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 forceBoundary between and within fluids with

different densities○ Air/ocean interface (ocean wavesocean waves)○ Air/air interface (atmospheric wavesatmospheric waves)○ Water/water interface (internal wavesinternal waves) –

movement of water of different densities

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

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.

Internal waves

Fig. 8.1a

Associated with pycnocline

Larger than surface waves – up to 100 m

Caused by tides, turbidity currents, winds, ships

Possible hazard for submarines

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

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

Other types of waves Splash waveSplash wave

Coastal landslides, calving icebergs

Seismic sea wave or Seismic sea wave or tsunamitsunamiSea floor movement

TidesTidesGravitational

attraction among Moon, Sun, and Earth

WakeWakeShips

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

Wave motion Waves transmit energy by

oscillating particles Cyclic motion of particles in

oceanParticles may move

○ Up and down○ Back and forth○ Around and around

Particles in ocean waves move in orbital pathsorbital paths

Progressive waves• Waves that travel without breaking• Types

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

• soundsound• TransverseTransverse – back and forth motion

• Only in solidsOnly in solids• OrbitalOrbital

• Combination of longitudinal and transverse• around and around motion at interface of two fluids

Orbital or interface wavesOrbital or interface waves Waves on ocean surface at water/air interface Crest, trough, wave height (H)Crest, trough, wave height (H) Wavelength (L)Wavelength (L)

Orbital waves Wave characteristics

Wave steepnessWave steepness = ratio of wave height to wave length H/L○ If wave steepness > 1/7, wave breaks

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

Wave frequencyWave 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

Orbital motion

Diameter of orbital motion decreases with depth of water

Wave baseWave base = ½ LHardly any motion below wave base due to

wave activity

Fig. 8.3C

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

wavelengthLonger 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 wavesCapillary waves (ripples) formed first

Rounded crests, very small wavelengthsProvide “grip” for the wind

Increasing energy results in gravity wavesgravity wavesSymmetrical waves with longer wavelengths

Wave development Increasing energy results in trochoidal trochoidal

waveformswaveformsCrests pointed, troughs rounded, greater wave

heights

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

www.poemsinc.org/ oceano/waves.htm

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

http://plaza.ufl.edu/mrosenme

Ripples

Choppy seas

Fully-developed Sea

Swell

Wave energy Factors that control wave energy

Wind speedWind speedWind durationWind durationFetchFetch – 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 seaFully developed sea

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

SwellSwellUniform, symmetrical

waves that travel outward from storm area

Long, rounded crests Transport energy long

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

Swell Longer wavelength

waves travel faster and outdistance other waves

Wave train Wave train = group of waves with similar characteristics

Sorting of waves by their wavelengths is wave dispersionwave dispersion

Wave train speed is ½ speed of individual wave

Wave interference patterns Different swells coming

together Constructive interferenceConstructive interference

In-phase wave trains with about the same wavelengths

Add to wave height Rogue wavesRogue waves – unusually

large waves○ Rare but can happen and

be unusually large

Wave interference patterns Destructive Destructive

interferenceinterferenceOut-of-phase wave

trains with about the same wavelengths

At least partially cancel out waves

Mixed interferenceMixed interferenceTwo swells with

different wavelengths and different wave heights

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

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

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://www.allhatnocattle.net

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)

Largest rogue wave rogue 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

- 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

• Storm surges • Large wave moving with a storm (not just

hurricanes)• Low pressure above water water level

rises at center

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 shallow-water waves (< L/2)

Wave base “touches” sea bottom

Waves approach shore

During transition to shallow-water waves Wave speed and wavelength decreasesWave height and steepness increasesWaves breakPeriod 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 floorWave 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 floorSpillingPlunging 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

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

WindOnshore

Plunging breaker

Curling crest Moderately steep sea

floor Wind “offshore” Wave energy

expended over shorter distance

Best for surfers

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

Wind

Offshor

e

http:// www.mikeladle.com

http://www.winona.edu/geology/oceanography http://www.seagrant.umn.edu/seiche/2002

Wind

Wind

Onshore

Offshor

e

Wind

Onshore

Wind

Offshore

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/

SurfSurf – nearly continuous breaking waves parallel to shore Breakers may reach 30-50 m high 14 m high breakers can move 2600 ton

blocks

horsesmouth.journalspace.com

About 10 m high

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

• SurfSurf beatbeat• SetsSets – series from relative calm to largest

waves• Interference in wave train cancel some,

adds to others• Destructive interference lull “between

sets”

Area of destructive interference

(lull)

Area of constructive interference

(set)

Area of destructive interference

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

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

Rip currents 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

Wave energy distribution at shoreline

Fig. 8.17b

Energy focused on headland Headland eroded

Energy dissipated in bay Bay filled up with sediment

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

www.jpl.nasa.gov/news

Landsat image before tsunami: 13-Dec. 2004

Landsat image after tsunami: 29-Dec. 2004

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

www.jpl.nasa.gov/news

** Note impacted area corresponds to 10 m contour

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 harborsWater “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 plantsHow to produce power consistently

Environmental issuesBuilding power plants close to shoreInterfering 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.