chapt09gh - Chapter 9 Circulation of the Ocean Surface...

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Chapter 9 Circulation of the Ocean Surface Currents Are Driven by the Winds The westerlies and the trade winds are two of the winds that drive the ocean’s surface currents. About 10% of the water in the world ocean is involved in surface currents , water flowing horizontally in the uppermost 400 meters (1,300 feet) of the ocean’s surface, driven mainly by wind friction. (left) Winds, driven by uneven solar heating and Earth’s spin, drive the movement of the ocean’s surface currents. The prime movers are the powerful westerlies and the persistent trade winds (easterlies). Surface Currents What are some effects of ocean currents? Transfer heat from tropical to polar regions Influence weather and climate Distribute nutrients and scatter organisms Surface currents are driven by wind: Most of Earth’s surface wind energy is concentrated in the easterlies and westerlies. Due to the forces of gravity, the Coriolis effect, solar energy, and winds, water often moves in a circular pattern called a gyre. Surface Currents Are Driven by the Winds A combination of four forces – surface winds, the sun’s heat, the Coriolis effect, and gravity – circulates the ocean surface clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, forming gyres. The North Atlantic gyre, a series of four interconnecting currents with different flow characteristics and temperatures. Surface Currents Flow around the Periphery of Ocean Basins Surface water blown by the winds at point A will veer to the right of its initial path and continue to the east. Water at point B veers right and continues to the west. Wind Surface water Net Direction of Ekman transport 4 5 ° Direction of motion Friction
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The Ekman spiral and the mechanism by which it operates. Surface Currents Flow around the Periphery of Ocean Basins 90 ° to the right of wind direction is up here At 15 ° N 3 0 ° 4 5 T r a d e w i n Stepped Art Fig. 9-6, p. 237 The effect of Ekman spiraling and the Coriolis effect cause the water within a gyre to move in a circular pattern. The movement of water away from point B is influenced by the rightward tendency of the Coriolis effect and the gravity- powered movement of water down the pressure gradient. Surface Currents Flow around the Periphery of Ocean Basins Surface Currents Flow around the Periphery of Ocean Basins The surface is raised through wind motion and Ekman transport to form a low hill. The westward-moving water at B ‘feels’ a balanced pull from two forces: the one due to Coriolis effect (which would turn the water to the right) and the one due to the pressure gradient, driven by gravity (which would turn it to the left). The hill is formed by Ekman
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This note was uploaded on 07/18/2011 for the course EARTH SCIE 180 taught by Professor Frankbuonaiuto during the Spring '11 term at CUNY Hunter.

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chapt09gh - Chapter 9 Circulation of the Ocean Surface...

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