Tides

A tide forms when there is an increase or decrease in the sea level that happens periodically because of the gravitational force of the moon and sun. There is movement in the water because of the change in atmospheric pressure and winds (also known as meteorological effects). These movements are known as surges. Unlike surges, tides are regular.

Reasons behind tide formation

Gravity: Tides are mainly caused due to the gravitational force that the moon exerts on the earth. The sun also exerts a gravitational force on the earth but at a much lesser scale.

Centrifugal force: The force that tries to counter the gravitational pull is known as centrifugal force.

Gravitational Pull: The part of the earth that faces the moon gives rise to a tidal bulge because of the moon’s gravitational pull. The tidal bulge also rises on the opposite side because of the centrifugal force.

The force that generates tides: Tide-generating force is the difference between the gravitational force and centrifugal force.

• When the earth’s surface is closest to the moon, it experiences a gravitational pull that is much higher than the centrifugal force. As a result, the net force creates a bulge at the side of the moon
• The earth’s surface that is opposite to the moon experiences quite less pull and therefore, the centrifugal force is greater here. Therefore, the net force acts in the moon’s opposite direction and builds a bulge on its opposite side
• On the earth’s surface, the force generated by the horizontal tides is far more essential than the vertical pull responsible for the tidal bulges
• When the tidal bulges occur on wide continental shelves, they possess a greater height
• As the tidal bulges appear on the mid-oceanic islands, their height becomes lower
• A tide’s intensity is also magnified by the estuaries and bay shapes that are located on a coastline. The tidal magnitudes get greatly affected by the bays that are funnel-shaped. Tidal currents are formed if the tides channelize into bays, estuaries, or between islands

Types of Tides

There are changes in the movement, direction, and frequency of the tides with respect to time and place. The types of tides vary according to their height and occurrence frequency in 24 hours.

Tides types as per the frequency

1. Mixed Tide: When tides vary in height, they are known as Mixed Tides. These types of tides are usually seen on the Pacific Ocean islands and along North America’s west coast.
2. Diurnal Tide: A high tide and low tide are observed every day. The consecutive low or high tides are around the same height.
3. Semi-diurnal Tide: Semi-diurnal Tide pattern is commonly observed that features 2 high and 2 low tides every day. The consecutive low or high tides are around the same height.

Tides types as per positions of the Earth, Moon, and Sun

The positions of the moon and sun as per the earth’s position influence the height of tides.

Spring Tides

• When earth, moon, and sun fall on a straight line, high tides are observed
• Spring tides occur twice every month on the full and new moon days

Neap Tides

• When the positions of the moon and sun create a right angle, their gravitational forces balance each other
• Moon’s gravitational pull is twice as strong as compared to the sun’s pull. However, it gets minimised by the sun’s force that counteracts it

Usually, the gap between neap and spring tides is 7 days.

Tidal Range

• When the moon’s orbit is nearest to the earth it is known as perigee. It happens once a month and causes low and high tides. At this tide, the tidal range is higher than normal
• When the moon’s orbit is farthest from the earth, it is known as apogee. It happens two weeks after the perigee and the gravitational pull of the moon is limited during this period. As a result, the tidal ranges are lower as compared to their average heights
• Tidal ranges are high when the earth is nearest to the sun. This phenomenon known as perihelion occurs every year somewhere near the 3rd of January. Unusual high and low tides are experienced during this period
• Tidal ranges are low as compared to the average when the earth is farthest from the sun. This phenomenon is known as aphelion and it occurs every year somewhere near the 4th of July

Conclusion

Any cyclic deformation of one astronomical entity induced by gravitational forces exerted by others is called a tide. Tides are the rise and fall of sea levels produced by the combined influence of the Moon’s and Sun’s gravitational forces, as well as the Earth’s rotation. They are, however, simply forecasts; wind and air pressure influence the actual timing and height of the tide.