Waves
Oceanography Notes
Anatomy of a Wave
• Wave height :vertical
distance between a
crest and the
preceding trough
• Amplitude: equal to
one-half the wave
height (point of
equilibrium surface
to the crest or trough
Sine Wave Characteristics
Diagram of a Wave: Wavelength
Basic Wave Diagram
http://www.onr.navy.mil/focus/ocean/motion/waves1.htm
Description of Periodic Motion
Motion which repeats itself precisely can be
described with the following terms:
Period: the time required to complete a full cycle,
T in seconds/cycle
Frequency: the number of cycles per second, f in
1/seconds or Hertz (Hz)
Amplitude: the maximum displacement from
equilibrium A
Wave Generating Forces
•
Sometimes waves are generated through
seismic motion or rock formations (ice
too) falling (like throwing a rock into the
water)
•
There are three basic factors in
generating surface waves (height)…
1. Wind speed
2. Wind duration
3. Fetch (the distance that the wind blows
Wave Motion
• Waves consist of orbits that are below the
sea surface
Deep Water Waves
• These are classified as waves that have a
depth that is at least one half of the
wavelength Depth = Wavelength (L)/2
• Wave speed (C) = L/T
or
L = C*T
C is equal to celerity (speed of one wave)
versus v (speed of a group of waves)
Wave Equations
• For any type of water wave, the wave's
wavelength (L), speed (C) and period (T)
are related by the following relations:
• L = C*T
• L = 1.56T2
• C = gT/2¶
• C = 1.56 * T
1.56 is in m/s2
Shallow Water Waves
A wave that enters water with a depth of less
than one-twentieth (D < L/20)
Shallow water wavelength and speed are
controlled only by the water depth (meters)
_____
C=√ g*D
(g = 9.81 m/s2)
Group Speed
• Waves can travel
in groups (speed)
• Waves move as
wave trains
V = C/2
Breaking Waves
http://oceanworld.tamu.edu/students/waves/index.html
http://search.live.com/images/results.aspx?q=Tsunami+diagrams%20|%20id:AE878E4D465DAB08
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Wave Breaking Diagram
http://geology.wr.usgs.gov/parks/sea/wave.gif
Wave Steepness
For a wave to break, wave steepness is
important. If the ratio of wave height to
wavelength is 1:7 or more, the wave will break
Surging Breakers happen on beaches
where the slope is very steep. The wave
does not actually break. Instead, it rolls
onto the steep beach. These kinds of
breakers are known for their destructive
nature
Plunging Breakers happen on beaches
where the slope is moderately steep.
This kind of wave normally curls over
forming a tunnel until the wave breaks.
Expert surfers love this type of wave!
Spilling Breakers occur on beaches with
gentle slopes. These waves break far
from the shore, and the surf gently rolls
over the front of the wave.
http://www.onr.navy.mil/focus/ocean/motion/waves2.
htm
Guess The Types of Breakers
Tsunami
Characteristics of a Tsunami
Shallow Water
Wave
characteristics in
deep water
Large
Wavelengths
(kms)
Fast Wave
Speeds
Depth less than
one-half of the
wavelength
Causes of Tsunami
Seismic disturbance causing
wave impulses
Waves and the Shoreline
• Waves enter the shoreline and can exhibit
the following characteristics…
Refraction
Reflection
Diffraction
Wave Diffraction
Interferences
• Constructive and Destructive
Constructive
Destructive