Waves

Wave Spectrum

Surface waves

deep-water waves

shallow-water waves

Wave Development

Wave Equations

Global Wave Heights

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Wave Spectrum

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Surface Waves

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Deep -water Waves

D > L/2

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08_06a

Movement of water parcels is circular and the orbit getssmaller with depth until there is no motion

at L/2.

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Shallow-water Waves

D < L/20

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Movement of water parcels is elliptical and the orbit getsflatter until it is just a back and forth movement at

the bottom.

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Wave Development

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Wave height depends on three factors:

1. Wind speed - how fast it blows

2. Wind duration - how long it blows

3. Fetch - the area over which the wind acts

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08_07

As wave speed increases, wavelengthand wave period also increase.

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With a constant wind speed, wave height, length, period and speedall increase as the fetch increases.

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Wind speed, fetch and wind duration are usually positively correlated;as they increase, wave characteristics increase.

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Wave Equations

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Know thisone

Know thisone

(D< L/20)

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Global Wave Heights

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October 1992 TOPEX/Poseidon satelliteOctober 1992 TOPEX/Poseidon satelliteHigh in high latitudes, low in low latitudes

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Northern HemisphereWinter, highest waves

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Southern HemisphereWinter, highest waves

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WindSpeed10/92

WaveHeight

WindSpeed10/92

WaveHeightWaveHeight

CauseAnd

Effect

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08_11

Highest wave recorded at sea - 34 meters (112 feet)

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Waves

Wave Spectrum

Surface waves

deep-water waves

shallow-water waves

Wave Development

Wave Equations

Global Wave Heights

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Shallow water waves “stack up” as they approach shore causingthe wavelength to become shorter and the height to increase.

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WAVE INTERFERENCEPATTERNS

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Two wave trains can produce either larger or smallerwaves after interacting with each other. Constructive

interference can be the cause of “rogue waves” thatoccasionally sink ships in the absence of a severe

storm.

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A Stationary or Standing Wave

Water flows back and forth about a node, a point with no vertical water motion. The endpoints are antinodes, points with maximum vertical water motion.

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Uninodal Standing Wave

Yellow dashed line indicates undisturbed sea level. Dots indicate water motion.

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Binodal Standing Wave

Yellow dashed line indicates undisturbed sea level. Dots indicate water motion.

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THE WILL BE A SEPARATE POWER POINT ON

TSUNAMIS

INTERNAL WAVES

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Internal waves occur along density boundaries, i.e. athermocline - the smaller the density difference, the larger

the waves that can be produced.

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Internal Wave Propagation

Yellow dashed line indicates undisturbed sea level. Dots indicate water motion.

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Atmospheric Internal Waves

Rising air cools, water condenses clouds form. Sinking air warms and clouds evaporate.

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Eighty Mile Beach, north coast of Australia.High altitude oblique photograph from theSpace Shuttle (November 1990). Shows reflections of internal (not surface) wave forms progressing toward shore. The distance betweenwave crests is approximately 4.5 km.

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Gulf of Aden and Horn of Africa, Somalia. High altitude oblique photograph from the Space Shuttle (September-October 1988). Internal waves are visible below the Gulf of Aden water surface off Somalia.Waves show refraction patterns produced by interaction with local seafloor topography, including submarine canyons that focus the waves near the center of the photograph.

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Strait of Gibraltar, Spain and Morocco. ERS-1 satellite Synthetic Aperture Radar (SAR)imagery with false colors added; image from 7 January 1992. This spectacular image showsinternal waves (with a wavelength of about 2km) progressing from the Atlantic Ocean intothe Mediterranean. These internal waves are generated at a salinity interface (halocline)between inflowing surface Atlantic waters and the deeper return flow of saline Mediterraneanwaters over the Gibraltar sill. The internal waves reach the surface some kilometers behindthe Strait; although not visible to the eye, the waves produce patterns of still and rough waterthat are picked up by radar imaging.

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Strait of Gibraltar, Gibraltar, southern Spain, northern Morocco. High altitude oblique photograph from theSpace Shuttle (October 1984). A spectacular set of internal waves are visible where surface waters pass fromthe Atlantic Ocean into the Mediterranean over deeper, denser waters exiting the Mediterranean. These largewavelength internal waves are visible here in sunglint off the thermocline despite the lack of any expressionat the ocean surface.

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STORM SURGE

Results from elevated sea levels pushed ahead from storms such as

hurricanes.

If they come ashore at high tide, they can cause considerable damage.

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The effects of storm surgeon coastal areas.

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