The Ocean General Circulation. Mean Circulation in the Ocean Gulf Stream.

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Presentation transcript:

The Ocean General Circulation

Mean Circulation in the Ocean Gulf Stream

Mean Circulation in the Ocean Gulf Stream California Current Oceans are filled with energetic eddies!!!

Gulf Stream, Plankton Bloom

Gulf Stream Spiral Eddies

Mediterranean Sea, Shear Wall Spiral Eddies

Tropical Atlantic, Spiral Eddy

Greek Island, Spiral Eddies and Wakes

Strait of Gibralter, Solitons

Eastern Pacific Internal Waves

Kelvin Wakes, from Ships

Coastal Dynamics California Filaments and Phytoplankton Hawaiian Island Wakes

Key questions: How does the wind drive surface currents? What drives oceanic gyres? What is Ekman transport? What drives upwelling and downwelling? Ocean wind driven circulation

Atmospheric winds “Hadley” regime Subtropical high Intertropical convergence zone (ITCZ) “Eddy” regime Variable weather Westerly wind

How is the energy of the winds transferred to the ocean? Ekman Theory …

How does wind force propagate in the ocean? surface balance between friction and rotation

F WIND F Coriolis 1)Surface water is pushed by the atmospheric wind 2)Coriolis force acting on surface current balances the wind stress 3)Surface current (averaged over tens of meters) points to the right of the direction of the wind Ekman transport: Balance between wind and Coriolis force Ekman transport Wind direction

What would happen to the Ekman transport under the cyclonic atmospheric circulation? L Wind stressEkman transport Ekman upwelling under cyclonic circulation

What would happen to the Ekman transport under the anti-cyclonic atmospheric circulation? H Wind stressEkman transport Ekman pumping under anti-cyclonic circulation

Ocean temperature structure Atlantic Ocean Temperature structure in the top 1,000m What controls this structure? H H L

Ekman Theory …and vertical advection in the ocean COASTAL UPWELLING and DOWNWELLING OPEN OCEAN EKMAN PUMPING

Subtropical “ocean gyre” is a geostrophic circulation 1)Atmospheric high pressure  Anti-cyclonic wind stress 1)Ekman transport converges toward the middle, raising up the sea surface slightly 2)Pressure force drives the geostrophic gyre circulation

F pressure F Coriolis 1)Particle will have the Coriolis force 90 degrees to the right 2)Particles will tend to move along line of constant pressure 3)Particles will have the high pressure on their right (same as Coriolis) Balance of forces: geostrophic balance High Pressure Low Pressure Applies to the Ocean same as Atmosphere!

Effects of Ekman Currents

Ocean general circulation

Heat transport by the ocean circulation

Regional circulation: Coastal upwelling

Equatorial upwelling