waves, tides, and currents revised
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Waves, Tides, and CurrentsWaves, Tides, and Currents
Chapter 16.2Chapter 16.2
MOTIONMOTION IN THE IN THE OCEANOCEAN
WavesWaves A disturbance which A disturbance which
moves through or moves through or over the surface of a over the surface of a fluidfluid
Mostly caused by Mostly caused by windswinds
(Also earthquakes, (Also earthquakes, volcanoes, grav. volcanoes, grav.
pull)pull)
Form of great energyForm of great energy
Wave CharacteristicsWave Characteristics
Parts of a WaveParts of a Wave CrestCrest = high point = high point
TroughTrough = low point = low point
HeightHeight = vertical = vertical distance from crest to distance from crest to troughtrough
WavelengthWavelength = = Horizontal distance Horizontal distance between crest to crest between crest to crest or trough to troughor trough to trough
Wave period : time for 2 crests to pass fixed point (T) sec
Wave speed (C) : C = wavelength / T (m/s)
Wave steepness : H / wavelength
When H / wavelength = 1/7 or angle at crest 120 or less = Breaker
Size of Wind Generated Size of Wind Generated WavesWaves
Depends on 3 thingsDepends on 3 things:: Wind SpeedWind Speed Wind Duration (length of Wind Duration (length of
time wind blows)time wind blows) ““Fetch” Extent of open Fetch” Extent of open
water across which the water across which the wind can blowwind can blow
Water Motion in WavesWater Motion in Waves
Water travels in vertical Water travels in vertical circular orbitscircular orbits
Wave moves, particles don’t!Wave moves, particles don’t!
Importance of WavesImportance of Waves
Shaping Shaping CoastlinesCoastlines Erode cliffsErode cliffs Grind rock into sandGrind rock into sand
EcologyEcology Returns OReturns O
2 2 to waterto water Stir up food for filter Stir up food for filter
feedersfeeders
Types of WavesTypes of Waves
CHOP – Short period (back bays)
SWELL – Long period (boat rolls; seasickness)
SWASH – water up beach BACKWASH – back down
Caused by undersea quake or volcano
• Wavelength = ~150 mi. Wave height = 6” – 1’
Can NOT perceive in boat Speed > 500 mph
Slows down to ~25 mph at shore; water builds up to ~65+ ft
TSUNAMI “TIDAL WAVE”
Tsunami Waves
Creation of a TsunamiCreation of a Tsunami
TidesTides The rhythmic rise and The rhythmic rise and
fall of the ocean’s waterfall of the ocean’s water
High tide = rising, incoming tide, flow
Low tide = receding, outgoing tide, ebb
Slack tide = vertical movement stops
Tides are very long, Tides are very long, slow wavesslow waves
They have a wave They have a wave period of 12 hours 25 period of 12 hours 25 minmin
Tidal day is 24 hours Tidal day is 24 hours 50 min50 min
NJ has 2 high and 2 NJ has 2 high and 2 low tides dailylow tides daily
1. Gravitational pull of 1. Gravitational pull of sun & moon on Earthsun & moon on Earth
What Causes Tides?What Causes Tides?
• Moon closer, therefore > effect
• Like magnet, pulls water away from surface = TIDAL BULGE
2. Centrifugal Forces
• Produced by motions of Earth, sun, & moon
• Bulge on opposite side because centr. force > pull of moon
Types of TidesTypes of Tides
2x’s/month2x’s/month
•Spring Tide - Moon and sun are in direct
line with one another- Results in unusually
high tidal range
-Tidal Range = vertical distance between high & low tides
Neap TideNeap Tide sun and moon are at sun and moon are at
right angles right angles
Pulls cancel each Pulls cancel each other out – causes a other out – causes a weak pullweak pull
unusually low tidal unusually low tidal rangerange
2 x’s / month2 x’s / month
Spring vs. Neap TidesSpring vs. Neap Tides
Distance bet. Moon & Distance bet. Moon & EarthEarth
Perigee TidesPerigee Tides• Moon closest to earth, very high tides (causes Moon closest to earth, very high tides (causes
flooding)flooding)
Apogee TidesApogee Tides• Moon farthest away from earth, very low tidesMoon farthest away from earth, very low tides
Types of Tides ContinuedTypes of Tides Continued Diurnal TidesDiurnal Tides
1 high & 1 low / day1 high & 1 low / day Parts of Gulf of Mexico and AsiaParts of Gulf of Mexico and Asia
Semi-Diurnal TidesSemi-Diurnal Tides 2 high & 2 low / day2 high & 2 low / day Atlantic coasts of North America and EuropeAtlantic coasts of North America and Europe
MixedMixed 2 high & 2 low / day (height varies)2 high & 2 low / day (height varies) Pacific coastPacific coast
Importance of TidesImportance of Tides
• Expose & submerge orgs
• Circulate water in bays & estuaries
• Trigger spawning (grunion, horseshoe crab)
• Circulates food, wastes, etc
CurrentsCurrents• What are currents?
- “Rivers” of circulating water
• Causes- Wind
- Rotating Earth
- Density Changes
Surface Ocean CurrentsSurface Ocean Currents
• Broad, slow drifts; never cross equator
• Wind generated; circular gyres
• Coriolis Effect
- N. Hemis – clockwise; Right
- S. Hemis – counterclockwise; Left
• Gulf Stream
- Brings warm water from equator north along east coast of N. A.
- N. Atlantic
-Sometimes form eddies – circulating water that pinches off from the current
MIGRATION NAVIGATION
WEATHER
Localized Surface Localized Surface CurrentsCurrents
Longshore CurrentLongshore Current..
Flows parallel to shore; move sedimentFlows parallel to shore; move sediment
RIP CURRENT
- Caused by converging longshore currents
- Very dangerous ; Red Flag
- DO NOT fight rip current; swim parallel to shore to get out of channel
Deep Ocean CurrentsDeep Ocean Currents
Separated from surface Separated from surface currents by boundary currents by boundary called a “called a “ThermohalineThermohaline” ” (diff in densities)(diff in densities)
Flow beneath surface; cross Flow beneath surface; cross equatorequator
Move North to SouthMove North to South
Importance Of Deep Importance Of Deep CurrentsCurrents UpwellingUpwelling
• Brings deep water to surf.Brings deep water to surf.• Circulates nutrients upCirculates nutrients up• Moves plankton & larvaeMoves plankton & larvae