1. Chapter 16 Section 2 Waves and Tides
The Dynamic Ocean
Chapter 16
Section 2
Waves and Tides

2. Chapter 16-2 Overview From where do ocean waves obtain their energy?
What three factors affect the characteristics of a wave?
How does energy move through a wave?
What causes tides?

3. So what are waves????
They obtain their energy and motion from wind.

4. Anatomy of a Wave Crest The tops of the waves Trough
The bottom of the waves

5. Anatomy of a Wave Picture

6. Wave Characteristics Wave height
The vertical distance between the trough and crest
Wavelength
The horizontal distance between two successive crests OR two successive troughs
Wave period
The time it takes one full wave (wavelength) to pass a fixed position

7. Wave characteristics are dependent on three factors:
Wind speed
Length of time wind has blown
Fetch
Distance the wind traveled across open water

8. Wave Motion Waves travel great distances.
The water does not travel the entire distance, but the wave does.
Consider the following: a floating object on the water such as a rubber duck
Disturb the water creating a wave
What motion does the duck exhibit? (Forward motion or up and down or both – Explain)

9. Water particle movement diagram

10. So what is the true motion of water particles?
Circular orbital motion, see pictures on page 456 and 457
It allows energy to travel forward yet the individual water particles only move in a circle

11. Breaking Waves continued
As the original wave advances toward shore:
It begins to “feel bottom” at a water depth = ½ of its wavelength

12. Tides Daily change in the elevation of the ocean surface.
Ocean tides result from the change in the gravitational attraction exerted upon Earth by the moon and the sun.

13. Ocean Tides The moon is the primary body influencing ocean tides
It takes the moon 29 ½ days to make one revolution around the Earth
The sun is farther away and only has about 46% of the moon’s effect

14. So how does this gravitational force work?
Consider tug of war between two teams – the Earth & the moon
The moon is pulling on the Earth’s water bodies that are closest to it --- this creates a bulge on the side closest to the moon
Therefore, the side farthest from the moon has less pull

15. So what does it look like?
When the “bulge” is the greatest, we see a high tide
When the pull is not great, we see a low tide
The moon makes a revolution around the Earth, but the Earth is rotating which changes its position of the pull from the moon
Water moves toward the pull giving the high tide where the pull is greatest and low tide where the pull is the least strong
Most coastal locations will see 2 high tides and 2 low tides each day

16. Tidal Cycle The sun has some influence on tidal bulges
Its influence is most noticed at full and new moons as they sun and moon are aligned
Alignment = combined forces pulling on the Earth’s water
Larger tidal bulges (higher hide tides) are created as are larger tidal troughs (lower low tides)

17. Tidal Cycle

18. Tidal range
Difference in height between successive high and low tides
Spring tides
Tides having the greatest tidal range due to the alignment of the Earth, moon & sun
Experienced during full and new moons
2 per month
Neap tides
When the daily tidal range is the least
Experienced at the first and third quarters of the moon (when the moon and sun act on Earth at right angles)
See figure 13, page 459

19. Tidal Patterns Three main tidal patterns: Diurnal tides
Semidiurnal tides
Mixed tides

20. Diurnal tides
A single high tide & a single low tide each day
Typical near Gulf of Mexico
Semidiurnal tides each day
Two high and two low tides
Highs are similar in height as are the lows
Common along the Atlantic coast of U. S.
Mixed tides
Similar to semidiurnal pattern BUT
Large inequality in high water heights and/or low water heights
Common along Pacific Coast of U. S. and other parts of world