INTRODUCTORY OCEANOGRAPHY

Specific Reading Assignments for EXAM 3

Chapter 10	WAVES, LONG WAVES & STANDING WAVES IN ENCLOSED BASINS	ALL
Chapter 11	TIDES & STANDING WAVES IN SEMI-ENCLOSED BASINS	ALL
Chapter 12	THE SHORE, COASTAL WATER & MARGINAL SEAS	ALL

Key Elements to Study

Chapter 10. Waves

1. Define or identify the following terms:

• wave energy spectrum
• wind fetch
• wind duration
• impact wave
• wind wave
• gravity waves
• capillary waves
• long waves
• free wave
• sea
• swell
• surf

2. Wave Identification

• Identify the parts of an ideal (sinusoidal) ocean wave (height (H), length (L), trough, crest, period (T)), and define what is meant by wave celerity (C).
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• Why is an ocean wave described as being an orbital progressive wave, and what is the path of water particles at and below the surface as this wave passes? See Figure 10.2.

3. Wave Classification - waves can be classified in at least three different ways.

• Water Depth - Explain the differences between waves classed as deep or shallow water waves, including how the shape of the water particle orbital paths differ.
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  • The wave celerity of each of these two types of waves is a function of different variables - what are they?. See Figure 10.6.
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• Period of Waves - How are waves classified by period and what are their principle generating and restoring forces? See Figure 10.5.
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• Relationship to Generating Force after Generation - What relationship do free waves and forced waves have to their generating force, and under what conditions may each of these classes of waves be found?

4. Wave Dispersion.

• Wave dispersion is directly proportional to wave celerity. For deep water, therefore, does wavelength or water depth govern wave dispersion?
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• How do dispersing waves sort themselves out, so that "order" is created from "chaos"?
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  • Do both wind waves and impact waves disperse?
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• Contrast and compare sea and swell. Figure 10.11.
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• How does wave interference occur, and what is the difference between constructive and destructive interference? Figure 10.15.
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5. Fully Developed, Wind-generated Sea

• What do we mean when we say a sea is fully developed.
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• How 'big' are the waves when the sea is fully developed and in what way may the wave steepness parameter, H/L, be used to explain this 'bigness'.
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• For a given wind speed, how can wind duration and wind fetch limit the sea from reaching full development?
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• How does the wave spectral-peak period, and the area under the curve of a wave energy spectrum (where wave energy is plotted as a function of wave period), grow as the wind speed, fetch, or duration increase? For a fixed wind speed:
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  • Explain how you would set up an experiment to determine Min. Fetch.
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  • Explain how you would set up an experiment to determine Min. Duration.
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• When do "white-caps" (the breaking of waves in deep water) form during the growth of a fully-generated sea?
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  • What relationship do white-caps have to the energy put into the sea by the wind?
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• Will a sea that is fully developed for a given wind speed, remain that way if the wind speed increases?
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6. Wave Breaking in the Surf Zone

• As waves shoal (enter increasingly more shallow water), why does wave celerity decrease?
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  • How does this decrease, and the resultant re-partitioning of energy from kinetic to potential, cause the wave height to increase.
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  • Explain why wavelength (L) also decreases during shoaling.
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• Explain why and how this process increases the wave steepness parameter, H/L, and why we call H/L > 1/7 the breaking criteria?
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• Describe how waves break.
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• What is the major difference in the movement of water in a breaking wave as compared to water movement in the same wave before it breaks? (See Figure 10.17).

7. Long Waves (Periods greater than 5 min.) - Figures 10.30 & 10.5

• In how many ways does storm surge differ from a Tsunami?
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• Why is a Tsunami always a shallow water wave?
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• Which of these two waves occurs most frequently and which does the most overall damage on an annual basis?

8. Wave Reflection/Refraction/Diffraction

• Contrast and compare the way that waves change direction during reflection, refraction and diffraction? (see Figures 10.20, 10.22 & 10.23)
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• What are wave rays (book calls them orthogonals) and how are they oriented with respect to the wave crestlines?
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• Under what depth and shoreline conditions are wave rays focused by refraction (Figures 10.20a & 12.4) and toward what shoreline depth do the wave crestlines (or wave rays) bend?
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9. Standing Waves in Enclosed Basins

• Standing waves are produced by the passage of two progressive waves of the same period in opposite directions (Figure 10.24).
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  • What are the differences in vertical and horizontal water movement under nodal lines and antinodal lines in a standing wave?
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• Standing waves in an enclosed basin (such as a lake) - Figure 10.28:
  • Only for the longest east-west oriented lakes may the moon and sun produce a measurable astronomical tide as a result of the tide-producing force (TPF).
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    • How large is the tidal range in this enclosed basin?
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    • Why is tides produced by the TPF called a forced wave?
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  • How does the wind set up a free standing wave (called a seiche) in this basin?
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    • Define the Characteristic Period (Tc) for this type of basin?
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    • Why is a seiche a free standing wave?
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  • What period and phase conditions between Tc and the TPF are required for the seiche to be enhanced to produce a free/forced standing wave called a resonance tide?
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Chapter 11. Tides

1. Define

• Tidal range
• High water/low water for diurnal tides
• High-high water (HHW), low-low water (LLW), high-low water (HLW), low-high water (LHW) for mixed or tropical tides
• Tidal period
• Mean sea level and mean tidal range
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2. Equilibrium Theory.

• Who formulated this theory and what are the theory's simplifying assumptions.
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  • What two forces are in equilibrium in this theory?
  •  
• Why are there two water "bulges" found on the earth in line with the position of moon above the earth? (see Figure 11.5 and Figure 11.6).
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• What does the theory predict about the movement and accumulation of water on the earth as a result of these bulges and the moon's movement around the earth?
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• The Equilibrium theory cannot be used to explain diurnal tides (that have only one high and low per day ), but it can give us insight into tides that have two highs and two lows in a day, and into combined tides produced by the sun and the moon:
  • Tides with 12 hr 25 min. periods. Explain why the semi-diurnal period is not 12 hr (the earth rotates once around its axis in 24 hrs, doesn't it?) - Figure 11.8.
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    • There are two different tides with two highs and two lows per day -- They are:
      • Semi-diurnal Tides - where the two high and low tides have equal heights. Why can we also call them equatorial tides? Figure 11.7.
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        • Why are these tides produced when the moon is directly over the equator?
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      • Mixed Tides - where the two highs that occur each day do not have equal heights. Why can we also call them tropical tides? Figure 11.10.
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        • Why is it necessary for the moon to be at the maximum declination angle?
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        • How is the diurnal inequality of a tropical/mixed tide defined? (see Figure 11.13c).
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          • Why is there not an inequality for an equatorial tide?
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    • During the passage of the moon in its orbit around the earth, the tides may alternate between being equatorial tides and tropical tides.
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      • How does the theory explain these changing tides and there different heights? Figure 11.10.
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  • Combined Effects of the Moon and Sun (with fortnightly period of 14 days).
    • How does the sun's tide-producing force combine with the moon's tide-producing force to create this twice monthly tide?
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      • What phase of the sun and moon will produce a spring tide?
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      • What about a neap tide? (Figure 11.11)?
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    • Which of these tides (spring or neap) has the maximum, and which the minimum, tidal range?

3. Dynamic Theory

• What are the benefits of assuming that tides are very long waves (recall the earlier classification of waves by period and that tides were the two 'spikes' on the figure are near 12 hrs. and 24 hrs)?
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• What are partial tides, and how do they compare with component waves found in "sea".
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  • How do partial tides combine to produce the actual tides observed, regardless of the tide's actual period?
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• Why do we need at least a year-long tidal height record at a particular spot in the coastal ocean before we can determine the importance of the partial tides present at that location, and be able to accurately predict future tidal heights at that location.
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• How can this theory be used to explain diurnal tides (one high and one low each day) that have a period of 24 hr 50 min., something the Equilibrium Theory cannot?
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4. Standing Waves and Tides in Wide Basins

• Standing waves in a basin open to the ocean - Figure 11.15:
  • What is the force that drives these standing waves?
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  • Why will the resonance tides produced here usually have larger ranges than those for lakes?
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  • What is a Kelvin Wave, and how is it produced in a broad basin?
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  • Why is the Coriolis effect required to produce these Kelvin waves?
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  • In what way are amphidromic points in wide basins comparable to nodal lines in narrow basins?
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    • Are amphidromic points found in the ocean?
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    • Are actual tides Kelvin Waves?
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  • What are cotidal lines and how are they related to the phase of the tide at a particular location in the ocean? See Figures 11.16 & 11.17
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• In what direction (clockwise or counterclockwise) do cotidal lines rotate in the northern hemisphere?

5. Tidal Currents - flow of water through a coastal inlet

• Differentiate between ebb, flood and slack tidal currents?
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• How are each of these currents associated with ocean tides, and the subsequent rise or fall of water in the ocean.

Chapter 12. The Shore, Coastal Waters and Marginal Seas

1. Land forms and Terminology of Coastal Regions

• Distinguish between offshore, nearshore, and foreshore
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• How does a coastline differ from a shoreline?
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• Distinguish between erosional shoreline features (sea caves, sea arches, stacks and wave-cut bench or terrace) and depositional shoreline features (barrier islands, bay barrier, spit and Tombolo).
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• In what zone (and how close to shore) are longshore currents found, and how are they created by ocean waves? Figure. 12.15.
  • What is longshore drift, and how is it related to longshore currents?
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  • What are rip currents and how are they formed?
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  • Define and explain what is meant by the equilibrium of a beach?
    • What is the relationship between beach slope and particle size on a beach?
      • See Table 12.1.
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    • What part do swash and backwash play in this relationship?
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    • What part does grain size play in this relationship (think void space)?

2. The Effect of Constructed Barriers. Figure 12.33.

• Contrast and compare jetties, groins, breakwaters and seawalls?
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• How do these man-made structures affect the movement of sand and change the erosion or deposition of sand in the dynamic zone?
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• What is meant by the dynamic zone of the shoreline?
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3. Estuaries

• What is an estuary and what relationship does it have to movement and interaction of ocean water and fresh water?
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• What are the names of the four major classes of estuaries (by origin), and what are their characteristics? Figure 12.29.
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• What are wetlands and what is their relationship to estuaries?
  • Contrast and compare salt marshes and mangrove swamps.

4. Marginal Seas

• What is the "American Mediterranean"?
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• What is the loop current in the Gulf of Mexico, and how is it associated with the Florida Current?
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• What causes the brine pools in the Red Sea, and how does the circulation with the Indian Ocean contribute?

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• Last update: July 30, 2005