A wave has both kinetic (moving) and potential (stored)
energy.
Total wave energy of the oceans is the result of adding
together the energies of different types of waves.
Once waves are created, they must have a restoring force
to sustain wave motion, but waves must be formed initially by a displacing
force.
Two restoring forces--gravity and surface tension--act
on all waves.
Planetary waves (Kelvin, Rossby, Equatorial, and Yanai
waves) depend on the rotation of Earth for a restoring force.
Surface waves are the waves that eventually break on
the beach. The restoring force is due to the large density contrast between
air and water at the sea surface.
Internal waves are subsea waves and are similar to surface
waves in some respects. The restoring force is due to vertical density
gradients within the sea.
Most waves are created by interactions of winds with
the water surface. Waves can also be created by:
Impacts on ocean water (earthquakes, volcanic explosions,
seafloor slumps, etc.)
Gravitational attraction between Earth, moon, and
sun and
The passage of vessels or marine animals through the
sea surface.
Impacts can create waves (with very long periods) called
tsunamis (seismic waves). Tsunami are occasional events and contribute
only a fraction of the total wave energy of the oceans, but they can be
extremely destructive.
Winds never blow uniformly over the water because they
are highly variable both in time and space. This variablility is visibly
apparent to the ocean observer. Here are some descriptions:
"Sea" - waves of different heights,
wave-lengths, and directions of travel
Calm - waves are insignificant and the sea is flat
Swell - waves are smooth, mostly of same wavelength
and from same direction.
The maximum height of waves depends on wind speed and
the length of time the wind blows. It also depends on wind
fetch, which
is the distance over which it blows.
The highest ocean waves are created when winds are strong
and blow persistently over long fetches.
Steep-sided waves can be created when waves travel in
the direction opposite that of a strong ocean current. These waves create
hazards for shipping lanes.
Heat
Three sources of heat have influence on the ocean:
Solar energy
Geologic sources:
Heat generated by the radioactive decay of elements
with Earth,
Heat left over from Earth's formation, and
Human-induced through the burning of fossil fuels.
Solar energy is by far the most important because it
is responsible for 3,200 times the contribution of the other two.
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