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2. MET 61 2 MET 61 Introduction to Meteorology 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

3. MET 61 3 MET 61 Introduction to Meteorology Review Answer the following question based on material covered in Chapter 11 of Ahrens. 1.Explain how and why the average surface pressure features shift from summer to winter 2.Why it is impossible on the earth for the Hadley cell to extend from the pole to the equator? 3.Why is the jet stream stronger in winter than in summer? 4.Explain physically what an El Nino event is. 5.Explain how the southern oscillation is related to El Nino. 6.Explain why the trade winds are NE and SE in the northern and southern hemispheres respectively.

4. MET 61 4 MET 61 Introduction to Meteorology Atmospheric Scales of Motion ScaleTime ScaleDistance ScaleExamples Macroscale -PlanetaryWeeks to years1000-40,000kmWesterlies, trade winds -SynopticDays to weeks100-5000kmCyclones, anticyclones and hurricanes MesoscaleMinutes to days1-100kmLand-sea breeze, thunderstorms and tornadoes MicroscaleSeconds to minutes<1kmTurbulence, dust devils and gusts

5. MET 61 5 MET 61 Introduction to Meteorology General Circulation of the Atmosphere  Large scale flow of the atmosphere  Focus on both upper level and lower level winds  Definitions: – –Westerly winds; comes from the west –Southwest winds, comes from the south west

6. MET 61 6 MET 61 Introduction to Meteorology General Circulation of the Atmosphere  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

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8. MET 61 8 MET 61 Introduction to Meteorology View of the atmosphere in motion  http://www.atmos.washington.edu/gfd_exp/exp_e/doc/bc/images/ bc01.gif http://www.atmos.washington.edu/gfd_exp/exp_e/doc/bc/images/ bc01.gif

9. MET 61 9 MET 61 Introduction to Meteorology Single Cell Model  Early description of general circulation  George Hadley (1685-1768) developed this model  Assumptions: –Earth is primarily heated in the tropics –  Surface heat imbalance produces air movement to balance.

10. MET 61 10 MET 61 Introduction to Meteorology Single Cell Model  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.

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12. MET 61 12 MET 61 Introduction to Meteorology Three Cell Model  Proposed to explain how the Earth’s heat balance is maintained  Good simple model of global circulation  Terms: –Hadley Cell: The tropical circulation   Horse Latitudes 

13. MET 61 13 MET 61 Introduction to Meteorology Three Cell Model  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

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16. MET 61 16 MET 61 Introduction to Meteorology Three Cell Model (2)  Explains much of the observed surface pressure distributions

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24. MET 61 24 MET 61 Introduction to Meteorology Monsoon circulation  The monsoon circulation involves a seasonal change in the wind direction.  Monsoon circulations have a distinct wet and dry season.  Monsoon circulations in various places around the globe. –Southern Asia –Northern Australia –Southwest USA

26. Cold and clear skies

27. Warm and cloudy

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36. MET 61 36 MET 61 Introduction to Meteorology 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.

37. MET 61 37 MET 61 Introduction to Meteorology 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

38. MET 61 38 MET 61 Introduction to Meteorology ‘Normal’ conditions (sea surface temps)

39. MET 61 39 MET 61 Introduction to Meteorology El Niño (sea surface temps)

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43. MET 61 43 MET 61 Introduction to Meteorology 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).

44. MET 61 44 MET 61 Introduction to Meteorology 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

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49. MET 61 49 MET 61 Introduction to Meteorology NAO Index is difference between the polar low and the subtropical high during the winter season (December through March)

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51. MET 61 51 MET 61 Introduction to Meteorology 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

52. MET 61 52 MET 61 Introduction to Meteorology 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

53. MET 61 53 MET 61 Introduction to Meteorology 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

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56. MET 61 56 MET 61 Introduction to Meteorology Activity 12 (Due May 9 th ) 1.Derive each component (horizontal and vertical) of the vorticity. 2.For incompressible flow, show how the meridional winds would change if there exists a positive zonal wind gradient and no vertical wind shear. 3.Chapter 11 (Ahrens: Meteorology Today): Questions for Review: 5,7,15, Questions for thought: 2,6