Chapter 8

Chapter 8 - Ch. 8: Ocean Circulation 2 Main types of...

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Unformatted text preview: Ch. 8: Ocean Circulation 2 Main types of currents Surface currents (< 1 km below surface)-wind driven (via friction at air-water interface)-ocean currents generally follow major wind belts on Earth-measured by tracking devices, accidental flotsam, satellites, propellers Density (gravity) currents-driven by temperature and salinity-measured by chemical tracers Radio-transmitted floating current tracking devices Propeller-based current meter (direction and speed) Objects accidentally spilled into the sea also have been used to track currents Satellite-derived data showing changes in topography over one year period; surface currents can be deduced from these changes in topography (shown with white arrows) Trade winds Westerlies Ocean currents Prevailing winds drive surface ocean circulation Boundary currents are guided by prevailing winds, shape of continents and Coriolis effect (to the right in N. Hemisphere, left in S. Hemisphere) Cool currents (blue) come from high latitude, warm (red) from low latitude. 5 subtropical gyres defined by circular currents: N. Atlantic Gyre; S. Atlantic Gyre; N. Pacific Gyre; S. Pacific Gyre; Indian Ocean Gyre Gyres rotate clockwise in N. hemisphere, counterclockwise in the S. hemisphere. Why? Fridtjof Nansen noticed that floating objects were generally carried to the right of wind direction in the N. hemisphere. Coriolis effect causes wind to drive objects at ~45 degrees angle to the right in N. hemsiphere. This deflection is propagated with depth as the successive depth layers interact with one another. Net deflection is about 90 deg to the right in N. hemisphere. Ekman Spiral Geostrophic Flow Coriolis effect causes water to pile up in the center of a gyre (up to 2 m). Gravity flow down the side of the bulge balances the Coriolis effect, resulting in idealized net flow around the base of the bulge called geostrophic flow. Because of friction, actual geostrophic flow is slightly down hill on the bulge....
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Chapter 8 - Ch. 8: Ocean Circulation 2 Main types of...

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