Chapter 7 Waves in the Ocean Words from these PPT slides are already on the course web site.

1. Chapter 7Waves in the OceanWords from these PPT slides are already on the course web site.

2. Properties of Ocean Waves • An ocean wave is an undulation of the sea surface. • Wave crest • Wave trough • Wave height • Wave length • Wave period • Progressive waves move across the sea surface. • Standing waves oscillate about a fixed point.

3. Wave Parameters(Figure 7-1a)

4. What Causes Waves? • Wind • Submarine disturbance • Gravitational attraction of sun and moon

5. Wind Generation of Waves • The type of wave generated by wind is determined by: • Wind velocity • Wind duration • Fetch (distance over which wind blows) • Simply put, wave size increases as the strength and duration of the wind, and distance over which it blows increases.

6. Progressive Waves • Wind-generated waves are progressive waves because they travel across the sea surface.

7. Progressive Wave Types • Sea - irregular waves in the area of generation • Swell - more regular waves beyond area of generation • Surf - waves that have reached the coast, grow in height, and break

8. Wave Motions • Two basic motions associated with an ocean wave • The forward movement of the wave form. • The orbital motion of water particles beneath the wave. • It is wave energy not water molecules that moves across the sea surface.

9. Flow of Energy,not Mass (Figure 7-2)

10. Wave Motion with Depth(Figure 7-3a)

11. Motion of Water Particles Beneath Waves(Figure 7-3b)

12. Motion Animation

13. Deep Water Waves(Figure 7-4a) In deep water most waves do not interact with the sea bottom and are called deep-water waves. The orbits of the water molecules are circular.

14. Shallow Water Waves(Figure 7-4b) Waves which interact with the sea floor are known as shallow-water waves. The orbits of the water molecules become elliptical.

15. Wave Speed • The speed(celerity) of the wave form can be calculated by • Dividing the wavelength by the wave period. • When wave passes, no net displacement of water. • It is the energy of the wave, not its mass that is in motion.

16. Life History of Ocean Waves • Waves originate in the fetch area. This area is characterized by a “confused” sea state with extensive wave interference. This interference may be • Constructive • Destructive

17. Rogue Waves?(Figure 7-6b) • Constructive wave interference occurs when several wave crests or troughs coincide. The crests build up and the troughs build down.

18. Destructive Waves(Figure 7-6c) • Destructive wave interference occurs when the crest of one wave coincides with the trough of another wave resulting in a cancellation.

19. Progressive Wave Types • Sea - irregular waves in the area of generation • Swell - more regular waves beyond area of generation • Surf - waves that have reached the coast, grow in height, and break

20. Transformation of Deep-water Waves:Dispersion(Figure 7-7a)

21. Shallow Waves Affected by Bottom • In shallow water, the sea bottom transforms the wave’s properties. This leads to wave refraction and waves collapse forming surf (breakers).

22. Wave Refraction(Figure 7-8a) • Bending of the wave crest as waves enter shallow water. It is due to • Drag along the bottom. • Differential speed along the crest.

23. Wave Refraction Animation

24. Shallow-water Wave Transformations • Interaction with the sea bottom. • Water depths are less than 1/20 the wave length. • Bottom friction alters both the • Wave form • Celerity

25. Waves Entering Shallow Water • As waves enter shallow water • Wavelength shortens • Height increases • Speed decreases • Formula on pg. 239

26. Transformation of Shallow-water Waves(Figure 7-7b)

27. Surf’s Up! • Shore breakers (surf) are collapsing waves. Breaking is determined by wave steepness • Wave height/wave length. • When this value is about 1/7, waves begin to break.

28. Waves Breakby SpillingPlunging, orSurging • depending on the slope of the bottom (Figure 7-9)