waves

waves transmit energy across surfaces, both at the surface and in the ocean's interior. They range from high-frequency ripples and capillary waves, to low-frequency long waves generated by tides, and the planetary effects of the earth's orbiting and spinning that, for example, send the signal of El Niños over the Pacific.

The most familiar waves are those that are generated by the frictional energy of winds blowing across the sea surface which have frequencies of 5 to 10 seconds. Wave heights (the height between the crests and the troughs), increase with increasing wind speeds. The longer the wave length (distance between successive crests) the faster a wave travels. Long waves generated by a storm travel faster and appear as swell before an approaching storm. Swells often travel across the local wind-generated waves, creating the confused seas so hated by those who suffer from sea-sickness. Tsunamis are some of the fastest travelling waves while rogue waves can generate a wall of water up to 30 metres (100 ft) high. They occur, though rarely, in regions where strong currents flow against the prevailing winds, and can cause immense damage to ships. In 2000 the cruise ship Oriana was struck by a 21-metre (70-ft) wave that smashed windows and sent water cascading through six of its decks.

In the open ocean waves do not result in flows of water. A cork floating in the water just bobs up and down and does not move laterally. However, as a wave approaches a shore, the frictional drag of the bottom slows its speed, so its leading face steepens and the distance between it and the wave before and after shortens. Eventually the wave crest overtakes the base of the wave and it breaks.

Waves predominantly travel in the direction of the prevailing wind. When waves approach a sandy beach at an angle they push the sand along the beach as they break, and then the swash moves the sand perpendicularly back down the beach. This results in longshore drift whereby sand moves sideways along a beach.

Waves contain considerable amounts of energy and can be very destructive. However, if we can learn to capture their energy efficiently, as we are beginning to do with tidal power, a vast amount of renewable energy will become available to us, and perhaps we will also be better able to protect our shore and installations from their destructive power.

A code of the sea state, modeled on the ^*Beaufort Scale:

Code	Description	Maximum height of waves in metres/feet
0	glassy calm	0
1	calm (ripples)	0.3/0–1
2	smooth (wavelets)	0.3–0.6/1–2
3	slight	0.6–1.2/2–4
4	moderate	1.2–2.4/4–8
5	rough	2.4–3.9/8–13
6	very rough	3.9–6.1/13–20
7	high	6.1–9.1/20–30
8	very high	9.1–13.7/30–45
9	phenomenal	over 13.7/45

M. V. Angel