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Ocean Waves
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A Little Math
l Wave speed = wave length/wave period
l C= L/T
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Relationship of Wave Length toDepth of Wave Motion
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Motion of Water as Wave Passes
Water in the crest of the wave move in the samedirection as the wave, but water in the trough move inthe opposite direction.
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Waves are classified on the basis of:lDisturbing forcelFree waves vs. forced waveslRestoring forcelWavelength
Classifying Waves
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Classifying Waves
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Types of Waves
Waves transmit energy across the ocean’s surface.
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Wind Waves
Wind waves are gravity waves formed by the transfer ofwind energy into water. Wind forces convert capillarywaves to wind waves.
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Wind strength - wind must be moving faster than the wavecrests for energy transfer to continue
Wind duration - winds that blow for a short time will notgenerate large waves
Fetch - the uninterrupted distance over which the windblows without changing direction
Factors Affecting Wind WaveDevelopment
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Factors Affecting Wind WaveDevelopment
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Relationshipbetween
wave heightand wave
energy
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Wave Dispersion
The longer the wave length, the faster thewave speed.
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Swell Formation and Dispersion
Wave separation, ordispersion, is a function ofwavelength. Waves with thelongest wavelength move thefastest and leave the area ofwave formation sooner. Thesmooth undulation of oceanwater caused by wavedispersion is called swell.
A wave train.
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When waves from different directions meet, theyinterfere with one another.
Wave interference can be:
Destructive interference – two waves that cancel each other out,resulting in reduced or no wave
Constructive interference – additive interference that results inwaves larger than the original waves
Rogue waves - freak waves that occur due to interference andresult in a wave crest higher than the theoretical maximum
Interference And Rogue Waves
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Wave Interference
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Wave Interference
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Waves Entering Shallow Water
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Shallow-Water Waves
When waves enter shallow water:
Wave speed decreases
Wave length decreases
Wave period does not change
Wave height increases
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Wind Waves ApproachingShore
What happens when wind waves break againstthe shore?
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Wave Steepness
Maximum height for a given wavelength is basedon H/L. If H/L > 1/7, wave becomes too steep.
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Plunging waves break violently against the shore, leaving an air-filledtube, or channel, between the crest and foot of the wave. Plungingwaves are formed when waves approach a shore over a steeply slopedbottom.
Spilling waves occur on gradually sloping ocean bottoms. The crest ofa spilling wave slides down the face of the wave as it breaks on shore.
Breaking Waves
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Wave refraction - the slowing and bending of waves inshallow water
Wave diffraction - propagation of a wave around anobstacle
Wave reflection - occurs when waves “bounce back” froman obstacle they encounter. Reflected waves can causeinterference with oncoming waves, creating standingwaves
Wave Refraction, Diffraction,and Reflection
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Wave Refraction
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Wave Refraction
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Wave Diffraction
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Internal Waves
Waves that occur at the boundaries of water layerswith different densities are called internal waves.
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Standing Waves or Seiches
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Sumatra-Andaman IslandEarthquake
l Magnitude 9.0l Sunday, Dec. 26, at 7:58 a.m. local timel 30 km off the west coast of northern
Sumatral 250 km SSE of Banda Acehl Fourth largest in the world since 1964
Prince William Sound, Alaska, quakel More casualties than any other tsunami in
recorded history
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Tsunami Warning Network
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Key Ideas
l Waves transmit energy, not water mass, across the ocean’ssurface.
l The behavior of a wave depends on the relation between thewave’s size and the depth of water through which it is moving.
l Wind waves form when energy is transferred from wind to water.
l Waves can change direction by refraction and diffraction, can interfere with one another, and reflect from solid objects.
44Parts of an ocean wave
Summary
