INCOIS issues Swell Surge Warning to Coastal States

Context

The Indian National Centre for Ocean Information Services (INCOIS) has issued a warning to the coastal states about the “complete suspension of operational and recreational activities.

Swell Surge Warning

• Potential for Swell Surges: This is due to the potential for swell surges and rough sea conditions caused by the influence of high-period swell waves approaching from the distant southern Indian Ocean. 
• Safety Advisory for Fishermen and Coastal Residents: They have been advised to exercise caution regarding potential wave surges, such as intermittent inundation of seawater in the nearshore and beach areas, especially in low-lying areas.
•  Origin and Movement of High-Period Swells: The high period swells had started at approximately 10,000 km away from the Indian coast in the southern Atlantic Ocean and slowly moved towards the southern Indian Ocean.
  • This had caused the high energy swell propagation towards the Indian coastal regions which is expected to hit the southern tip of India in the early hours of May 4. 
  • These long-period swells combined with high tide conditions can cause coastal flooding in the low-lying areas on May 4 & 5.

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Swell Waves

These waves are formed by an ocean swell, hence the name swell waves/swell surge. A swell wave is the formation of long wavelength waves on the surface of the seas. They propagate along the interface between water and air.  Thus, they are often referred to as surface gravity waves. 

• Origin: Ocean swells do not occur due to the local winds, but rather due to distant storms like hurricanes, or even long periods of strong winds. 
  • Usually, states like Kerala witness swell waves as a result of strong winds in the southern part of the Indian Ocean, where an ocean swell is generated, and the waves then travel north to reach the coast in two or three days.
• Influencing Factors: The speed of the wind, the amount of ocean surface area affected by wind blowing in the same direction (also known as fetch), and the amount of time those winds blow over the same part of the ocean.

Features of Swell Waves:

• Narrow range of Frequencies: Swells have a narrower range of frequencies and directions than locally generated wind waves.
  • Swells take on a more defined shape and direction and are less random than locally generated wind waves.
  • In terms of directionality, they are characterised by the direction from where it emanates instead of where it is headed. 
• Wavelength: Swell waves often have a long wavelength but this varies with the size of the water body. Their wavelengths may rarely exceed more than 150 m. 
  • Swell wavelength, also, varies from event to event. Occasionally, swells which are longer than 700 m occur as a result of the most severe storms.

Earlier Instances of Swell Waves in India: The swell waves in March were generated after a low atmospheric pressure system moved over the region from the South Atlantic Ocean.

• The arrival of the pressure system resulted in strong winds, which led to the formation of swell waves of up to 11 metres in height. These waves hit the Kerala coast and Lakshadweep.

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Difference between Swell waves and Tsunamis

Unlike swell waves, a tsunami is a series of enormous waves created by an underwater disturbance usually associated with earthquakes occurring below or near the ocean.

• Tsunamis are around 10 times faster than swell waves. Although both swell waves and tsunamis slow down near the coast, the swell waves hit land at 30–50 km/h.

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