Chapter 10: Tides

1. Chapter 10: Tides Fig. 10-6 Fig. 10-7

2. Tide-producing forces • Gravity and motions among Earth, Moon, and Sun Fig. 10-2

3. Centripetal force “tethers” Moon to Earth • Directed away from barycenter Fig. 10-4 a,b

4. Resultant tidal forces • Gravitational force, Earth and Moon • Centripetal force, Earth and Moon • Resultant force moves ocean water horizontally Fig. 10-6 Fig. 10-7

5. Tidal bulges • Two equal and opposite tidal bulges • Earth rotates beneath tidal bulges • Two high tides • Two low tides • Per day Fig. 10-8

6. Complications to simplest equilibrium theory • Oceans do not cover entire Earth • Oceans do not have uniform depth • Friction between ocean and seafloor • Continents • Moon not always in same place with respect to Earth • Lunar day longer than solar day

7. Lunar day • Moon revolves around Earth • Earth has to “catch up” with Moon to reach same position Fig. 10-9

8. Time between successive high tides shifts day after day • Moon rises later each successive night

9. Solar tidal bulges • Tide-producing force of Sun less than half of Moon’s • Sun much farther away

10. Month tidal cycle • Spring tides • New Moon, Full Moon • Earth, Moon, Sun syzygy • Higher than usual high tides Fig. 10-12

11. Neap tide • First Quarter, Last Quarter • Earth, Moon, Sun quadrature • Lower than usual high tide Fig. 10-12

12. Declination of Sun and Moon • Orientation of Sun, Moon to Earth’s equator • Sun 23.5o N and S, yearly cycle • Moon 28.5o N and S, monthly cycle • Unequal tides • Successive tides different tidal range

13. Unequal tidal range Fig. 10-15

14. Elliptical orbits • Perigee • Lunar tidal force greater • Higher high tides • Apogee • Lunar tidal force lesser • Lower high tides Fig. 10-16

15. Dynamic theory of tides • Tide shallow-water wave • Speed varies with depth • Lags behind Earth’s rotation • Rotary flow in open ocean basins • Amphidromic point • Cotidal lines

16. Rotary flow • Crest (high tide) rotates • Counterclockwise in Northern Hemisphere • Clockwise in Southern Hemisphere

17. Tidal patterns • Diurnal • One high, one low tide per lunar day • Period of tidal cycle 24 hours 50 minutes • Semidiurnal • Two high, two low tides per lunar day • Period 12 hours 25 minutes • Equal range

18. Mixed • Two high, two low tides per lunar day • Unequal range • Most tides are mixed

19. Standing waves • Forced standing wave caused by tides • Free-standing waves caused by strong winds or seismic disturbances Fig. 10-22

20. Node maximum horizontal flow • Antinode maximum vertical flow Fig. 10-23

21. Bay of Fundy • Largest tidal range (spring tide max 17 m) • Shape of basin • Oscillation period close to tidal period • Shoals and narrows to north • Basin oriented toward right (Coriolis moves water toward right) Fig. 10-24

22. Tidal bores • Wave created by tide rushes upstream • Large tidal range • Low-lying coastal river • Max 8 m high Fig. 10A

23. End of Chapter 10: Tides Fig. 10-6 Fig. 10-7