Atmosphere – Air Streams (Model Answer)
Describe and explain the characteristics of the Tropical Maritime and the Tropical
Continental air masses (8)
The Tropical Maritime (mT) air mass brings with it south westerly trade winds.
These winds are onshore winds that have blown from the Atlantic Ocean.
As air
streams bring with them the associated weather from their place of origin, this
particular air mass brings very wet and rainy conditions,
as it has picked up moisture
from over the Atlantic Ocean.
They can also bring very thundery conditions to
countries.
The Tropical Continental (cT) air mass brings north-easterly trade winds.
These
winds are offshore winds that have blown from the Sahara Desert.
Because these
winds have blown from the Sahara they then bring very dry and dusty weather, as well
as sunny conditions.
Using the maps to help you, describe and account for the climate in either Lagos or
Ouagadougou. (8)
Lagos
Lagos is situated on the west coast of Africa, very near to the Equator. Lagos receives
over 1500mm of rainfall per year and as such it has an equatorial climate.
Lagos is affected by the seasonal movement of the ITCZ. This is the point at which the
north east trade winds and the south-westerly winds meet. It is a band of very low
pressure that moves with the overhead sun.
As the ITCZ moves towards the Tropics of Capricorn in January, the ITCZ follows the
coast of West Africa because land heats up quicker than oceans.
This means that
Lagos and other countries south of the ITCZ will be affected by the Tropical Maritime
air streams which bring very wet weather.
When the ITCZ moves north towards the
Tropics of Cancer, much more of Africa is being affected by the Tropical maritime air
mass.
Lagos receives such high amounts of rain because the ITCZ is always either directly
above Lagos or north of Lagos and therefore this country is always being affected by
the Tropical Maritime air mass
which brings such heavy rain.
Therefore, Lagos
will have no months without rainfall.
Ouagadougou
Ouagadougou is situated on the west side of Africa, and receives between 500 and
1000mm of rainfall per year.
Ouagadougou is affected by the seasonal movement of the ITCZ. This is the point at
which the north-east trade winds and the south-westerly winds meet. IT is a band of
very low pressure that moves with the overhead sun.
During the months of December and January the ITCZ is over the Tropic of Capricorn,
and so Ouagadougou is being affected by the Tropical Continental air mass.
This air
stream blows from the Sahara desert and so brings very warm, dry weather.
During
these months Ouagadougou will receive no rainfall at all.
When the ITCZ moves
north towards the Tropic of Cancer in June, Ouagadougou will be affected by the
Tropical Maritime air stream that blows over the Atlantic Ocean.
This air stream
brings very wet weather.
The seasonal movement of the ITCZ means that whenever it is north of Ouagadougou,
Ouagadougou will receive rain, which is why the total annual rainfall is between 500 and
1000mm per annum.
However, in the months that the ITCZ is south of Ouagadougou,
Ouagadougou will receive very warm and dry weather.