little or no wind is to be found, as many a sailor has learned to his or her dismay.
A similar pattern exists in the South Pacific, off the coast of Chile, in the North and South Atlantic, and in the South Indian Ocean. As stated in Chapter 1, Columbus noted this pattern and gambled that the Northeast Trade Winds (blowing westerly) would carry him all the way to Japan and China. He was right about the wind, but underestimated the distance to Asia and did not know that the continents of North and South America blocked his course west.
The winds that sailors sense are the surface winds—air currents that move along the bottom of the earth’s atmosphere. In addition, there are other circulating currents of air, some of which are vertical, moving down to or rising up from the surface. These are called Hadley cells, after George Hadley (1685-1768), the British meteorologist who discovered them in 1735. There are three such cells in the northern hemisphere and an equal number in the southern hemisphere. Warm air rises near the equator and descends at 30 degrees north and south latitudes. Warm air rises again around 60 degrees north and south latitude, to descend once again near the poles. The area near the equator where this occurs is known to meteorologists as the Intertropical Convergence Zone (but is known to sailors as the doldrums because of light and variable winds), and at 30 degrees it is called the northern subtropical divergence zone (known to sailors as the horse latitudes, similarly for lack of wind). The origin of the term “horse latitudes” is a reference to the difficulties faced by early voyagers. Vessels were often becalmed so long that the horses being brought to the New World became part of the sailor’s diet.
High above the surface of the sea, the air flow again becomes horizontal and is characterized by the jet streams that blow from west to east and are familiar to all who have made cross-country airplane flights. The complex pattern of vertical and horizontal wind circulation is repeated in both the northern and the southern hemispheres. Weather patterns are similar, except for one difference that is important to those interested in extreme waves: the weather pattern of Antarctica.
Because of its massive ice cover—9,000 feet thick at the South