Oceans IIOceans II

Surface CurrentsSurface Currents

Heat VariationsHeat VariationsLatitudeLatitude

• Depends on angle sunlight hits surfaceDepends on angle sunlight hits surface

– At equator, sunlight covers less area; more At equator, sunlight covers less area; more heat heat

– Sunlight at polar latitudes covers wider area; therefore, Sunlight at polar latitudes covers wider area; therefore, less heatless heat

Heat TransferHeat Transfer

• Heat is transferred from equator to polesHeat is transferred from equator to poles– Air CirculationAir Circulation– Ocean currentsOcean currents

Origin of CurrentsOrigin of Currents

•Ocean surface currents are wind drivenOcean surface currents are wind driven

• Air movement due to Air movement due to less denseless dense air rising and air rising and more more densedense air sinking air sinking

• Horizontal air flow along Earth’s surface is Horizontal air flow along Earth’s surface is windwind• Air circulating in this manner is Air circulating in this manner is convection currentsconvection currents

Wind MovementWind MovementNon-rotating EarthNon-rotating Earth

•Simple wind patternSimple wind pattern– Warm air rises at equator, flows toward polesWarm air rises at equator, flows toward poles– Air cools at poles, sinks, and flows toward equatorAir cools at poles, sinks, and flows toward equator

• Winds named by direction Winds named by direction fromfrom which they blow which they blow– North-blowing winds = southerly windsNorth-blowing winds = southerly winds– South-blowing winds = northerly windsSouth-blowing winds = northerly winds

Wind MovementWind MovementRotating EarthRotating Earth

•At equator, warm air risesAt equator, warm air rises– Zone of low pressureZone of low pressure

– Clouds and precipitationClouds and precipitation

– Reaches troposphere Reaches troposphere and moves polewardand moves poleward

– As it spreads, it As it spreads, it coolscools• 3030° N&S, cool air sinks° N&S, cool air sinks

– Area of high pressureArea of high pressure

– Dry conditionsDry conditions

– Location of world desertsLocation of world deserts

• 60° N&S, air masses meet60° N&S, air masses meet– Form Form Polar FrontPolar Front– Air masses rise, diverge Air masses rise, diverge

and sink @ 90° and 30° and sink @ 90° and 30° N&SN&S

Wind MovementWind Movement

• Air that sinks does not flow back in a straight north-south Air that sinks does not flow back in a straight north-south path – it curves (Coriolis Effect)path – it curves (Coriolis Effect)

• At equator, warm air rises, condenses and precipitatesAt equator, warm air rises, condenses and precipitates

• At 30° and 90°, cool air sinksAt 30° and 90°, cool air sinks

Rotation on a GlobeRotation on a Globe

• Buffalo and Quito located on same line of Buffalo and Quito located on same line of longitude longitude (79ºW)(79ºW) • Both cities circles the globe in one day (360Both cities circles the globe in one day (360º/º/24 hours = 1524 hours = 15º/1 hour)º/1 hour)• Quito has larger circumference; thus, travels fartherQuito has larger circumference; thus, travels farther

• Quito needs to travel faster than BuffaloQuito needs to travel faster than Buffalo

Apparent DeflectionApparent Deflection• Hypothetical war gameHypothetical war game

• If a cannonball is shot If a cannonball is shot north from Quitonorth from Quito

• It will travel a straight pathIt will travel a straight path

• But, because Earth is But, because Earth is rotating east to westrotating east to west

• The cannonball appears The cannonball appears to veer to the right in to veer to the right in Northern HemisphereNorthern Hemisphere

• This is the Coriolis EffectThis is the Coriolis Effect

Wind MovementWind MovementCoriolis EffectCoriolis Effect

•Deflected winds due to Deflected winds due to movement over spinning movement over spinning objectobject

• In Northern Hemisphere:In Northern Hemisphere:

• In Southern Hemisphere:In Southern Hemisphere:

– Winds are deflected to the rightWinds are deflected to the right

– Travel clockwise around high PTravel clockwise around high P

– Winds are deflected to the leftWinds are deflected to the left

– Travel counter-clockwise Travel counter-clockwise around high Paround high P

–Produce wind bandsProduce wind bands

Assume water-covered Earth

Surface Current CirculationSurface Current Circulation

WavesWaves

• Transport energy over a body of waterTransport energy over a body of water

Wave TerminologyWave Terminology

•Still water line – level of ocean if it were flat w/o wavesStill water line – level of ocean if it were flat w/o waves• Crest – highest part of waveCrest – highest part of wave• Trough – lowest part of waveTrough – lowest part of wave

• Amplitude – distance between crest and still water lineAmplitude – distance between crest and still water line• Wave height (H) – vertical distance between crest and troughWave height (H) – vertical distance between crest and trough

• Wavelength (L) – horizontal distance from each crest or each Wavelength (L) – horizontal distance from each crest or each troughtrough

– ½ the wave height½ the wave height

– Or any point with the same successive pointOr any point with the same successive point

Still water lineHeight

• Steepness = Height (H)/length (L)Steepness = Height (H)/length (L)

Wave ParametersWave Parameters

•Period (T) – the time it takes for two successive Period (T) – the time it takes for two successive waves to pass a particular pointwaves to pass a particular point

• Frequency (f) – the # of waves that pass a Frequency (f) – the # of waves that pass a particular point in any given time periodparticular point in any given time period

Deep Water WaveDeep Water WaveMotionMotion

•Water particles move in orbitsWater particles move in orbits

• Particle motion ceases at ½ Particle motion ceases at ½ wavelengthwavelength

• Diameter of orbits decrease with Diameter of orbits decrease with depthdepth

• Waves transmit energy, not water massWaves transmit energy, not water mass

Shallow Water WavesShallow Water Waves

3. Orbits progressively flatten at depth3. Orbits progressively flatten at depth

6. Just above seafloor particles move in back-and-forth motion6. Just above seafloor particles move in back-and-forth motion

4. Wave height (H) increases and wavelength (L) decreases4. Wave height (H) increases and wavelength (L) decreases

1. Swell feels bottom at depth < ½ wavelength1. Swell feels bottom at depth < ½ wavelength2. Wave crest peaks and wave slows2. Wave crest peaks and wave slows

5. Wave breaks when H/L ratio > 1/75. Wave breaks when H/L ratio > 1/7

Breaking WavesBreaking Waves

TsunamiTsunamiCharacteristicsCharacteristics

•Shallow water waveShallow water wave

• Energy passes through Energy passes through entire water columnentire water column

• Long periods (T)Long periods (T)

• long wavelengths (L)long wavelengths (L)

• Travel at great speedsTravel at great speeds

• Deep wave baseDeep wave base

– T = 10-20 min.T = 10-20 min.

– L = 100-200 kmL = 100-200 km

– c = 200 m/sc = 200 m/s

• Small Height (H)Small Height (H)–H = 1-2 mH = 1-2 m

TsunamiTsunamiCrest and TroughCrest and Trough