Intertropical Convergence Zone

FOCUS QUESTION:

What are the weather conditions associated with Intertropical Convergence Zone (ITCZ) Caribbean systems and formation? Intertropical Convergence Zone is a key component of the global circulation system.

The ITCZ is a very large feature which circles the globe. It is a belt of converging trade winds and rising air that encircles the Earth near the equator.

Near the equator, from about 5° north and 5° south, the northeast trade winds and southeast trade winds converge or meets in a low-pressure zone known as the Intertropical Convergence Zone, or ITCZ.

It affects many tropical areas around the world, including territories in the southern Caribbean.

As these winds converge, moist air is forced upwards, forming one portion of the Hadley cell. The air cools and rises, causing water vapour to be formed, which results in a band of heavy precipitation around the globe. So, rising air produces high cloudiness, frequent thunderstorms and heavy rainfall. Air that rises along the ITCZ moves away from the equator and sinks in the subtropics at the Horse Latitudes, rounding out the Hadley Circulation. The doldrums, oceanic regions of calm surface air, occur within the zone.

The ITCZ has been called the doldrums by sailors because there is essentially no horizontal air movement; that is, no wind (the air simply rises). The ITCZ is not stationary. The ITCZ shifts north and south seasonally with the sun. It moves north of the equator during the northern hemisphere summer, bringing heavy rain to Trinidad and Tobago and Grenada. It then moves south, crossing the equator and moving into the southern hemisphere.

It moves towards the southern hemisphere from September through February and reverses direction in preparation for northern hemisphere summer.

The ITCZ reaches its most southerly point during the northern hemisphere winter, bringing heavy rain to Brazil.

The ITCZ crosses Guyana as it travels to the north and then again as it moves south, giving this country two periods of heavy rainfall each year. Over the Indian Ocean, it undergoes especially large seasonal shifts of 40°- 45° of latitude. The ITCZ moves farther north or south over land than over the oceans because it is drawn towards areas of the warmest surface temperatures. The ITCZ is less mobile over the ocean. ITCZ is characterised by strong convective weather consisting of cumulus and cumulonimbus clouds with turbulence and heavy rain at times.

The exact location varies with the seasons throughout the year and follows the sun’s zenith point.