Tides and Currents

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Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun on Earth, and the rotation of the Earth. We have two tides a day.

High Tide - When the see level is up. Low Tide - When the see level is down or less.

During a full moon or the new moon, the difference between the tides is the greatest, because at that time all 3 bodies - the Moon, Earth and the Sun are in line, hence the gravitational pull is at its strongest.

Tides and ocean currents are the vital concepts in oceanography.

Why do we have two tides a day?

As the Earth spins on its axis,

  • One side of the Earth faces the Moon. The Moon's gravitational pull causes the first high tide of the day, also called the first tidal bulge.

  • The second high tide of the day, or the second tidal bulge, is caused by the centrifugal force of the Earth spinning. It is the same force when you spin a bucket full of water in rounds, but the water still stays in. Centrifugal force is sometimes used to create artificial gravity. This bulge occur on the opposite side of the Earth from the side facing the Moon.


Current (when used in oceanography) means the motion of the water. Oceanic currents are influenced by 3 main factors, like tides, wind, and thermohaline circulation. These factors create the currents near the shore, bay or coasts. Hence, also referred as Tidal Currents. Winds also plays a major factor in current movements. Thermohaline circulation - a process characterised by the movement of seawater in the flow dependent on variations in density because of temperature (thermo) and salinity (haline) in ocean.