Ocean Tides: Seawater is not stationary but rises and falls twice a day at constant intervals. This periodical rise and fall of the sea level, once or twice a day, is called a tide. Twice a day, about every 12 hours and 26 minutes, the sea level rises, and it falls twice a day. The rise in sea level is known as the flood tide, and the fall is known as the ebb tide. This occurs mainly due to the gravitational interaction of the earth, the sun, and the moon; along with this, the earth’s rotation also has an impact on the way tides are formed. The movement of water caused by meteorological effects (winds and atmospheric pressure changes) is called a surge. Surges are not regular like tides.
Ocean Tides Diagram
Here is the illustration of Ocean Tides:
Ocean Tides Causes
- The Moon’s gravitational pull.([Significant factor)
- The Sun’s gravitational pull. (Lesser factor)
- The force that acts as a counterbalance to gravity is known as centrifugal force.
- The two major tides on Earth are caused by gravitational pull and centrifugal force.
- The gravitational pull of the Moon causes a tidal bulge on the moonward side of the earth, and centrifugal force causes a bulge on the opposite side of the earth.
- The highest tides in Canada have been observed on the Bay of Fundy; they are approximately 15-16 m high.
Ocean Tides Formation
Tides are caused by the Sun’s and Moon’s gravitational pulls. Their gravitational pull tugs on Earth’s atmosphere, oceans, and lithosphere; as a result, they all experience some stretching. To a greater extent, the moon’s gravitational pull and to a lesser extent, the sun’s gravitational pull are the major causes of the occurrence of tides. Another force that acts complimentary to the gravitational force is the centrifugal force. The centrifugal force acts in the direction opposite to the gravitational pull of the planets. Tides are a result of the continuous balance of all these forces.
Influenced by the moon’s gravitational pull, the oceans towards the side of the moon are pulled toward it, making the first tidal bulge (high tide). At the same time, the ocean water on the opposite side of the Earth experiences an outward-flying force called the centrifugal force of inertia and forms the other tidal bulge. Troughs (low tides) are located on the sides of the Earth halfway between the two tidal bulges. These bulges and troughs sweep across the Earth’s surface as it rotates on its axis every day. A tidal current’s strength is determined by the volume of water and the area through which it flows. A large tidal volume moving over a large area may only generate a weak tidal current. These bulges and troughs sweep across the Earth’s surface as it rotates on its axis every day. Tidal bores occur where rivers meet the ocean. If the incoming tidal current is stronger than the river outflow, the tidal bore appears as a wave or moving wall of water that moves up the river as the tide comes in.
Ocean Tides Classification
Tides are classified based on the frequency of occurrence and the height of the rising water (influenced by the position of the earth, the sun, and the moon).
Classification Based on the Frequency
1. Semi-diurnal Tide
The semi-diurnal tidal pattern features two high tides and two low tides every day. The height of the successive high and low tides is approximately the same. This is the most typical type of tide. They have a period of 12 hours and 25 minutes and a wavelength of more than half the circumference of Earth. It is also the type of tidal cycle one could expect from a planet covered entirely with water and without any continents obstructing the free movement of water.
2. Diurnal Tides
A diurnal tidal cycle is a cycle with only one high and low tide each day. The Gulf of Mexico and the East coast of the Kamchatka Peninsula have diurnal tidal cycles.
3. Mixed Tides
A mixed tidal cycle is a cycle with two high and low tides of different sizes each lunar day. The difference in height between successive high (or low) tides is called diurnal inequality. Areas with a mixed tidal cycle can be found alongside the West coast of the USA, in parts of Australia, and in South East Asia.
Classification Based on the Height of the Tides
The high tide fluctuates significantly based on the sun’s and moon’s positions in relation to the earth. This results in two types of tides: the spring and the neap tides.
1. Spring Tides
We know that tidal height is directly related to the location of the sun and moon with respect to the earth. The tide will be higher when the sun, moon, and earth are all in a straight line. Spring tides occur twice a month, once at the full moon and once at the new moon.
2. Neap Tides
The solar tidal force partially cancels the Moon’s gravitational force. Although the Moon’s attraction is more than twice as strong as the sun’s, it is weakened by the sun’s gravitational pull. These tides occur at certain times in the lunar cycle when the range of the tide is at its smallest. The spring and neap tides are separated by seven days in most cases.
These tides occur twice a month, just like spring tides.
Ocean Tides Significance
Tides may seem relatively isolated geographical phenomena concerning their direct impact on the lives of humans. However, this is not true; tides play an essential function in our day-to-day activities.
1. Ship Navigation
Tides play a critical part in ship navigation. They assist by enabling some rivers to become accessible for ocean-going vessels. They aid ships in simply approaching the harbour as well as during docking. The presence of tides, particularly in harbours along with rivers and on estuaries with shallow entrances, is critical because strong tides aid navigation across the channel, which would otherwise be impossible. For example, navigation to the tidal ports of London and Kolkotta is reliant on the tides’ aid.
High tides are a fisherman’s dream. During high tide, the fish get closer to the coast, and this helps the fishers with a better catch.
As rivers combine with the ocean, they deposit a lot of silt in their mouths. These silts obstruct the free flow of water from rivers, rendering them impossible. The tides’ forward and backward movement inside the water channels aid in sediment desilting and removing contaminated water from river estuaries.
4. Generation of Electricity
Tides are a mechanical movement of water that can be used to generate electricity. Tidal energy is a good non-renewable energy source. This has been successfully used in Canada, France, Russia, and China. In India, a 3 MW tidal power project was built in the Sunderbans of West Bengal’s Durgaduani.
Ocean Tides UPSC
Tides make ocean water move vertically. Tides are the periodic rise and fall of the sea level caused by the gravitational pull of the Moon and Sun, which occurs once or twice a day. Ocean tidal waves are characterised by the rhythmic rise and fall of ocean water twice a day. A solid understanding of this subject is required to help individuals pass competitive exams. On that note, we have covered this topic exclusively for students preparing for the UPSC and IAS exams.