Roaring Forties
Encyclopedia
The Roaring Forties is the name given to strong westerly
winds found in the Southern Hemisphere
, generally between the latitude
s of 40 and 49 degrees. Air displaced from the Equator
towards the South Pole
, which travels close to the surface between the latitudes of 30 and 60 degrees south, combines with the earth's rotation to cause west-to-east air currents. Because there is little land below the 40th parallel south
, greater wind speeds are able to build than in the same region of the Northern Hemisphere
.
The Roaring Forties was a major aid to trade ships sailing from Europe to the East Indies
or Australasia
during the Age of Sail
, and in modern usage is favoured by yachtsmen on round-the-world voyages and competitions. The location of the Roaring Forties is not consistent, and shifts north or south depending on the season. Similar conditions occur in more southerly latitudes, and are referred to as the Furious Fifties and Shrieking or Screaming Sixties.
and is pushed towards the poles by cooler air travelling towards the Equator (an atmospheric circulation feature known as the Hadley Cell
). At about 30 degrees from the equator, the outward-travelling air sinks to lower altitudes, and continues toward the poles closer to the ground (the Ferrel Cell), then rises up again from about 60 degrees as the air joins the Polar vortex
. This travel in the 30 to 60 degree zone combines with the rotation of the earth to move the air currents from west to east, creating westerly winds. The change in the rotational speed of points on the surface (while a point on the equator moves at 1500 kph, a point at 30 degrees latitude moves at 260 kph causes an observer on the surface to experience faster winds as they travel further south.
Unlike the northern hemisphere, the large tracts of open ocean below 40th parallel south
(interrupted only by Tasmania
, New Zealand
, and the southern part of South America
) mean that higher windspeeds—the Roaring Forties—can develop. Similar but stronger wind conditions are prevalent closer to the South Pole
; these are referred to as the "Furious Fifties" (50 to 59 degrees south), and the "Shrieking" or "Screaming Sixties" (below 60 degrees south). The latitude ranges for the Roaring Forties and similar winds are not set in stone, shifting towards the South Pole in the southern summer, and towards the Equator in the southern winter.
During the Age of Sail
, ships travelling from Europe to the East Indies
or Australasia
would sail down the west coast of Africa, round the Cape of Good Hope
, and use the Roaring Forties to speed their passage across the Indian Ocean, then on the return leg continue eastwards via the Pacific Ocean and under Cape Horn
before sailing up the east coast of the Americas
to home. "To run the easting down" was the phrase used to describe the fast passages achieved in the Roaring Forties.
Round-the-world sailors also take advantage of the Roaring Forties to speed travel times, in particular those involved in record attempts or races
.
Westerlies
The Westerlies, anti-trades, or Prevailing Westerlies, are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. These prevailing winds blow from the west to the east, and steer extratropical...
winds found in the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
, generally between the latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s of 40 and 49 degrees. Air displaced from the Equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
towards the South Pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...
, which travels close to the surface between the latitudes of 30 and 60 degrees south, combines with the earth's rotation to cause west-to-east air currents. Because there is little land below the 40th parallel south
40th parallel south
The 40th parallel south is a circle of latitude that is 40 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, the Indian Ocean, Australasia, the Pacific Ocean and South America....
, greater wind speeds are able to build than in the same region of the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
.
The Roaring Forties was a major aid to trade ships sailing from Europe to the East Indies
East Indies
East Indies is a term used by Europeans from the 16th century onwards to identify what is now known as Indian subcontinent or South Asia, Southeastern Asia, and the islands of Oceania, including the Malay Archipelago and the Philippines...
or Australasia
Australasia
Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...
during the Age of Sail
Age of Sail
The Age of Sail was the period in which international trade and naval warfare were dominated by sailing ships, lasting from the 16th to the mid 19th century...
, and in modern usage is favoured by yachtsmen on round-the-world voyages and competitions. The location of the Roaring Forties is not consistent, and shifts north or south depending on the season. Similar conditions occur in more southerly latitudes, and are referred to as the Furious Fifties and Shrieking or Screaming Sixties.
Mechanics
Hot air rises at the EquatorEquator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
and is pushed towards the poles by cooler air travelling towards the Equator (an atmospheric circulation feature known as the Hadley Cell
Hadley cell
The Hadley cell, named after George Hadley, is a circulation pattern that dominates the tropical atmosphere, with rising motion near the equator, poleward flow 10–15 kilometers above the surface, descending motion in the subtropics, and equatorward flow near the surface...
). At about 30 degrees from the equator, the outward-travelling air sinks to lower altitudes, and continues toward the poles closer to the ground (the Ferrel Cell), then rises up again from about 60 degrees as the air joins the Polar vortex
Polar vortex
A polar vortex is a persistent, large-scale cyclone located near one or both of a planet's geographical poles. On Earth, the polar vortices are located in the middle and upper troposphere and the stratosphere...
. This travel in the 30 to 60 degree zone combines with the rotation of the earth to move the air currents from west to east, creating westerly winds. The change in the rotational speed of points on the surface (while a point on the equator moves at 1500 kph, a point at 30 degrees latitude moves at 260 kph causes an observer on the surface to experience faster winds as they travel further south.
Unlike the northern hemisphere, the large tracts of open ocean below 40th parallel south
40th parallel south
The 40th parallel south is a circle of latitude that is 40 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, the Indian Ocean, Australasia, the Pacific Ocean and South America....
(interrupted only by Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, and the southern part of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
) mean that higher windspeeds—the Roaring Forties—can develop. Similar but stronger wind conditions are prevalent closer to the South Pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...
; these are referred to as the "Furious Fifties" (50 to 59 degrees south), and the "Shrieking" or "Screaming Sixties" (below 60 degrees south). The latitude ranges for the Roaring Forties and similar winds are not set in stone, shifting towards the South Pole in the southern summer, and towards the Equator in the southern winter.
Use for sailing
Age of Sail
The Age of Sail was the period in which international trade and naval warfare were dominated by sailing ships, lasting from the 16th to the mid 19th century...
, ships travelling from Europe to the East Indies
East Indies
East Indies is a term used by Europeans from the 16th century onwards to identify what is now known as Indian subcontinent or South Asia, Southeastern Asia, and the islands of Oceania, including the Malay Archipelago and the Philippines...
or Australasia
Australasia
Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...
would sail down the west coast of Africa, round the Cape of Good Hope
Cape of Good Hope
The Cape of Good Hope is a rocky headland on the Atlantic coast of the Cape Peninsula, South Africa.There is a misconception that the Cape of Good Hope is the southern tip of Africa, because it was once believed to be the dividing point between the Atlantic and Indian Oceans. In fact, the...
, and use the Roaring Forties to speed their passage across the Indian Ocean, then on the return leg continue eastwards via the Pacific Ocean and under Cape Horn
Cape Horn
Cape Horn is the southernmost headland of the Tierra del Fuego archipelago of southern Chile, and is located on the small Hornos Island...
before sailing up the east coast of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
to home. "To run the easting down" was the phrase used to describe the fast passages achieved in the Roaring Forties.
Round-the-world sailors also take advantage of the Roaring Forties to speed travel times, in particular those involved in record attempts or races
Around the world sailing record
The first around the world sailing record was, logically, set by the first person who circumnavigated the world: Juan Sebastián Elcano and the remaining members of Ferdinand Magellan's crew who completed their journey in 1522. The first solo record was set by Joshua Slocum in the Spray .Most races...
.