Ay, and the elves and gyre -carlings frae the bonnie bairn, grace be wi' it? New Word List Word List. Save This Word! See synonyms for gyre on Thesaurus. Freebase 0. Alex US English. David US English. Mark US English. Daniel British. Libby British. Mia British. Karen Australian. Hayley Australian. Natasha Australian. Veena Indian. To better understand how currents move people and things, NOAA collects and shares data on tides and currents.
This data guides safe navigation of coastal waters, search and rescue operations, disaster clean up, and design of coastal development projects.
Home Ocean Facts What is a gyre? What is a gyre? Their effects can also extend down for miles, in some places reaching the ocean bottom. Currents are coherent streams of water moving through the ocean and include both long, permanent features such as the Gulf Stream, as well as smaller, episodic flows in both coastal waters and the open ocean.
They are formed primarily by wind blowing across the surface of the ocean and by differences in the temperature, density and pressure of water and are steered by Earth's rotation as well as the location of the continents and topography of the ocean bottom.
Gyres are spiraling circulations thousands of miles in diameter and rimmed by large, permanent ocean currents.
Eddies are smaller, temporary loops of swirling water that can travel long distances before dissipating. Wind is the primary force that creates and moves surface currents; Earth's rotation plays an important role in steering the water's motion. Persistent subtropical high pressure systems centered at about 30 degrees north and south latitude create patterns of strong winds known as the trades and the westerlies.
Friction between the air and the water sets the sea surface in motion. As this topmost layer of water moves, it pulls on the water directly beneath it, which in turn pulls on the layer of water beneath that to create the beginnings of an ocean current.
The resulting motion is not in line with the wind, however. Earth's rotation causes an apparent force known as the Coriolis effect to deflect straight-line movement across the surface about 45 degrees to the right in the Northern Hemisphere and 45 degrees to the left in the Southern Hemisphere.
In addition, each successive layer of water is slightly deflected from the motion of the one above, like a deck of cards fanned out.
This forms a phenomenon called an Ekman spiral that was first described by Swedish mathematician Vagn Walfrid Ekman in , but it was not until the late s that a team from WHOI first observed it in the open ocean. The net wind-driven movement of water, known as Ekman transport, creates a bulge in each ocean basin that is as much as three feet one meter higher than mean global sea level.
The force of gravity pulling on this large mass of water creates a pressure gradient similar to that in an atmospheric high pressure system which in turn leads to a stable, rotating mass of water. Five permanent subtropical gyres can be found in the major ocean basins—two each in the Atlantic and Pacific Oceans and one in the Indian Ocean—turning clockwise in the Northern Hemisphere and counterclockwise in the Southern.
Smaller counterclockwise gyres centered at around 60 degrees north latitude are created by the prevailing winds around permanent sub-Arctic low-pressure systems. Another subpolar gyre, the only one centered on a landmass, circles Antarctica driven by the near-constant westerly winds that blow over the Southern Ocean, unimpeded by land.
The subtropical gyres are surrounded by four linked currents: two boundary currents oriented roughly north-south at their eastern and western edges and two east-west currents at the northern and southern extent of the gyre. Western boundary currents are also among the fastest non-tidal ocean currents on Earth, reaching speeds of more than five miles per hour 2.
As these warm western boundary currents slow and spread out, they turn east to form the most poleward currents of their associated gyre. In the north, they also act as the southern boundary of the sub-polar gyres, permitting the exchange of water between the subtropics and the Arctic. In the south, the Antarctic Circumpolar Current connects to the southern subtropical gyres through these currents in a similar way. The colder eastern boundary currents, which flow from the high latitudes toward the equator, are the slowest and most diffuse currents around the gyre.
As they reach the equator, they turn west and pick up speed, driven by the trade winds and heat from the tropical sun. Eddies are relatively small, contained pockets of moving water that break off from the main body of a current and travel independently of their parent. They can form in almost any part of a current, but are especially pronounced in western boundary currents.
Once the fast-moving currents leave the confining influence of land, they become unstable and, like a fire hose with no one holding it, begin to meander and bend. If a current becomes so tightly bent that it doubles back on itself, that section of flow may "pinch off" and separate from the main body of the current like an oxbow bend in a river.
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