Introduction to
Oceanography
Dynamic Oceanography: Waves
Overview
* Waves transmit energy, not water mass, across the ocean’s
surface.
* Waves are classified by several characteristics.
* The behavior of a wave depends on the relation between the
wave’s size and the depth of water through which it is moving.
* Wind waves form when energy is transferred from wind to water.
* Waves can change direction by refraction and diffraction, can
interfere with one another, and reflect from solid objects.
7-1
Properties of Ocean Waves
Waves are the undulatory motion of a water surface.
• Parts of a wave are, Wave crest,Wave trough, Wave height (H),
Wave Amplitude, Wave length (L),and Wave period (T).
• Wave period provides a basis for the wave classifications:
Capillary waves, Chop, Swell, Tsunamis, Seiches.
Most of the waves present on the ocean’s surface are
wind-generated waves.
• Size and type of wind-generated waves are controlled by:
Wind velocity, Wind duration, Fetch, and Original state of
sea surface.
• As wind velocity increases wave length, period and height
increase, but only if wind duration and fetch are sufficient.
• Fully developed sea is when the waves generated by the
wind are as large as they can be under current conditions of
wind velocity and fetch.
• Significant wave height is the average wave height of the
highest 1/3 of the waves present and is a good indicator of
potential for wave damage.
Ocean Waves
What are the parts of an ocean wave?
Classifying Waves
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Ocean Waves
Orbital waves are waves in which the particles of water move in
closed circles as the wave passes.
Progressive waves are waves of moving energy in which the wave
form moves in one direction along the surface (or junction) of the
transmission medium. Orbital waves are a type of progressive wave
because the waveform moves forward
Wave Motions
7-2
Progressive waves are waves that move forward
across the surface.
• As waves pass, wave form and wave energy move rapidly
forward, not the water.
• Water molecules move in an orbital motion as the wave passes.
• Diameter of orbit increases with increasing wave size and
decreases with decreasing water depth.
• Wave base is the depth to which a wave can move water.
• If the water is deeper than wave base, orbits are circular and
there is no interaction between the bottom and the wave, but if
the water is shallower than wave base, orbits are elliptical and
become increasingly flattened towards the bottom.
Ocean Waves
Note that the water molecules in the crest
of the wave move in the same direction as
the wave, but molecules in the trough move
in the opposite direction.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
7-2
Wave Motions
• There are three types of waves defined by water depth: Deepwater wave, Intermediate-water wave, and Shallow-water
wave.
• Celerity is the velocity of the wave form, not the water.
C = L/T
• The celerity of a group of waves all traveling at the same
speed in the same direction is less than the speed of the
waves within the group.
Deep Water Waves, Shallow Water Waves
Note the importance of the
relationship between wavelength and
depth in determining wave type.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Factors Affecting Wind Wave Development
What factors affect wind wave development?
Wind strength - wind must be moving faster than the wave crests for
energy transfer to continue
Wind duration - winds that blow for a short time will not generate large
waves
Fetch - the uninterrupted distance over which the wind blows without
changing direction
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Factors Affecting Wind Wave Development
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
7-3
Life History of Ocean Waves
Fetch is the area of contact between the wind and
the water and is where wind-generated waves begin.
• Seas is the term applied when the fetch has a chaotic jumble
of new waves.
• Waves continue to grow until the sea is fully developed or
becomes limited by fetch restriction or wind duration.
• Wave interference is the momentary interaction between
waves as they pass through each other. Wave interference
can be constructive or destructive.
• Because celerity increases as wave length increases, longer
waves travel faster than short waves.
Wind Waves
Wind waves are gravity waves formed by the transfer of wind energy
into water. Wind forces convert capillary waves to wind waves.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Interference And Rogue Waves
What happens when waves from different storm systems exist
simultaneously?
When waves meet up, they interfere with one another.
Wave interference can be:
Destructive interference – two waves that cancel each other out,
resulting in reduced or no wave
Constructive interference – additive interference that results in
waves larger than the original waves
Rogue waves - these freak waves occur due to interference and
result in a wave crest higher than the theoretical maximum
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Swell Formation and Dispersion
Wave separation, or dispersion, is a
function of wavelength. Waves with
the longest wavelength move the
fastest and leave the area of wave
formation sooner. The smooth
undulation of ocean water caused by
wave dispersion is called swell.
(left) The process known as a wave
train.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
7-3
Life History of Ocean Waves
The shallower the water, the greater the interaction
between the wave and the bottom alters the wave
properties, eventually causing the wave to collapse.
• Celerity decreases as depth decreases.
• Wave length decreases as depth decreases.
• Wave height increases as depth decreases.
• Troughs become flattened and wave profile becomes extremely
asymmetrical.
• Period remains unchanged. Period is a fundamental property of
a wave
• Refraction is the bending of a wave into an area where it travels
more slowly.
7-3
Life History of Ocean Waves
Wave steepness (stability) is a ratio of wave height
divided by wave length (= H/L).
• In shallow water, wave height increases and wave length
decreases.
• When H/L is larger than or equals 1/7 (H/L  1/7), the wave
becomes unstable.
• There are three types of breakers:, Spilling breakers, Plunging
breakers, and Surging breakers.
Wind Waves Approaching Shore
What different ways can waves break against the shore?
Plunging waves break violently against the shore, leaving an air-filled
tube, or channel, between the crest and foot of the wave. Plunging
waves are formed when waves approach a shore over a steeply sloped
bottom.
Spilling waves occur on gradually sloping ocean bottoms. The crest of
a spilling wave slides down the face of the wave as it breaks on shore.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Wave Refraction, Diffraction, and Reflection
What can affect the way that waves travel?
Wave refraction - the slowing and bending of waves in shallow water.
Wave diffraction - propagation of a wave around an obstacle
Wave reflection - occurs when waves “bounce back” from an obstacle
they encounter. Reflected waves can cause interference with
oncoming waves, creating standing waves.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Wind Waves Approaching Shore
What happens when wind waves break against the shore?
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
7-3
Life History of Ocean Waves
Storm surge is the rise in sea level resulting from low
atmospheric pressure associated with storms and the
accumulation of water driven shoreward by the
winds.
• Water is deeper at the shore area, allowing waves to progress
farther inland.
• Storm surge is especially severe when superimposed upon a
high tide.
7-4
Standing Waves
Standing waves or seiches consist of a water surface
“seesawing” back and forth.
• A node is an imaginary line across the surface which
experiences no change in elevation as the standing wave
oscillates. It is the line about which the surface oscillates.
• Antinodes are where there is the maximum displacement of
the surface as it oscillates and are usually located at the edge
of the basin.
• Geometry of the basin controls the period of the standing
wave. A basin can be closed or open.
• Standing waves can be generated by storm surges.
7-5
Other Types of Progressive
Waves
Internal waves form within the water column on the
pycnocline.
• Because of the small density difference between the water
masses above and below the pycnocline, wave properties are
different compared to surface waves.
• Internal waves display all the properties of surface progressive
waves including reflection, refraction, interference, breaking,
etc.
• Any disturbance to the pycnocline can generate internal waves,
including: Flow of water related to the tides., Flow of water
masses past each other, Storms, or Submarine landslides.
• Resonance amplifies the displacement at the nodes and occurs
when the period of the basin is similar to the period of the
force producing the standing wave.
Internal Waves
Waves that occur at the boundaries of water layers
with different densities are called internal waves.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
7-5
Other Types of Progressive
Waves
Tsunamis were previously called tidal waves, but are
unrelated to tides.
• Tsunamis consist of a series of long-period waves
characterized by very long wave length (up to 100 km) and
high speed (up to 760 km/hr) in the deep ocean.
• Because of their large wave length, tsunamis are shallowwater to intermediate-water waves as they travel across the
ocean basin.
• They only become a danger when reaching coastal areas where
wave height can reach 10 m.
• Tsunamis originate from earthquakes, volcanic explosions, or
submarine landslides.