In “The Rime of the Ancient Mariner,” English poet Samuel Taylor Coleridge chronicles the adventures and misfortunes of a sailing vessel. Among the challenges was a time when the winds died, leaving the ship motionless, which the mariner describes like this:
Day after day, day after day,
We stuck, nor breath nor motion;
As idle as a painted ship
Upon a painted ocean.
The ship was stuck in the doldrums, a zone near the equator with little wind but frequent clouds and storms.
Scientists call this region the Intertropical Convergence Zone — the ITCZ. Trade winds from the northern and southern hemispheres converge there. As they meet, the air rises, helped by the heat of the warm water. The rising air eventually turns toward the north or south, traveling thousands of miles before descending back to the surface.
Since the air is moving upward, there’s little wind in this region — and sometimes none at all. That can leave a sailing vessel stuck for days. But the rising air is quite humid, so as it reaches higher altitudes, it cools and condenses to form clouds, and sometimes thunderstorms.
The ITCZ spans all the world’s oceans. In the Pacific and Indian Oceans, it’s right along the equator. It’s also near the equator in the Atlantic, between Africa and South America.
Spending days becalmed in this zone left many sailors feeling dull and depressed. So they gave it their own name, adapted from a word that described a period of low spirits and lack of energy: the doldrums.