Tides are caused by the differential gravitational forces of the moon and sun on the Earth. This results in two bulges in the ocean on opposite sides of the Earth, creating two high tides and two low tides per day. The highest tides occur during spring tides at new and full moons when the gravitational forces add, while the lowest tides occur during neap tides at half moons when the forces compete. Tides vary in type depending on the moon's declination, with semidiurnal tides occurring most frequently. Local geographic features also influence tide heights and times.

1. Tides

2. Tides

3. At earth’s center: centripetal acceleration = centrifugal acceleration (at common center of mass). The period of rotation about this common center of mass is 27.32 days (sidereal month). Everywhere else on the earth, there is an imbalance between the centripetal (inward) and centrifugal (outward) accelerations. The centrifugal acceleration is the same everywhere on the earth, but the gravitational force due to the moon varies over the surface of the earth.

4. This results in the tide-generating force, TGF, since on the side of the earth toward the moon the gravitational force exceeds the centrifugal force, and on the side of the earth away from the moon the centrifugal force exceeds the gravitational force. The �sideways� forces, or horizontal component, of the TGF is called the tractive force. Note: Centripetal Force and Centrifugal Force is the action-reaction force pair associated with circular motion (Newton’s Third Law).

5. The equilibrium tide is that which would result from the TGFs if the earth were completely covered by water and responded instantly to the changing forces (i.e. no inertia and no friction). As a result of the tractive forces, the equilibrium tide has two bulges, one on either side of the earth. Thus, you see 2 highs and 2 lows per lunar day (semidiurnal lunar tidal constituent). It has a period of 12.42 hours and is denoted by the symbol M2.

6. The lunar day (also known as a tidal day), 24.84 hrs, exceeds the solar day (24 h) since the moon is revolving around the earth with a period of 27.32 days.

9. Moon declination effect A = Semidiurnal B = Mixed C = Diurnal

10. Tides [14.79 days]

12. Earth orbit around the sun

13. Tides There are three types of tides: Semidiurnal Mixed Diurnal

14. Tides: Moon declination effect A = Semidiurnal B = Mixed C = Diurnal

15. Monthly tides

16. Global distribution of tides

17. Local influences on tides Shape of the land Shape of the ocean floor (bathymetery) Depth of water Restrictions to flow (narrow inlets to bays, etc.) Local winds

18. How do we predict tides? XTide Tide Prediction Server http://www.mobilegeographics.com:81/ http://tidesonline.nos.noaa.gov/monitor.html http://www.mobilegeographics.com:81/zones/:America/Puerto_Rico

19. Tidal “Wave”

20. Tidal Waves (Tsunamis)

21. http://www.ssc.erc.msstate.edu/Tides2D/tides_synopsis.html

22. Tidal “Wave”

23. Tidal “Wave” No rotation With rotation http://earthguide.ucsd.edu/earthguide/diagrams/waves/swf/wave_seiche.html

24. Tides San Juan, Puerto Rico

25. Largest tides Bay of Fundy, Nova Scotia, Canada

26. Largest tides Bay of Fundy, Nova Scotia, Canada Tidal range = 15 m (50 feet or a 3-story building) The largest tidal bore occurred in Hangzhou Bay, China, 1993. The bore was 9.14 m (30 ft) high.

27. Internal Waves Barotropic Wave Baroclinic Wave (internal tide or wave)

28. Internal Waves Red Sea True-color Terra MODIS, July 26, 2003.

29. Important terms: Barycenter Centripetal force Lunar and solar declination Tropics of Cancer and Capricorn Apogee Perigee Aphelion Perihelion Tidal day Semidiurnal, mixed, and diurnal tides Spring tides (syzygy) Neap tides (quadriture) Amphidromic point

31. Consequences of tidal fluctuations Navigation – depth and currents Intertidal – range and type of organisms Larval retention and dispersal Internal waves Migrations synced with tides

32. Tidal Resources http://tidesandcurrents.noaa.gov/ http://oceanservice.noaa.gov/education/kits/tides/tides01_intro.html http://tidesonline.nos.noaa.gov/ http://www.mobilegeographics.com:81/zones/:America/Puerto_Rico