Tides!!!!!!!!!!!
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Tides!!!!!!!!!! !
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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. - PowerPoint PPT Presentation
Transcript of 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
•Distance plays a larger role than
the masses of the bodies involved
Tidal Range
• The difference in ocean level between high and low tide
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 interfereLarge tidal range
Neap tideEarth-Moon-Sun system at right angles (quadrature)Lunar and solar bulges destructively interfereSmall tidal range
Spring Tides
• Earth, Moon, and Sun are lined up• High Tides are higher and Low Tides
are lower than normal
Neap Tides
• Earth, Moon, and Sun form right angles• High Tides are lower and Low Tides are
higher than normal
Variations in tidal form world wide
Tidal patternsDiurnal
One high and one low tide each (lunar) daySemidiurnal
Two high and two low tides of about the same height daily
MixedCharacteristics of both diurnal and semidiurnal with successive high and/or low tides having significantly different heights
Variable Tides
Monthly tidal curves
Figure 9-16
semidiurnal
Mixed, SD dominant
Mixed, D dominant
diurnal
The Bay of Fundy: Site of the world’s largest tidal range
Tidal energy is focused by shape and shallowness of bayMaximum spring tidal range in Minas Basin = 17 meters (56 feet)
Figure 9-17
Bay of Fundy
High tide
Low tide(6 hours later)
Video Clip:http://www.youtube.com/watch?v=qfhNjpu_IU4
• St. Michel, N. coast of France
• ~16.8 m highest tidal range in Nova Scotia
Coastal tidal currentsTidal 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
Tidal bore = a true tidal waveWall of water that moves upriverCaused by an incoming high tideOccurs in some low-lying riversCan be large enough to surf or raft
Figure 9B
Video Clips:http://www.youtube.com/watch?v=LWumonz87rAhttp://www.youtube.com/watch?v=IKA39LQOIck
Grunion and the tidesGrunion are the only fish that come completely out of water to spawnSpawning cycles are timed precisely with the tides
Figure 9C
Video Clip:http://www.youtube.com/watch?v=udRDj2Ez8kI
Sites with high potential for tidal power generation
Figure 9-19
