Winds, Rise and fall of tides and Thermohaline circulation.
When used in association with water, the term “current” describes the motion of the water. Some currents you may be familiar with are the motion of rainwater as it flows down the street etc.
This motion is caused by gravity. The speed and direction (velocity) of currents can be measured and recorded.
1) Oceanic currents are driven by several factors. One is the rise and fall of the tides, which is driven by the gravitational attraction of and moon on Earth’s oceans.
Tides create a current in the oceans, near the shore, and in bays and estuaries along the coast. These are called “tidal currents.” Tidal currents are the only type of currents that change in a very regular pattern and can be predicted for future dates.
2) A second factor that drives ocean currents is wind. Winds drive currents that are at or near the ocean’s surface. These currents are generally measured in meters per second or in knots (1 knot = 1.15 miles per hour or 1.85 kilometres.)
3) A third factor that drives currents is thermohaline circulation – a process driven by density differences in water due to temperature (thermo) and salinity (haline) in different parts of the ocean.
Currents driven by thermohaline circulation occur at both deep and shallow ocean levels and move much slower than tidal or surface currents. per hour).
Winds drive currents near coastal areas on a localized scale, and in the open ocean on a global scale.