then south along the east coast of Australia. There is a similar pattern in the Atlantic Ocean. The North Equatorial Current begins near the Cape Verde Islands and flows west at an average speed of 0.7 knots.9 The South Equatorial Current flows from the west coast of Africa to South America, commencing at a speed of around 0.6 knots but increasing to as much as 2.5 knots as it approaches Brazil. At the “hump” of Brazil (the state of Pernambuco), it divides—one portion going north; the rest, south.
Differences in water density (due to either temperature or salinity) will also create a current. Water flows from areas of lower density (where water depth is slightly greater) to areas of high density, where depth is less). As in the atmosphere, there are both surface currents and deep-ocean currents, again modified by the presence of landmasses that sometimes constrict or channel the flow. Analogous to the patterns of the wind in the atmosphere, these great currents flow generally in circular patterns in the world’s oceans and are called gyres. Gyre circulation is of critical importance because it is a major mechanism for global heat transport.
In addition to the major currents described above, there are dozens of other named currents that profoundly affect navigation and coastal weather in specific areas. For the purposes of this book, some of the more important ones are shown in Figure 4. The numbered currents in particular should be noted, because they have special significance for the purposes of this book, as described later. To best understand how huge waves can arise, I believe it is important to be able to visualize not only the sea in motion but also the various forces that act on it to create extreme waves, particularly in those areas where of necessity oceangoing vessels must pass to make their way from one ocean to another, from one port to the next.
Oceanographers study current flow by using floating instruments with small position-indicating radio transmitters or by the simple expedient of dumping a lot of labeled bottles into the ocean. Recently, bad weather has expanded our knowledge of Pacific Ocean currents and provided data for comparison with computer models currently in use.