The Waves An Introduction to the World’s Oceans Sverdrup et al. - Chapter Ten - 8th Ed.

How a Wave Begins Generating forces –Wind, atmospheric pressure, storm surge, tsunami, faulting of seafloor, volcanic eruption, landslide,gravitational attraction, Earth rotation. Restoring force –Surface tension Very small waves –Earth’s gravity Larger waves Energy transfer between air and water –Ripples or capillary waves –Fetch, wind speed & duration control wave size

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10.2 Anatomy of a Wave Crest Trough Wavelength Wave period Wave height and amplitude

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10.3 Wave Motion Particle motion Particle orbits Mean transport of water

10.4 Wave Speed C: wave speed or celerity L: wave length T: wave period C = L / T

Deep-Water Waves Storm centers –Winds flow around low pressure –Forced waves –Variety of periods and heights are generated Dispersion –Free waves –Wave sorting –Swell Group speed –Speed of energy transport Wave interaction –Wave interference –Breaking of large amplitude waves produced by constructive interference

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Wave Height Controls on wind wave heights: –Wind speed –Wind duration –Fetch Episodic waves –Intersecting wave trains, changes in depths, and currents Wave energy –Potential energy –Kinetic energy Wave steepness –Wave breaking Universal Sea State Code

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Table 10.2

Shallow-Water Waves Refraction –Bending of waves because of variations in wave speed –Concentration of wave energy Reflection –Spreading and converging wave rays Diffraction –Spreading of wave energy around gaps and obstacles Navigation from wave direction –Wave patterns –Polynesian seafarers

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The Surf Zone Breakers –Water particle orbital motions –Plungers and spillers –Sorted and unsorted waves Water transport –Net drift of water in the direction of the waves –Rip currents Energy release –Narrow surf zones –Sandbars

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10.9 Tsunami Seismic sea waves Vertical sea floor displacement Shallow water waves –Long wavelength –Low period Wave height –At point of origin –Close to shore where depth decreases Destructive power

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“Shark food” waiting to see the tsunami.

Boxed Reading: Tsunami Warning Systems Seismic stations Computer wave models Tide gauges and bottom pressure sensors Warning time

Box Fig. 1, pg. 264

Box Fig. 2, pg. 265

10.10 Internal Waves Oscillating pycnocline Displacement of pycnocline –By low-pressure storms –Currents moving over bottom topography Dead water effect Relationship between wavelength and wave speed

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10.11 Standing Waves Reflected progressive waves Nodes and antinodes Seiches

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10.12 Practical Considerations: Energy from Waves Tremendous amount of wave energy Methods of harnessing wave energy Cost, location, lack of regularity, and environmental effects

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The End