Roaring Forties

The Roaring Forties are strong, persistent westerly winds in the Southern Hemisphere, especially between 40° and 50° south. They arise from atmospheric circulation over broad, relatively unobstructed ocean.

Westerlies: Prevailing winds that blow from west to east in the middle latitudes of both hemispheres. The Roaring Forties are the Southern Hemisphere’s particularly strong midlatitude westerlies.
Furious Fifties: Strong westerly winds in the Southern Hemisphere, commonly associated with latitudes between 50° and 60° south. This neighboring wind belt continues poleward beyond the Roaring Forties.
Clipper route: A nineteenth-century sailing route carrying ships around the Cape of Good Hope and Cape Horn through the Southern Ocean. Sailing ships used the Roaring Forties to make fast eastward passages between Europe and Asia.
Age of Sail: The period when sailing ships powered by wind dominated long-distance maritime transport, from the sixteenth to the mid-nineteenth century. The winds became especially consequential when ships depended on sail for ocean crossings.
Ocean surface wave: A disturbance that propagates along the boundary between the ocean and the atmosphere. The Roaring Forties transfer energy to the sea, building large waves across long fetches.
Ferrel cell: A midlatitude atmospheric circulation cell in which surface air generally moves poleward and eastward. Its surface circulation contributes to the westerly flow at these latitudes.
Screaming Sixties: A traditional name for strong westerly winds near 60° south, where ocean encircles Antarctica. The name marks the still more southerly extension of the same broad westerly circulation.
Cape Horn: A headland on Hornos Island at the southern tip of South America, near the Drake Passage. Ships rounding Cape Horn faced the Roaring Forties and their powerful seas.
Clipper ship: A fast sailing ship developed in the nineteenth century, designed to carry cargo over long distances at high speed. Clipper crews sought the Roaring Forties for rapid eastbound passages.
Wind-driven circulation: Large-scale ocean circulation caused mainly by momentum transferred from winds to the sea surface. These westerlies are a major force driving Southern Ocean surface currents.

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