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Waves in the Ocean
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7.1 Properties of Ocean Waves
An ocean wave is an undulation of the sea surface.
• Wave parameters:
–Wave crest
–Wave trough–wave height (H)
–wave amplitude (1/2H)
–wave length (L)
–wave period (T).
• Progressive waves move across the sea surface.
–Surface waves
–Internal waves
–Tsunamis Surface waves
• Standing waves oscillate about a fixed point.
–Seiches
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Defintions and symbols
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Definition of terms- elementary, sinusoidal, progressive wav
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7.1 Properties of Ocean Waves
Idealized Wave Spectrum
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7.1 Properties of Ocean Waves Wind Generation of Waves
• The type of wave generated by wind isdetermined by:
–Wind velocity
–Wind duration
–Fetch (distance over which wind blows)• Simply put, wave size increases as the strength
and duration of the wind, and distance overwhich it blows increases.
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Progressive waves are waves that “move”
forward across a surface.• As waves pass, wave form and wave energy
move forward, but not the water.
• Water molecules move in an orbital motion as
the wave passes.
• Diameter of orbit increases with increasingwave size and decreases with depth below thewater surface.
7-2 Wave Motions
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Progressive Wave Types
• Sea - irregular waves in the area of generation
• Swell - more regular waves beyond area of generation
• Surf - waves that have reached the coast, grow in height,and break
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Orbit Diameter and Stokes Drift
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7-2 Wave Motions
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Deep- and Shallow-Water Motion
• Wave base is the depth
to which a surface wavecan move water.
• If the water is deeperthan wave base:
– orbits are circular
– no interaction between thebottom and the wave.
• If the water is shallowerthan wave base
– orbits are elliptical – orbits become increasingly
flattened towards thebottom.
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Flow of Energy,not Mass
7-3 Life History of Ocean Waves
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7-3 Life History of Ocean Waves
seas insidefetch area.
Swells:wavefound
outsidethe fetc
Fetch is the area of contact between the wind and the water and is wherwind- enerated waves be in.
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Progressive Wave Types
Sea
Swell
Surf
• Sea - irregular waves in the area of generation
• Swell - more regular waves beyond area of generation
• Surf - waves that have reached the coast, grow in height, and break
• Wave interference is the momentary interaction between
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Wave interference is the momentary interaction betweenwaves as they pass through each other. Wave interferencecan be constructive or destructive.
7-3 Life History of Ocean Waves
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7 3 Life History of Ocean Waves
•Dispersion: Gradual separation of wave types
based on their relative wavelengths and speeds
•Because celerity increases as wavelengthincreases:
-long waves travel faster than short waves.
-This causes dispersion outside of the fetch andregular ocean swell.
Transformation : Dispersion
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7-3 Life History of Ocean Waves
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7 3 Life History of Ocean Waves
Transformation : Shoaling
7-3 Life History of Ocean Waves
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The shallower the water, the greater the
interaction between the wave and the bottomalters the wave properties, eventually causingthe wave to collapse.
• Wave speed decreases as depth decreases.
• Wavelength decreases as depth decreases.
• Wave height increases as depth decreases.
• Troughs become flattened and the wave profile becomesextremely asymmetrical.
• Period remains unchanged. Period is a fundamental
property of a wave.• Celerity equation of shallow water wave.
y
Transformation : Shoaling
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Transformation : Breaking
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Spilling, Plunging and Surging Breakers
•Spilling breaker: Top of wave crest ‘spills over’
wave. Energy releasedgradually across entiresurf zone.
•Plunging breaker: Crest ‘curls over’ front of wave. Energy dissipates
quickly. Common atshorelines with steepslopes
•Surging breaker: Neverbreaks as it never
attains critical wavesteepness. Commonalong upwardly slopingbeach faces or seawalls.Energy releasedseaward.
Transformation : Breaking
7-3 Life History of Ocean Waves
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Wave steepness is a ratio of wave height
divided by wavelength (H/L).• In shallow water, wave height increases and
wave length decreases.
• When H/L is larger than or equals 1/7 (H/L 1/7), the wave becomes unstable and breaks.
• There are three types of breakers: spillingbreakers, plunging breakers, and surgingbreakers.
Transformation : Breaking
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7-3 Life History of Ocean Waves
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• Water is deeper at theshore area, allowing
waves to progressfarther inland.
• Storm surge isespecially severe
when superimposedupon a spring hightide.
Storm surge is the rise in sea level resulting from lo
atmospheric pressure and the accumulation of watedriven shoreward by storm winds.
Transformation : Storm Surge
7-4 Standing Waves
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• Resonance amplifies the displacement at the nodes andoccurs when the period of the basin is similar to the period
the force producing the standing wave.
7 4 Standing Waves
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Standing waves or seiches consist of a water
surface “seesawing” back and forth.
• Node : The line about which the surfaceoscillates.
– Located in centers of enclosed basins and toward theseaward side of open basins.
• Antinodes: Points where there are the maximumdisplacement of the surface as it oscillates.
– Antinodes usually located at the edge of the basin.
7-4 Standing Waves
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• Geometry of the basin controls the period of the
standing wave. A basin can be closed or open.• Standing waves can be generated by storm
surges.
• Resonance amplifies the displacement at the
nodes and occurs when the period of the basin issimilar to the period of the force producing thestanding wave.
7-4 Standing Waves
7-3 Life History of Ocean Waves
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A first order seiche. The undisturbed sea level is indicated the broken yellow line. Three water particles are shown as
an indication of water movement in the seiche.Note the node in the centre and that water under the nodemoves only horizontally, while water at both ends of thebasin moves vertically.
Standing wave
7-3 Life History of Ocean Waves
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A first order seiche in a basin open to the deep ocean. Theundisturbed sea level is indicated by the broken yellow line.
Two water particles are shown as an indication of watermovement in the seiche.Note the node at the connection of the basin to the deep oceaand that water under the node moves only horizontally, whilewater at the end of the basin moves vertically
Seiche
7-5 Other Types of Progressive Waves
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Internal waves form within the water columnon the pycnocline.
• Because of the small density difference betweethe water masses above and below thepycnocline, wave properties are differentcompared to surface waves.
• Internal waves display all the properties of surface progressive waves including reflection,refraction, interference, breaking, etc.
• Any disturbance to the pycnocline can generate
internal waves, including: Flow of water relatedto the tides., Flow of water masses past eachother, Storms, or Submarine landslides.
yp g
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An internal wave propagating on the interface between twolayers. The undisturbed sea level is indicated by the yellowline. Water particles are shown as yellow and magenta dotsYellow dots sit in the middle of the water column and moveonly up and down. Magenta dots sit at the top and bottom othe water column and move only in the horizontal.
By watching a yellow dot you can see how a water particle the middle of the water column moves up and down, but donot move horizontally, as the wave passes through.
Internal Waves
Other Types of Progressive Waves
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Internal waves form within the water column
along the pycnocline.
Other Types of Progressive Waves (Tsunami)
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Tsunamis were previously called tidal waves,but are unrelated to tides.
• Tsunamis consist of a series of long-periodwaves characterized by very long wavelength(up to 100 km) and high speed (up to 760km/hr) in the deep ocean.
• Because of their large wavelength, tsunamis areshallow-water to intermediate-water waves asthey travel across the ocean basin.
• They only become a danger when reachingcoastal areas where wave height can reach 10
m.
• Tsunamis originate from earthquakes, volcanicexplosions, or submarine landslides.
Generation of a Tsunami
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Generation of a Tsunami
Tsunamies Generation
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Tsunamies Generation
Generation of a Tsunami
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Generation of a Tsunami
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Wh t I R W ?
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What Is a Rogue Wave?
A "rogue wave" is typically used to describe a wave that is significantly
larger than other waves during a given time, at a given location. Severalfactors can create rogue waves. Multiple waves can intersect to create a
much larger wave- up to the sum of the heights of the waves that combine.
Additionally, currents can contribute to the formation of rogue waves. And
rogue waves can result as a normal part of the wave spectrum. In other
words, waves are not created individually but rather, in large groups. And awave(s) within this group can be significantly larger than the rest.
Rogue waves have been witnessed all around the world. The North Sea,
Gulf of Alaska, S. African coasts are infamous for producing rogue waves-
some that have approached 100 feet in height.
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Coastal
Rogue Wave
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ل خ ا ي ا آ
ن آو 45 ف ث لخا ة خ ا ه
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اه لع
هآCoast Beach or shoreاخن Nearshore zoneاخهدطقة
آز ور
Offsh
قطلخاآهآCoastal area
قعخاBackshore لخاForeshore
Surf Zone
Shoreface or Inshoreاخ ة
جسBottom
دگهقطةPlunge Pointفآ
Bermم
Crest of Berm طثآز
Coastرخادآ
ا آ د :آز ه ا آ آر طآ و د ن ا ث رد ا ارد و ف ل ج نآع و درا آت در آ آز و قط نخاا زآ ك ا
ا آت ج ارد و .
آخ اطقة اخل:آز ه ل ث ت آخن ا(اآز ا(آدر ث آخن )و ا آ)آدر ست قط اث و .اآدآ و
قخ ا گ د زل:آخا آ ر آ ع اث و و اخن درا در ث ا زآ ج ل دو ع تآ يآ قط6 رآد آدآ ارد ن ثآز ر در دآ ث ا .ج آز
ل خ ا ي ا آ
ن آو 46
ار
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اه لع