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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