Waves and Tides: Types, Characteristics, Impact

Ocean water is in constant motion, both horizontally and vertically, shaping our marine environment. Horizontal movements, driven by ocean currents and waves, ripple across the surface, while vertical motions, like upwelling and tides, add depth to the aquatic dance. Understanding these movements is key to unlocking the secrets of our oceans and their impact on our planet.

Horizontal and Vertical Ocean Motion: Waves and Tides

Waves

• Energy in Motion: Waves are actually the energy, which moves across the ocean surface. Water particles only travel in a small circle as a wave passes.
• Frictional Force: Most of the waves are caused by the frictional force of the wind, which provides energy to the waves.
• Friction and Breakage: It slows down as it approaches the beach due to the friction occurring between the water and the sea floor. 
  • When the depth of water is less than half the wavelength of the wave, the wave breaks.
• Largest Waves: are found in the open oceans.
• Origin of Waves: A wave’s size and shape reveal its origin. 
  • Steep Waves: are young and formed by local winds, whereas slow and steady waves are older and originate from far away places.
• Wave Height: It is determined by the strength of the wind i.e., how long it blows and the area over which it blows in a single direction.

Characteristics of waves

• Crest and Trough: The highest and lowest points of a wave are called the crest and trough respectively.
• Wave Height: The vertical distance from the bottom of a trough to the top of a wave crest is wave height. 
• Wave Amplitude: is half of the wave height.
• Wave Period: Time interval between two successive wave crests or troughs as they pass a fixed point.
• Wavelength: Horizontal distance between two successive crests.
• Wave Speed: Rate at which the wave moves through the water.
• Wave Frequency: Number of waves passing a given point during a one-second time interval.

Tides

• Definition: The periodic rise and fall of ocean water twice a day mainly due to the attraction of the sun and the moon.
• Reasons for Tides: The gravitational pull of the sun and moon and the centrifugal force are responsible for creating the two major tidal bulges on the earth.
• Tidal Bulges: On the side of the earth facing the moon, a tidal bulge occurs due to the pull of the moon, 
  • While on the opposite side, the centrifugal force causes a tidal bulge on the other side. [UPSC 2015]
• Tidal Currents: When the tide is channelled between islands or into bays and estuaries, they are called tidal currents.
• Tidal Range: The vertical distance between high tide and low tide is the tidal range.
• Surges: Movements of water caused by meteorological effects (winds and atmospheric pressure changes) are called surges.

Types of Tides Based on Frequency

• Semi-diurnal Tide: two high tides and two low tides each day; successive high or low tides are of the same height.
• Diurnal Tide: only one high tide and one low tide during each day; successive high or low tides are of the same height.
• Mixed Tide: Variations in height of tides, generally occur along the west coast of North America and islands of the Pacific Ocean.

Tides Based on Sun, Moon and Earth Positions

• Spring Tides: When the sun, moon and earth are in a straight line, the height of the tide will be higher than the usual height 
  • It occurs twice a month, once during the full moon period and again during the new moon period
  • Seven days’ interval between the spring tides and neap tides.
• Neap Tides: The sun and moon are at right angles to each other and the forces of the sun and moon tend to counteract one another.
  • Further, once in a month, when the moon’s orbit is closest to the earth (perigee), unusually high and low tides occur. 
  • Two weeks later, when the moon is farthest from Earth (apogee), tidal ranges are less than their average heights.
• Position of Earth: Similarly, when the earth is closest to the sun (perihelion), around 3rd January each year, tidal ranges are also much greater. 
  • When the earth is farthest from the sun (aphelion), around 4th July each year, tidal ranges are much less than average.
• Ebb: The time between the high tide and low tide, when the water level is falling.
• Flow or Flood:  The time between the low tide and high tide, when the tide is rising.

Significance of Tides

• Navigation
• Desilting the sediments
• Removing polluted water from river estuaries 
• Electricity generation makes it possible for big ships to enter shallow harbors.

Conclusion

• The ebb and flow of ocean waters reveal a rhythmic symphony of nature, governed by the gravitational pull of the sun and moon. 
• From the gentle lapping of waves on the shore to the majestic rise and fall of tides, each movement plays a vital role in the life of our oceans and our world. 
• Harnessing the power of these movements holds promise for navigation, energy generation, and environmental stewardship, ensuring a sustainable future for generations to come.

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