TIDES
Tides are the periodic rise and fall of sea levels caused by the gravitational forces exerted by the moon and the sun on Earth's oceans. Tidal patterns result from the gravitational pull and the relative positions of the Earth, moon, and sun
Tides, the rhythmic rise and fall of the ocean's surface, are a captivating phenomenon with wide-ranging impacts. While not technically waves, they play a crucial role in shaping coastlines, influencing marine ecosystems, and holding cultural significance for communities around the globe
Relation between Gravitational Forces and Tides
- The moon exerts a gravitational force on Earth, pulling water towards itself. This gravitational force is stronger on the side of the Earth facing the moon, causing a bulge of water known as the tidal bulge
- Simultaneously, the moon's gravitational force is weaker on the opposite side of the Earth (the side away from the moon). This weaker gravitational pull allows for a centrifugal force to become more prominent, leading to a second tidal bulge on the far side of the Earth
- The combined effect of the moon's gravitational pull and the Earth's rotation results in two tidal bulges—one facing the moon and one on the opposite side
- The sun also exerts a gravitational force on Earth's oceans, contributing to tidal patterns. While the sun's gravitational force is significant, it is weaker than the moon's force due to the sun's greater distance from Earth
- The rise and fall of tides also generate horizontal water movements known as tidal currents. Flood currents move shoreward during high tide, and ebb currents move seaward during low tide
- The inclination of the moon's and sun's orbits with respect to Earth's equator influences tidal variations. Changes in the declination affect the alignment of gravitational forces and contribute to variations in tidal patterns
Tidal Currents
Tidal currents are horizontal movements of seawater that result from the rise and fall of tides. They are influenced by the gravitational forces of the moon and the sun, Earth's rotation, and the shape of coastlines and seabeds
Factors Affecting Tidal Currents:
- Tidal range: Locations with larger tidal ranges (difference between high and low tide) typically experience stronger tidal currents.
- Local geography: Features like coastlines, bays, and underwater structures can influence the speed and direction of tidal currents in specific areas.
- Moon's phase: As mentioned earlier, spring tides (during new and full moons) have higher highs and lower lows, resulting in stronger tidal currents compared to neap tide
Direction of Tidal Currents:
- Flood Currents: Tidal currents that move toward the shore during the rising tide. They occur when the water level is increasing.
- Ebb Currents: Tidal currents that move seaward during the falling tide. They occur when the water level is decreasing
Timing with Tides:
- Flood Tide: The period during which water levels rise, typically accompanied by flood currents moving toward the shore.
- Ebb Tide: The period during which water levels fall, accompanied by ebb currents moving away from the shore
Types of Tides
| Category | Type | Description | Frequency | Occurrence | Impact |
|---|---|---|---|---|---|
| Based on Frequency | Semi-Diurnal | Two high tides and two low tides per lunar day (roughly 24 hours and 50 minutes). | Most common type | Occurs in most open ocean locations. | Strongest tidal currents, significant impact on coastal ecosystems. |
| Diurnal | One high tide and one low tide per lunar day. | Less common | Found in some bays and gulfs with specific geographical features. | Weaker tidal currents, less pronounced impact than semi-diurnal tides. | |
| Mixed | A combination of semi-diurnal and diurnal characteristics, resulting in tides with varying heights and intervals. | Variable | Observed in some locations influenced by complex geographical factors. | Can be complex to predict, varying impacts depending on specific characteristics. | |
| Based on Sun & Moon Position (SME) | Spring Tides | Occur during new and full moons when the Sun and Moon's gravitational forces combine, amplifying the tidal effect. | Twice per lunar month | Highest high tides and lowest low tides, strongest tidal currents. | Significant impact on coastal areas, influence on navigation and marine ecosystems. |
| Neap Tides | Occur during first and third quarter moons when the Sun and Moon's gravitational forces partially counteract each other, reducing the tidal effect. | Twice per lunar month | Smaller variations in tide height, weaker tidal currents. | Less impact on coastal areas compared to spring tides, more predictable for navigation. |
Importance of Tides
- Tides influence water levels and currents, impacting maritime navigation. Mariners need to consider tidal patterns for safe passage through channels, straits, and coastal areas
- Fishermen often use tidal cycles to predict the best times for fishing. Tidal currents bring nutrient-rich water, influencing the distribution of marine life. Aquaculture practices may also consider tidal patterns
- Coastal engineers must understand tides to design structures such as docks, piers, and harbors. Tidal variations impact the stability and functionality of these structures
- Tidal forces contribute to erosion and sediment transport along coastlines. High tides can lead to coastal erosion, while tidal currents play a role in the movement of sediments
- Tidal energy, generated by the movement of tidal currents, is a form of renewable energy. Tidal power plants harness the energy from the rise and fall of tides to generate electricity
- Tides play a vital role in estuarine ecosystems. They influence the mixing of freshwater and saltwater, affecting the distribution of nutrients and supporting diverse marine life
- Tidal cycles help regulate the intrusion of saltwater into coastal freshwater systems. Understanding tidal patterns is crucial for managing freshwater resources in coastal regions
- Tidal variations contribute to the creation of tidal pools, which can be popular recreational and educational spots. Coastal tourism often considers the timing of tides for activities such as beachcombing and tidepool exploration
- Tidal patterns contribute to ocean circulation, influencing climate patterns. Studying tides is essential for understanding the dynamics of the Earth's climate system
- Tides provide valuable opportunities for scientific research and educational activities. Observing tidal phenomena helps enhance our understanding of Earth's gravitational interactions and their effects on the oceans
- Tidal datums serve as reference points for surveys and mapping activities. Mean Higher High Water (MHHW) and Mean Lower Low Water (MLLW) are common tidal datums used for elevation references
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Previous Year Questions
1.Tides occur in the oceans and seas due to which among the following? (UPSC CSE 2015)
1. Gravitational force of the Sun.
2. Gravitational force of the Moon
3. Centrifugal force of the Earth
Select the correct answer using the code given below
A.1 only
B.2 and 3 only
C.1 and 3 only
D.1, 2 and 3
Answer (D)
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