INTRODUCTORY OCEANOGRAPHY

Specific Reading Assignments for EXAM 2

Chapter 6	PROPERTIES OF WATER	ALL
Chapter 8	AIR-SEA INTERACTION	ALL
Chapter 9	OCEAN CIRCULATION	ALL

Key Elements to Study

Chapter 6. Properties of Water

1. Structure of H₂O Molecule

• Explain how the unique asymmetric structure of the water molecule results in a dipolar electrical distribution of charges on the molecule. What is the net (i.e., positive minus negative) charge of this molecule? Fig. 6.1
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• What are hydrogen bonds and how are they associated with the structure of the water molecule? How do they differ from the chemical bonds (covalent and ionic)?
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• How do the hydrogen bonds result from the dipole structure of this molecule and cause the unique properties found in water (e.g., surface tension, dissolving power, thermal properties, existence of water in liquid form at normal earth temperatures, etc.)?

2. Thermal Properties of Water

• What are the three states of matter for H₂O?
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• If the structure of the water molecule was symmetric, what is its estimated freezing and boiling temperatures as projected by plots of other molecules with similar structures? -- see the figure in Chapter 6, Part 1.
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• Heat Capacity.
  • Heat capacity is the ability of a substance to absorb heat without a large rise in temperature. Also define it in terms of the number of calories required to raise the temperature of 1 gram of water by 1C (the standard is fresh water which requires only 1 calorie -- how many calories are required for ice or water vapor and, therefore, how do these heat capacities compare with that of water?).
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  • Use heat capacity to explain why the air temperature range, between winter and summer extremes, is much smaller over the ocean than over land. Why is the concrete area around a swimming pool so much hotter than the water in the pool, if they both receive the same solar radiation - i.e., which has the higher heat capacity?
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• What is Latent Heat, and what are the magnitudes of latent heats involved in the changes of phase between ice and liquid, and between liquid and vapor? Recall that the latent heat of evaporation is higher than that shown for vaporization.
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• Explain how heat capacity, high latent heats and high phase boundary termperatures are inter-related by hydrogen bonds.
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• What is the difference between sublimation, vaporization and evaporation?

3. Relative Humidity - RH

• Define RH and explain what, for instance, 25% RH means. To what is the humidity of air relative?
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• How does unsaturated air reach the dew point?
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  • What is the dew point temperature?
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  • How do you find the dew point temperature from the Table of Air Saturation values given in class?
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• Why do we overheat under conditions of high humidity (i.e., R.H. > 60%)?

4. Seawater Salinity

• What is the definition of salinity? How is a measure of salinity obtained from a 1 kg sample of seawater?
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• For a salinity of 34.7 parts per thousand (ppt or ‰), approximately how many grams of "salt residue" will be found in 1 kg of seawater?
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• What are the six major ionic constituents in seawater? List by sign of ionic charge - Fig. 7.4.
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• How can the "rule of constant proportions" be used to determine seawater salinity?
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• Contrast and compare the two ways salinity is determined.
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• What is the "standard salinity" value for the ocean?

5. Water Density

• What is the definition of density?
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• What are the dimensions of density used in oceanography?
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• For freshwater, what is the proportionality relationship of density to temperature and pressure?
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• For seawater, what is the additional proportionality relationship of density to salinity?

6. Temperature of Maximum Density, Density Anomaly

• When fresh (zero salinity) water is cooled, the maximum density of the water is reached at a higher temperature than the freezing temperature. What are these two temperatures for fresh water, and how do they change for water with salinities greater than zero?
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• Why do we call the fact that maximum density is reached at a higher temperature than the freezing point a "density anomaly"? Why does this anomaly no longer exist for salinities greater than about 25 ‰ - Figure 6.3.
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7. Water Stability Conditions and the Freezing of Ice on a Water Surface

• How does the change of water density with depth affect the stability of the vertical water column?
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• What is the difference between neutral, stable and unstable stability conditions, and in which will vertical convection occur?  
  • Use an understanding of the density anomaly discussed earlier, and of the stability conditions, to explain the process of freezing ice on a fresh water lake. Why is the water temperature no lower than 4 C a few feet below the ice at the moment when ice freezes on the lake surface?
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  • Generalize the observations about the freezing process just described to apply to all bodies of water with salinities < 25 ‰. In particular, at what temperature will the water beneath the ice be when ice first freezes for these salinities?
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  • How is the process of freezing ice on the surface of water with salinities > 25 ‰, different from that for salinities < 25 ‰?
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    • Why is the temperature of the water below newly frozen ice on the ocean (which has a salinity of about 35 ‰) lower than the temperature of water at the same depth below newly frozen ice on a fresh water lake?
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    • In what ways do the freezing temperature and the vertical stability condition of this ocean water explain this lower temperature?

8. Ocean Water Density

• Why, and how, do oceanographers re-express density (r_s,t,p -- with dimensions of grams/cm³) as Oceanographer's Density (s_s,t,p -- which has no dimensions)?
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• Why is Sigma-T (s_T) a special case of Oceanographer's Density (i.e., which of the three factors affecting density (temperature, salinity and pressure) is ignored in definition of Sigma-T)?
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• For a fixed salinity of 35 ‰, why is Sigma-T affected more by a 5C change in temperature at the equator than at the higher latitudes?
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• Define thermocline, pycnocline, halocline, isothermal, isopycnal and isohaline.
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• Look at Figure 6.13 to learn how temperature, salinity and density varies in oceanic water at different latitudes on the earth
  • at which latitude does temperature have the largest affect on density?
  • at which latitude does salinity have the largest affect on density?

Chapter 8. Atmospheric Circulation and Air-sea Interaction

1. Radiation Laws and Light Transmission

• What feature of the electromagnetic spectrum does Wein's displacement law define, and how is it related to the temperature of a radiating body?
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• What are the upper and lower wavelength limits of the Visible portion of the solar energy spectrum?
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• In which parts of the solar energy spectrum do the Ultra-violet (UV) and Infra-red (IR) portions reside?
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• Which wavelengths of visible light are least attenuated (absorbed) in water? Which are most attenuated?
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• What are the definitions and dimensions of the heat flux terms Qs and Qb?

2. Greenhouse Effect

• Use the information just given to explain how the short-wave radiant energy from the sun is temporarily retained in the earth's atmosphere in what is called the Greenhouse Effect.
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  • To what general wavelength must this solar radiation be converted before it can be effectively retained in the atmosphere?
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• What atmospheric gases are most important to this process, and how do they interact with these radiant energies at different wavelengths?
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• Does reflection of solar energy play any part in the Greenhouse Effect?
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• For how many degrees rise in air temperature does the Greenhouse Effect actually account, and which of the gases in the air has the largest effect?

3. Heat Loss and Gain by Conduction (Qc)

• By what process is heat moved during conduction, and why is it called sensible heat?
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• Heat conduction is directly proportional to the temperature gradient dT/dz - what does this mean?
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  • In what direction across the air-sea boundary does sensible heat move?
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• Why is heat most efficiently transferred across the ocean surface when the air is colder than the water?
  • Ignore differences in the specific heats of water and air -- look only at the stability conditions in the water and air, and the resulting convection for unstable conditions and their combined effect on the temperature gradient, to provide the answer.

4. Heat and Water Loss by Evaporation (Qe)

• Does air temperature alone determine whether evaporation (E) takes place?
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• Latent heat and liquid water are extracted from the ocean during evaporation and enter the atmosphere together in the form of water vapor (i.e., the gaseous form of H₂O).
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  • When and by what process is this latent heat actually released to warm the atmosphere? What happens to the water?

5. Heat Budget for the Ocean

• The Heat Budget is defined as the rate of heat gained by ocean = rate of heat lost from ocean.
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• Contrast and compare the four principle processes (two radiative and two non-radiative; Qs, Qb, Qe, and Qc) for transferring heat across the boundary between the ocean and the atmosphere?
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• Which of these processes are losses from and which are gains to the ocean, and what are their relative rates?
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• Write the Heat Budget equation in terms of these four principle processes (remember the sign of the conduction term).

6. Coriolis Effect (CE)

• How does the earth's rotation cause the CE?
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• In which direction, relative to a moving object, does the CE act in each hemisphere, and what effect does this have on the object?
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• The CE is directly proportional to what two things?
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• Is the CE ever equal to zero?
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7. Water Budget

• A Water Budget is defined as the rate of fresh water gained by ocean area = rate of fresh water lost by ocean area
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• Why is E minus P (written E-P) defined as the Net evaporation at any particular place in the ocean? E is evaporation and P is precipitation of water (both measured in grams, or in centimeters of water).
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• Why is E-P highest in the trade wind regions and lowest in the doldrums region (5 N latitude)?
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• If you look at the average E-P distribution by latitude in the Atlantic Ocean, where would you expect to see: the lowest average surface salinity; the highest average surface salinity?
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8. The Ocean's Weather and Climate

• What is the difference between weather and climate?
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• In the Northern Hemisphere, sinking air is associated with what kind of pressure cell? What about rising air?
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  • The Coriolis effect will cause the air in each of these cells to flow in what direction?
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• How do warm and cold fronts differ, and which usually results in the most violent storms?
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• Contrast and compare NE & SW Monsoons in the Indian Ocean and Land and Sea Breezes on coastlines.
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• What is El Nino - Southern Oscillation (ENSO), and how does it affect our climate and weather?

Chapter 9. Ocean Circulation

1. Atlantic Ocean Surface (Horizontal) Circulation

• What winds are the primary driving force of the Atlantic Ocean currents? - Figure 9.1.
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• Why does the Gulf Stream in the North Atlantic have a much larger volume transport than the comparable Brazil Current in the South Atlantic? - Figure 9.8.

2. Ekman Spiral and Transport

• According to Ekman, when the wind blows on the ocean surface, in what direction and angle, relative to the wind, does the top most layer ("lamina") of the surface water move? Why? Fig. 9.5b
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• How is the Ekman Spiral created and what does it represent (Figure 9.5c)?
• What is the depth of frictional influence, how deep does it normally extend, and how is the Ekman Transport related to it?
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  • How does the Ekman Transport cause coastal upwelling (the vertical upper-ward movement of water), and what are the favorable wind directions (relative to the coastline) for upwelling to occur? What about coastal downwelling? - Figure 9.16 and 9.17.
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  • How does the Ekman Transport cause equatorial upwelling? - Figure 9.15.

3. Geostrophic Current

• A Geostrophic Current is a horizontal ocean current that exists, by definition, when the down-slope component of gravity - the result of a slight slope in the sea surface - is balanced by the Coriolis force
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• How can Newton's first law of motion be used to explain and understand the formation and maintenance of the Geostrophic current that results from this balance?
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• How can you determine sea surface height at, and sea surface slope between, two hydrographic stations in the ocean using a knowledge of the average water density at each station?
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  • In what direction does the sea surface slope if you know that one station has a lower average density than the other?
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• If the sea surface slope has already been determined, why do you need to know which hemisphere you are in before the direction of the geostrophic current can be determined?
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  • At what angle, relative to the cross-section between the two stations, does the current flow?

4. Thermohaline (Vertical) Circulation

• How can increased density near the surface drive the deep ocean currents?
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• What are conservative and non-conservative properties of a fluid?
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• How can ocean temperature and salinity (both conservative properties) be used in the tracing of water masses under the ocean surface using a T-S Diagram? Figure 9.21.
• What distinguishes Antarctic Intermediate Water (AAIW) on the T-S Diagram; i.e., does it have a fixed T and S like North Atlantic Deep Water (NADW), wherever it is found? Figure 9.21.

5. Westward Intensification of a Current

• Currents on the western side of an ocean basin, such as the Gulf Stream, are faster, narrower and extend to greater depths than currents on the eastern boundary. Figures 9.7 & 9.13.
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• What three rotational (vorticity) forces, when balanced, cause this intensification?
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• Would the intensification occur if the earth did not rotate around it's axis?
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• In addition to the Gulf Stream, which of the following currents also are intensified: Kuroshio, Brazil, Canary or California (look at Figure 9.9).
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6. Gulf Stream Eddies

• Eddies are rotating rings of very warm water with warm- or cold-water cores, found on both sides of a western boundary current such as the Gulf Stream. Figure 9.12.
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• How are these eddies formed from meanders in the Gulf Stream? Figure 9.11
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• The water inside the core of each of these eddies comes from what two locations, and on what sides of the Gulf stream are cold-core and warm-core eddies each found after their formation -- in what direction do their rings rotate?
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• How long do each of these eddies last before they lose their identity - what causes them to disappear?

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