13.2. TIDES

The periodical rise and fall of the sea level, once or twice a day, mainly due to the attraction of the sun and the moon, is called a tide.

Tides are the regular movements of ocean water that result in a noticeable rise and fall of sea levels. These movements occur approximately once or twice a day and are primarily influenced by gravitational forces, specifically from the moon and, to a lesser extent, the sun. This creates a rhythmic pattern in water levels that can be observed along coastlines.

Think of tides as the ocean taking a deep breath. When the moon pulls on the water, it causes the sea to rise up, and when that pull weakens, the water flows back, similar to the way air moves in and out of your lungs.

Movement of water caused by meteorological effects (winds and atmospheric pressure changes) are called surges. Surges are not regular like tides.

In addition to tides, which are predictable and follow a consistent pattern, there are other movements of ocean water called surges. Surges are primarily influenced by weather conditions such as strong winds and changes in atmospheric pressure. Unlike tides, surges do not follow a set schedule and can happen suddenly due to external weather factors.

Consider surges like sudden gusts of wind that unexpectedly push a beach ball across the sand. Just as the ball moves erratically due to random wind patterns, surges can cause irregular movements of water that don’t adhere to the predictable schedule of tides.

The moon’s gravitational pull to a great extent and to a lesser extent the sun’s gravitational pull, are the major causes for the occurrence of tides. Another factor is centrifugal force, which is the force that acts to counterbalance the gravity.

The primary forces behind tides are the gravitational pulls of the moon and the sun. While the moon has a stronger effect because it is closer to Earth, the sun also plays a significant role. Additionally, centrifugal force, which occurs due to the Earth's rotation, counterbalances gravity and also contributes to the creation of tidal bulges. Together, these forces create higher water levels (bulges) on the side of Earth facing the moon and on the opposite side.

Imagine swinging a toy on a string; the tension from your hand is like gravity pulling the water towards the moon, while the centrifugal force is created by your hand moving in a circle. The toy swings away from your hand just like the water bulges on the opposite side due to the centrifugal effect.

Together, the gravitational pull and the centrifugal force are responsible for creating the two major tidal bulges on the earth.

Due to the interplay between gravitational and centrifugal forces, two prominent tidal bulges form on Earth. One bulge is on the side closest to the moon, where the gravitational pull is strongest. The second bulge is on the side opposite the moon, where the centrifugal force is greater than the gravitational pull. This phenomenon creates a pattern of high and low tides experienced by coastal areas.

Think about how if you sit in a spinning chair holding a water balloon, the water might collect towards your sides as you spin around—a similar effect happens in oceans with tidal bulges forming where gravitational forces pull and centrifugal forces push.

On wide continental shelves, tidal bulges have greater height. The shape of bays and estuaries along a coastline can also magnify the intensity of tides.

Tide heights can be influenced by geographical features such as wide continental shelves and specific coastal shapes like bays and estuaries. In areas with extensive continental shelves, tidal bulges can be larger due to the broad surface area they affect. Additionally, the funnel shape of certain bays can increase tidal heights as the incoming volume of water is forced into a narrower area.

Imagine filling a wide funnel with water; when you pour water into the wide part, it takes a lot of time to fill up. However, when it reaches the narrow part, the water level rises quickly. Similarly, tides can rise more dramatically in narrow bays due to the constriction.

Tides may be grouped into various types based on their frequency of occurrence in one day or 24 hours. Tides based on Frequency: Semi-diurnal tide, Diurnal tide, Mixed tide.

Tides can be categorized based on how many high and low tides occur in a day. A 'semi-diurnal tide' features two high tides and two low tides daily, whereas a 'diurnal tide' has only one of each. 'Mixed tides' exhibit variations in height and can occur in different regions. Understanding these patterns helps in predicting when tides will occur.

Think of tide patterns like a concert schedule. Some concerts have two sets (like semi-diurnal tides), others have just one set (diurnal tides), and some have a varying format (mixed tides). Knowing the lineup helps fans plan their night!

Spring tides and neap tides come under this category. Spring tides occur when the sun, moon, and earth are in a straight line, resulting in higher tides. Neap tides occur when the sun and moon are at right angles to each other, leading to lower tides.

Spring tides are the result of the sun and moon's gravitational forces aligning with the Earth, which enhances tidal heights. This alignment happens during full and new moons. In contrast, neap tides occur when the sun and moon are positioned at right angles relative to the Earth, counterbalancing each other's pull, resulting in lower tidal levels.

Imagine pulling two magnets toward a third object at the same time. When they both pull together (spring tide), the force is stronger, just like the higher tides. But when one pulls left and the other pulls right (neap tide), the force is weaker, resulting in lower tides.

The time between the high tide and low tide, when the water level is falling, is called the ebb. The time between the low tide and high tide, when the tide is rising, is called the flow or flood.

The movement of tides is not just about the high and low points but also involves the transition periods known as ebb and flow. Ebb refers to the receding water after high tide, while flow describes the incoming water before it reaches high tide. These transitions are crucial for understanding coastal ecosystem dynamics and navigation.

Think of the ebb and flow like a yo-yo on a string. As you pull the yo-yo up (high tide), it eventually needs to come back down (ebb). Then, it rolls back up again (flow) in a continuous cycle, similar to the water levels in the ocean.

Since tides are caused by the earth-moon-sun positions which are known accurately, the tides can be predicted well in advance...

Tides are vital for various human activities due to their predictable nature, influenced by the positions of the sun, moon, and Earth. Fishermen, sailors, and navigators depend on accurate tidal predictions for safe and effective operation. Moreover, tides help maintain the cleanliness of river estuaries and can serve as a renewable energy source through tidal power projects.

Consider a baker who sets a timer for when a cake should rise. Just like the baker relies on the timer, navigators rely on tidal predictions for planning their trips safely, enabling them to understand when to approach or leave coastal waters.

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