Download - Topic 16 Waves
![Page 1: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/1.jpg)
Topic 16Waves
GEOL 2503Introduction to Oceanography
![Page 2: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/2.jpg)
What is a wave?
• Energy moving through some medium
2
![Page 3: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/3.jpg)
3
![Page 4: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/4.jpg)
How a Wave Begins
• How do we put energy into the ocean surface to form waves?
• Called the generating force
4
![Page 5: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/5.jpg)
Generating Force
• Wind, for most waves• Pebble in a pond• Earthquake• Meteorite impact
5
![Page 6: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/6.jpg)
Restoring Force
• Force that causes water to return to its undisturbed level
• Surface tension for very small waves (called ripples or capillary waves)
• Gravity for large waves
6
![Page 7: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/7.jpg)
Ripples (capillary waves) on top of waves 7
![Page 8: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/8.jpg)
Most Waves of Interest
• Surface waves– travel on the water surface
• Gravity waves– gravity is the major restoring force
• Wind waves– wind is the major generating force
• Progressive waves– Moving forward through the water
8
![Page 9: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/9.jpg)
Waves
• Energy moving through a medium• Water is the medium• Sound is also energy moving through air,
water, walls, etc. • Waves move through the medium, but the
medium is not transported
9
![Page 10: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/10.jpg)
Wave Terminology• Crest = highest water level• Trough = lowest water level• Height = H = distance from crest to trough• Amplitude = A = distance from still water
level to crest or trough• Period = T = time (in seconds) for two
successive crests to pass fixed point• Frequency = F = number of wave crests to
pass a fixed point in a given amount of time10
![Page 11: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/11.jpg)
Fig. 10-2, p. 266
Direction of wave motion
A BWavelength
Height
Still water level Crest Trough
Frequency: Number of wave crests passing point A or point B each second
Orbital path of individual water molecule at water surface
Period: Time required for wave crest at point A to reach point B
11
![Page 12: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/12.jpg)
Wave Motion
• Energy moves through the water, but the water is not transported
• Individual water particles move in a circular path called a wave orbit
12
![Page 13: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/13.jpg)
1. As wave trough passes, water particles begin to rise and move backward
2. At the midpoint of crest approach, water particles stop moving backward, continue to rise, and begin moving forward
3. Under crest, particles have stopped rising and are moving forward with speed of the crest
4. As crest passes, particles fall and stop moving forward
5. As trough advances, particles move backward
6. At bottom of trough, maximum backward speed
The bird, cork, boat, or water particles have no net forward motion, they move in circular orbits
Orbital Wave Motion1
2
3
4
5
6
13
![Page 14: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/14.jpg)
Note the ½ wavelength depth and orbital diameter
14
![Page 15: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/15.jpg)
Wave Speed L (wavelength)• C = —— T (time)
C = Celerity, speed at which a wave moves across the sea surface
Once a wave is created, its speed may change, but its period remains the same
The speed of a wave is the distance traveled by its crest per unit time. It is known as celerity, thus the “C.”
15
![Page 16: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/16.jpg)
16
![Page 17: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/17.jpg)
Deep-Water Waves
• Waves in water deeper than one-half the wave’s length
• DWWs move at a speed controlled by their wavelength
• Leads to wave dispersion
17
![Page 18: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/18.jpg)
Storm Centers
• Most waves are progressive wind waves• Generated by wind• Restored by gravity• Progress in a particular direction• Formed in local storm centers or in trade wind belts
18
![Page 19: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/19.jpg)
Sea
• In the storm center, winds are variable and turbulent
• Sea surface is a mixture of waves of all heights, lengths, and periods
• Called a “sea” (waves in the area of generation)
• Waves move outward in all directions
19
![Page 20: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/20.jpg)
Wave Dispersion
• Waves from storm center move at speeds controlled by wavelength
• The greater the wavelength, the greater the speed
• Faster, longer waves gradually move through and ahead of shorter, slower waves
• This is called sorting, or dispersion
20
![Page 21: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/21.jpg)
Wave Dispersion
21
![Page 22: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/22.jpg)
Sea—waves in the area of generation
22
![Page 23: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/23.jpg)
Swell—waves after dispersion
23
![Page 24: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/24.jpg)
In a sea, the waves are sharp-crested, choppy, and irregular,with a mixture of wave heights, lengths, and periods
24
![Page 25: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/25.jpg)
Swell—very regular and long-crested waves
25
![Page 26: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/26.jpg)
Wave Train
• As wave train progresses, leading waves lost
• Energy used to advance wave form into undisturbed water
• Therefore, speed of each individual wave (C) in the group is greater than the speed of the leading edge of the wave train
26
![Page 27: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/27.jpg)
Progress of a wave train
27
![Page 28: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/28.jpg)
Group Speed• Wave train moves at speed of one-half that
of the individual waves• Group speed = ½ wave speed = speed of
energy transport
CV = ——
2
28
![Page 29: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/29.jpg)
Wave Height
• Wave height depends on
1. Wind speed2. Wind duration3. Fetch (area over which the blows)
29
![Page 30: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/30.jpg)
30
![Page 31: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/31.jpg)
31
![Page 32: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/32.jpg)
Wave Terminology
• Fully developed sea—when the local wind speed, duration, and fetch have transferred maximum energy, thus creating the largest possible waves for that set of conditions
• Maximum wave height—largest recorded• Average wave height—average of all• Significant wave height—average height
of the highest one-third of waves over long time periods
32
![Page 33: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/33.jpg)
33
![Page 34: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/34.jpg)
Wave Interaction
• Waves are likely to meet other waves from other storm centers
• Waves may intersect at any angle• Form interference patterns
34
![Page 35: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/35.jpg)
1 2
a
b
Constructive interference
(addition)
Destructive interference (subtraction)
Constructive interference
(addition)
35
![Page 36: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/36.jpg)
Episodic Waves
• Also called “rogue waves”• Combination of intersecting waves,
changing depths, and currents• May be responsible for sudden
disappearance of ships
36
![Page 37: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/37.jpg)
Usually many different storms, producing waves of different characteristics. They interfere with each other to produce small swell.
When they become synchronized they can produce huge waves that can overwhelm small boats. Waves can have amplitudes of between 5 and 15 m.
Rogue Waves
37
![Page 38: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/38.jpg)
Wave Steepness
• There is a maximum possible height for any given wavelength
• Ratio of wave’s height to length• S = H/L• Called wave steepness
38
![Page 39: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/39.jpg)
When S approaches 1/7 (wave crest angle of about 120° ) the wave becomes too steep and breaks
39
![Page 40: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/40.jpg)
Shallow-Water Waves
• As deep-water waves approach shore, wave orbits interact with sea bottom
• Orbits gradually become ellipses (flattened circles)
• SWW speed is controlled by water depth• Leads to refraction and wave breaking
40
![Page 41: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/41.jpg)
Video
• Watch the learner.org video on Waves, Beaches and Coasts to see more about shallow water waves
• http://www.learner.org/resources/series78.html
41
![Page 42: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/42.jpg)
Wave Refraction
• Refraction means bending• Waves usually approach shore at an angle• Part in shallower water moves slower• So part of the wave is in deeper water and
moves faster• The wave bends or refracts• Waves end up more parallel to shoreline
42
![Page 43: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/43.jpg)
Wave Refraction
43
![Page 44: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/44.jpg)
Wave Refraction
Figure 20-544
![Page 45: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/45.jpg)
Wave refraction around a rocky point
45
![Page 46: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/46.jpg)
Wave refraction around a rocky island
46
![Page 47: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/47.jpg)
Wave refraction into a small bay
47
![Page 48: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/48.jpg)
Wave Refraction
48
![Page 49: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/49.jpg)
Wave Breaking
• The surf zone is the shallow area along the coast where waves slow, steepen, break, and expend their energy
• Waves in the surf zone do transport water forward
49
![Page 50: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/50.jpg)
Deep-water waves transitioning to surf
50
![Page 51: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/51.jpg)
51
![Page 52: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/52.jpg)
52
![Page 53: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/53.jpg)
The type of breaking wave depends on the steepness of the seafloor
• Spilling breaker: Top of wave crest ‘spills over’ wave. Energy released gradually across entire surf zone.
• Plunging breaker: Crest ‘curls over’ front of wave. Energy dissipates quickly. Common at shorelines with steep slopes
• Surging breaker: Never breaks as it never attains critical wave steepness. Common along upwardly sloping beach faces or seawalls. Energy released seaward.
53
![Page 54: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/54.jpg)
Longshore Current
• Water is transported shoreward in breaking waves
• Waves often approach the beach at an angle• So water is moved along the beach in the
direction of travel of the waves
54
![Page 55: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/55.jpg)
55
![Page 56: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/56.jpg)
Rip Currents
• Water piled up against the shore by breaking waves returns to sea in narrow currents called rip currents
56
![Page 57: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/57.jpg)
57
![Page 58: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/58.jpg)
58
![Page 59: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/59.jpg)
59
rip currents
![Page 60: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/60.jpg)
60
![Page 61: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/61.jpg)
61
![Page 62: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/62.jpg)
Tsunamis
• Seismic sea waves• Japanese for “harbor wave”• Not tidal waves• Generating force is seismic event
– Earthquake– Submarine volcano– Submarine landslide
62
![Page 63: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/63.jpg)
63
![Page 64: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/64.jpg)
Tsunami Characteristics
• Extremely long wavelengths (100-200 km)• Long periods (10-20 minutes)• Low wave heights (1-2 meters)• Shallow water waves
64
![Page 65: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/65.jpg)
Tsunami caused by fault
65
![Page 66: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/66.jpg)
2004 Indonesian Tsunami
66
![Page 67: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/67.jpg)
Indonesian tsunami, December 26, 2004
67
![Page 68: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/68.jpg)
Banda Aceh Shore, Indonesia: before68
![Page 69: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/69.jpg)
Banda Aceh Shore, Indonesia: after 69
![Page 70: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/70.jpg)
Gleebruk Village (1): before 70
![Page 71: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/71.jpg)
Gleebruk Village (1): after 71
![Page 72: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/72.jpg)
Internal Waves
• We’ve been discussing surface waves• Some waves form on boundary between
water of slightly different densities• Slower than surface waves
72
![Page 73: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/73.jpg)
Internal Waves
73
![Page 74: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/74.jpg)
Standing Waves
• Waves that do not progress• Often formed when waves are reflected
back on themselves• Crests and troughs move up and down in
place
74
![Page 75: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/75.jpg)
--At nodes there is no displacement--At antinodes there are alternately crests and troughs
Standing Waves
75
![Page 76: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/76.jpg)
Water sloshes up and down around a central node 76
![Page 77: Topic 16 Waves](https://reader036.vdocuments.us/reader036/viewer/2022062501/56816630550346895dd99864/html5/thumbnails/77.jpg)
Summary: Types of waves
77