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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