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Tides are the daily rise and fall of ocean water. Twice each day in most location, Water rises up over the shore until it reaches its highest level called high tide and water level is down from the shore until it reaches it lowest level called low tide.

The tide occurring due to the gravitational pull of the moon and the sun as well as that of the earth and Centrifugal force generated due to the rotation of the earth. The moon is closer to the earth than the sun; hence its gravitational force becomes more effective than that of the sun.

When there is high tide at 0° meridian, the 180° meridian also experiences high tide. The meridians that are at 90°to those having high tide will experience low tide at the same time.

Types of tides: Spring tides and neap tides are the two types of tides

Spring tide: On new moon and full moon days, the gravitational pull of the sun and the moon act in the same direction. Due to this, the total pull increases. Hence the tide on these days is much higher than the average high tide. This is known as spring tide.

As the bulge at the high tide is greater, the water at low tide recedes much more. The water level during spring tide is higher than the average high tides and lower than the average low.

Neap tide: While revolving around the earth, the moon makes a right angle with respect to the earth and the sun, twice a month. This position occurs on the first and the third quarter of each month. On both these days, the forces of both the sun and the moon operate at right angles on the earth. At the places where the sun causes high tide, the gravitational pull of the moon which is at right angles also acts on the sea water. Due to such conditions, the water level rise is less than usual at the time ofhigh tide. Similarly, fall in water level is less than usual at the time of low tide. This is because the attraction of the sun and the moon are not complementary but at right angles to each other. Such tides are called neap tides. Neap tides are a little lower than the average high tides and a little higher than the average low tides.

After every 12 hours and 25 minutes, a cycle of high tide and low tide gets completed.

Tidal Range:

The difference in the water level of the high tide and the low tide is called tidal range.

In open seas, this range is about 30 cm. However, towards the coastal areas it goes on increasing. Along the coast of Peninsular India the range is around 100 to 150 cm for most of the part. The highest tidal range in the world is observed at Bay of Fundy along the Atlantic Coast of North America. Here the tidal range is about 1600 cm. In India, the highest tidal range is in the Gulf of Khambhat. It is about 1100 cm.

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