Post on 20-Jan-2016
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Ocean Surface Circulation
Ocean Surface Circulation
Motion in the Ocean, Part I, or Why does the ocean have currents, and
why do they move in circles?
Motion in the Ocean, Part I, or Why does the ocean have currents, and
why do they move in circles?
Two types of Ocean Circulation:
Two types of Ocean Circulation:
Surface Circulation -- Wind-driven
Deep Circulation -- Density (T,S) driven
Surface Circulation -- Wind-driven
Deep Circulation -- Density (T,S) driven
Atmospheric CirculationAtmospheric Circulation
Temperature and Pressure
Temperature and Pressure
As the Earth’s surface is heated, air is warmed, expands and rises (Low P)
Warm air carries water vaporIn the upper atmosphere the air cools and sinks (High P)
This round-trip is called a “cell”
As the Earth’s surface is heated, air is warmed, expands and rises (Low P)
Warm air carries water vaporIn the upper atmosphere the air cools and sinks (High P)
This round-trip is called a “cell”
Things get interesting!Things get
interesting!On a rotating planet, moving objects appear to be deflected
Why is this?
On a rotating planet, moving objects appear to be deflected
Why is this?
Coriolis Deflection (aka “I Could Care Less”
force)
Coriolis Deflection (aka “I Could Care Less”
force)Apparent force due to Earth’s rotation
Deflection in path of motion when viewed from a rotating reference frame
Gustave-Gaspard Coriolis (1835)Familiar from merry-go-roundsSignificant only for large distances (not toilets and billiards!)
Apparent force due to Earth’s rotation
Deflection in path of motion when viewed from a rotating reference frame
Gustave-Gaspard Coriolis (1835)Familiar from merry-go-roundsSignificant only for large distances (not toilets and billiards!)
Coriolis DeflectionCoriolis Deflection
Consequences of Coriolis
Consequences of Coriolis
Moving fluids (atmosphere and ocean) turn to the right in the Northern Hemisphere
Moving fluids (atmosphere and ocean) turn to the left in the Southern Hemisphere
Moving fluids (atmosphere and ocean) turn to the right in the Northern Hemisphere
Moving fluids (atmosphere and ocean) turn to the left in the Southern Hemisphere
Global Wind CirculationGlobal Wind Circulation
Wind-Driven Ocean Circulation
Wind-Driven Ocean Circulation
Steady winds produce waves and set the surface water in motion
Moving water is deflected to the right (N.Hemisphere) or left (S.Hemisphere)
This starts the main “gyre” motion of the surface ocean
Steady winds produce waves and set the surface water in motion
Moving water is deflected to the right (N.Hemisphere) or left (S.Hemisphere)
This starts the main “gyre” motion of the surface ocean
Surface Ocean Circulation
Surface Ocean Circulation
Main FeaturesMain Features
Five large gyresAntarctic Circumpolar CurrentEquatorial CountercurrentVelocities vary -- fastest are meters/sec
Five large gyresAntarctic Circumpolar CurrentEquatorial CountercurrentVelocities vary -- fastest are meters/sec
106 m3/sec (Sverdrup) = all the rivers
106 m3/sec (Sverdrup) = all the rivers
Gulf Stream - Benj Franklin
Gulf Stream - Benj Franklin
Gulf StreamGulf Stream
So, do the gyres just follow the
winds?
So, do the gyres just follow the
winds?Not exactly! But the winds get the motion in the ocean started
The oceans respond by flowing and turning
Water piles up in the center of gyres -- several meters high
Not exactly! But the winds get the motion in the ocean started
The oceans respond by flowing and turning
Water piles up in the center of gyres -- several meters high
Ekman Transport -- moves water 90° to the
winds
Ekman Transport -- moves water 90° to the
winds
Upwelling and Oregon’s Ocean
Upwelling and Oregon’s Ocean
Winter winds from the south -- downwelling
Summer winds from the north -- upwelling
Winter winds from the south -- downwelling
Summer winds from the north -- upwelling
Winter SummerWinter Summer
Global Wind CirculationGlobal Wind Circulation
Geostrophic CurrentsGeostrophic Currents
Coriolis deflection plus the Pressure Gradient steers the currents around
the gyres
Coriolis deflection plus the Pressure Gradient steers the currents around
the gyres
Northern Hemisphere Gyres
Northern Hemisphere Gyres
Surface CirculationSurface Circulation
How do we track ocean circulation?
How do we track ocean circulation?
Fixed Buoys -- measure current speed and direction
Drifters -- travel with the currents and transmit their location
Fixed Buoys -- measure current speed and direction
Drifters -- travel with the currents and transmit their location
Beach Swap Meets!Beach Swap Meets!
Tracking Currents:The Story of the Lost
Nikes
Tracking Currents:The Story of the Lost
Nikes 1: 60,000 shoes spilled, May 1990
2-8: 1990-’91 9: 1993 10: 1994
1: 60,000 shoes spilled, May 1990
2-8: 1990-’91 9: 1993 10: 1994
Marine Debris: Pacific Trash
Marine Debris: Pacific Trash
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.QuickTime™ and a
TIFF (Uncompressed) decompressorare needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
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