Tides

1. Tides ‪commons.wikipedia.org

2. What Are Tides? • Tides are the daily rise andfallof Earth’s waters on its coastlines • As the tide comes in, the level of water on the beach rises, and as the tide goes out, the level of water on the beach goes down • Tides occur in allbodies of water • But most noticeable along the shore of large lakes and the ocean

3. High Tides • High tides are when the water reaches its highestpoint.

4. Low Tides • Low tides are when the water reaches its lowestpoint

5. Tidal range: the difference between high and low tide Intertidal zone High tide Low tide

6. Alma at High Tide Alma at Low Tide

7. Tides are generated by: • Gravitational pull of the moon and sun • Centripetal force of the rotating Earth

8. The Cause of Tides • Gravitational and centripetal forces pull ocean water into a huge wave with a wavelength the size of an ocean basin. • In principle, the sun and moon create two bulges on opposite sides of the Earth. • The relative positions of the sun and moon change slowly, so the bulge changes position • Tidal bulges follow Moon as it rotates around Earth • The earth is also rotating, so as a coastline rotates into the bulge, the tide rises. As it rotates out, the tide falls.

9. Centripetal force vs Centrifugal force

10. Why the Moon is Stronger than the Sun • Which has a bigger effect on the earth and its tides?

11. The Sun, Moon, and Types of Tides Neap Tides

12. The Sun, Moon, and Types of Tides • When the moon is in a quarter phase, the lines from it and the sun to the Earth form a right angle. • The sun’s gravitation pulls to the side of the moon’s tidal bulge. • This tends to raise the low tide and lower the high tide. • These weaker tides are called neap tides.

13. The Sun, Moon, and Types of Tides Spring Tides

14. Spring tides • When there’s a new moon (no moon visible), both the sun and the moon are aligned on the same side of Earth, and during a full moon, the sun and moon are aligned on opposite sides of Earth. • When the sun, the moon, and the Earth are aligned on a 180° plane, their gravity works together, raising the height of the tidal water bulges

15. GRAVITATIONAL FORCE CENTRIPETAL GRAVITATIONAL & CENTRIPETAL

17. The Cause of Tides • Isaac Newton proposed a simplistic explanation of tides • equilibrium theory, which assumes that the Earth is perfectly uniform • His Universal Gravitation theory helped to explain how the gravity of the moon (and the sun) were related to tides

18. Universal Gravitation Law • Newton’s law states that all particles of mass have a gravitational attraction for all other particles • Gravitational force is: • proportional to the sum of the two masses • inversely proportional to the square of the distance between their centers of mass

19. The moon’s gravitational pull on liquids is much more noticeable than on solids. • Because liquids move more easily than solids

20. The Cause of Tides • Pierre-Simon Laplace modified Newton’s model to account for tidal variations • His model is called dynamic theory of tides • lunar and solar gravity • imperfect sphere of the Earth • the season • time of the month • shape of the ocean basin • Obstacles, reefs, islands • Coriolis effect all influence the tides

21. Amphidromic points • Tides rotate around more than a dozen amphidromic points • where the water doesn’t rise and fall with the tides • tides occur in a pinwheel-shaped, standing-wave pattern • There is no vertical tidal movement at an amphidromic point, but away from that point there may be magnified tidal motion as the tides change throughout the day

22. Tidal flow around an amphidromic point. tidal magnitude is shown on the dotted lines and the pinwheel represents the progression of the tide around the basin.

23. Tidal Patterns • diurnal tide - a single high and low tide daily • The Gulf of Mexico has diurnal tides. • semidiurnal tides - two roughly equal high and low tides daily, as predicted by Newton’s model. • The east coast of US has semidiurnal tides, Cape Cod • mixed tides – two unequal high and low tides daily • Hawaii, Pacific coast of the US have mixed tides • Lunar day has 24.8 hr or 24 hr 50 min • Lunar day is 50 minutes longer than a solar day because the Moon is moving in its orbit around Earth

25. TIDAL CURRENTS: The rise and fall of the tide is accompanied by the horizontal flow of water called a tidal current. The usual terms used to describe the direction of this horizontal movement are ebb and flood. Ebb currents occur when tidal currents are moving away from the coast - seaward. Flood currents move toward the coast - landward. Under certain conditions, tidal currents can move more than 10 knots.

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

27. http://www.youtube.com/watch?v=u3LtEF9WPt430 sec bay of fundy time lapse tides good • http://www.youtube.com/watch?v=dmcMQU5AAg4best 2 min  • http://www.youtube.com/watch?v=LWumonz87rA1.5 min nova scotia fast but wind noise

28. Highest Tides • One of the world's largest tides occurs in Turnagain Arm south of Anchorage Alaska – 42 feet • http://margymuses.blogspot.com/2010/03/tidal-flats-anchorage.html mud flats near anchorage in cook inlet • Tides in Lake Superior are measured in inches

29. Tidal Patterns and Currents • daily tides create a current that flows into and out of bays, rivers, harbors, and other restricted spaces • The inflow is called a flood current • the outflow is called a slack current • The midpoint between high and low tides creates slack tide, when there is little water moving • Large ships may only be able to enter or exit a harbor during high tide to ensure sufficient water depth for travel

30. Tidal bore • The incoming high tide produces a wave that flows into a river, bay, or other relatively narrow area • is a true tidal wave and can be several meters high • On the Amazon River in South America and the Severn River in England,surfers can take long rideson the tidal bore

31. Tidal bore • http://www.youtube.com/watch?v=xiKoWAiqufE quintang river 1 min news report 90 ft • http://www.youtube.com/watch?v=J8Q1ecIr-NM3 min in Chinese good • http://www.youtube.com/watch?v=SNjVlUBmtGo50 http://www.youtube.com/watch?v=4DlqVuNMydk national geographic 1 min

32. Sites with high potential for tidal power generation

33. Grunion Grunion are the only fish that come completely out of the water to spawn Spawning cycles are timed precisely with the tides

34. Grunion, Coral spawning –Lunar Effects on life…

35. Palolo worm • The Pacific palolo worm (Eunice viridis) and its West Indian relative (E. fucata) incredible reproductive behavior linked to the lunar cycle • the rear half of each worm transforms dramatically, developing fast-growing reproductive organs. The worm itself reverses its position within its tube, so that it is now pointing head-down, • the posterior body half breaks off from the rest of the worm and swims up toward the sea's surface - it has developed a pair of eyes to assist it • At the surface, the bag bursts, releasing its contents – millions of palolo worms have all undergone this radical metamorphosis at precisely the same time, the sea is soon awash with a mass of sperm and eggs, • It occurs twice a year on the neap tides of the last quarter moon in October and November for the Pacific species, and the third quarter moon in June and July for the West Indian species of palolo worm

36. Palolo worm spawning palolo_smitsonian2_lge

37. Atmospheric Tides • Lunar gravitational affects earth’s atmosphere • Cause slight periodic fluctuations in weather patterns