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Tides!!!!!!!!!!!

Tides!!!!!!!!!!!. Tides. Periodic, short-term changes in ocean height. What causes tides?. Gravitational force of the sun and moon. Sun is 27 million times more massive than the moon…. But the sun is 387 times farther away.

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Tides!!!!!!!!!!!

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  1. Tides!!!!!!!!!!!

  2. Tides • Periodic, short-term changes in ocean height

  3. What causes tides? • Gravitational force of the sun and moon

  4. Sun is 27 million times more massive than the moon…

  5. But the sun is 387 times farther away

  6. Distance plays a larger role than the masses of the bodies involved

  7. Tidal Range • The difference in ocean level between high and low tide

  8. The monthly tidal cycle(29½ days) • About every 7 days, Earth alternates between: • Spring tide • Alignment of Earth-Moon-Sun system (syzygy) • Lunar and solar bulges constructively interfere • Large tidal range • Neap tide • Earth-Moon-Sun system at right angles (quadrature) • Lunar and solar bulges destructively interfere • Small tidal range

  9. Spring Tides • Earth, Moon, and Sun are lined up • High Tides are higher and Low Tides are lower than normal

  10. Neap Tides • Earth, Moon, and Sun form right angles • High Tides are lower and Low Tides are higher than normal

  11. Variations in tidal form world wide

  12. Tidal patterns • Diurnal • One high and one low tide each (lunar) day • Semidiurnal • Two high and two low tides of about the same height daily • Mixed • Characteristics of both diurnal and semidiurnal with successive high and/or low tides having significantly different heights

  13. Variable Tides

  14. Monthly tidal curves Figure 9-16

  15. semidiurnal Mixed, SD dominant Mixed, D dominant diurnal

  16. The Bay of Fundy: Site of the world’s largest tidal range • Tidal energy is focused by shape and shallowness of bay • Maximum spring tidal range in Minas Basin = 17 meters (56 feet) Figure 9-17

  17. Bay of Fundy High tide Low tide (6 hours later) Video Clip: http://www.youtube.com/watch?v=qfhNjpu_IU4

  18. St. Michel, N. coast of France ~16.8 m highest tidal range in Nova Scotia

  19. Coastal tidal currents • Tidal currents occur in some bays and rivers due to a change in tides • Ebb currents produced by outgoing tides • Flood currents produced by incoming tides Figure 9-18

  20. Tidal bore = a true tidal wave • Wall of water that moves upriver • Caused by an incoming high tide • Occurs in some low-lying rivers • Can be large enough to surf or raft Figure 9B Video Clips: http://www.youtube.com/watch?v=LWumonz87rA http://www.youtube.com/watch?v=IKA39LQOIck

  21. Grunion and the tides • Grunion are the only fish that come completely out of water to spawn • Spawning cycles are timed precisely with the tides Figure 9C Video Clip: http://www.youtube.com/watch?v=udRDj2Ez8kI

  22. Sites with high potential for tidal power generation Figure 9-19

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