Doldrums

Doldrums, also called equatorial calms, equatorial regions of light ocean currents and winds within the intertropical convergence zone (ITCZ), a belt of converging winds and rising air encircling Earth near the Equator.

The “doldrums” is a popular nautical term that refers to the belt around the Earth near the equator where sailing ships sometimes get stuck on windless waters. Because the air circulates in an upward direction, there is often little surface wind in the ITCZ.

There’s science behind it. The effects of the Doldrums are caused by solar radiation from the sun, as sunlight beams down directly on area around the equator. This heating causes the air to warm and rise straight up rather than blow horizontally. The result is little or no wind, sometimes for weeks on end.

Unable to sail and resupply due to lack of wind, crews often ran out of drinking water. To conserve scarce water, sailors on these ships would sometimes throw the horses they were transporting overboard. Thus, the phrase ‘horse latitudes’ was born.

Doldrums and horse latitudes are situated in different locations near the equator. Doldrums are placed at five degrees north and south of the equator. Meanwhile, horse latitudes are located at 30 degrees north and south latitude. The air existing in doldrums is moist, while horse latitudes’ air is dry.

The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend towards the poles and steer extratropical cyclones in this general manner.

Westerlies