Chapter 8 waves and water dynamics
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CHAPTER 8 Waves and Water Dynamics. Waves are visual proof of the transmission of energy across the ocean. Origin of waves. Most waves are wind-driven Moving energy along ocean/air interface Wind main disturbing force Boundary between and within fluids with different densities

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CHAPTER 8 Waves and Water Dynamics

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CHAPTER 8Waves and Water Dynamics


  • Waves are visual proof of the transmission of energy across the ocean


Origin of waves

  • Most waves are wind-driven

  • Moving energy along ocean/air interface

    • Wind main disturbing force

    • Boundary between and within fluids with different densities

      • Air/ocean interface (ocean waves)

      • Air/air interface (atmospheric waves)

      • Water/water interface (internal waves) – movement of water of different densities

Atmospheric Kelvin-Helmholtz waves are caused when a certain type of cloud moving horizontally one way interacts with a stream of air moving horizontally at a different speed. Eddies develop, making beautiful, unusual, curling waves of cloud.

http://www.siskiyous.edu/shasta/map/mp/bswav.jpg


Internal waves

  • Associated with pycnocline

  • Larger than surface waves – up to 100 m

  • Caused by tides, turbidity currents, winds, ships

  • Possible hazard for submarines

Fig. 8.1a

Internal waves (wavelength about 2 km) which seem to move from theAtlantic ocean to the Mediterranean Sea, at the east of Gibraltar and Ceuta

http://envisat.esa.int/instruments/images/gibraltar_int_wave.gif


http://www.youtube.com/watch?v=HOYEWMgTogE

Other types of waves

  • Splash wave

    • Coastal landslides, calving icebergs

  • Seismic sea wave or tsunami

    • Sea floor movement

  • Tides

    • Gravitational attraction among Moon, Sun, and Earth

  • Wake

    • Ships


Wave motion

  • Waves transmit energy by oscillating particles

  • Cyclic motion of particles in ocean

    • Particles may move

      • Up and down

      • Back and forth

      • Around and around

  • Particles in ocean waves move in orbital paths


Progressive waves

  • Waves that travel without breaking

  • Types

    • Longitudinal– push/pull waves in direction of energy transmission

      • sound

  • Transverse– back and forth motion

    • Only in solids

  • Orbital

    • Combination of longitudinal and transverse

    • around and around motion at interface of two fluids


  • Orbital or interface waves

    • Waves on ocean surface at water/air interface

    • Crest, trough, wave height (H)

    • Wavelength (L)


    Orbital waves

    • Wave characteristics

      • Wave steepness = ratio of wave height to wave length H/L

        • If wave steepness > 1/7, wave breaks

      • Wave period(T) = time for one wavelength to pass fixed point

      • Wave frequency= # of wave crests passing fixed location per unit of time, inverse of period or 1/T


    Circular orbital motion

    • Water particles move in circle

    • Movement up and down and

    • Back and forth

    Fig. 8.4


    Fig. 8.3C

    Orbital motion

    • Diameter of orbital motion decreases with depth of water

    • Wave base= ½ L

      • Hardly anymotion below wave base due to wave activity


    Types of Waves dependent on interaction with bottom


    Deep-water waves

    • No interference with ocean bottom

    • Water depth is greater than wave base ( > 1/2L)

    • Wave speed (celerity) proportional to wavelength

      • Longer the wave, the faster it travels

    Fig. 8.5a


    Shallow-water wave

    • Water depth is < 1/20L

      • Wave “feels” bottom, because water is shallower than wave base

      • Orbits are compressed  elliptical

    • Celerity proportional to depth of water

      • The deeper the water, the faster the wave travels

    Fig. 8.5c


    Transitional waves

    • Characteristics of both deep and shallow-water waves

    • Celerity depends on both water depth and wavelength

    Fig. 8.5b


    Wave development

    • Most ocean waves wind-generated

    • Capillary waves(ripples) formed first

      • Rounded crests, very small wavelengths

      • Provide “grip” for the wind

    • Increasing energy results in gravity waves

      • Symmetrical waves with longer wavelengths


    Wave development

    • Increasing energy results in trochoidal waveforms

      • Crests pointed, troughs rounded, greater wave heights

    • “Sea”= area where waves generated by winds or storm

    www.poemsinc.org/ oceano/waves.htm


    Ripples

    Fully-developed Sea

    Choppy seas

    Swell

    http://plaza.ufl.edu/mrosenme

    http://www4.ncsu.edu/eos/users/c/ceknowle/public/chapter10


    Wave energy

    • Factors that control wave energy

      • Wind speed

      • Wind duration

      • Fetch– distance of uninterrupted winds


    Maximum wave height caused by wind that is known

    • Reliable measurement

      • Measured on US Navy tanker caught in typhoon

  • Wave height 34 m or 112 ft

  • Fig. 8.10


    Wave energy

    • Fully developed sea

      • Maximum wave height, wavelength for particular fetch, speed, and duration of winds at equilibrium conditions

    • Swell

      • Uniform, symmetrical waves that travel outward from storm area

      • Long, rounded crests

      • Transport energy long distances

    http://www4.ncsu.edu/eos/users/c/ceknowle/public/chapter10


    Swell

    • Longer wavelength waves travel faster and outdistance other waves

    • Wave train = group of waves with similar characteristics

    • Sorting of waves by their wavelengths is wave dispersion

    • Wave train speed is ½ speed of individual wave


    Wave interference patterns

    • Different swells coming together

    • Constructive interference

      • In-phase wave trains with about the same wavelengths

      • Add to wave height

      • Rogue waves– unusually large waves

        • Rare but can happen and be unusually large


    http://www.ethnomusic.ucla.edu/courses/ESM172a

    Wave interference patterns

    • Destructive interference

      • Out-of-phase wave trains with about the same wavelengths

      • At least partially cancel out waves

    • Mixed interference

      • Two swells with different wavelengths and different wave heights


    • Wave height is extremely variable

      • ~50% of all waves are less than 2 m (6-7 ft)

      • 10-15% are greater than 6 m

        • Up to 15 m in Atlantic and Indian oceans

        • Up to 34 m in Pacific - long fetch (speed at 102 km/hr)

     Global wind speed (Oct 3-12, 1992)

    Global wave height (Oct 3-12, 1992) 

    http://topex-www.jpl.nasa.gov/education/images


    • Largestrogue wave can sink largest vessels

      • Largest = 34 m (120 ft) high (above theoretical max)

      • 1:1200 over 3x average height;

      • 1:300000 over 4x height

    • Waves hitting current may double height suddenly and break

    • Most common near strong currents, long fetches, storms

    Rogue waves that rise as high as 10-story buildings and can sink large ships are far more common than previously thought, imagery from European Space Agency satellites has shown. A rogue wave is seen in this rare 1980 photo taken aboard a supertanker during a storm near Durban, South Africa. (Reuters)

    http://www.allhatnocattle.net


    • Storm surges

      • Large wave moving with a storm (not just hurricanes)

      • Low pressure above water  water level rises at center

    • Up to 3-4 m higher than normal

    • Preceded by low sea-level in front of storm

  • Added to increased wind waves + high tide  most damage

  • http://www2.sunysuffolk.edu/mandias/38hurricane


    Hurricane Katrina – 2005Record storm surge in Pass Christian, MS - ~27.8 ft


    Waves approach shore

    • Deep-water swell waves shoal 

    • Transitional waves 

    • Become shallow-water waves (< L/2)

      • Wave base “touches” sea bottom


    Waves approach shore

    • During transition to shallow-water waves

      • Wave speed and wavelength decreases

      • Wave height and steepness increases

      • Waves break

      • Period remains constant


    Wave Motion and Wave Refraction When Approaching Shore


    Shoaling waves

    Fig. 8.15


    Breakers in surf zone

    • Top of wave topples over base because of decrease in wave speed due to friction with sea floor

      • Wave form not sustained at about 3:4 ratio of height/water depth

      • Breaking waves releases lots of energy

    http://www.poemsinc.org/oceano/ocean05.gif


    Breakers in surf zone

    • Different types of breakers associated with different slope of sea floor

      • Spilling

      • Plunging

      • Surging

    http:// www.mikeladle.com


    Spilling breaker

    • Water slides down front slope of wave

    • Gently sloping sea floor

    • Wind “onshore”

    • Wave energy expended over longer distance

    Wind

    Onshore

    http://www.winona.edu/geology/oceanography


    Plunging breaker

    • Curling crest

    • Moderately steep sea floor

    • Wind “offshore”

    • Wave energy expended over shorter distance

    • Best for surfers

    Wind

    Offshore

    http://www.seagrant.umn.edu/seiche/2002


    http://www.winona.edu/geology/oceanography

    http://www.seagrant.umn.edu/seiche/2002

    Wind

    Onshore

    Wind

    Offshore

    Wind

    Wind

    Onshore

    Offshore

    http:// www.mikeladle.com


    Surging breaker

    • Breakers on shore

    • Steepest sea floor

    • Energy spread over shortest distance

    • Challenging for surfers

    http://www.bbc.co.uk/wales/surfing/images/ecards/400_232/hawaii/sandy_beach_bridgey.jpg


    Wave refraction

    • As waves approach shore, they bend so wave crests are nearly parallel to shore

    • Wave speed proportional to depth of water (shallow-water wave)

    • Different segments of wave crest travel at different speeds


    Wave refraction

    Fig. 8.17a


    www.lineup.com.au/gallery/ newzealand/

    horsesmouth.journalspace.com

    About 10 m high

    • Surf – nearly continuous breaking waves parallel to shore

      • Breakers may reach 30-50 m high

      • 14 m high breakers can move 2600 ton blocks


    www.crazyjs.com/ surf/gallery/peaks03.htm

    Area of destructive interference

    Area of constructive interference (set)

    Area of destructive interference (lull)

    • Surfbeat

      • Sets – series from relative calm to largest waves

      • Interference in wave train cancel some, adds to others

      • Destructive interference  lull “between sets”


    http://www.ripcurrents.noaa.gov/overview.shtml

    • Rip currents are wave energy escaping shoreline

      • Stream of water returning out to sea through surf zone

      • Flows up to a few hundred meters offshore then dissipates

    http://www.ocean.udel.edu/mas/wcarey


    Wave energy distribution at shoreline

    • Energy focused on headland

      • Headland eroded

    • Energy dissipated in bay

      • Bay filled up with sediment

    Fig. 8.17b


    Wave Motion and Wave Refraction When Approaching Shore


    Tsunami or seismic sea wave

    • Sudden changes in sea floor caused by

      • Earthquakes, submarine landslides, volcanic eruptions

    • Long wavelengths ( > 200 km or 125 m)

    • Shallow-water wave characteristics (<L/2)


    • Speed proportional to water depth so very fast in open ocean

      • Not steep when generated (low H/L ratio)

      • Crest of only 1-2 ft over 16 min period

      • Move very fast -- up to 212 m/sec (470 mile/hr)


    • As crest arrives on shore, slows but grows in height quickly

      • Sea level can rise up to 40 m (131 ft) when tsunami reaches shore

      • Fast, onrushing flood of water rather than a huge breaker

      • Series of waves

      • Warning initial rushing out of water from shore


    Tsunami or seismic sea wave

    Fig. 8.20a


    Tsunami


    Tsunami or seismic sea wave

    • Most occur in Pacific Ocean (more earthquakes and volcanic eruptions)

    • Damaging to coastal areas

    • Loss of human lives

      • Krakatau eruption (1883) in Indonesia created tsunami that killed more than 36,000 people

      • Aura, Japan (1703) tsunami killed 100,000 people

      • Indonesia (Dec. 26, 2004) tsunami killed over 229,000 around Indian Ocean

    http://nctr.pmel.noaa.gov/images/sumatra_tsunami.jpg


    Speed of tsunami

    Undersea earth-quake at 6:59 AM


    Scale of tsunami damage on Sumatran coast in Aceh province

    Landsat image before tsunami: 13-Dec. 2004

    ** Note sediment covered area impacted by tsunami 1-5 km inshore

    Landsat image after tsunami: 29-Dec. 2004

    www.jpl.nasa.gov/news


    ** Note impacted area corresponds to 10 m contour

    www.jpl.nasa.gov/news


    Tsunami watches and warnings

    • Pacific Tsunami Warning Center

      • Seismic waves forecast possible tsunami

      • Issues tsunami watches and warnings

    • Increasing damage to property as more infrastructure constructed near shore

    • Evacuate people from coastal areas and send ships from harbors

      • Water “sucked” out before first

    http://www.drgeorgepc.com/tsuStationsTravelChart.jpg


    Waves as a source of producing electricity

    • Lots of energy associated with waves

    • Mostly with large storm waves

      • How to protect power plants

      • How to produce power consistently

    • Environmental issues

      • Building power plants close to shore

      • Interfering with life and sediment movement

    • Offshore power plants?


    Wave power plant at Islay, Scotland

    Fig. 8.25b


    Global coastal wave energy resources

    Fig. 8.26


    Ocean Literacy Principles

    • 1.c – Throughout the ocean there is one interconnected circulation system powered by winds, tides, force of the Earth’s rotation, the Sun, and water density differences. The shape of ocean basins and adjacent land masses influence the path of circulation.

    • 5.h - Tides, waves, and predation cause vertical zonation patterns along the shore, influencing the distribution and diversity of organisms.


    Sunshine State Standards

    • SC.6.E.6.2 - Recognize that there are a variety of different landforms on Earth's surface such as coastlines, dunes, rivers, mountains, glaciers, deltas, and lakes and relate these landforms as they apply to Florida.

    • SC.7.P.11.2 - Investigate and describe the transformation of energy from one form to another.

    • SC.8.P.8.4 - Classify and compare substances on the basis of characteristic physical properties that can be demonstrated or measured; for example, density, thermal or electrical conductivity, solubility, magnetic properties, melting and boiling points, and know that these properties are independent of the amount of the sample.

    • SC.912.E.7.2 - Analyze the causes of the various kinds of surface and deep water motion within the oceans and their impacts on the transfer of energy between the poles and the equator.


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