winters in northern Canada and Greenland • mild and wet winter conditions in Eastern US MET 61 Introduction to Meteorology

  44. Phases of the NAO • A negative index • weaker than usual subtropical high pressure • weaker than normal Icelandic low. • The increased pressure gradients produces: • fewer winter storms crossing the Atlantic Ocean • Cold air to northern Europe • Milder winters in Greenland • More cold outbreaks and snowy conditions to the Eastern US MET 61 Introduction to Meteorology

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  47. Activity 12 (Due May 9th) • Derive each component (horizontal and vertical) of the vorticity. • For incompressible flow, show how the meridional winds would change if there exists a positive zonal wind gradient and no vertical wind shear. • Chapter 11 (Ahrens: Meteorology Today): Questions for Review: 5,7,15, Questions for thought: 2,6 MET 61 Introduction to Meteorology

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