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How the ITCZ Works
The windless nature of the ITCZ is a result of the convergence of trade winds traveling northwest from the southern hemisphere and southwest from the northern hemisphere. The ITCZ appears on the Earth's surface where solar radiation is strongest, and the heat from the sun warms the air, creates a low-pressure zone, and sucks in the trade winds around it. When they converge at the equator, the winds push each other upwards, uplifting the air and leaving little wind on the surface. The result is a collection of high cumulus clouds that occasionally and violently thunderstorm and rain, but relative quiet most of the time.
Effects on the Climate
The ITCZ has a major impact on the creation of monsoons and other forms of violent rain in the equatorial region. At the very center of the ITCZ, there are two brief rainy seasons roughly six months apart; on the fringes of the ITCZ, these rainy seasons are longer and closer together, resulting in one medium-length rainy season. During rainy seasons, also known as monsoon seasons in Asia, rain usually falls in excess of an inch an hour, which may cause flooding. Between or around rainy seasons are the dry seasons, which are characterized by little to no rain and low humidity. These seasons repeat annually and greatly impact the cultures, economies and agricultural practices of those peoples who live in the range of the ITCZ.
Alternative Names
There are a number of alternative names that relate to the weather conditions created by the ITCZ. Because the ITCZ is a low-pressure zone along the equator, it is sometimes referred to as the equatorial trough or the near-equatorial trough. In parts of Asia and northern Australia, where the ITZC causes monsoons and exacerbates rains, it is sometimes called the monsoon trough. In local languages, the ITCZ is often called the windless zone because of the calm air even as the sky is full of high, looming clouds.
The Doldrums
The ITCZ is most commonly colloquially known as the doldrums. This term originated with European sailors who struggled to sail through the equatorial waters of the Atlantic and, later, Pacific. Because of the convergence of winds from the north and south, there is very little wind in the ITCZ, and when there is wind, it is of short duration and little force. The result is that ships would become trapped without wind to push them onward, and sailors recognized the danger and frustration this zone could cause. Sailors reporting that their ships had been stalled in the ITCZ described themselves as being "in the doldrums," meaning in a state of boredom and listlessness, but the term soon became associated with the equatorial windless zone.