1. 1 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.

2. 2 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.

3. 3 INTER-TROPICAL CONVERGENCE ZONE (ITCZ) Today: –Climate graphs –Air Masses in West Africa CLIMATE GRAPHS These graphs show rainfall and temperature throughout the year. You may be asked to construct, describe or interpret graphs. A line graph is used to show temperature in degrees Celsius. A bar graph shows rainfall in mm. ACTIVITY Describe in detail the climate of Hebron, Canada

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5. 5 INTER-TROPICAL CONVERGENCE ZONE (ITCZ) ACTIVITY Describe in detail the climate of Hebron, Canada What questions do we need to ask ourselves? 1.Is the temperature the same all year? If yes, give the temperature and comment on it Cool, temperate, warm or hot? If no what is the range? When is the maximum and minimum? Are there definite seasons? 2.Is the rainfall consistent throughout the year? Note the distribution across the year – wet and dry season? How much rainfall in each month? Very wet, dry, moderate etc. Overall amount of rain in a year? Very wet, dry, moderate etc. 3.Can you identify the climatic region? By the exam you will be able to pick out equatorial and savanna climatic graphs

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7. 7 INTER-TROPICAL CONVERGENCE ZONE (ITCZ) CASE-STUDY – EQUITORIAL & SAVANNA REGIONS OF AFRICA Main climatic regions: 1.Equatorial Climate 2.Tropical Climate 3.Hot Deserts These zones merge into one another Key difference is the rainfall rather than temperature Therefore seasons tend to be wet season and dry season rather than summer and winter ACTIVITY: On your blank map of Africa show: i. lines of latitude 0°, 10°N and 20°N ii. label Equatorial, Tropical Continental and Hot Desert climate regions iii. describe the rainfall in each

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9. 9 INTER-TROPICAL CONVERGENCE ZONE (ITCZ) SUMMARY NOTE: ITCZ –A zone of convergence is where winds meet –Converging winds include the trade winds which meet at the equator – called the ITCZ –Associated low pressure: calm, warm conditions EFFECT OF THE EARTH’S ORBIT ON THE ITCZ –Latitude receiving the most intense heating from the sun –This areas moves between the tropics due to the Earth’s orbit –The area of maximum heating is known as the thermal equator –Sun overhead at the Tropics at the solstices (once in N. Hemisphere and once in the S.) –Sun directly over the equator twice a year – equinoxes –This migration of the thermal equator shifts the belts of winds and pressure systems north and south over the year Remember Hadley Cell

10. 10 ITCZ JULY ITCZ JANUARY

11. 11 ITCZ JULY ITCZ JANUARY What is the impact of land and sea on the migrating ITCZ?

12. 12 INTER-TROPICAL CONVERGENCE ZONE (ITCZ) SUMMARY NOTE (Cont.): EFFECT OF LAND AND SEA MASSES ON ITCZ –Rates of heating vary greatly over land and sea –Temperature extremes are greater over land – it heats and cools at a faster rate –This means that the ITCZ (zone of low pressure) moves at a different rate around the world –As a result the ITCZ moves further N and S over land than sea

13. 13 INTER-TROPICAL CONVERGENCE ZONE (ITCZ) CASE-STUDY – EQUITORIAL & SAVANNA REGIONS: AFRICA The key underlying influence on climate regions, vegetation and land use is rainfall and the migration of the ITCZ: 1.Equatorial 2.Tropical 3.Desert These zones, although distinct, merge together

14. 14 INTER-TROPICAL CONVERGENCE ZONE (ITCZ) CASE-STUDY – EQUITORIAL & SAVANNA REGIONS OF AFRICA Climate matters, can be the difference between life and death Food and water shortages http://www.bbc.co.uk/scotland/learning/learningzone/clips/6182/ Land degradation / Desertification Poor grazing Migration http://www.bbc.co.uk/scotland/learning/learningzone/clips/4324/ Decisions around these matters are influenced by climate - Seasonality - Unreliability of rainfall

15. 15 ITCZ: CASE-STUDY – EQUITORIAL & SAVANNA REGIONS: AFRICA AIR MASSES You should be able to describe and explain the origin, nature and weather characteristics of Tropical Maritime (mT) and Tropical Continental (cT) air masses which affect West Africa 1.Explain the terms source area and air mass 2.Which are the two main air masses that influence the tropical areas of Africa? 3.Study figure 2.23. Draw a table to summarise the differences between Tropical Continental and Tropical Maritime air masses 4.Explain the term relative humidity Read pages 22

16. 16 ITCZ: AFRICA AIR MASSES Large parcels of air influenced by the earth’s surface are known as air masses. The source area is important in determining the weather associated with an air masses. Tropical Continental: Origin = Sahara Desert – large land mass in the Tropics Nature = warm, dry, stable air Characteristics = Very warm, dry weather in winter. Extremely hot, dry weather in summer. Relatively low humidity (<20%) Tropical Maritime: Origin = Atlantic Ocean – tropics Nature = Warm, moist and unstable Characteristics = hot/very hot weather (65 – 82% relative humidity). Rainfall

17. 17 ITCZ: AFRICA AIR MASSES – IMPACT ON WEST AFRICA Due to the seasonal change in the position of thermal equator means reality is different from textbook models. See figure 2.21 and 2.22 on page 21 As the ITCZ migrates the influence of air masses moves also This movement determines the supply of rainfall and subsequent climatic graphs. You should be able to explain climate graphs in West Africa