This is a text version of the notes presented in class.

Feel free to email the instructor (dpalmer@kent.edu) with any
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1. Tides
- Tide Generating Forces - Inertia and Gravity
-Dynamic Tides
- Seiches in Enclosed Basins
 

2. Wave Energy Revisited

3. Gravity and Tides
Gravitational attraction between the Earth and other astronomical bodies
  gives rise to tides
Strength of gravitational attraction depends on:
 - masses of the two bodies
 - distance between the two bodies
The strongest tides are forced by:
 - the Earth and moon
 - the Earth and sun

4. Tide Generating Forces - Gravity
Gravity pulls each point on Earth toward the center of the moon
   Gravitational force (pink arrows):
    - varies in strength (the arrows are different lengths)
    - is not oriented the same direction everywhere

See Figure 11-11 to 11-13

5. Tide Generating Forces - Inertia
Inertia exerts an outward pull away from the center of mass of the Earth and moon
   Inertial force (blue arrows):
    - is the same strength everywhere
    - is oriented in the same direction everywhere

6. Combined Result of Inertia and Gravity
The ocean is pulled:
- toward the moon on the side of the Earth closest to the moon
-away from the moon on the side of the Earth opposite the moon
 

7. High and Low Tides
High and low tides occur as the Earth spins under tidal bulges
 

8. Solar and Lunar Tides
Lunar tides (Earth/moon)
Solar tides  (Earth/sun)
Spring tide - solar and lunar tidal bulges add
Neap tide - solar and lunar tidal bulges cancel
See Figures 11-8 and 11-9

9. Spring and Neap Tides
Spring tide:
 - large difference between high and low tide
 - Earth, moon and sun are lined up (new and full moon)
Neap tide:
 - small difference between high and low tide
 - Earth, moon and sun at right angles (1st and 3rd quarter moon)

The tides cause a transfer of energy between the earth and the moon. Pictured below.

10. Dynamic Tides
The previous explanation of tides (equilibrium theory):
 - neglects blocking of tidal progression by continents
 - assumes that tides can adjust infinitely fast
In reality, tides
 - propagate within ocean basins
 - behave like shallow water waves
 - the speed of tidal propagation is slowed by friction
      against the bottom of the ocean
These "dynamic" aspects of tides result in variations in the number of high and
   low tides per day at different  locations

11. Semidiurnal, Diurnal and Mixed Tides
Semidiurnal - two high and two low tides per day (about same height)
Diurnal -one high and one low tide per day
Mixed - two high and two low tides per day (different heights)

See Figure 11-10

12. Distribution of Tidal Patterns

13. Tides and the Coriolis Effect
Because of the Coriolis effect, tide crests rotate:
- counterclockwise around northern hemisphere ocean basins
- clockwise around southern hemisphere ocean basins

See Figure 11-14

14. Amphidromic Points
Amphidromic points are no-tide points within ocean basins
- tide heights increase with distance from the AP
- there can be more than one AP in an ocean basin
See Figure 11-15.

15. Amphidromic Points in the World Ocean
Lines show the location of the tide crest:
 1=location of tide crest at hour 1
 2=location of tide crest at hour 2
See figure 11-16

16. Tides in Confined Basins
In confined basins tides can either set up as mini-amphidromic systems OR
slosh in and out of the basin from the sea
 

17. Seiches in Enclosed Basins
Seiche = rocking of water in an enclosed area (such as a large lake)
Causes:
    changes in air pressure
   wind
   seismic activity
   tidal forcing
 

18. Seiches and Lake Erie
Seiches frequently occur on Lake Erie due to winter storms
- changes in atmospheric pressure or strong winds can set up higher lake levels at one end of the lake than at the other
- the water then sloshes within the lake as a seiche

19. Effects of Seiches on Lake Erie
Typical Lake Erie seiche:
- 14 hours between high and low water at a given location
- 2 meter change in lake level (up to 5 meter changes have been observed)
Effects on society:
 Shoreline flooding
 Erosion
 Damage to shoreline structures

20. Preview of Next Lecture
Tsunami (Seismic Sea Waves)
Focus Question:  Why do Tsunamis travel so fast and why are they so destructive?