Feel free to email the instructor (dpalmer@kent.edu) with any
comments about the format and ease of use of these online notes.

1.  Ocean Waves-today we will look at one of the most obvious aspects of the ocean-the waves that we see.  We will consider classes of waves, look into what deep and shallow waves are, how waves form, and why they break.  There are 2 simple but useful formulas to take note of:

Wave speed   =  wave length / wave period      (same idea as speed = distance/time)

  Wave Steepness  =  Height / wave length

2.  What is a wave?
A wave is a disturbance caused by the movement of energy through a medium
As the energy passes through, the medium moves in specific ways
Waves move across the surface but water particles do not move along with the wave
See Figure 10-9

3.  Parts of a Wave
Crest -highest part of the wave
Trough - lowest part of the wave
Wavelength - distance between adjacent crests
Wave height -vertical distance from the trough to the crest
Period - time needed for the wave to move a distance of one wavelength
See Figure 10-5 and 10-16.

4. Classifying Ocean Waves
Ocean waves are classified by:
 - the disturbing force that creates them
 - the restoring force that tries to flatten them
 - the influence of the disturbing force once they are formed
 - their wavelength
Disturbing forces                                     Restoring forces
 wind                                                          gravity
 low atmospheric pressure due to storms      surface tension
 disturbance of the sea floor

5. Ocean Waves Classified by Restoring Force
Gravity ("gravity waves"):
 - wavelength > 2 cm
 - wind waves, seiches, tsunamis, tides
 - can travel long distances
 - can carry a lot of energy
Surface tension ("capillary waves):
 - wavelengths < 2 cm
 - very small wind waves (ripples)
 - vertical motions of the sea surface
 - do not travel long distances
 - carry very little energy

6. Ocean Waves Classified by Disturbing Force
Wave Type               Disturbing Force                   Typical Wavelength
Wind wave                   wind                                  60-150 m
Seiche           changes in atmos. pressure                basin-scale
Seismic sea           landslide, volcanic                       200 km
 wave (tsunami)     eruption, earthquake
Tide                      gravity, rotation of Earth         1 / 2 Earth's circumference

7. Forces and Ocean Waves
See Table 10-1

8. Orbital Motion
Water particles move in "orbits" as a wave passes
Wave motion is the result of the combined motion of all of the orbiting water particles
Water particles do not move along with most ocean waves - most ocean waves transfer
energy not mass
Figure 10-9
 

9. Deep vs Shallow Water Waves
Deep water waves:
 - water deeper than 1/2 wavelength
 - circular orbits that do not extend to the bottom
Shallow water waves:
 - water shallower than 1/20th wavelength
 - elliptical orbits that extend to the bottom
Transitional waves:
 - water depths between 1/2 and 1/20th wavelength
Figure 10-9 (again)
 

10. How Do Wind Waves Grow?
Wind waves form when wind transfers energy to the water
Many wind waves grow from capillary waves
Capillary waves disrupt the ocean's surface, allowing more efficient transfer of energy
   from the waves to the water
As the wind continues to blow, waves grow and become more peaked
See Figure 10-13

11. Factors Affecting Wind Wave Development
- How stong the wind blows
- How long the wind blows
- The distance over which the wind blows (fetch)

12. Fully Developed Seas
Are attained when additional forcing by the wind does not increase wave height
Occurs when energy added by the wind is equal to the energy removed by wave breaking
Fully developed seas can have large or small waves

13. Wave Dispersion
Long waves leave the region of formation first
Short waves leave the region of formation last
Dispersion sorts waves over time
See Figures 10-18 and 10-19

14. Wave Interference - Building a Rogue Wave or a Superwave
When two waves meet, they interfere
Destructive interference - waves cancel each other out, forming smaller waves
Constructive interference - waves add together, forming bigger waves (can produce very
   dangerous "rogue" waves)
See figure 10-10

15. Why Do Waves Break at the Shore?
As waves approach shore:
- deep water waves become shallow water waves and begin losing energy to the sea bottom
   (the wave "feels" the bottom)
- interaction with the bottom slows the wave and reduces the wavelength
- waves break when they become sufficiently steep
- As wavelength shortens, height grows, and they reach a 1: 7 ratio of height to wavelength.  They then topple over.
See Figure 10-16  see also Table 10-3

16. Plunging and Spilling Breakers
Plunging breakers
- Hollow tube formed between the falling crest and the foot of the wave
- Form over steeply sloping bottoms

17. Terminology Introduced in this Lecture
Wave            capillary wave
crest            deep water wave
trough           shallow water wave
wavelength       fully developed sea
wave height       fetch dispersion
dispersion         steepness
period               swell
disturbing force    constructive interference
restoring force     destructive interference
forced wave       plunging breaker
free wave         spilling breaker
gravity wave

Next Lecture:  Tides
Focus Question:  Why does Earth have tides?