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. Wave Parameters(Figure 7-1a)

3. 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 wavesmove across the sea surface. • Standing wavesoscillate about a fixed point.

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 wavesbecause 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) Waves do not interact with the seafloor Orbits of the water molecules are circular.

14. Shallow Water Waves(Figure 7-4b) Waves interact with the seafloor are known as Orbits of the water molecules become elliptical.

15. 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

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

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

18. 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

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

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

21. 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.

22. Shallow-water Wave Transformations • Interaction with the sea bottom. • Bottom friction alters both the • Wave form • Wavelength shortens (decreases) • Height increases • Celerity (speed) • decreases

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

24. 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.

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