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Inter Tropical Convergence Zone (ITCZ)

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Inter Tropical Convergence Zone


The Inter Tropical Convergence Zone, or Inter Tropical Convergence Zone (ITCZ), is the belt of low pressure girdling the Earth, near the equator, where the trade winds of the Northern and Southern Hemispheres come together. It is formed by the vertical ascent of warm, moist air from the latitudes above and below the equator. As the air ascends it cools, releasing the accumulated moisture in what can be an almost continuous series of thunderstorms.


The position of the ITCZ varies with the seasons. In July, over the Atlantic and Pacific, the ITCZ is between 5 and 15 degrees north of the Equator, but further north over the land masses of Africa and Asia. In January, over the Atlantic, the ITCZ sits no further south than the Equator, but extends much further south over South America, Southern Africa, and towards Australia. Over land, the ITCZ tends to follow the sun's zenith point.

Where the trade winds are weak, the ITCZ is characterised by isolated Cumulus and Cumulonimbus (Cb) (Cb) cells. However, where the trade winds are stronger, the ITCZ can be a solid line of active Cb cells embedded with other cloud types developing as a result of instability at higher levels. Cb tops can reach and sometimes exceed an altitude of 55,000 feet, and the ITCZ can be as wide as 300 nautical miles in places presenting a formidable obstacle to aircraft transit.


Aircraft flying through the ITCZ will encounter all the hazards associated with Cb clouds such as icing, turbulence, lightning, and wind shear. However, it is in this zone where the most severe effects may often be encountered. In particular, it is within the ITCZ where convective breakthroughs of the Tropopause often occur, with the majority occuring over land especially in the second half of each day and much less often over oceanic areas where the phenomoenon is more likely to occur with more isolated cells and in the early hours of each day. Research sponsored by National Aeronautics and Space Administration has shown that 1% of tropical deep convective activity exceeds 46,000 ft altitude, with a small prportion of this reaching much greater heights. For further information on the potential hazards of tranit through or near Cb cloud, see the article Cumulonimbus (Cb).

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