waves and water dynamics
TRANSCRIPT
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Chapter 9: Waves and Water Dynamics
Fig. 9-10
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Waves are moving energy
Forces cause waves to move along air/water or within water Wind (most surface ocean waves) Movement of fluids with different
densities Internal waves often larger than surface
waves Mass movement into ocean
Splash waves
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Seafloor movement Tsunami or seismic sea wave
Gravitational attraction Earth, Moon, Sun Tides
Human activities Wakes of ships Explosions
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Progressive waves Longitudinal
“Push-pull” Transverse
Side-to-side or up-and-down Orbital
Circular orbit Ocean surface waves
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Types of waves
Fig. 9-3a
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Wave characteristics
Crest, trough Wave height is proportional to
energy Wave length Wave height/wave length = wave
steepness Waves break when H/L is 1/7
Wave period, frequency
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Wave characteristics Wave base is 1/2 wave length
Negligible water movement due to waves below this depth Fig.9-6a
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Deep-water wave
Depth of water is greater than 1/2 wavelength
Speed of wave form (celerity) is proportional to wavelength
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Shallow-water wave Water depth is less than 1/20 wavelength Friction with seafloor retards speed Wave speed (celerity) is proportional to
depth of water Orbital motion is flattened
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Transitional waves
Water depth is 1/2 to 1/20 of wavelength
Characteristics of deep and shallow-water waves
Wave speed (celerity) is proportional to both wavelength and depth of water
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Three types of waves
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Wave equations
Wave speed = wavelength/period S = L/T
Frequency = 1/period F = 1/T
Wave speed (m/s) = 1.56 x period S = 1.56 x T
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Surface ocean waves
Most wind-driven Small wind-driven waves
Capillary waves Larger wind-driven waves
Gravity waves
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Sea
Storm at sea creates waves Wave energy depends on
Wind speed Fetch Duration
Chaotic mixture of different wavelengths and wave heights
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Wave dispersion
Longer wavelength waves outdistance shorter wavelength waves
Waves travel in groups or trains with similar characteristics
Swell made up of waves of similar wavelength and period
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Wave interference Constructive
Wave heights increase Destructive
Wave heights decrease Mixed
Wave heights vary in wave train (surf beat)
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Interference illustrated
Fig. 9-14
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Rogue waves
Unusually large waves Constructive interference Waves meet strong ocean current
Fig. 9-16
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Rare photo of Rogue wave off Durban, South Africa in 1980. The tower at the front right is 25 mabove sea level during flat seas!
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Click on Picture
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Shoaling waves Waves reach surf zone
Wave speed decreases Wave length decreases Wave height increases
Wave steepness 1/7, wave breaks Surface tension no longer able to hold wave together
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Wave speed and length decreases and wave height increases. WhenWave steepness reaches 1/7 the wave will break.
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Breakers
Spilling Gentle beach slope
Plunging Moderately steep slope
Surging Abrupt slope
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Spilling Breakers occur on beaches with gentle slopes. These waves break far from the shore, and the
surf gently rolls over the front of the wave.
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Plunging Breakers happen on beaches where the slope is moderately
steep. This kind of wave normally curls over forming a tunnel
until the wave breaks. Expert surfers love this type of wave!
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Surging Breakers happen on beaches where the slope is very steep. The wave does not actually break. Instead, it rolls
onto the steep beach. These kinds of breakers are known for their
destructive nature.
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Wave refraction Shoaling waves bend so wave fronts
approach a shore nearly parallel
Fig. 9-19a
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Wave energy focused on headland
Wave energy dispersed over bay
Fig. 9-19b
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Wave diffraction
Wave energy transferred around or behind barriers
Fig. 9-20
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Wave reflection
Waves bounce back from steep slopes or seawalls
Reflected wave may constructively interfere with other waves
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Standing waves
Two waves with same wavelength moving in opposite directions
Node – no vertical movement Greatest horizontal movement
Antinode – greatest vertical movement
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Fig. 9-22
Click on Picture to See Surfers Riding Standing Waves
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Tsunami or seismic sea wave
Caused by sudden changes in volume of ocean basin Mainly submarine faults Volcanic eruptions Submarine landslides
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Fig. 9-23a
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Tsunami Very long wavelength Travels fast Raises sea level as crest shoals
Trough causes sea level to fall Disastrous for infrastructure at
coasts Possibly much loss of life
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Tsunami warning system
Monitor seismic activity Monitor changes in unusual
wave activity Warning
People evacuate
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End of Chapter 9: Waves and Water Dynamics
Fig. 9D