NDRRMC Weather Advisory No. 1 for Intertropical Convergence Zone (ITCZ)
ATMO 4 itcz
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Transcript of ATMO 4 itcz
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ATMOSPHERE
CASE STUDY AREA- the ITCZ in AFRICA
You will need to be able togive very detailed answersto a question on this areain an assessment.
This case study shows the way that the movement ofthewind belts between their summer and winterpositions has a profound effect on the lives indeed
the very survival- of people who live in the Sahel zoneof northern Africa.
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ATMOSPHERE
vThe ITCZ is an areawhere two air masses
meet- it brings heavyrain to the areas itpasses over.
vIt happens all roundthe world between theEquator and about 20degrees N/S.
vIts full name is theInter Tropical
Convergence Zone. It ispart of the Hadleyconvection cells, and hasthe Doldrums within itsboundary.
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ATMOSPHERE
The ITCZ does
not stay in thesame area allyear round butmigrates to thenorth and then
back south again.It is thismovement thatmatters so muchto the people and
animals of thearea.
The AFRICAN ITCZ REGION
Discussthisdiagram
Learnthesetwo
boxes!
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ATMOSPHERE
The trade winds ( mT air mass) comeinto the zone from the Atlantic,south of the Equator, and havetravelled over oceans; they are there-fore carrying a lot of moisture.This is their position in January.
Once in the hotter latitudes, they areenergised into huge towering cumulo-nimbusthunderclouds. These can be anything up to 10kmsacross, and groups of clouds can form covering
1000kms. In between the clusters are often sunnycloud-free areas.
The clusters are particularly found over land, not sea.
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WetwarmmT air
HEAVY RAINS
ATMOSPHERE
S N
Gulf ofGuinea
Coastalareas-equatorialclimate
Inland areas-savannaclimate type
Sahara-Desertclimatetype
Moves this way
HotdrycTair
Harmattan wind
IN JANUARY
Copy diagram
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ATMOSPHERE
In January, the sun is
overhead near the Tropicof Capricorn, in thesouthern hemisphere.
The ITCZ zone of
meeting air lies well tothe south, as seen here.
The rains brought by thezone are confined to thevery coastal areas of
Nigeria, Togo, Ghana andtheir neighbours.
ITCZJANUARY
Case study area
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ATMOSPHERE
Here, the moist warm mT air from the Atlantic Oceanmeets the hot dry cT air coming out of the SaharaDesert. Note that the desert is an area of HIGH pressure in winter andparticularly strong winds blow AWAY from such areas.
The cT wind is called the HARMATTAN and is extremely
hot, dry and dusty. Of course, the Harmattan cannot bring any rainto the area it travels over, and all the northern part of Africa is
influenced totally by it.No crops can grow.
In the south, however, the wet moist winds from the
sea are forced upwards over the land where they drenchthe land in life-giving torrential rains. Here crops can beeasily grown, providing the soil is fertile enough and not washed away.
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ATMOSPHERE
During the spring, the ITCZ moves slowly northwards,the Harmattan losing its dominance over the land bitby bit.
Places further and further inland get the rains that
they so desperately need for people, crops andanimals alike. The slight drawback is that the further the ITCZtravels north, the less water it can bring to the rainy area, so crops tothe north get less than those to the south.
By mid spring, places like northern Ghana, northern
Benin and central Nigeria are getting the rains. Thewells are re-filled, the grass for feeding animals starts to grow and
farmers can start off their crops.
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WetwarmmT air
HEAVY RAINS
ATMOSPHERE
S N
Gulf ofGuinea
Coastalareas-equatorialclimate
Inland areas-savannaclimate type
Sahara-Desertclimatetype
Moves this way
HotdrycTair
Harmattan wind
IN JANUARY
Copy diagram
Rememberthis?
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ATMOSPHERE
S N
Gulf ofGuinea
Coastalareas-equatorialclimate
Inland areas-savannaclimate type
Sahara-Desertclimatetype
WetwarmmT air
HotdrycTair
Harmattan wind
IN JULY
Moves this way
HEAVY RAINS LIGHT RAINS
Copy diagram
Compare the January and July diagrams.
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ATMOSPHERE
By July the ITCZ has reached as farnorth as it will go, reaching central
Mali, northern Niger and northernChad. There the Harmattan is confined to thevery edges of the Sahara desert, the weakest it
gets all year.
This is the Sahel zone, the area mostprone to DESERTIFICATION
Without these rains most years, the desert will takeover yet more land, forcing poverty-stricken, hungry
people to migrate southwards into other peoplesterritory, with their thirsty cattle and goats.
ITCZ JULY
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ATMOSPHERE
After July, the belt moves back down south
again, giving a second rainy spell to the luckyareas in its path.
No more rain will fall this far inland until nextyear!
The people rely on these rains that arrive within aweek or two of the same time every year.
Recently, there have been several years wherethe rain has not got as far inland as normal !
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Watch!
ATMOSPHERE
SecondLot ofrain
SN
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ATMOSPHERE
Look carefully at these three graphs.
Without using an atlas, can you say roughly whereeach place is likely to be using only the rainfallpattern. Use words like inland, coastal, further,Sahel.
Can you say why?
2 31
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ATMOSPHERE
A question asking about the ITCZ, with graphs andmaps, will need you to do the following things;explain-
They arelooking
for.
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ATMOSPHERE
END
The people rely on these rains that should arrive
within a week or two of the same time every year.Recently, there have been several years wherethe rain has not got as far inland as normal !
What do you think has been the result of this?