Page 9 - Wind Waves and Weather

Petroleum Extension-The University of Texas at Austin
Waves and Sea

States

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everal forces form ocean waves. These forces include the Waves
Sfrictional contact between the wind and the ocean, the tidal
attraction of the sun and the moon, and the vibration of the earth.

Formed by the contact of wind with the ocean’s surface, wind Wind Waves
waves are the type of waves that affect offshore operations the
most. As wind blows over an ocean, friction occurs between the
wind and the ocean’s surface. This friction is a form of energy
and it moves the ocean’s surface. Wind energy only affects the
top of the water. However, the top layer of water imparts energy
to the water directly beneath it. The water eventually absorbs
this energy as depth increases. This transfer of energy through
friction forms wind waves.
Wind waves develop and grow where the wind blows from
the same direction for a long time. Oceanographers call this area
of wave development fetch. Fetch is the distance over which the
wind blows to generate the observed waves at a given position.
A fetch may be hundreds of miles long. Maximum wave heights
occur on the downwind boundary of the fetch. Oceanographers
call waves that are still in the fetch, and under the influence of
its wind, sea. They call waves that have moved out of their fetch
and into weaker winds swell. Swell decreases in height and has
regular movement. Sea appears choppy, while swell appears

WIND DIRECTION

FETCH BOUNDARY

SWELL
SEA
Figure 14. Sea, fetch
boundary, and swell

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