Ocean gyre

In oceanography, a gyre (ˈdʒaɪər) is any large system of circulating ocean surface currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity, horizontal friction and vertical friction determine the circulatory patterns from the wind stress curl (torque). Gyre can refer to any type of vortex in an atmosphere or a sea, even one that is human-created, but it is most commonly used in terrestrial oceanography to refer to the major ocean systems. The following are the five most notable ocean gyres: Indian Ocean Gyre North Atlantic Gyre North Pacific Gyre South Atlantic Gyre South Pacific Gyre They flow clockwise in the Northern hemisphere, and counterclockwise in the Southern hemisphere. Tropical gyres are less unified and tend to be mostly east–west with minor north–south extent. Atlantic Equatorial Current System (two counter-rotating circulations) Pacific Equatorial Current System Indian Monsoon Gyres (two counter-rotating circulations in northern Indian Ocean) Subtropical gyres are formed by an intricate process involving both Coriolis force and Ekman transport. As global winds, caused by Earth's rotation, blow across the ocean surface they are acted upon by Coriolis causing movement to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. These winds cause frictional surface currents as the wind transfers energy to the ocean allowing the water to move in a circular motion. As Ekman transport acts on these circular currents the net transport of water is actually 90 degrees which drives regions of convergence, allowing water to pile up in the center of the ocean basin forming a bulge. The center of a subtropical gyre is a high pressure zone, while the outer edges of the gyre are a low pressure zone. This difference in pressure causes a pressure gradient allowing the diffusion of water from the high pressure zone in the bulge to the low pressure zone on the outer edges of the gyre.