How are ocean currents formed and how do they work?

Currents can be produced if the winds are constantly blowing from the same direction regularly. on the surface of the ocean. These sea streams are like rivers of water moving through the seas. Currents range in size from insignificant coastal currents (typical currents near a beach) to currents that extend across and across the great oceans. The prevailing winds produce large-scale ocean basin currents.

Currents are only 50 to 100 meters deep. Although shallow, they are extremely important in determining the world’s climate and distributing the heat and nutrients of the ocean, which are key factors for marine life. Winds are defined by the direction they blow, and rivers by the direction they flow.

Ekman’s spiral

Ocean currents are produced by the friction created by the wind blowing on the surface of the water. Again, the direction and speed of water currents are not the same as those of wind currents blowing over them. That is, a wind of 20 km/h blowing from the east will not produce a current of 20 km/h to the east. Ocean currents are much slower than winds due to friction and also move at an angle to the direction of the wind. On the other hand, Earth’s rotational motion also affects ocean currents.

Surface water flows 20º to 45º to the right of the wind in the northern hemisphere and 20º to 45º to the left of the wind in the southern hemisphere. This deviation in the movement of water is due to the Coriolis effect of the Earth’s rotation.

The Coriolis effect affects the ocean surface as well as the deeper layers of ocean water created by small differences in temperature and salinity. These lower layers of water move when surface water moves, but Each successively deeper layer deviates further to the wind in the northern hemisphere and to the left in the southern hemisphere.. As the depth increases, the speed of each layer decreases. As the current moves down the water column, some of the water begins to flow in the opposite direction of the surface current. This current pattern is called the Ekman spiral and is therefore the result of the ‘drag’ created by increasing ocean depth.

Looking at the average of the motion of all layers affected by the Ekman spiral, water in a wind-driven stream moves approximately 90° to the right of the wind in the Northern Hemisphere and 90° to the left of the wind in the Southern Hemisphere. The movement that occurs in surface currents is called Ekman convection. For example, if the wind blows from south to north, the current flows 90˚ to the right, that is, directly to the east.

It is not a fixed rule. In the open ocean, turbulent mixing of surface waters or strong waves often interrupt the Ekman spiral. And in deep water, this spiral stops ‘working’ between 150 and 300 m deep.

The ‘turns’ of north and south

On the other hand, ocean currents tend to form annular circulation systems called eddies.. These are circular ocean currents made up of a combination of prevailing winds, Earth’s rotation, and land masses because the continents interfere with the movement of winds and surface currents. Eddy vortices form in the northern and southern hemispheres.

in the northern hemisphereNear the equator, trade winds direct the currents westward, creating a north equatorial (NE) current that moves at about 1 meter per second. At the western boundary of an ocean basin, water turns and flows towards the North Pole, forming western ocean boundary currents that are very strong. Two examples are the Gulf Stream (GS) flowing in the Atlantic Ocean basin and the Kuroshio Current (N) flowing in the Pacific Ocean basin. They are narrower but deeper and faster than other currents in the eddy. For example, velocities of 2 m/s have been measured in the Gulf Stream.

Eventually, the western boundary currents come under the influence of westerly winds and begin to flow eastward, forming the North Atlantic Current (NA) and the North Pacific Current (NP). As the continents approach the eastern ocean boundaries, they turn and flow southward, forming the eastern ocean boundary currents.

For its part, the boundary currents of the eastern ocean are shallower and slower than those of the western ocean. They flow over the continental shelves near the coast, carrying cooler waters from north to south. Two examples are the California Current (Cal) in the Pacific Ocean Basin and the Canary Current (Can) in the Atlantic Ocean Basin.

The North Equatorial Current (NE) and the South Equatorial Current (SE) flow in the same direction. Southeast turns south and behaves in the opposite direction of the Northern Hemisphere’s turns. Spins in the Northern Hemisphere move clockwise, while spins in the Southern Hemisphere move counterclockwise. It takes about 54 months for water to circulate in the North Pacific eddy, while it takes only 14 months for the North Atlantic eddy.

There is a certain situation. A mainstream, lequatorial countercurrent (EC) seems to be an exception to the circulation model created by the turns. The EC forms just north of the equator in the region between the North Equatorial Current and the South Equatorial Current and flows in the opposite direction.

Reference article: https://manoa.hawaii.edu/exploringourfluidearth/physical/atmospheric-effects/ocean-surface-currents

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Contact address of the environment department: crizclimatica@prensaiberica.es