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date: 20 February 2018

inter-tropical convergence zone

A Dictionary of Geography

Susan Mayhew

inter-tropical convergence zone (ITCZ) 

That part of the tropics where the opposing north-east and south-east trade winds converge. It is not a continuous belt, more like a necklace with groups of clouds as the ‘beads’; in places there may be two or more ‘strings’. The zone is narrower over the oceans, and broader over the continents, where other wind systems may be involved; in West Africa the ITCZ is the convergence of the Guinea monsoon and the Harmattan (Miskolczi et al. (1997) J. Appl. Met. 36, 5). See Yancheva et al. (2007) Nature 445 on the influence of the ITCZ on the East Asian monsoon.

The ITCZ moves north and south; moving more over land, and arriving in the summer in each hemisphere. Its position is affected by the apparent movement of the overhead sun, the relative strengths of the trade winds, and the changing locations of maximum sea-surface temperatures (R. D. Thompson1998). This means that the movements of the ITCZ are highly unpredictable. In May 2005, the African portion of the ITCZ was 1° south of the average; a period of drought near the Sahel. In July 2003, it was around 0.9° north of the average; heavy rains fell in Ethiopia, with flooding in Khartoum. The movements of the ITCZ also affect bush/forest fires in South-East Asia (P. Kershaw et al. 2001). Over the oceans, the ITCZ is broad, and often loses its identity.