1. Fur Fun: Riding Giants

2. Class 28 WAVES IN THE OCEAN Origin/Types
Parameters -- how we describe waves
Orbital motion
Wind-generated waves

6. Waves: Origins/Types 1. Wind-generated waves -- most common
2. Tsunamis -- earthquake-generated (Pacific)
3. Tides -- gravity of Moon, Sun; forces in Earth's rotation
4. Seiches -- standing waves, “bathtub”

7. Wave Parameters: How do we state the height, spacing, etc?
Crest and Trough
Height = H
Wavelength = L
Steepness = H/L

10. More Wave Parameters:
Period (time between crest arrivals) = T
Speed of an individual wave: S = L/T
Speed of a wave group = V (V < S)
Water Depth = D

11. Interference between two waves
Destructive Interference

12. Interference between two waves
Constructive Interference

13. Orbital Motion of Water in Waves
Circular motion of water as a wave passes
Amount of motion decreases with depth
No motion at D > 1/2 L
In deep water, waves are unaffected by the ocean bottom

14. Orbital Motion: Shallow Water Waves
In shallow water, the circular motion becomes “flattened” near the bottom
The wave “feels bottom”, and motion is impeded by the bottom

15. Shallow Water Waves
If D < 1/20L --> Shallow-water waves
If D >1/2L --> Deep-water waves
In between 1/20L and 1/2L: intermediate waves

18. Shallow Water Wave Model
Deep Water Wave Model
is different from
Shallow Water Wave Model
Deep water wave model applies when D > ½ x L
Shallow water wave model applies when D < 1/20 x L
(no simple model for the in-between waves)

19. Shallow Water Waves
If D < 1/20L --> Shallow-water waves
If D >1/2L --> Deep-water waves
In between 1/20L and 1/2L: intermediate waves

21. WAVES IN THE OPEN OCEAN Caused by wind D > 1/2 L Deep-water waves
H = m
L = m
T = sec
S = km/hr

22. Deep Water Waves:
1. Wavelength, L, depends on period, T
L = (g/2π)T2 (g = 9.8 m/s2)
2. Speed = S = L/T, so....
S = 1.56 m/s2 x T
The bottom line:
a) Both C and L increase with increasing T
b) If you measure T, you can calculate S and L

23. Size and speed of wind-generated waves
Wind speed (most important)
Wind duration
Wind fetch (the distance over which wind blows in one direction)
Increase speed, duration, fetch --> increase H, T, L, C

24. Dispersion: Waves moving away from a stormy area
Waves with long L have highest speed
Short L waves weaken
Long waves dissipate more slowly
This gives us "swells" -- long-T waves