Learn about the location of the doldrums and the mechanisms that create them. Understand how they are part of the general circulation of Earth and the importance of the doldrums on a global scale.
Definition of the Doldrums
Way back in the 1700’s, sailing voyages became more common and people started sailing farther. In both the Pacific and Atlantic Oceans, the sailors noticed that there was an area near the Equator where there was little or no wind.
Without the wind to move their sail-powered boats, they would sometimes be stuck for days or weeks. They started calling these areas the doldrums. To be in the doldrums means to be depressed, to have low spirits, or to be inactive. This described what it was like when they got stuck crossing the Equator, and people have been calling these areas the doldrums ever since.
The actual name of the doldrums is the Intertropical Convergence Zone (ITCZ), and it is an important part of Earth’s general circulation system.
Earth has a global pattern of winds that looks like the picture here, but the only part necessary to understanding the doldrums are the winds closest to the Equator. The winds there are part of the Hadley cells in which warm air rises at the doldrums near the Equator high into the atmosphere. That air then flows north in the Northern Hemisphere and south in the Southern Hemisphere. When it gets to about 30 degrees north or south latitude, the air is cooled off and sinks.
It then flows back toward the Equator creating what are called the trade winds.As the trade winds flow back toward the Equator, they mostly cross over ocean, so they pick up a lot of moisture. When they meet again at the doldrums, the air is warm and moist. The warm, moist air rises, and the cycle starts over. It is the rising of air at the doldrums, as opposed to the horizontal wind of the trade winds, that causes sailboats to get stuck. But the doldrums are important for another reason.
The warm, moist air that rises creates lots of rain and thunderstorms. This rain is very important in certain parts of the world.
The Importance of Doldrums
The doldrums, or ITCZ, are located roughly at the Equator, but they also migrate with the seasons. They are 50 to 250 miles wide, so the rain produced by the rising air is significant.
In the Northern Hemisphere’s summer, the doldrums migrate as far as 25 degrees north latitude up to southern Asia. In winter, they go as far south as 20 degrees south latitude down to northern Australia and southern Africa. As the doldrums migrate, they bring much needed annual rains to tropical areas of Earth.For example, in the summertime the doldrums bring rain to India that allows crops to grow and feed over a billion people there. The same is true in Australia during the summertime in the Southern Hemisphere. In the Kalahari Desert in southern Africa, the doldrums provide rain that lets vegetation grow so that lions and other wildlife can survive there.
If it wasn’t for the doldrums bringing rain, it could cause widespread hunger, economic problems, and damage to ecosystems.
While crossing the Equator, sailors in the 1700’s would often get their boats stuck due to lack of wind. They called this area the doldrums. The doldrums, or ITCZ, are part of the general circulation system of the Earth. Parts of the system are the Hadley cells, which is where warm air rises at the doldrums near the Equator high into the atmosphere, and the doldrums at the Equator are the key to making them work.
Warm air rises at the doldrums, travels north and south until it cools and sinks, then returns to the Equator as the trade winds. These winds that get more moist and warm as they travel to the Equator meet at the doldrums. There the air rises, so there is little wind, and hence ships would get stuck at sea for days or even weeks; and rain forms. The doldrums shift north and south with the seasons, bringing important rains to areas like India, Australia, and Africa.