Chapter 9: Waves and Water Dynamics

1. Chapter 9: Waves and Water Dynamics Fig. 9-10

2. 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

3. Seafloor movement • Tsunami or seismic sea wave • Gravitational attraction Earth, Moon, Sun • Tides • Human activities • Wakes of ships • Explosions

4. Progressive waves • Longitudinal • “Push-pull” • Transverse • Side-to-side or up-and-down • Orbital • Circular orbit • Ocean surface waves

5. Types of waves Fig. 9-3a

6. 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

7. Wave characteristics • Wave base is 1/2 wave length • Negligible water movement due to waves below this depth Fig.9-6a

8. Deep-water wave • Depth of water is greater than 1/2 wavelength • Speed of wave form (celerity) is proportional to wavelength

9. 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

11. 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

12. Three types of waves

13. 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

14. Surface ocean waves • Most wind-driven • Small wind-driven waves • Capillary waves • Larger wind-driven waves • Gravity waves

15. Sea • Storm at sea creates waves • Wave energy depends on • Wind speed • Fetch • Duration • Chaotic mixture of different wavelengths and wave heights

16. 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

17. Wave interference • Constructive • Wave heights increase • Destructive • Wave heights decrease • Mixed • Wave heights vary in wave train (surf beat)

18. Interference illustrated Fig. 9-14

19. Rogue waves Fig. 9-16 • Unusually large waves • Constructive interference • Waves meet strong ocean current

20. 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

21. Breakers • Spilling • Gentle beach slope • Plunging • Moderately steep slope • Surging • Abrupt slope

22. Wave refraction • Shoaling waves bend so wave fronts approach a shore nearly parallel Fig. 9-19a

23. Wave energy focused on headland • Wave energy dispersed over bay Fig. 9-19b

24. Wave diffraction • Wave energy transferred around or behind barriers Fig. 9-20

25. Wave reflection • Waves bounce back from steep slopes or seawalls • Reflected wave may constructively interfere with other waves

26. Standing waves • Two waves with same wavelength moving in opposite directions • Node – no vertical movement • Greatest horizontal movement • Antinode – greatest vertical movement

27. Fig. 9-22

28. Tsunami or seismic sea wave • Caused by sudden changes in volume of ocean basin • Mainly submarine faults • Volcanic eruptions • Submarine landslides

29. Fig. 9-23a

30. 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

31. Tsunami warning system • Monitor seismic activity • Monitor changes in unusual wave activity • Warning • People evacuate

32. End of Chapter 9: Waves and Water Dynamics Fig. 9D