1. Monsoon Meteorology ATS 553

2. Monsoon: A reversal of the wind direction at the surface, usually accompanied by the change in the precipitation regime, that occurs in the tropics on a seasonal time scale.

3. Caused by: …the fact that water takes so much longer to heat up or cool down than land does.

4. Three Reasons

5. 1. Cooling by Evaporation

7. 2. Cooling by Mixing

11. 3. High Specific Heat of Water

12. Therefore… In the SUMMER hemisphere, tropical land masses are much hotter than the surrounding ocean. In the WINTER hemisphere, tropical land masses are much colder than the surrounding ocean. Formation of HEAT LOWS and POLAR HIGHS:

13. Heat Lows 1000mb 850mb 700mb 500mb

14. Heat Lows 1000mb 850mb 700mb 500mb

15. Heat Lows 1000mb 850mb 700mb 500mb

16. Heat Lows 1000mb 850mb 700mb 500mb

17. Heat Lows 1000mb 850mb 700mb 500mb

18. Heat Lows 1000mb 850mb 700mb 500mb

19. Polar Highs 1000mb 850mb 700mb 500mb

20. Polar Highs 1000mb 850mb 700mb 500mb

21. Polar Highs 1000mb 850mb 700mb 500mb

22. Polar Highs 1000mb 850mb 700mb 500mb

23. Polar Highs 1000mb 850mb 700mb 500mb

24. Polar Highs 1000mb 850mb 700mb 500mb

25. Polar Highs 1000mb 850mb 700mb 500mb

26. Fig 6-27 in Ramage

28. Fig 6-32 in Ramage

29. Monsoon Regions

30. Major shift or reversal of the circulation features.

31. Monsoon Regions Prevailing wind isn’t just a statistical average—it reflects the real flow in the atmosphere.

32. Monsoon Regions The prevailing wind needs to be reasonably robust.

33. Monsoon Regions Monsoons are NOT just a shift in the storm track, bringing sequences of highs and lows.

34. Fig 6-28 in Ramage India IND West Africa WAFR East Africa EAFR Southeast Asia SEASIA Australia AUS

35. Where don’t monsoons happen? South America –1. Cold upwelling means that the land is ALWAYS warmer than the surrounding oceans.

36. Where don’t monsoons happen? South America –2. SAMER is too narrow at subtropical southern latitudes for a planetary scale anticyclone to form.

37. Where don’t monsoons happen? South America –3. In the NH, SAMER doesn’t extend to regions of subsidence (which favor heat low formation).

38. Where don’t monsoons happen? Mexico, SW US –1. No region has a 120° wind shift

39. Where don’t monsoons happen? Mexico, SW US –2. Central America is too narrow for formation of polar highs.

40. Where don’t monsoons happen? Mexico, SW US –3. Weather is more driven by synoptic disturbances. However, a monsoon trough does form over the eastern Pacific..

41. Precipitation Regimes in the Wet Season

42. What You Don’t Know About West Africa Is A Lot ATS 553

43. Political Geography

44. Historically… Grain CoastIvory CoastGold Coast Slave Coast

45. Vegetation

46. NDVI in WAFR

47. Sahara

49. Sahel

51. Savanna (Soudanian Zone) baobob trees

52. Soudanian Zone

53. Cotton Harvest in Burkina Faso

54. Rainforest

55. Niger River Basin

56. Inland Delta Great Mosque at Jenne

57. Landforms

58. Jos Plateau

59. Atakora Mountains

60. Aïr Mountains

61. Oueme River Valley

62. Climatology of WAFR Monsoon

63. 925mb Winds in June

64. 925mb Winds in September

65. Time-latitude diagrams along 2.5°E (Parakou, Benin)

66. V 925mb along 2°E

67. U 925mb along 2°E

68. OLR along 2.5°E

69. Thermal Fields in the WAFR Monsoon

70. Surface Temperature NCEP Climatology

71. Temperature on 2-sep-04

72. Atlantic GuineaSoudanianSahelian Sahara

73. Vertical Cross-Section Atlantic GuineaSoudanianSahelian Sahara Boundary between the warn and cold air mass is sloped with height, just like a cold front or a warm front.

74. Vertical Cross-Section Atlantic GuineaSoudanianSahelian Sahara Boundary between the warn and cold air mass is sloped with height, just like a cold front or a warm front. Saharan Air Layer (SAL) Monsoon Layer

75. Vertical Cross-Section Atlantic GuineaSoudanianSahelian Sahara In the SAL, dry convection keeps the layer well-mixed: Saharan Air Layer (SAL) Monsoon Layer

76. Well-Mixed Air Atlantic GuineaSoudanianSahelian Sahara Temperature decreases according to the dry adiabatic lapse rate (DALR). Potential temperature is constant with height. Stability: Statically Neutral! Saharan Air Layer (SAL) Monsoon Layer

78. http://cimss.ssec.wisc.edu/tropic/real-time/wavetrak/sal-atl.html

79. Monsoon Layer Atlantic GuineaSoudanianSahelian Sahara Tends to be CONDITIONALLY UNSTABLE due to cool conditions at the surface and higher potential temperatures aloft. Temperature decreases by the moist adiabatic lapse rate. Potential temperature increases slowly with height. Saharan Air Layer (SAL) Monsoon Layer

80. Isentropes Atlantic GuineaSoudanianSahelian Sahara SAL: Neutral at SFC, stable in upper trop, very stable above tropopause Monsoon Layer: Conditionally unstable in lower trop, stable in upper trop, very stable above tropopause Low θ High θ