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The simplest way to tell them apart: tides go up and down, and currents move side to side. The two are connected, though — the rise and fall of the tides is one of the forces that makes water flow.
Low tide in Islesboro, Maine. Tides create currents in the ocean, near the shore, and in bays and estuaries. Credit: NOAA.
Tides
Tides are driven by the gravitational pull of the moon and sun, and they are the up-and-down movement of water over a long period of time.
Currents
A current is the motion of the water. Three main forces drive the ocean's currents:
| Driver | What kind of current | What sets it apart |
|---|---|---|
| The tides | tidal currents, in the ocean, near shore and in bays and estuaries | the only currents that change in a very regular pattern, so they can be predicted for future dates |
| The wind | currents at or near the surface — local ones near the coast, global ones in the open ocean | usually measured in meters per second or in knots |
| Thermohaline circulation | currents driven by differences in density from temperature (thermo) and salinity (haline) | found at both deep and shallow levels, and much slower than tidal or surface currents |
Measuring speed
Surface currents are commonly measured in knots. One knot equals 1.85 kilometers per hour, or 1.15 miles per hour.
Sources
Based on "What's the difference between a tide and a current?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
Licença: CC0 1.0 (domínio público) · Adaptado de oceanservice.noaa.gov
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