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Generalized Surface Circulation

A

A

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Nansen’s Trip in the “frozen” Fram (1893-96)

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Nansen’s Observations about Surface Currents

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Ekman’s Force Balance

Current direction is to the right of the wind in N. Hemisphere

Wind

Coriolis

Drag

Current

Walfred Ekman

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Ekman’s Three Force Vector Balance(in the northern hemisphere)

Wind Stress Force

Current Direction (not a force)

Coriolis Force (always perpendicular to the Current direction)

Frictional Force (always opposes direction of current)

Resulting Force

(the combination of the Coriolis Force and Frictional Force yields a Resulting force that is equal to and in opposite direction to the Wind Stress Force)

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Ekman Spiral

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Ekman Spiral Observations(surface layer in the N. Atlantic)

Wind Direction

Measured Current Directions and Velocities at 5, 10, 15 and 25 m depths

8

Generalized Pattern of

Surface Winds

July

January

Arrows indicate direction of Ekman Transport

9

Map of Sea Surface Height (ARGO floats) (in dynamic cms relative to 1500 dbar)

Sea surface height range is ~300cm or 3 m.

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Pressure

P = g ρ Z

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Horizontal Pressure Gradients

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Geostrophic Force

Balance

13

Geostrophic Current Flow around a dome of pressure

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Sea Surface Height Anomaly (dynamic centimeters)

(Arrows represent direction of geostrophic current flow)

(dynamic height is relative to 1000dbar)

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Barotropic and Baroclinic Conditions

Size of arrow indicates speed of current

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Depth Profile of Typical Geostrophic Current Velocity

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Cross Section of Density in Pacific Ocean

What meridional trend in sea surface height would be implied under baroclinic conditions?

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Phosphate Distribution in Surface Ocean

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Chlorophyll in the Surface Ocean

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Gulf Stream

Franklin’s map of Gulf Stream and ‘gyre’ in 1785

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Temperature and Salinity

Sections across the

Gulf Stream

Pot. Temp.

Salinity

22

Current Velocities in the Region of the Gulf Stream

White= northward flow

Blue = southward flow

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Sea Surface Temperatures and Major Warm and Cool Currents

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Gulf Stream Rings

Gulf Stream Ring Movie

picture of SST observed from satellites

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Temperature Anomalies of Gulf Stream Rings