What are ocean currents?

The oceans don't remain still; their water is constantly moving in giant circles known as currents. In the Northern Hemisphere, surface currents move clockwise, while in the Southern Hemisphere they move counterclockwise. Currents help to moderate temperatures on land in places like the British Isles—which are farther north than the U.S.-Canadian border—by sending warm water from the Caribbean northeast across the Atlantic Ocean to northern Europe. A current known as the Antarctic Circumpolar Current circles the southern continent. The North Atlantic and North Pacific oceans each have a large clockwise current, while the South Atlantic and South Pacific oceans each have a large counterclockwise current.

What is an Ekman spiral?

Vagn Walfrid Ekman (1874-1954), a Swedish physicist and oceanographer, discovered that a combination of the Coriolis effect, the movement of surface waters, and the friction caused by winds blowing on the ocean's surface have an influence on current direction. In the Northern Hemisphere, the end result is that currents will be pushed to the right, and in the South the opposite occurs, forming spirals like weak whirlpools in the water. The effect, however, penetrates the ocean's surface only to a degree (the null point), as the influence of these factors weakens with water depth. (The layer affected by the spiral is called the Ekman layer). Scientists have noted that the Ekman spiral is most obvious underneath sea ice, because waves and other forces in the open sea nearly cancel out the effect. However, the Ekman spiral also applies to the Earth's atmosphere, where they are seen in surface winds.

How do ocean currents affect weather?

The world's oceans cover about 70 percent of our planet's surface. Thus, ocean water also absorbs more heat from the Sun than the land does. In addition to this, water absorbs and emits heat energy more slowly than land does. Warm water, therefore, remains warm longer, and cold water remains cold longer. As the world's ocean waters circulate through the action of currents, this warm or cold water can be transported long distances before it changes temperature. This is an important way that Earth distributes its heat energy. Warm waters in the tropical Atlantic Ocean are carried north as far as England and Scandinavia, for instance, while warm waters in the Indian Ocean circulate down toward Australia and South Africa. Land barriers, such as that formed by Central America, are vital for diverting currents in various directions. It's because of this that currents from western Africa move toward the Caribbean, and are then deflected north. Without Central America, Great Britain would be as frigidly cold as the remote wastes of northern Siberia.

Do ocean currents affect coastal weather?

Yes, ocean currents have the effect of moderating climates along coastal regions. Ocean waters tend to stabilize temperatures, which is why living on the coast of Southern California, for example, is a much more pleasant climatic experience than living farther inland, where it is much drier and warmer.

What are the fastest currents in the world's oceans?

The fastest known current is part of the Gulf Stream system: It heads north from the southern tip of Florida toward Cape Hatteras, North Carolina, flowing up to 3.3 to 6.6 feet (1 to 2 meters) per second, with some estimates as high as 7.5 feet (2.3 meters) per second. The Kuro Siwo Current in the Pacific Ocean runs a close second in terms of speed—around 1.3 to 4 feet (0.4 to 1.2 meters) per second.

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