What are Swell waves?

About Swell Waves: 

• A swell is the formation of long wavelength waves on the surface of the seas. These are composed of a series of surface gravity waves.
• Swell waves organise themselves into groups of similar heights and periods, and then travel long distances without much change. 
• Formation:
  • They occur not due to the local winds, but rather due to distant storms like hurricanes, or even long periods of fierce gale winds.
  • 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.
• Features
  • Swells have a narrower range of frequencies and directions than locally generated wind waves, 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.
• In India early warning systems like the Swell Surge Forecast System launched by the Indian National Centre for Ocean InformationServices (INCOIS) in 2020 — gives forewaring seven days in advance.

Q1: What is Storm Surge?

Storm surge is the abnormal rise in sea level generated by a hurricane or other intense storm, over and above the predicted or normal astronomical tide. It is caused mainly by atmospheric weather systems such as tropical cyclones, hurricane winds shoving the ocean water up over the coast, although low pressure in the eye also contributes a much smaller amount.

Source: What are swell waves? | Explained