These are also called zones of equatorial calm and it is due a climatic phenomenon that is placed near the Earth equator, attributed to the soft winds, that are called calm winds as well; accompanied by systems of abundant rains and heat.
In this area periods of great calm occur when the winds virtually disappear completely, trapping the sailing ships for long periods (days or weeks). This is why the term doldrum became popular as a colloquial expression in the eighteenth century, to refer to "the caprice of the wind that slows down the navigation to sail".
The zone is located in the place where two trade winds meet, this means the trade winds of the northern hemisphere converge with those of the southern hemisphere, that is why this region is related to the intertropical convergence zone.
