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What you should know by the end of this lesson:
What you should know by the end of this lesson:
What is the Inter-Tropical Convergence Zone (ITCZ)
The Air Masses of the ITCZ
How the ITCZ affects variations in rainfall across Western Africa
What is the ITCZ?
What is the ITCZ?
The Inter-Tropical Convergence Zone is the area where the two Hadley Cells meet. It is an area of low pressure that brings heavy rain. It marks the thermal equator.
As the Hadley Cells move north and south due to the Earth’s orbit, so does the ITCZ.
This has a significant impact on the regions in West Africa.
ITCZ Air Masses
ITCZ Air Masses
Digital Workbook and Paper Jotter
Take a note of the 2 different types of air Masses in West Africa and the types of weather they bring.
Air Masses
Air Masses
An Air Mass is a large body of air that has taken on the characteristics of the surface area beneath it. Within the Air Mass, there is a great uniformity of temperature and humidity
Air Masses can be classified as Tropical, Polar, or Arctic (relating to Temperature)
Air Masses can be classified as Continental or Maritime (relating to Humidity)
Tropical Continental (cT)
What type of weather it brings:
It is very hot
It is dry with low humidity
The air is stable due to High Pressure (Sub-Tropical High-Pressure Belt)
Often poor visibility due to sandstorms
Weather is monotonous (always hot and dry!)
Air moves Southwards as the NE Trade Winds or Harmattan Winds
Tropical Maritime (mT)
What type of weather it brings:
It is hot or very hot
It is moist (High rainfall or showers and intense thunderstorms)
Relatively high humidity
The air is unstable and will rise (allowing the development of rain!)
Air moves Northwards as the SE Trade Winds or SW Monsoon
Each of these air masses has an impact on the people living in West Africa.
At different points in the year, they will each dominate. This is controlled by the ITCZ.
ITCZ Movements
ITCZ Movements
The thermal equator changes throughout the year with the earth’s orbit. The ITCZ moves north and south with the change in seasons.
Digital Workbook (or with printer access)
Download a copy of the worksheet for this lesson
Shade/Highlight where the ITCZ would be in January and July
Annotate each map with the dominant air mass and type of weather experienced
OR
Paper Jotter (No printer access)
Make 2 rough sketches of the West of Africa
Shade/Highlight where the ITCZ would be in January and July
Annotate each map with the dominant air mass and type of weather experienced
ITCZ in January
ITCZ in January
In January the Tropical Continental air mass is dominant bringing with it hot and dry weather to Western Africa.
ITCZ in July
ITCZ in July
In July the Tropical Maritime air mass moves North bringing with it hot and moist weather (thunderstorms) to Western Africa
ITCZ and rainfall in West Africa
ITCZ and rainfall in West Africa
Climate Graphs - Reminder
Climate Graphs - Reminder
Temperature, usually shown in oc or of, is a red line graph. Make sure to read the correct axis for values.
Precipitation (rainfall), usually shown in mm or days, is a blue bar graph. Make sure to read the correct axis for values.
When describing climate graphs, pay attention to major patterns and maximum/minimum values of temperature and precipitation
Digital Workbook (or with printer access) and Paper Jotter
Answer the question below
Read the question carefully and the hints about how to answer it
Use the drop-down menus for further information on the 4 subheadings for answering the question.
Question:
Using your knowledge of Air Masses in Western Africa and the ITCZ, can you EXPLAIN the variations in rainfall across western Africa (10)
Hints
Hints
Relate to the ITCZ; the area of intense solar heating; the impact of Tropical Maritime and Tropical Continental Air Masses
Hints
Hints
Organise your points under the following headings and avoid repeating similar arguments for the different statements
The further North the Smaller the Annual Rainfall
The further North the Smaller the Annual Rainfall
The ITCZ is always North of Abidjan and so it always experiences Tropical Maritime air (Hot and Wet) giving higher rainfall.
The further north you travel the shorter the time affected by the ITCZ and the shorter the rainy season. In the North of the region, the Tropical Continental air mass is dominant, giving little chance of rain.
The Further North the shorter the wet season and the fewer the number of rainy days
The shorter wet season is due to the fact the ITCZ is only at its northernmost point for a very short period of time, limiting the amount of rainfall experienced in Gao.
Bobo-Dioulasso has a long wet season due to the dominance of the TM air mass as the ITCZ moves north towards the Tropic of Cancer.
The further North the more the rain is concentrated in the summer months
Abidjan experiences two rainfall peaks when the ITCZ is directly overhead as it moves North and then South
Gao is only affected by the ITCZ in the summer months as this is when the sun moves the ITCZ North. Gao only experiences the ITCZ rains once and for a short time before they begin to move South again
The further North the rainfall is more variable from year to year
Further North the rainfall is more localised and so more variable from place to place
Gao may only be affected by the edge of the ITCZ rather than the main rain band, so that less direct heating occurs and less convection rain is produced
Some years the ITCZ and the main rain band may not move as far north as Gao causing the rains to fail altogether
Check your Learning
Check your Learning
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Lesson Complete
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