2. 1 HIGHER GEOGRAPHY PHYSICAL CORE ATMOSPHERE

3. 2 By the end of this topic you should be able to:  explain with the aid of an annotated diagram, why Tropical latitudes receive more of the sun’s energy than Polar regions explain why there is a net gain of solar region in the Tropical latitudes and a net loss towards  the poles  describe the role of atmospheric circulation in the redistribution of energy over the globe  describe and explain the earth’s energy exchanges shown on a diagram  describe the factors which affect the amount of sunlight reflected from the earth’s surface  describe and account for the generalised pattern of atmospheric circulation and global winds, or ocean currents shown on a world map  describe the variations in world temperature for the last 100 years (showneg. on a graph) and suggest both physical and human reasons for these variations  describe and explain the origin, nature and weather characteristics of Tropical Maritime (mT) and Tropical Continental (cT) air masses which affect West Africa  with reference to the Inter-Tropical Convergence Zone and the movement of air masses, describe and account for the variations in West African rainfall.

4. 3 GMTs  describe and interpret climate maps, diagrams and graphs  construct and analyse climate graphs  describe and explain climate graphs  comment on the accuracy of statements which describe climate patterns shown on maps etc.

5. 4

6. 5 Troposphere = main zone of weather and climate. lapse rate = decrease in temperature with altitude = 6.4ºC for every 1000metres

7. 6 Mt Everest (8800metres) Calculate the difference in temperature between sea level and the summit of the mountain.

8. 7 Nitrogen - 78% Oxygen - 21% Carbon dioxide - 0.036% …...and rising!! Water vapour - variable - up to 4% over tropical oceans. (as humidity increases the relative amounts of other gases decrease). ATMOSPHERIC GASES

9. 8 Global extremes of Temperature 58ºC San Luis Potosi, Mexico Al Aziziyah, Libya -88ºC Vostok Antarctica In the absence of an atmosphere the Earth would average about 30ºC less than it does at present. Life (as we now know it) could not exist.

10. 9 absorbed by clouds and dust, water vapour and other gases in the atmosphere absorbed by surface reflected by clouds and dust, water vapour and other gases in the atmosphere reflected by surface 100% 23% 25% 52% 6% 46% SOLAR INSOLATION

11. 10 absorbed by surface reflected by atmosphere reflected by surface 100% 23% 25% 52% 6% 46% absorbed by atmosphere solar insolation reaches surface TOTAL ALBEDO = 25 + 6 = 31% TOTAL ABSORPTION = 23 + 46 = 69% SOLAR INSOLATION

12. 11 The Earth's atmosphere is put into motion because of the differential heating of the Earth’s surface by solar insolation. The Poles receive less heat than the Tropics because: 1. Insolation has to pass through more of the Earth’s atmosphere 2. the angle of incidence of insolation and 3. higher levels of surface albedo. ENERGY SURPLUS and DEFICIT

13. 12 1 2 3 1 2 3 Insolation has to pass through more of the Earth’s atmosphere The angle of incidence of insolation - energy is spread out over a larger area because the sun’s rays strike the surface at a lower angle. Higher levels of surface albedo - the ice-cap reflects more solar insolation

14. 13 In theory an imbalance in energy receipt could result in lower latitudes becoming warmer and higher latitudes becoming even colder. In reality energy is transferred from lower latitudes (areas of surplus) to higher latitudes (areas of deficit) BY 1. ATMOSPHERIC CIRCULATION and 2. OCEAN CURRENTS

15. 14 0º Equator 90º Pole SURPLUS DEFICIT 1. ATMOSPHERIC CIRCULATION 2. OCEAN CURRENTS

16. 15 0º Equator90º Pole surplus deficit

17. 16 0º Equator90º Pole TRANSFER of ENERGY by ATMOSPHERIC CIRCULATION

18. 17 TRANSFER of ENERGY by OCEAN CURRENTS 0º Equator 90º Pole

19. 18

20. 19 0º Equator90º Pole LP HP  At the Equator the atmosphere is heated  Air becomes less dense and rises.  Rising air creates low pressure at the equator.  Air cools as it rises because of the lapse rate.  Air spreads.  As air mass cools it increases in density and descends.  Descending air creates high pressure at the Poles.  Surface winds blow from HP to LP. SINGLE CELL MODEL

21. 20  warm air is less dense therefore lighter  air rises in the Tropics  this creates a zone of LOW PRESSURE  air spreads N and S of the Equator  air cools and sinks over the Poles  this is a zone of HIGH PRESSURE  air returns as surface WINDS to the Tropics

22. 21 This was later improved and a three cell model was developed. The single cell model of atmospheric circulation was developed to explain the transfer of energy from the Tropics to the Poles. SINGLE CELL MODEL Today the three cell model is also considered to be an oversimplification of reality.

23. 22 ITCZ = Inter-tropical convergence Zone (Low Pressure) STH = Sub-tropical High (High Pressure) HADLEY CELL ITCZ

24. 23 0º Equator90º Pole30º60º LP HP Hadley Cell Polar Cell Ferrel Cell THREE CELL MODEL

25. 24 Warm air rises at the Equator - Inter-Tropical Convergence Zone (ITCZ). Equatorial air flows to ~30º N then sinks to the surface and returns as a surface flow to the tropics. This is the Hadley cell. Cold air sinks at the North Pole. It flows S at the surface and is warmed by contact with land/ocean, by ~60º N it rises into the atmosphere. This the Polar cell. Between 60º N and 30º N there is another circulation cell. This is the Ferrel cell. The Hadley cell and the Polar cell are thermally direct cells. The Ferrel cell is a thermally indirect cell. ENERGY TRANSFER

26. 25 ENERGY TRANSFER Hadley Cell Polar Cell Ferrel Cell Heat energy is transferred from the Hadley Cell to the Ferrel Cell and from the Ferrel Cell to the Polar Cell. In this way heat is transferred from the Equator where there is an energy surplus to the Poles where there is an energy deficit.

27. 26 0º Equator90º Pole30º60º LP HP convergence divergence convergence divergence winds blow from high pressure zones to low pressure zones WINDS

28. 27 CONVERGENCE and …………DIVERGENCE

29. 28

30. 29

31. 30 Coriolis occurs because the Earth rotates. Earth rotates about its axis every 24 hours. Distance around the equator is ~25,000 miles the earth is travelling east at ~ 1,000 miles per hour. Distance around the Earth at 40ºN ~19,000 miles the earth is travelling east at ~800mph. The Coriolis effect results from this difference in velocity. In the Northern hemisphere the Coriolis effect deflects movement to the right. In the Southern hemisphere Coriolis effect deflects movement to the left. The combination of atmospheric cells and Coriolis effect lead to the wind belts. Wind belts drive surface ocean circulation

32. 31 WIND Coriolis effect High Pressure Low Pressure pressure gradient force Winds are named by the direction they blow from. PLANETARY WINDS

33. 32 Be very, very careful what you put that head, because you will never, ever get it out. Thomas Cardinal Wolsey (1471-1530) The water in a sink rotates one way as it drains in the northern hemisphere and the other way in the southern hemisphere. Called the Coriolis Effect, it is caused by the rotation of the Earth. This is NOT true! The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore than it does the direction of a spinning CD. CORIOLIS

34. 33 90ºS 90ºN 0º Equatorial Low - Doldrums LP 30ºN Sub-tropical High - Horse Latitudes HP30ºS Sub-tropical High - Horse Latitudes HP 60ºS Temperate Low LP 60ºNTemperate Low LP Polar easterlies South westerlies NE Trades Polar easterlies North westerlies SE Trades WIND BELTS

35. 34 90ºS Polar easterlies South westerlies NE Trades Polar easterlies North westerlies SE Trades 0º convergence Inter-tropical convergence zone LP 30ºS divergence Sub-tropical High HP 30ºN divergence Sub-tropical High HP 60ºN convergence LP 60ºS convergence LP WIND BELTS

36. 35 WIND BELTS

37. 36 Northern Hemisphere Polar Easterlies Blowing from the Polar High Pressure zone to about 60ºN Westerlies Blowing from Sub-Tropical High Pressure zone to about 60ºN Northeast Trade Winds Blowing from Sub-Tropical High Pressure zone to Equatorial Low Pressure zone. Southern Hemisphere Southeast Trade Winds Blowing from Sub-Tropical High Pressure zone to Equatorial Low Pressure zone. Westerlies Blowing from Sub-Tropical High Pressure zone to about 60ºS Polar Easterlies Blowing from the Polar High Pressure zone to about 60ºS WIND BELTS

38. 37 Series of High and Low pressure centres approx. every ? latitude ? pressure zones associated with descending air ( ? ) Low pressure zones associated with ? air (convergence) ? circulation cells in each hemisphere: ? ? ? Polar Cell Wind is the horizontal movement of air arising from differences in ?. Very little wind at the Equator ( ? ) because air is being convected ?. Little wind at 30ºN and S (Horse Latitudes) because direction of air movement is down. Winds always blow from an area of ? Pressure to ? Pressure. Winds are affected by the ? Effect. Coriolis is a consequence of motion on a rotating sphere. Acts to the ? of direction of motion in Northern Hemisphere Acts to the ? of direction of motion in the Southern Hemisphere Major wind belts of the Earth surface 0 to 30ºN ? ? ? Southeast Trades 30 to 60ºN/S ? 60 to 90ºN/S Polar ? SLIDE 37

39. 38 Series of High and Low pressure centres approx. every 30º latitude High pressure zones associated with descending air (divergence) Low pressure zones associated with rising air (convergence) Three circulation cells in each hemisphere: Hadley Cell thermally direct Ferrel Cellthermally indirect Polar Cellthermally direct Wind is the horizontal movement of air arising from differences in pressure. Very little wind at the Equator (Doldrums) because air is being convected upward. Little wind at 30ºN and S (Horse Latitudes) because direction of air movement is down. Winds always blow from an area of High Pressure to Low Pressure. Winds are affected by the Coriolis Effect. Coriolis is a consequence of motion on a rotating sphere. Acts to the Right of direction of motion in Northern Hemisphere Acts to the Left of direction of motion in the Southern Hemisphere Major wind belts of the Earth surface 0 to 30ºN Northeast Trades 0 to 30ºS Southeast Trades 30 to 60ºN/S Westerlies 60 to 90ºN/S Polar easterlies

40. 39

41. 40 23  º The most intense heating of the sun, occurring at the so-called thermal equator, annually moves between the tropics. On or around June 20th each year the sun is overhead at 23½ºN, the Tropic of Cancer. On or around December 20th the sun is at overhead at 23½ºS, the Tropic of Capricorn. These two dates are the solstices. Twice a year, at the equinoxes, on or around March 20th and September 20th the overhead sun crosses the equator. This annual north to south and back again "shift" of the thermal equator shifts the belts of planetary winds and pressure systems to the north and to the south as the year turns.

42. 41 0º EQUATOR 23½ºN TROPIC of CANCER 23½ºS TROPIC of CAPRICORN December Winter Solstice September Autumn Equinox June Summer Solstice March Spring Equinox

43. 42 ITCZ

44. 43 ITCZ JULY ITCZ JANUARY

45. 44 The location of the ITCZ varies throughout the year The ITCZ over land moves farther north or south than the ITCZ over the oceans due to the variation in land temperatures. ITCZ JULY ITCZ JANUARY

46. 45 http://www.cla.sc.edu/geog/faculty/carbone/modules/newmods/africa-itcz/ The blue shading on the map shows the areas of highest cloud reflectivity, which correspond to the average monthly position of the ITCZ.

47. 46 The migration of the inter-tropical convergence zone (ITCZ) in Africa affects seasonal precipitation patterns across that continent.

48. 47 DESERT SAVANNA RAINFOREST dry all year ITCZ moves north in summer dry ‘winter’ wet ‘summer’ wet all year

49. 48 Tropical rainforest savanna

50. 49 The further North of the Equator in tropical Africa:-  the lower the annual rainfall  the more the rainfall is concentrated in the summer months  the more variable the rainfall.

51. 50 0º20ºN10ºN RAINFOREST GUINEA SAVANNA SAHEL SAVANNA DESERT rainfall decreases seasonality increases variability increases

52. 51 LAGOS SOKOTO TIMBUKTU

53. 52 savannaclimate tropical summer rain

54. 53 savannavegetation

55. 54 savanna ‘parkland’

56. 55 savanna ‘parkland’

57. 56 savanna ‘parkland’

58. 57 savanna ‘parkland’

59. 58 baobab tree

60. 59 acacia tree

61. 60 acacia thorns

62. 61 desertification

63. 62

64. 63 4 forces: > solar heating > surface winds > Coriolis effect > and surface winds result in a clockwise circulation of water in the Northern hemisphere. This circulation is known as a GYRE.

65. 64 OCEAN CURRENTS IN THE NORTH ATLANTIC 0º Equator 90º Pole 1 2 3 4 5 6 1 2 3 4 5 6 NORTH EQUATORIAL CURRENT GULF STREAM NORTH ATLANTIC DRIFT LABRADOR CURRENT CANARIES CURRENT NORTH ATLANTIC DRIFT

66. 65

67. 66

68. 67

69. 68 The greenhouse effect is the name applied to the process which causes the surface of the Earth to be warmer than it would have been in the absence of an atmosphere. Global warming enhanced greenhouse effect or the enhanced greenhouse effect is the name given to an expected increase in the magnitude of the greenhouse effect, whereby the surface of the Earth will amost inevitably become hotter than it is now.

70. 69 About 70% of the sun's energy is radiated back into space. But some of the infrared radiation is trapped by greenhouse gases and warms the atmosphere,

71. 70

72. 71 Water vapour accounts for 98% of the natural Greenhouse effect. Water vapour has lower ‘radiative forcing’ properties than some other atmospheric gases such as carbon dioxide, methane and nitrous oxide which are naturally present in the atmosphere in small quantities. Since the Industrial Revolution the proportion of these gases has increased significantly.

73. 72 CO 2 CFCs N2ON2O CH 4 1 Carbon Dioxide > fossil fuels, vehicle emissions, forest clearance 2 Methane > rice cultivation, biomass burning, digestive fermentation, termites, sewage, landfill, natural gas production 3 CFCs > aerosol propellants, refrigerants, foaming agents 4 Nitrous oxide > nitrogen fertilisers, industrial pollution

74. 73 Carbon Dioxide: 280 ppm 360 ppm (+30%) Methane: 0.70 ppm 1.80 ppm (+145%) Methane c25 x effect of CO 2 CFCS (chlorofluorocarbons) recent significant decrease due to concern about OZONE LAYER CFCs c10,000 x effect of CO 2 BUT CONCENTRATION CHANGES SINCE 1750

75. 74

76. 75

77. 76

78. 77 °C Temperature anomalies from the period 1961-1990