1. The Tides EARTHSYS 8: The Oceans Reading: Investigating Oceanography, Chapter 9 Lecturer: Kate Lowry

2. The Tides Outline Tide patterns & characteristics Theoretical: What causes tides? Real tides: effects of land/rotation Energy considerations

3. Motivation: Tide Pool Field Trip

4. Tide Patterns Which type of tide is in each place? Diurnal Semi-Diurnal Semi-Diurnal Mixed

5. Tide Patterns Tide patterns vary regionally

6. Tide Characteristics Tidal Datum Flood/Ebb Slack Water Minus Tide Classifying tide levels & motion

7. What causes tides? Recall Earth & Moon Orbit

8. What causes tides? Gravity & inertia balance Earth & Moon; Imbalance of forces at surface creates tides

9. What causes tides? Simplified Earth-Moon System Two tidal bulges per day with rotation, assuming uniform ocean and no land

10. What causes tides? Simplified Earth-Moon System The moon orbits as Earth rotates Tidal day: 24 hours and 50 minute

11. What causes tides? Semi-diurnal Tidal Wave Period = 12 hours & 25 minutes Wavelength = half of Earth’s circumference

12. What causes tides? Effects of the Solar Tide Sun tidal force is 46% of lunar tide Enhanced tide when sun & moon in phase

13. What causes tides? Effects of the Solar Tide Sun tidal force is 46% of lunar tide Dampened tide when sun & moon at 90°

14. What causes tides? Declination favors diurnal tides Sun declination cycle = 1 year (23.5°N/S) Moon declination cycle = 18.6 years (28.5°)

15. What causes tides? Role of elliptical orbits The sun plays a larger role in tides during the winter when it is closer

16. Activity Tide Chart for Field Trip on May 11th Princeton/Half Moon Bay How would you describe the tide for this day & location?

17. Activity Tide Chart for Field Trip on May 11th Princeton/Half Moon Bay How might the sun and moon influence the tide on this day? Consider: Lunar phase Solar declination

19. May 2016 Princeton/Half Moon Bay

20. Real tides – effects of land/rotation The tide wave is discontinuous

21. Real tides – effects of land/rotation The tide behaves as a shallow water wave Ocean is ‘shallow’ compared to wavelength Speed controlled by depth and rotation At low latitudes, rotation causes displacement of tide – deflected ’forced tide’

22. Real tides – effects of land/rotation Tides and rotation form tidal currents Circular motion in same pattern as gyres

23. Real tides – effects of land/rotation Complex tide behavior depends on basin

24. Tidal bores Large amplitude tide in shallow region Fast moving forced tide; quickly floods area Real tides – effects of land/rotation

25. Tide tables and charts Combination of long-term local measurements & astronomical data Real tides - predictions

26. Satellite tide measurements Real tides - predictions

27. Using turbines to capture tidal energy Video: Harvesting Tide EnergyHarvesting Tide Energy What do you think the implications are? Energy from Tides