Winds create two kinds of giant rivers in the sea
There are two kinds of ocean currents: surface (or drift) currents and stream currents. They are much like rivers in the sea, except that their lateral boundaries are not as clearly defined.A surface current is the result of wind action. A wind blowing steadily from one direction for 12 hours or more creates a surface current with a speed of about 2 percent of the wind’s average speed.A stream current is a surface
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| The principal currents of the world. |
current that has been confined to narrow waters, or one that has been deflected from its original course by the coast or a shallowing seabed.Currents do not usually flow in exactly the same direction as the wind, however, because of the inertial effects of the Earth’s rotation, known as the Coriolis force. In the Northern Hemisphere, the current is deflected to the right; in the Southern Hemisphere, it’s deflected to the left.The amount of deflection varies with latitude, ranging from about 15 degrees to as much as 45 degrees. The nearer the poles, the greater is the deflection. The depth of the water also has an effect: the shallower the water, the greater the deflection.Ocean currents generally circulate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, spurred on by the constant westward push of the trade winds toward the equator. There are exceptions, however, one notable one being the Pacific Equatorial Countercurrent, which runs almost due east to return the vast quantities of water moved west by the Pacific Equatorial Currents to the north and south of it.Fast currents such as the Mozambique or Agulhas Current, which can reach 4 knots at times, are a source of dangerous seas when strong winds blow against them.A current is described by its set (the direction
toward which it flows) and its drift (its speed in knots).See also
Coriolis Force; Trade Winds
