What is it?
Swells are commonly known as surface gravity waves. These series of surface gravity waves are not pointed wind waves caused by neighboring local winds, but rounded waves caused by distant weather systems.
Waves usually have a long wavelength, but this is dependent on the size, strength, and duration of the weather system and the size of the water body. Therefore, the wavelength of a wave is highly variable. For short waves, the wavelength is 100 meters or less and the period is 8 seconds or less. Medium waves have a wavelength of 100-200 meters and a period of 8-11 seconds, while long waves have a wavelength of more than 200 meters and a period of more than 11 seconds.
Generally speaking, waves with wavelengths greater than 700 meters are usually caused by very powerful storms. Waves have a narrower range of frequency and direction than locally generated wind waves because the waves disperse and dissipate in the area of origin. Therefore, there is little tendency for randomness, and the shape and direction of the waves are well defined. The sound direction is the direction in which the sound is coming from. This is usually denoted by °, but is also called NNW waves or SW waves.
Swell-like waves occur when, despite clear weather and little wind, the speed of the waves suddenly increases and the waves surge, causing a large amount of seawater to rush up and over the seawall at the shoreline.
Swell waves typically have a period of 15 to 20 seconds, but can be much longer. Swell-like waves are difficult to predict and difficult to evacuate because they are often not observed in the distant sea, but suddenly high waves approach the coast. Therefore, accidents often occur when people are fishing on the rocks or breakwaters and are swept away by swell-like waves.
The waves, which occur frequently on the east coast of Korea in winter, are caused when a mid-latitude low pressure system originating from inland China advances into the East Sea, lowers the central pressure, forms a strong pressure ridge around it, and continuously blows strong northeasterly winds on the East Sea.
Among the recent waves that caused major damage to the east coast, the waves that occurred in October 2005 and October 2006 were dominated by wind waves, while the waves that occurred in February 2008 are believed to have been caused by a primary increase in wave height due to wind waves, followed by a secondary increase in wave height due to waves with a longer period.