The Atlantic wind and current system

node · earth · Atlantic Ocean, both hemispheres

The Atlantic is not an undifferentiated sheet of water but a pair of rotating systems, and every sailing route across it is a description of them. North of the equator the north-east trades blow steadily westward in the belt roughly between 5° and 30° N, while the mid-latitude westerlies blow eastward roughly between 30° and 60° N; together they turn clockwise as the North Atlantic gyre. South of the equator the pattern mirrors, turning anticlockwise. Between the two trade belts lies the doldrums — the intertropical convergence zone — where a square-rigged ship could lie becalmed for weeks. The practical consequence is severe and asymmetric: a ship leaving Iberia can run south to the Canaries and then west on the trades almost effortlessly, but it cannot come home the same way. It must climb north out of the trade belt into the westerlies first. Prevailing wind, not distance, is what made an ocean crossable in one direction and not the other, and it is why the Atlantic opened from its eastern shore.