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As the depth into the ocean increases, the radius of the elliptical motion decreases. At a depth equal to half the Wavelength λ, the orbital movement is zero. The Speed of the surface wave is also called celerity or Phase Velocity because it corresponds the speed of the shape of the wave, but is different from the speed of the water particles. This celerity is well approximated by

:c=\sqrt{ rac{g \lambda}{2\pi} anh \left( rac{2\pi d}{\lambda} ight)}

where
:c = phase speed in m/s;
:\lambda = wavelength in m;
:d = water depth in m;
:g = Gee in m/s2.

In deep water, where d \ge rac{1}{2}\lambda, so rac{2\pi d}{\lambda} \ge \pi and the hyperbolic tangent approaches to 1, c approximates 1.25\sqrt\lambda.
This expression tells us that waves of different wavelengths travel at different speeds: waves disperse. The fastest waves in a storm are the ones with the longest wavelength. As a result, when after a storm waves arrive on the coast, the first ones to arrive are the long swells.

When several wave trains are present, which is always the case in the ocean, the waves form groups. In deep water the groups travel at a Group Velocity which is half of the phase velocity. Following a single wave in a group one can see the wave appearing at the back of the group, growing and finally disappearing at the front of the group.

As the water depth d decreases towards the Coast , this will have an effect on the speed of the Crest and the trough of the wave; the crest moves faster than the trough. This causes Surf , a breaking of the waves.

Individual " Freak Wave s" (also "rogue waves", "monster waves" and "king waves") sometimes occur in the ocean, often as high as 30 Metre s. Such waves are distinct from Tide s, caused by the Moon and Sun 's pull, and Tsunami s that are caused by underwater Earthquake s or Landslide s.

The movement of ocean waves can be captured by Wave Energy Devices . The energy of regular sinusoidal waves contained in 1 m2 of sea depends on the water Density ho, gravity acceleration g and the wave height ''h'' (= 2· Amplitude (a):

:E= rac{1}{8} ho g {h}^2= rac{1}{2} ho g a^2.


TYPES OF WAVES


When waves "break", they have different characteristics depending on factors including the structure of the ocean floor. There are three main types that are identified by Surfers or Surf Lifesavers : plunging waves (also known as "dumpers"), spilling waves and surging waves. Their varying characteristics make them more or less suitable for surfing and present different dangers. Surfers often call these characteristics a "haydon" or "haydon's"


SEE ALSO

Artificial Wave


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