Atmosphere

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Atmosphere

  1. 1. Higher Geography Core Unit ATMOSPHERE
  2. 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 (shown eg. 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.
  3. 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.
  4. 4. The Atmosphere The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity. This mixture of gases is commonly known as air . The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.
  5. 5.
  6. 6. For tomorrow’s lesson…
  7. 7. ATMOSPHERIC GASES 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). Inert gases, dust and pollutants make up the rest of the atmosphere.
  8. 8.
  9. 9. Troposphere <ul><li>The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its water vapor and aerosols. </li></ul>
  10. 10.
  11. 11. Tropopause
  12. 12. Stratosphere
  13. 13. Mesosphere
  14. 14. Thermosphere
  15. 15. Thermosphere
  16. 16. Troposphere = main zone of weather and climate. lapse rate = decrease in temperature with altitude = 6.4ºC for every 1000metres
  17. 17. Mt Everest (8800metres) Calculate the difference in temperature between sea level and the summit of the mountain.
  18. 18. 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.
  19. 19. The Global Heat Budget
  20. 20. 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% 18% 26% 56% 6% 50% SOLAR INSOLATION
  21. 21. absorbed by surface reflected by atmosphere reflected by surface 100% 18% 26% 56% 6% 50% absorbed by atmosphere solar insolation reaches surface TOTAL ALBEDO = 26 + 6 = 32% TOTAL ABSORPTION = 18 + 50 = 68% SOLAR INSOLATION
  22. 22. In the previous lesson… <ul><li>You learn the different players of atmosphere which is categorized by using two variables: temperature and altitude. </li></ul><ul><li>You also learnt about the global heat budget. In this section it is important to remember that: </li></ul><ul><ul><ul><li>% on your diagram tend to vary a bit from book to book, so do not be alarmed by slight variations. </li></ul></ul></ul><ul><ul><ul><li>This model does not take into account the global variation due to different locations. i.e. as you move away from the equator towards the Poles there is a latitudinal variation in the heat budget. </li></ul></ul></ul>
  23. 23. In case you are not sure…
  24. 24. <ul><li>The proportion of radiation reflected or absorbed depends on the object's reflectivity or albedo , respectively. </li></ul><ul><li>An ideal white body has an albedo of 100% and an ideal black body, 0%. </li></ul>TOTAL ALBEDO = 26 + 6 = 32%
  25. 25. <ul><li>Albedo works on a smaller scale, too. People who wear dark clothes in the summertime put themselves at a greater risk of heatstroke than those who wear lighter color clothes </li></ul>
  26. 26. Mark in the Urban range Albedo effect of different materials
  27. 27.
  28. 28.
  29. 29.
  30. 30.
  31. 31. Albedo Variation? Seasonal Vegetation Location Natural Material Clouds Man-made
  32. 32. Earth as a natural system (long wave radiation) … is neither getting colder nor warmer. Out of the 50% of solar energy absorbed by the Earth. 7% is re-radiated directly back into space and 43% is absorbed by greenhouse gases (Carbon dioxide, methane, water vapour) Incomeing solar radiation = outgoing solar radiation TOTAL ABSORPTION = 18 (by atmosphere) + 50 (by earth’s surface) = 68%
  33. 33. 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
  34. 34. So why is Alaska so cold???
  35. 35. Why is Alaska so cold? Global Heat Variation
  36. 36. Places at the equator or between the tropics are always hotter than places at higher latitudes. This is because the earth is a sphere and the sun’s rays strike the area around the centre of the sky at right angles. (high in the sky)
  37. 37. In polar areas the radiation has to pass through a greater depth of atmosphere (more scope for absorption, scattering or reflecting). Compared the width of XY and AB. At higher latitude the rays strike the surface at a wider angle. Similar amounts of solar radiation cover a greater area at the Poles. Compare the areas XY with AB.
  38. 38.
  39. 39. As you move from the Tropics to the Poles, there is variation and decrease in the time the sun releases solar radiation over the surface. i.e… We see the sun less or more depending on the position of over head sun. Also know was seasons.
  40. 40. Absorption at the surface is dependent upon the ‘albedo’ effect (whether the surface reflects more or less radiation). For example, a dark surface (a forest) has low reflection, and a light surface (snow, ice, sand, water) has high reflection.
  41. 41. Other variables include increased sunspot activity, an increased in atmospheric dust (after a volcanic eruption), and the tilt of the Earth’s axis and the varying distance of the Earth’s orbit around the sun.
  42. 42. 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
  43. 43. SQA <ul><li>Explain why tropical latitudes receive more solar radiation than polar latitudes. (8) </li></ul><ul><li>Textbook page 6-7 “Energy Receipt and Latitude” </li></ul>
  44. 44.
  45. 45. 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 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 &quot;shift&quot; of the thermal equator shifts the belts of planetary winds and pressure systems to the north and to the south as the year turns. Reasons for Seasons
  46. 46.
  47. 47.
  48. 48. http://msnbcmedia3.msn.com/j/msnbc/319000/319772.hlarge.jpg
  49. 49. 2008   Spring Equinox Mar 20 2008   Summer Solstice Jun 20 2008   Autumnal Equinox Sep 22 2008   Winter Solstice Dec 21 2008
  50. 50. 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
  51. 51. SURPLUS DEFICIT 1. ATMOSPHERIC CIRCULATION 2. OCEAN CURRENTS 0º Equator 90º Pole
  52. 52. NO! not directly 0º Equator 90º Pole surplus deficit
  53. 53. TRANSFER of ENERGY by ATMOSPHERIC CIRCULATION 0º Equator 90º Pole
  54. 54. TRANSFER of ENERGY by OCEAN CURRENTS 0º Equator 90º Pole
  55. 55. ATMOSPHERIC CIRCULATION
  56. 56. <ul><li>At the Equator the atmosphere is heated </li></ul><ul><li>Air becomes less dense and rises. </li></ul><ul><li>Rising air creates low pressure at the equator. </li></ul><ul><li>Air cools as it rises because of the lapse rate. </li></ul><ul><li>Air spreads. </li></ul><ul><li>As air mass cools it increases in density and descends. </li></ul><ul><li>Descending air creates high pressure at the Poles. </li></ul><ul><li>Surface winds blow from HP to LP. </li></ul>SINGLE CELL MODEL 0º Equator 90º Pole LP HP
  57. 57.
  58. 58.  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
  59. 59. 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.
  60. 60. Three Cell Model
  61. 61. Three Cell Model
  62. 62.
  63. 63. Three Cell Model
  64. 64. Hadley Cell Polar Cell Ferrel Cell THREE CELL MODEL 'horse latitude' 0º Equator 90º Pole 30º 60º LP HP LP HP
  65. 65. Three Cell Model
  66. 66. Hadley Cell- see your notes on “single cell model” <ul><li>Warm air rises at the equator: Inter-Tropical Convergence Zone. </li></ul><ul><li>The rising warm air carries a lot of moisture which cools, resulting in tall tower of cumulo-nimbus clouds and heavy precipitation. </li></ul>
  67. 67. <ul><li>Equatorial air flows to ≈ 30°N then sinks to the surface (HP) and returns as a surface wind to the equator. </li></ul><ul><li>Some of this wind heads to the other LP point northwards. </li></ul>
  68. 68. ITCZ = Inter-tropical convergence Zone (Low Pressure) STH = Sub-tropical High (High Pressure) HADLEY CELL ITCZ
  69. 69. Ferrel Cell (Thermally indirect cell- powered by other two cells) <ul><li>At 30 °N some of the air heads towards the North Pole as wind. </li></ul><ul><li>This wind is usually known as mid-latitude westerlies , which is warm and moist. </li></ul><ul><li>At 60 °N the warm mid-latitude westerlies meets the cold air from the polar cell. </li></ul>
  70. 70. <ul><li>The warm air rises over the cold air and travels higher into the atmosphere. </li></ul><ul><li>Here the air cools down and spread out. </li></ul><ul><li>The air which spread out back south towards the equator completes this Ferrel cell circulation. </li></ul>
  71. 71. Polar Cell <ul><li>At the North Pole (90 °N) the air is very cold and dense  it sinks down creating a HP. </li></ul><ul><li>It then flows southwards towards 60°N and is warmed by the land and ocean  it rises up into the atmosphere to completes it’s circulation. </li></ul>
  72. 72. 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
  73. 73. ENERGY TRANSFER 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. Hadley Cell Polar Cell Ferrel Cell
  74. 74. Three Cell Model Hadley Cell. Warm air rises at the equator: Inter-Tropical Convergence Zone. The rising warm air carries a lot of moisture which cools, resulting in tall tower of cumulo-nimbus clouds and heavy precipitation. Equatorial air flows to ≈ 30°N then sinks to the surface (HP) and returns as a surface wind to the equator. Some of this wind heads to the other LP point northwards. Ferrel Cell. At 30 °N some of the air heads towards the North Pole as wind. This wind is usually known as mid-latitude westerlies , which is warm and moist. At 60 °N the warm mid-latitude westerlies meets the cold air from the polar cell. The warm air rises over the cold air and travels higher into the atmosphere. Here the air cools down and spread out. The air which spread out back south towards the equator completes this Ferrel cell circulation. Polar Cell At the North Pole (90°N) the air is very cold and dense  it sinks down creating a HP. It then flows southwards towards 60°N and is warmed by the land and ocean  it rises up into the atmosphere to completes it’s circulation.
  75. 75. Basic Principle <ul><li>Hot air rises  low pressure. </li></ul><ul><li>Cold air sinks  high pressure. </li></ul><ul><li>Air moves from high to low pressure. </li></ul><ul><li>Air is deflected by the spinning of the Earth  Coriolis effect . </li></ul>
  76. 76. LP HP LP HP convergence divergence convergence divergence winds blow from high pressure zones to low pressure zones WINDS 0º Equator 90º Pole 30º 60º
  77. 77. Coriolis effect occurs because the Earth rotates. CORIOLIS <ul><li>Earth rotates about its axis every 24 hours. </li></ul><ul><li>Distance around the equator is ~25,000 miles ( 40 233.6 km) </li></ul><ul><li>the earth is travelling east at ~ 1,041 miles per hour. ( 1675km) </li></ul><ul><li>Distance around the Earth at 40ºN ~19,000 miles </li></ul><ul><li>the earth is travelling east at ~800mph. </li></ul><ul><li>The Coriolis effect results from this difference in velocity. </li></ul>
  78. 78. Coriolis occurs because the Earth rotates. CORIOLIS 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
  79. 79. Rossby wave and the Jet Stream
  80. 80. Happens ≈30 º~ 60º N/S
  81. 81. Cold air is transferred southwards and warm air to the north
  82. 82.
  83. 83.
  84. 84. Geographic coordinates: 54 00 N, 2 00 W
  85. 85. <ul><li>Rossby waves in the atmosphere are easy to observe as (usually 4-6) large-scale meanders of the jet stream. </li></ul><ul><li>When these loops become very pronounced, they detach the masses of cold, or warm, air that become cyclones and anticyclones and are responsible for day-to-day weather patterns at mid-latitudes. </li></ul>
  86. 86. CONVERGENCE and …………DIVERGENCE
  87. 87. Cirrus Clouds
  88. 88.
  89. 89.
  90. 90. PLANETARY WIND SYSTEM
  91. 91.
  92. 92. Coriolis effect occurs because the Earth rotates. CORIOLIS <ul><li>Earth rotates about its axis every 24 hours. </li></ul><ul><li>Distance around the equator is ~25,000 miles ( 40 233.6 km) </li></ul><ul><li>the earth is travelling east at ~ 1,041 miles per hour. ( 1675km) </li></ul><ul><li>Distance around the Earth at 40ºN ~19,000 miles </li></ul><ul><li>the earth is travelling east at ~800mph. </li></ul><ul><li>The Coriolis effect results from this difference in velocity. </li></ul>
  93. 93. Coriolis occurs because the Earth rotates. CORIOLIS 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
  94. 94. WIND Coriolis effect High Pressure Low Pressure pressure gradient force Winds are named by the direction they blow from. PLANETARY WINDS
  95. 95. 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
  96. 96. Polar easterlies South westerlies NE Trades Polar easterlies North westerlies SE Trades WIND BELTS 90ºS 90ºN 0º Equatorial Low - Doldrums LP 30ºN Sub-tropical High - Horse Latitudes HP 30ºS Sub-tropical High - Horse Latitudes HP 60ºS Temperate Low LP 60ºN Temperate Low LP
  97. 97. Homework for Monday 15 th Sept <ul><li>What is the Inter-tropical Convergence Zone (Doldrums Doldrums)? – where is it found? What conditions? What happens? (4) </li></ul><ul><li>Explain why at the equator (Doldrums) we have very calm condition? – why do we have very little wind at the birth place of wind??? </li></ul><ul><li>(5) </li></ul>
  98. 98. Home work answer <ul><li>ITCZ or otherwise known as the Doldrums is found between 0-10 º north and south of the equator. </li></ul><ul><li>Since is it close to the equator it receives the strongest solar radiation. This creates a hot and humid condition. </li></ul><ul><li>The intense sun heats the atmosphere and ocean  hot air rises  strong upwards convection current  the air becomes heavy with moisture. </li></ul><ul><li>We usually find massive rain clouds like cumulus nimbus . </li></ul><ul><li>Atmospheric condition is usually very calm at ITCZ because… due to the strong overhead sun the air is being convected upwards. </li></ul><ul><li>Main movement of air is upwards. </li></ul><ul><li>This creates an area of low pressure. Wind travels from high pressure to low pressure. So by the time Trade winds have made it back to the equator it has weakened. </li></ul>
  99. 99. Polar easterlies South westerlies NE Trades Polar easterlies North westerlies SE Trades WIND BELTS 90ºS 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
  100. 100. WIND BELTS
  101. 101.
  102. 102. 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
  103. 103. 10 minutes Once you have finished… Try drawing the global wind circulation diagram from memory.
  104. 104. 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: ? ? direct ? thermally indirect Polar Cell thermally direct 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
  105. 105. 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 Cell thermally indirect Polar Cell thermally 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
  106. 106.
  107. 107. 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 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 &quot;shift&quot; of the thermal equator shifts the belts of planetary winds and pressure systems to the north and to the south as the year turns. Reasons for Seasons
  108. 108.
  109. 109.
  110. 110. http://msnbcmedia3.msn.com/j/msnbc/319000/319772.hlarge.jpg
  111. 111. 2008   Spring Equinox Mar 20 2008   Summer Solstice Jun 20 2008   Autumnal Equinox Sep 22 2008   Winter Solstice Dec 21 2008
  112. 112.
  113. 113.
  114. 114. Land or Ocean- Which one stays warmer???
  115. 115. Answer <ul><li>In winter the continental cool down more quickly than oceans and so they have a lower pressure. </li></ul><ul><li>In summer the continents heat up more quickly and so have lower pressure. </li></ul><ul><li>Summer: Land / Ocean </li></ul><ul><li>Winter: Land / Ocean </li></ul>
  116. 116. Inter-tropical Convergence Zone (ITCZ)
  117. 117. 0º EQUATOR 23½ºN TROPIC of CANCER 23½ºS TROPIC of CAPRICORN December Winter Solstice September Autumn Equinox June Summer Solstice March Spring Equinox
  118. 118. Where is it? <ul><li>Near the equator, from about 5° north and 5° south. the northeast trade winds and southeast trade winds converge in a low pressure zone known as the ITCZ. </li></ul>
  119. 119. How does it work? <ul><li>ITCZ is formed by the vertical ascent (rise) of warm moist air from the latitudes north and south of the equator. </li></ul><ul><li>The air is drawn into the inter-tropical convergence zone by the action of the Hadley cell. </li></ul>
  120. 120. <ul><li>Equatorial region experience precipitation up to 200 days each year, making the equatorial and ITCZ the wettest on the planet. </li></ul><ul><li>The equatorial region lacks a dry season and is constantly hot and humid. (this is why the “rainforest” is found in the equatorial region) </li></ul>What does it do?
  121. 121. <ul><li>The location of the ITCZ varies throughout the year and while it remains near the equator, the ITCZ over land ventures farther north or south than the ITCZ over the oceans due to the variation in land temperatures. </li></ul><ul><li>The location of the ITCZ can vary- they usually travel within the latitude of 25 ° north or south of the equator based on the pattern of land and ocean. </li></ul>Why is it important?
  122. 122.
  123. 123. ITCZ JULY ITCZ JANUARY
  124. 124.
  125. 125.
  126. 126. Case Study of West Africa
  127. 127. <ul><li>Areas next to the Equator have high annual rainfall totals because of the continued uplift of air which results from the convergence of the Trade winds and strong convectional currents (upward movement of warm air). </li></ul><ul><li>Further away from the equator the annual rainfall decreases and the length of the dry seasons increases. </li></ul><ul><li>(equator=2000mm/year, Sahara= 250mm/year) </li></ul>
  128. 128. <ul><li>The twin Hadley Cell structure means converging and ascending air near the Equator and descending and diverging air over the sub-tropical deserts. </li></ul>
  129. 129. <ul><li>The inner zone of convergent air is known as the Inter-Tropical Convergence Zone (ITCZ) which provides the source of the majority of rainfall. </li></ul><ul><li>The Hadley Cells, the ITCZ and the Trade belts swing North and South, following the overhead sun, during the course of the year. This movement controls the seasonal rainfall and temperature- the maximum rainfall occurs 1-2 months after the passages of the overhead sun. </li></ul>
  130. 130.
  131. 131. <ul><li>Between March and July the ITCZ moves northwards across West Africa bringing cloudy and humid conditions. As the moist Tropical Maritime (mT) air moves northwards  heavy rainstorm develops. </li></ul><ul><li>During the winter dry Tropical Continental air (cT) blows over the Sahara moving southwards to enable the dry north-east Trade winds to blow into the Sahel. </li></ul>
  132. 132. <ul><li>Tropical Maritime (mT) air </li></ul><ul><li>South-Western Monsoon winds </li></ul><ul><li>High temperature </li></ul><ul><li>High rainfall </li></ul><ul><li>Tropical Continental (cT) air </li></ul><ul><li>North-East Trade winds </li></ul><ul><li>High temperature </li></ul><ul><li>Very low or no rainfall </li></ul>Page 17
  133. 133. Read Page 16-19 Summary Note
  134. 134.
  135. 135.
  136. 136. http://www.cpc.ncep.noaa.gov/products/fews/ITCZ/itcz.shtml Latest Data
  137. 137. 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.
  138. 138. The migration of the inter-tropical convergence zone (ITCZ) in Africa affects seasonal precipitation patterns across that continent.
  139. 139. DESERT SAVANNA RAINFOREST dry all year ITCZ moves north in summer dry ‘winter’ wet ‘summer’ wet all year DESERT SAVANNA RAINFOREST
  140. 140. Tropical rainforest savanna
  141. 141. <ul><li>The further North </li></ul><ul><li>of the Equator in tropical Africa:- </li></ul><ul><li>the lower the annual rainfall </li></ul><ul><li>the more the rainfall is concentrated in the summer months </li></ul><ul><li>the more variable the rainfall. </li></ul>
  142. 142. RAINFOREST GUINEA SAVANNA SAHEL SAVANNA DESERT rainfall decreases seasonality increases variability increases 0º 20ºN 10ºN
  143. 143. LAGOS SOKOTO TIMBUKTU
  144. 144. savanna climate tropical summer rain
  145. 145. savanna vegetation
  146. 146. savanna ‘parkland’
  147. 147. savanna ‘parkland’
  148. 148. savanna ‘parkland’
  149. 149. savanna ‘parkland’
  150. 150. baobab tree
  151. 151. acacia tree
  152. 152. acacia thorns
  153. 153. desertification
  154. 154. OCEAN CURRENTS Responsible for ≈ 20% of redistribution of energy.
  155. 155. What is it? <ul><li>An ocean current is continuous, directed movement of ocean water. Ocean currents are “rivers” of hot or cold water within the ocean. The currents are generated from the forces acting upon the water like the planet rotation, the wind, the temperature and salinity differences and the gravitation of the moon. </li></ul><ul><li>Ocean currents play an important role in redistributing energy. </li></ul>
  156. 156.
  157. 157.
  158. 158. Where is it?
  159. 159. <ul><li>Energy is redistributed in the oceans by ocean currents, this is called oceanic circulation . </li></ul><ul><li>Ocean currents can flow for thousands of kilometers. They are very important in determining the climates of the continents, especially climate regions next to oceans. </li></ul>
  160. 160.
  161. 161. How does it work? <ul><li>Ocean currents are driven by thermohaline circulation. </li></ul><ul><li>Thermo= heat </li></ul><ul><li>Haline= salt </li></ul>together they determine the density of sea water.
  162. 162. How does it work? <ul><li>Uneven heating of surface water in high and low latitudes sets up convection currents which transfer energy. </li></ul><ul><li>The water round the Poles is more dense than at the equator because it contains more salt. Salt does not freeze. </li></ul>
  163. 163.
  164. 164. How does it work? <ul><li>Global Winds cause frictional drag on large water surfaces. </li></ul><ul><li>Ocean currents therefore tend (but not always) to follow prevailing wind directions. </li></ul>
  165. 165. How does it work? <ul><li>The Coriolis force winds are deflected to the right in the northern hemisphere and to the left in the southern hemisphere. </li></ul><ul><li>Ocean currents are also deflected in the same way. </li></ul>
  166. 166. How does it work? <ul><li>Ocean currents direction is modified by the shape of the continents. </li></ul><ul><li>Consequently the major oceanic basin have huge, roughly circular shaped loops of water called gyres. </li></ul>
  167. 167. <ul><li>4 forces: </li></ul><ul><li>solar heating </li></ul><ul><li>salt </li></ul><ul><li>Coriolis effect </li></ul><ul><li>and surface winds </li></ul><ul><li>result in a clockwise circulation of </li></ul><ul><li>water in the Northern hemisphere. </li></ul>This circulation is known as a GYRE.
  168. 168. 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
  169. 169.
  170. 170.
  171. 171.
  172. 172.
  173. 173.
  174. 174.
  175. 175. GLOBAL WARMING
  176. 176. <ul><li>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. </li></ul><ul><li>Global warming 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 almost inevitably become hotter than it is now. </li></ul>
  177. 177.
  178. 178. 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,
  179. 179.
  180. 180. 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.
  181. 181. 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 CO 2 CFCs N 2 O CH 4
  182. 182. 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
  183. 183.
  184. 184.
  185. 185.
  186. 186. °C Temperature anomalies from the period 1961-1990
  187. 187. Solar energy Ocean Currents Volcanic activities Astronomical changes Natural Causes
  188. 188. Human Causes
  189. 189. http://delicious.com/MissTomitaka/atmosphere
  190. 190.
  191. 191.
  192. 192. <ul><li>Watch a short clip from youtube called “ geography seasons” </li></ul><ul><li>http://www.youtube.com/watch?v=taHTA7S_JGk </li></ul><ul><li>Then answer the following question: Why do we have seasons? How does it work? (4 Marks) </li></ul><ul><li>Then complete the “summer solstice” diagram by adding the latitude and length of daylight. </li></ul>

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