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Lesson N°6 :
The properties of Ocean waves
An ocean wave is an undulation of the sea surface , usually created by
the wind. When undisturbed by wind (or some other factors , such as
earthquakes ), the sea surface is naturally smooth. An ocean wave
represents the sea surface in regular motion , as water rises to a wave
crest (the highest part of the wave) and sinks to a wave trough (the
lowest part of a wave).
If the seas are not too chaotic , a regular up-and-down motion is evident
on the water surface affected by the passages of waves.
Waves are distinguished from one another by the following properties :
Wave height :the vertical distance separating the crest from the trough.
Wave length :the horizontal distance between the crest of one wave and
the crest of an adjacent wave.
Wave period :the time it takes two successive crests to pass a fixed
point , such as the piling of a pier.
The wave period , it turns out , is a useful way to classify waves. The
smallest water waves , which have period s of less than one-tenth of a
second , are called capillary waves.
Locally generated waves, termed chop ,have periods of about 1second ,
ocean swell , about 10 seconds.
Very long periods on the order of minutes and tens of minutes are
associated with seismic sea waves , or tsunamis , and with the backand- forth sloshing of water in harrbors , called seiches.
Wind generation of waves :
A visit to the seashore on most days reveals a connection between the
strength of the wind and the size of waves : the stronger the wind , the
larger the waves.