Mechanics
See also: Atmospheric circulationHot air rises at the Equator 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.
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 60 degrees south), and the "Shrieking" or "Screaming Sixties" (below 60 degrees south). The latitude ranges for the Roaring Forties and similar winds are not consistent, shifting towards the South Pole in the southern summer, and towards the Equator in the southern winter.
Read more about this topic: Roaring Forties
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