Skip to main content. You are here Home » The Library. How are Ocean Currents Formed? Winds Wind is the primary force driving surface currents in the ocean. The sun heats the surface of the earth unevenly because of the shape and tilt of the earth. Warmer air masses rise into the atmosphere, creating areas of low pressure. Near Antarctica the circulation is somewhat different. Because there is little in the way of continental land masses between o south, the surface current created by the westerly winds can make its way completely around the Earth, creating the Antarctic Circumpolar Current ACC or West Wind Drift WWD that flows from west to east Figure 9.
The Antarctic Circumpolar Current is the only current that connects all of the major ocean basins, and in terms of the amount of water that it transports, it is the largest surface current on Earth. Above 60 o latitude the prevailing winds are the polar easterlies , which create a current flowing from east to west along the edge of the Antarctic continent, the East Wind Drift or the Antarctic Coastal Current.
The Antarctic Circumpolar Current creates the southern boundary for all of the Southern Hemisphere gyres. Not all of the equatorial water that is moved westward by the trade winds and reaches the continents gets transported to higher latitudes in the gyres, because the Coriolis Effect is weakest along the equator. Instead, some of the water piles up along the western edge of the ocean, and then flows eastward due to gravity, creating narrow Equatorial Countercurrents between the North and South Equatorial Currents Figure 9.
Some of this water also moves east as equatorial undercurrents that flow at depths between m, underneath the Equatorial Currents. Share and Connect. We invite you to share your thoughts, ask for help or read what other educators have to say by joining our community. Partner Organizations. Professional Development. Purchase a membership! Flow meters are small, often handheld devices used to measure current flow. Water current spins a propeller as it moves past the meter.
The amount the propeller spins can be correlated with current speed. Some meters can also report the direction of water flow. Flow meters are useful in smaller bodies of water. Clod cards are small blocks of plaster or a similar type of material used to measure relative flow rate between sites. As water current flows over the blocks, they dissolve. The faster the water flow, the more the clod cards dissolve.
Clod cards are useful tools for measuring water flow near ocean bottom. Shallow water drifters float near the surface of the water and are pushed by the predominant surface current.
The distance traveled, time, and direction of a drift can be measured by an observer or GPS device.
The picture is a Davis drifter, which uses underwater sails moved by current flow. Deep ocean drifters flow with the current below the surface. They are programmed to descend to a predetermined depth for several days and then rise to the surface. While underwater, they record their position and then transmit information back to scientists when they surface. Deep ocean drifters are useful for long-term deployment in deep water as they can surface and sink through many cycles.
An ADCP emits sound pulses underwater and then measures the frequency of the sound bouncing back off of the water particles. If the water particles are moving away from the ADCP, then the frequency will be longer.
If the particles are moving toward the ADCP, then the frequency will be shorter. ADCPs are useful for measuring flow in bays. They can also be mounted on the bow of ships. In the Indian Ocean, the equatorial countercurrent is located several hundred mi. In all three oceans, the equatorial countercurrent is concentrated in the upper ft. The intensity of the equatorial countercurrent varies from season to season and from month to month.
The strongest seasonal changes occur in the Atlantic Ocean. Eastward flow reaches a maximum in the summer and fall, with speeds of up to 12 in. Seasonal changes are weaker in the Pacific Ocean.
Here, the equatorial countercurrent exists year-round, and is strongest in the fall and winter, with speeds slightly.
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