Learn

Intertropical Convergence Zone (ITCZ)

The Intertropical Convergence Zone, or ITCZ, is a band of low pressure around the Earth which generally lies near to the equator. The trade winds of the northern and southern hemispheres come together here, which leads to the development of frequent thunderstorms and heavy rain. These thunderstorms can reach, and sometimes exceed, 16 kilometres, 55,000 feet or 10 miles in height above the surface.

The air that is forced to rise along the ITCZ moves towards the poles and slowly descends leading to large areas of high pressure in the sub-tropics, sometimes known as the horse latitudes, and bring largely benign weather conditions to places like the Azores. The resulting circulation that forms with air converging near the surface around the equator and diverging above is known as the Hadley Cell.

The ITCZ moves throughout the year and follows the migration of the Sun’s overhead position typically with a delay of around 1-2 months. As the ocean heats up more slowly than land, the ITCZ tends to move further north and south over land areas than that over water. In July and August, the ITCZ lies well to the north of the equator over Africa, Asia and Central America before moving south into South America, central Africa and Australia by January and February.

Another term for the ITCZ, used historically in seafaring circles, is the ‘doldrums’ since the winds along the band of low pressure are typically calm, trapping ships for days or even weeks at time leaving them stranded.