WAVES

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WAVES

• disturbance caused by the movement of energy from
  a source through some medium (solid, liquid or
  gas).
• THERE ARE MANY DIFFERENT SIZES AND SHAPES OF WAVES

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Global Wave Height
Fig 9-10, p.181
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WAVES

• The energy is moving at the speed of the wave,
  but NOT the water

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Fig 9-1, p.174
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WAVES

• The parcel of water moves in a circular motion
  orbit
• water is displaced very little across the sea
  surface as the illusion of a wave suggests

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Fig 9-2, p.175
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Fig 9-3, p.175
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WAVES

• Because the wave form moves forward these are
  called progressive waves

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Wind wave ratio of height to wavelength (wave
steepness) 1 to 7
Fig 9-11, p.181
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Fig 9-12, p.182
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Components

• Crest
• Trough
• Wavelength
• Height
• Frequency
• Fetch
• Wavebreak
• refraction

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Fig 9-2, p.175
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Wave fetch uninterrupted distance over which
the wind blows w/o significant change in
direction.
Fig 9-9, p.180
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Wavebreak ratio of wave height to water depth
is 3 to 4
Fig 9-15, p.183
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Wave refraction
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Wave crests bend 90 degrees as they move around
point (Hawaii) refraction
Fig 9-17, pg. 185
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Fig. 9-17a, p. 185
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types of waves

• Shallow water wave
• Deep water wave
• swell (capillary wave)

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Deep water wave
Shallow water wave
Fnft
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Orbits

• The diameter of the orbits diminishes rapidly
  with depth
• Wave motion in deep water is negligible past ½
  the wavelength

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Fnft
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Stokes Drift or Mass Transport

• Small net movement of water in the direction of
  the wave

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Figure not from book
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Classifying Waves

• disturbing force the energy that cause waves to
  form
• restoring force the dominant force trying to
  return surface water to flatness
• wavelength

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Wave energy as a function of wave period
Fig 9-4, p.177
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Wave Types

• Capillary waves
• Wind
• Surface tension

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Capillary waves interrupt the smooth surface,
deflect upward, Slow cause winds energy to be
transferred into the water. A crest Btrough
Fig 9-7, p.179
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Swell mature, regular, wind waves
Fig 9-8, p.165
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Deep vs Shallow Water waves

• The orbits of water molecules in a wave are
  circular only when the wave is in deep water
• A wave cannot feel the bottom if it is in water
  deeper than ½ its wavelength
• a deep water wave

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Deep vs Shallow Water Waves

• Shallow water waves moving in water shallower
  than 1/20 it wavelength
• Water at the bottom moves back and forth

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Deep vs Shallow Water Waves

• Transitional waves travel through water deeper
  than 1/20 their wavelength and shallower than ½
  its wavelength

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Deep vs Shallow Water Waves

• ONLY WIND WAVES CAN BE DEEP WATER WAVES

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Fig. 9-5, p. 177
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How waves break at shore...

• A deep water waves feels bottom and becomes a
  transitional wave
• orbits become elliptical
• crests become peaked
• wave height increases
• wave slows down
• wave length decrease

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Wavebreak ratio of wave height to water depth
is 3 to 4
Fig 9-15, p.183
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How waves break at shore...

• The wave becomes too high for its wavelength and
  the wave breaks
• The surf zone is the region between the breaking
  waves and the shore.

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INTERFERENCE

• Destructive interference cancellation effects
  of subtraction
• When a wave crest and another waves trough
  coincide

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INTERFERENCE

• Constructive interference addition effects that
  form large crests and deep troughs
• When crests coincide

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Fig 9-14, p.182
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Wave Refraction

• When waves do not approach parallel to shore
• The wave line will bend to become more parallel
  to shore

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Wave refraction
Fnft
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Wave crests bend 90 degrees as they move around
point (Hawaii) refraction
Fig 9-18b, p.185
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Types of Waves

• Tsunamis
• Seismic Sea Waves

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Types of Waves

• Tsunamis long wavelength, shallow water
  progressive waves caused by rapid displacement of
  ocean water. This is caused by sudden vertical
  movement of earth along a fault line, causing a
  Seismic Sea Wave.
• Origination on seafloor, a problem for
  continental populations if this is close to land
  or in a confined space!

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Tsunami

• A tsunami can be a wave w/ a wavelength up to 125
  miles!
• Remember the deepest ocean basin is 7() miles
  deepif a wave ½ wavelength its still not
  enough room to move (do the math!)
• Problem a tsunami wave can reach a height of
  over 100

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Fig 9-27, pg. 192
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1946 Hawaiian tsunami
Fig 9-21, p.188
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5 hrs. earlier earthquake
Sequence 1957 Hawaii tsunami
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15 minutes later
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2 hrs. total duration 56 total wave height,
25 million in damages
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Fig. 9-CO, p. 172
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Fig 9-26, p.191