Transcript ITCZ Aim- Describe and account for rainfall patterns across West Africa

ITCZ
Aim- Describe and account for rainfall patterns across West
Africa
ITCZ
Aim- Describe and account for rainfall patterns across West
Africa
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Read over hand out.
Read pages 23-25 of the Higher textbook.
Complete the past paper questions.
Complete worksheet on construction and
analysis of climate graphs.
ITCZ
Aim- Describe and account for rainfall patterns across West
Africa
• Lagos receives a high amount rainfall all year round with
1625mm. There are two distinct peaks in summer and
autumn. Rainfall in January is low at about 50mm, this is
because the ITCZ is lying to the south of Lagos and the
mT air mass is offshore. As the ITCZ starts its migration
northwards the rainfall begins to increase to a maximum
of 350mm. This is because the rainfall belt is 300500km behind the ITCZ and the mT air mass dominates.
There is however a decrease at the height of summer
probably because the ITCZ is too far north and the rain
belt no longer extends as far south as Lagos. As the
ITCZ migrates more rapidly south in autumn Lagos
receives a second peak in rainfall, decreasing towards
the end of the year when the ITCZ is further south.
ITCZ
Aim- Describe and account for rainfall patterns across West
Africa
• Kano located in central west Africa and has one distinct rainy
season. In January there is no rainfall and this is because the ITCZ
is lying to the south of Kano. Thus the cT air mass is dominating
over much of north west Africa bringing very dry conditions
(harmattan wind), and warm temperatures. As the ITCZ starts to
move northwards in spring a small amount f rainfall is received in
Kano, it isn’t until the summer that a maximum of 300mm of rainfall
is received because the ITCZ is now north of Kano and the rain belt
is 300-500km behind. The temperature is decreased in the summer
because the mT air mass dominates over much of the continent it
brings slightly cooler temperatures on shore from the sea. As the
ITCZ migrates south again in the autumn the rainfall decreases and
the cT air mass dominates once more bring dry warm weather
again.
ITCZ
Aim- Describe and account for rainfall patterns across West
Africa
• 1995 Ouagagougou
• January very warm and dry because the cT air mass is
blowing out of the Sahara, with a hot dusty wind
(harmattan).
• Spring, the temperature will increase with the movement
of the overhead sun.
• Summer- temperature decreases and rainfall reaches it
seasonal maximum. Due to the mT air mass bring
cooler temperatures. The ITCZ is to the north bringing
the rain belt 300-500km behind it.
• Autumn- Temperatures begin to rise again, before falling
back to winter low and rainfall decreases. Because the
ITCZ moves southwards and the cT air mass returns
with warm dry weather.
ITCZ
Aim- Describe and account for rainfall patterns across West
Africa
• There is a varied rainfall distribution over west Africa. Lagos in the
south receives the highest amount of rainfall, 1800 mm. Whereas
Agades in the far north, receives the least amount of rainfall at
160mm. As you move northwards rainfall levels decline, Minna
1350mm and Zinder 550mm.
• Rainfall is associated with the movement of the ITCZ, this is where
the trade winds converge at the thermal equator. The thermal
equator moves in accordance to the seasons, i.e. the position of the
overhead sun. The sun is directly over head at the equator twice a
year, meaning that the ITCZ is over Lagos twice in the year.
Whereas in the north the ITCZ is only overhead once. When the
ITCZ lies to the south, the cT air mass dominates over much of
north Africa bring very dry conditions. The Harmatten wind blows
southwards from the Sahara, it is very dry and dusty. Its only when
the ITCZ starts migrating northwards that the mT air mass
dominates bringing with it moist unstable air, and producing rain
where it meets the cT at the ITCZ.
ITCZ
Aim- Describe and account for rainfall patterns across West
Africa
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Points could include for Jos:
Marked seasonal variation in precipitation- High annual total but most rain
falls between April and September.
Dry Between November and February, due to dominant hot, dry cT air mass
blowing outwards from the Sahara. Reference may also be made to the
hot, dry, dusty Harmattan wind.
Increase in temperature (monthly peak of 23 C in March) before onset of
rainy season.
Temperatures decrease in summer months ( Mean low of 17 C in July) as
rainfall increases to a maximum. The steady rise in rainfall amounts from
March’s modest 20mm, to far more significant totals in April and May and
the high amount in June-September can be attributed to the northward
movement of the I.T.C.Z. and the increasing influence of the moist mT air
from the Gulf of Guinea.
Mark out of 10, award up to 6 marks for either Description or Explanation.