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Ocean Tides UPSC |Oceanography | Physical Geography

Ocean Tides:

Due to the attraction of the sun and the moon, ocean water raised up and falls down twice a day, this rise up and fall down of ocean water is called tides. 
Ocean Tides are one type of wave characterized by rhythmic rise and fall of ocean water twice a day.
Tides are one type of vertical movement of ocean water, other vertical movements of ocean water are upwelling and sinking of water.
Ocean tides

The study of tides is complex, spatially, and temporally; as it has great variation in frequency, magnitudes, and height.

Cause of tides

The tide-generating force is the difference between the gravitation attraction of the moon and centrifugal forces. The gravitational pull of the Moon is the major factor in tide occurrence as compared to the gravitation pull of the Sun.
Centrifugal force is the force that works as a counterbalance of the gravitation pull of the moon and sun. Gravitation pull and centrifugal force are responsible for the creation of two major tides on earth.
On the moonward side of the earth, a tidal bulge is caused by the gravitational pull from the Moon, and the opposite side of the earth's bulge is caused by centrifugal force.
The highest tides are experienced on the Bay of Fundy in Canada; it is approx 15-16 m high.

Types of tides:

Based on the frequency of tides, there are three types of tides namely semi-diurnal tides, diurnal tides, and mixed tides.

Semi-diurnal tides are the most common tides, featuring two high and two low tides each day. The successive high or low tides are approximately the same height.

Diurnal tides have one high and one low tide each day. The successive high or low tides are approximately the same height.

Mixed tides have variations in height. Mixed tides generally happen along the west coast of North America and the Pacific ocean's islands. 

Based on Sun, Moon, and earth's Position, there are two types of tides namely spring tides and neap tides.

The position of the Sun and Moon with reference to the earth is directly proportional to the height of tides.

Spring and neap tides

Spring Tides :

During full moon and new moon days, the sun, moon, and earth are on the same line. So this position, the gravitation pull of the moon and sun get combined hence the height of tides is higher. This type of tide is called a spring tide. It occurs twice a month, one during the full moon and one in the new moon period.  

Neap Tides :

When the moon and sun make the right angles [ 90 degrees angle ], neap tides come which are lower in height. In this position, the gravitation pull of the moon gets counterbalanced by the gravitation pull of the sun.
There are seven-day intervals between the spring and neap tides. 

The factors affecting the height of the tides:
  • When the Moon is close to earth at the Perigee position then tides are higher than normal.
  • When the Moon is the farthest from the earth at apogee position then tides are less than average height.
  • When the Earth is close to Sun at the Perihelion position; experiences higher tides or greater than the normal tides.
  • When the Earth is the farthest from the Sun at the aphelian position; experiences less than average tides bulge.
  • The position of the sun and moon with reference to the earth also affect the height of the tides which we have seen in spring and neap tides.
  • It is the time between the high tide and low tides when water is falling.
Flood or flow;
  • It is the time between the low tide and high tide when the water is rising.

Importance of tides:

The time of high tide is known precisely. Therefore, it has the following utilities:

  • High tides help navigation and help ships to reach shores.
  • High tides help in fishing and enable fishermen to catch fish near shorelines.
  • Tides help to generate tidal energy. for example, a 3 MW tidal power project at Durgaduani in the Sundarban of West Bengal is planning to be set up.
  • Tide helps with the desilting of the sediments and removes pollutants from river estuaries.

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