Swell wave

About Swell wave:

• Swell waves are long-wavelength ocean waves formed on the surface of the seas and travel away from their places of origin.
• These are composed of a series of surface gravity waves.
• Swell waves are also called Kallakkadal waves in India, which is a colloquial term used by Keralam fishermen.
• These waves organise themselves into groups of similar heights and periods, and then travel long distances without much change. 
• Formation:
  • They are usually created by windstorms or other weather systems.
    • Windstorms and other powerful air current systems transfer energy from the air to water, making swell waves more powerful than locally generated waves. 
    • During such storms, huge energy transfer takes place from the air into the water, leading to the formation of very high waves. Such waves can travel thousands of kilometres from the storm centre until they strike shore.
  • They occur not due to the local winds, but rather due to distant storms like hurricanes, or even long periods of fierce gale winds.
• Features:
  • Swells have a narrower range of frequencies and directions than locally generated wind waves.
    • It is because swell waves have dispersed from their generation area, have dissipated and therefore lost an amount of randomness, taking on a more defined shape and direction.
  • These waves can propagate in directions that differ from the direction of the wind, in contrast to a wind sea.
  • 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.
  • It occurs without precursors or any kind of local wind activity and as a result.
• Early warning systems in India: Indian National Centre for Ocean Information Services (INCOIS) launched the Swell Surge Forecast System in 2020 which gives forewaring seven days in advance.