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.

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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 thesun’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 globalwinds, 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.

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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 patternsshown on maps etc.

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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.

ACTIVITYDescribe in detail the climate of Hebron, Canada

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INTER-TROPICAL CONVERGENCE ZONE (ITCZ)ACTIVITYDescribe in detail the climate of Hebron, CanadaWhat 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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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°Nii. label Equatorial, Tropical Continental and Hot Desert climate regionsiii. describe the rainfall in each

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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

RememberHadley

Cell

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ITCZ JULYITCZ

JANUARY

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ITCZ JULYITCZ

JANUARY

What is the impactof land and sea on the migrating ITCZ?

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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

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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

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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

Migrationhttp://www.bbc.co.uk/scotland/learning/learningzone/clips/4324/

Decisions around these matters are influenced by climate- Seasonality- Unreliability of rainfall

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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 mass2. 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

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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 TropicsNature = warm, dry, stable airCharacteristics = Very warm, dry weather in winter. Extremely hot, dry weather in summer. Relatively low humidity (<20%)

Tropical Maritime:Origin = Atlantic Ocean – tropicsNature = Warm, moist and unstableCharacteristics = hot/very hot weather (65 – 82% relative humidity). Rainfall

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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