chapter 9: waves and water dynamics
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Chapter 9: Waves and Water Dynamics. Fig. 9-10. WAVE CHARACTERISTICS. Waves are moving energy. Forces cause waves to move along air/water interface or within water Wind (most surface ocean waves) Movement of fluids with different densities Internal waves often larger than surface waves - PowerPoint PPT PresentationTRANSCRIPT
Chapter 9: Waves and Water Dynamics
Fig. 9-10
WAVE CHARACTERISTICS
Waves are moving energy
Forces cause waves to move along air/water interface 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(e.g. land
slide) Splash waves
Seafloor movement Tsunami or seismic sea wave
Gravitational attraction Earth, Moon, Sun Tides
Human activities Wakes of ships Explosions
Progressive waves Longitudinal
“Push-pull” Transverse
Side-to-side or up-and-down Orbital
Circular orbit Ocean surface waves
Types of waves
Fig. 9-3a
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
Wave characteristics Wave base is 1/2 wave length
Negligible water movement due to waves below this depth Fig.9-6a
Deep-water wave
Depth of water is greater than 1/2 wavelength
Speed of wave form (celerity) is proportional to wavelength
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
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
Three types of waves
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
Surface ocean waves
Most wind-driven Small wind-driven waves
Capillary waves Larger wind-driven waves
Gravity waves
Sea
Storm at sea creates waves Wave energy depends on
Wind speed Fetch Duration
Chaotic mixture of different wavelengths and wave heights
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
Wave interference Constructive
Wave heights increase Destructive
Wave heights decrease Mixed
Wave heights vary in wave train (surf beat)
Interference illustrated
Fig. 9-14
Rogue waves
Unusually large waves Constructive interference Waves meet strong ocean current
Fig. 9-16
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
Breakers
Spilling Gentle beach slope
Plunging Moderately steep slope
Surging Abrupt slope
Wave refraction Shoaling waves bend so wave fronts
approach a shore nearly parallel
Fig. 9-19a
Wave energy focused on headland
Wave energy dispersed over bay
Fig. 9-19b
Wave diffraction
Wave energy transferred around or behind barriers
Fig. 9-20
Wave reflection
Waves bounce back from steep slopes or seawalls
Reflected wave may constructively interfere with other waves
Standing waves
Two waves with same wavelength moving in opposite directions
Node – no vertical movement Greatest horizontal movement
Antinode – greatest vertical movement
Fig. 9-22
Tsunami or seismic sea wave
Caused by sudden changes in volume of ocean basin Mainly submarine faults Volcanic eruptions Submarine landslides
Fig. 9-23a
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
Tsunami warning system
Monitor seismic activity Monitor changes in unusual
wave activity Warning
People evacuate