Transcript Atmosphere 7 - ITCZ and West Africa Cont

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.
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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 patterns
shown 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.
ACTIVITY
Describe in detail the climate of Hebron, Canada
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INTER-TROPICAL CONVERGENCE ZONE (ITCZ)
ACTIVITY
Describe in detail the climate of Hebron, Canada
What questions do we need to ask ourselves?
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Is the temperature the same all year?
If yes, give the temperature and comment on it
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Cool, temperate, warm or hot?
If no what is the range?
When is the maximum and minimum?
Are there definite seasons?
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.
Can you identify the climatic region?
By the exam you will be able to pick out equatorial and savanna climatic
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graphs
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INTER-TROPICAL CONVERGENCE ZONE (ITCZ)
CASE-STUDY – EQUITORIAL & SAVANNA REGIONS OF AFRICA
Main climatic regions:
ACTIVITY:
1.
Equatorial Climate
2.
Tropical Climate
3.
Hot Deserts
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
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
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INTER-TROPICAL CONVERGENCE ZONE (ITCZ)
SUMMARY NOTE:
Remember
Hadley
Cell
ITCZ
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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
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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
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ITCZ
ITCZ JULY
JANUARY
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ITCZ
JANUARY
ITCZ
JULY
What is the impact
of land and sea on
the migrating
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ITCZ?
INTER-TROPICAL CONVERGENCE ZONE (ITCZ)
SUMMARY NOTE (Cont.):
EFFECT OF LAND AND SEA MASSES ON ITCZ
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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:
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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
Migration
http://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
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Explain the terms source area and air mass
Which are the two main air masses that influence the tropical
areas of Africa?
Study figure 2.23. Draw a table to summarise the differences
between Tropical Continental and Tropical Maritime air masses
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 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
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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
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