Gulf stream, recirculation, and Gulf stream, recirculation, and other western boundary layer other western boundary layer currents currents

• 1. the Gulf Stream1. the Gulf Stream

• 2. the coriolis force ant the gyre2. the coriolis force ant the gyre

• 3.the western boundary current layer3.the western boundary current layer

The Gulf StreamThe Gulf Stream• powerful, warm, and powerful, warm, and

swift Atlantic ocean swift Atlantic ocean current current

• originates in the Gulf originates in the Gulf of Mexico, follows the of Mexico, follows the eastern coastlines of eastern coastlines of the United States, the United States, and exits through the and exits through the Strait of Florida. Strait of Florida.

The Gulf StreamThe Gulf Stream• Modifying influence of the climate Modifying influence of the climate

of the east cost of north America. of the east cost of north America. • extension toward Europe,(North extension toward Europe,(North

Atlantic drift): Western Europe Atlantic drift): Western Europe warmer. warmer.

• For example, in January, the For example, in January, the temperature difference between temperature difference between coastal Norway and northern coastal Norway and northern parts of continental Canada is parts of continental Canada is approximately 30 °C on average, approximately 30 °C on average, even if they are the same even if they are the same latitude.latitude.

The Gulf StreamThe Gulf Stream• Finally, the Gulf Stream is one of the Finally, the Gulf Stream is one of the

strongest ocean currents known: strongest ocean currents known: • transporting 1.4 petawatts of power. transporting 1.4 petawatts of power. • moves at a rate of 30 million cubic meters moves at a rate of 30 million cubic meters

per second. per second. • The volume of the Gulf Stream dwarfs all The volume of the Gulf Stream dwarfs all

rivers that empty into the Atlantic rivers that empty into the Atlantic combined, which barely total 1 million cubic combined, which barely total 1 million cubic meters per second.meters per second.

The Coriolis force and the The Coriolis force and the GyreGyre

HistoricallyHistorically

• Some early writers thought the mighty Some early writers thought the mighty Mississippi River empties in the Gulf of Mexico, Mississippi River empties in the Gulf of Mexico, and from there become the Gulf Streamand from there become the Gulf Stream

• Later, Benjamin Franklin understood that Later, Benjamin Franklin understood that winds were the supreme current-producing winds were the supreme current-producing power in the sea. power in the sea.

• In the middle of the 19th century, Commander In the middle of the 19th century, Commander M.F Maury understood, that M.F Maury understood, that the currents do the currents do not invariably follow the windsnot invariably follow the winds, but run at , but run at right angles, or even against the windright angles, or even against the wind

The Coriolis ForceThe Coriolis Force• Every moving object Every moving object

responds to the responds to the ""Coriolis forceCoriolis force." ."

• In the northern In the northern hemisphere the hemisphere the Coriolis force always Coriolis force always deflects objects to the deflects objects to the right.right.

• In the southern In the southern hemisphere the hemisphere the Coriolis force deflect Coriolis force deflect objects to the left.objects to the left.

The GyreThe Gyre• Trade winds set up a large-Trade winds set up a large-

scale gyre motion of surface scale gyre motion of surface waters in each ocean basin, waters in each ocean basin, centered roughly on the tropics centered roughly on the tropics of Cancer and of Capricorn.of Cancer and of Capricorn.

• Because of the Coriolis force, Because of the Coriolis force, surface water is deflected surface water is deflected toward the interior of the gyres toward the interior of the gyres

• if the wind should cease, the if the wind should cease, the water will attempt to run water will attempt to run downhill from the center of the downhill from the center of the gyre, and be deflected by the gyre, and be deflected by the Coriolis forceCoriolis force

• The gyre keeps turning, while The gyre keeps turning, while balancing the forces of gravity balancing the forces of gravity with those of the Coriolis forcewith those of the Coriolis force

Western boundary current Western boundary current layerlayer

• The Gulf Stream is just a portion of the circle of the North Atlantic Current The Gulf Stream is just a portion of the circle of the North Atlantic Current

• Why is it so strong compared to its symmetric towards Europe costs?.  Why is it so strong compared to its symmetric towards Europe costs?.  

The asymmetryThe asymmetry• Coriolis: f=2*W*sin(theta)Coriolis: f=2*W*sin(theta)

• Define Beta:Define Beta:

• 3 attemps to explain: limit condition in PDEs3 attemps to explain: limit condition in PDEsSverdrupSverdrupStommelStommelMunkMunk

Sverdrup’s theory of the Sverdrup’s theory of the Oceanic CirculationOceanic Circulation

Stommel theory of Western Stommel theory of Western boundary currentsboundary currents• He adds a botom stress proportional to velocityHe adds a botom stress proportional to velocity• Coriolis depending or not on latitude explains Gulf Coriolis depending or not on latitude explains Gulf

StreamStream

Munk’s solutionMunk’s solution• He adds lateral frictionHe adds lateral friction

Thanks, may I help you?Thanks, may I help you?