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Oceans Waves

• When the wind blows across the ocean surface, it creates small capillary waves (typical size about 1 mm).
• As the wind continues, or becomes stronger, the waves grow in height, wave length and period.
• If the wind has blown at a certain speed over a sufficiently large area for a long time, the wave field becomes “fully developed” (the waves do not change their characteristics any more).
• In a fully developed wave field there are waves of all sizes, but there is a wave height/period where the energy is largest.
• Once the wind stops, the small, short-period waves disappear and the remaining (smoother) wave is called swell.
• Swell typically has a period of about 8-15 seconds and a height of about 1 m or more.

Waves are normally very irregular (not as smooth as indicated in the figure below) but have crests and troughs. The horizontal distance between two crests is the wavelength, and the vertical distance between a crest and a trough is the wave height. The time it takes two successive peaks to pass an observer is called the wave period.

As the swell approaches the shore, the shallower bottom topography causes the swell to become larger, reaching a point where it can no longer support itself, and breaks. This is the point at which white foam is visible on the edge of the wave, and the optimum time to catch a wave! people.bath.ac.ukpeople.bath.ac.uk.

Introduction to Ocean Sciences, D. A. Segar, 1997 & www.people.batch.ac.uk