Intertropical Convergence Zone ITCZ

Figure 12.1 shows that winds between the tropics converge on a line which we call the Intertropical Convergence Zone (i.e. ITCZ) or equatorial trough. This line of convergence near the equator is also discernible in a map of streamlines (Figure 12.2; Note 12.A). It is actually a band a few hundred kilometres wide, enclosing places where winds flow inwards (are 'confluent') and subsequently rise convectively. It is the latitude of the highest air temperature and vapour pressure near the surface, and the

Intertropical Convergence Zone Map

Figure 12.1 Maps of the global-scale surface winds prevailing in January and July. The line near the equator shows the Intertropical Convergence Zone (ITCZ), where Trade winds from the two hemispheres meet. A spur from this line over southern Africa is called the Zaire Air Boundary (ZAB), where air converges from the Indian and Atlantic oceans, respectively, and another spur over the western South Pacific is known as the South Pacific Convergence Zone (SPCZ). The letter H indicates a centre of high pressure (i.e. a 'high'), and an L stands for a 'low'.

Figure 12.1 Maps of the global-scale surface winds prevailing in January and July. The line near the equator shows the Intertropical Convergence Zone (ITCZ), where Trade winds from the two hemispheres meet. A spur from this line over southern Africa is called the Zaire Air Boundary (ZAB), where air converges from the Indian and Atlantic oceans, respectively, and another spur over the western South Pacific is known as the South Pacific Convergence Zone (SPCZ). The letter H indicates a centre of high pressure (i.e. a 'high'), and an L stands for a 'low'.

Map With Spcz And Itcz
Figure 12.2 Mean streamlines of surface winds in January. Note the convergence of winds at the ITCZ, as in Figure 12.1. The whorls correspond to highs.

coldest and driest air at the tropopause. As a result, convective uplift yields copious condensation well above the ground, which releases notable amounts of latent heat, and that in turn stimulates convection.

The ITCZ lies at about 5°N on average. This is known as the meteorological equator, matching the equators of radiation (Section 2.2) and temperature (Section 3.2). It wanders seasonally (Figure 12.3), lagging about two months behind the change of the Sun's declination (Section 2.2), this being the time taken for the surface to respond to the Sun's heating. The latitudinal variation is most pronounced Asian continent to the north. The ITCZ does not move with the seasons over the eastern Pacific and Atlantic oceans, being permanently confined to the northern hemisphere by the cold Peru and Benguela currents (Figure 11.15) in the south. (There is no surface convergence of winds where the surface is cool.) This explains why the meteorological equator is slightly north of the geographic equator.

The movement of the ITCZ across South Africa (Figure 12.1) is complicated by the land's shape, elevation and location, and there is a southerly spur called the Zaire Air Boundary (ZAB). Similarly, there is a spur over South America

^ Equatorial trough X

/ x \ / / \ / / \ / / \ / \ / \

\ x /

\

\ /Sun

i i i I

1 1 1

Sept Nov Jan Mar May July Sept

Figure 12.3 The annual march of the latitude of the noon Sun (i.e. the declination) and of the 'equatorial trough', i.e. the mean latitude of the ITCZ.

Sept Nov Jan Mar May July Sept

Figure 12.3 The annual march of the latitude of the noon Sun (i.e. the declination) and of the 'equatorial trough', i.e. the mean latitude of the ITCZ.

east of the Andes as far south as Paraguay in February. But the largest and most over the Indian Ocean because of the large persistent spur to the ITCZ is over the southwest Pacific, known as the South Pacific Convergence Zone (SPCZ). It is related to the 'warm pool' near Papua (Section 11.2) and is most prominent in summer, contracting towards Fiji in winter. Unlike other spurs, it lies mostly over water (Figure 12.1). There is a convergence of (i) moist northeasterlies from the semi-permanent high in the south-east Pacific (Figure 12.1) and (ii) southeasterlies from mobile highs moving across the south-west Pacific in summer. The zone is unique in spawning both tropical cyclones and 'frontal depressions' (which are both discussed in Chapter 13).

Winds at the ITCZ are commonly light or non-existent, creating maritime calms called the doldrums. But there is occasionally a week or two of strong westerlies, called a westerly wind burst, especially during November to March. The disturbances seem to occur each 40-50 days or so, and this loose rhythm is known as the Madden-Julian Oscillation, first noted in 1971. It is associated with a zone of active convection within the ITCZ, moving eastwards from Sumatra into the western Pacific. Meanwhile, cloud clusters move west within the zone, affecting the amounts and distribution of rainfall, including the timing of the Wet in northern Australia. Then the disturbance weakens.

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Responses

  • michael bannerman
    How are the geographical equator, meteorological equator, and ITCZ related?
    6 years ago
  • Berhane
    How are the geographic equator, meterological equator, and itcz related?
    6 years ago
  • dina
    Is the itcz stronger in january or july?
    6 years ago
  • alessandra
    Which climate zone is most associated with alaska and wich is most associated with the itcz?
    6 years ago
  • karoliina
    How is SPCZ and ITCZ linked?
    6 years ago
  • laura
    What climate is associated with the intertropical convergence zone (ITCZ)?
    5 years ago
  • peter bone
    What is the approximate latitudenal position of the ITCZ in january and in july?
    5 years ago
  • susan
    How does the itcz change climate?
    5 years ago
  • fiorenzo
    What weather is associated with the ITCZ?
    4 years ago
  • SARAH
    How are the geographic equator meteorological equatir and ITCZ related?
    4 years ago
  • evan marshall
    What are the weather systems associated with the inter tropical convergence zone?
    4 years ago
  • eric
    What is the approximate latitudinal position of the ITCZ in january an in july?
    4 years ago
  • quintilia
    What is inter tropical boundary?
    4 years ago
  • goldilocks
    Which of the following climate types is most associated with the ITCZ?
    4 years ago
  • Gregory
    Why is the ITCZ called the meteorological equator?
    4 years ago
  • fatimah
    Where on the map of Ghana is the inter topical convergence zone in January found?
    3 years ago
  • Licia
    What is the approximate latitude position of the ITCZ in january and in July?
    3 years ago
  • halfred
    What is the latitudinal positions of itcz in winter?
    3 years ago
  • Hiewan
    Where is the itcz between may and sept...?
    3 years ago
  • Amanda
    Where does the inter tropical convergence zone meet in January in ghana?
    2 years ago
  • Abaalom Mustafa
    What are the climates beween the itcz?
    1 year ago
  • lavinia sandheaver
    Where is the location of itcz during january and july?
    1 year ago
  • may
    Why is the equatorial trough/ITCZ so wet?
    1 year ago
  • NEGISTI ROBEL
    How the position of ITCZ affect climate and weather syestems?
    1 year ago
  • WOLFGANG
    What climate conditions prevail at the ITCZ?
    10 months ago

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