SIO 210 Talley Lectures 2 and 3: Properties of seawater and dynamical quantities

Lynne Talley, November 7, 1996
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Reading and study questions

Reading (on reserve):

Seawater properties:

Pickard and Emery, chapter 3.1-3.5
(Gill, Appendix 3 - just note existence - very useful for equation of state etc.)
Reid, J.L. and R. J. Lynn, 1971. On the influence of the Norwegian-Greenland and Weddell seas upon the bottom waters of the Indian and Pacific oceans. Deep-Sea Res., 18, 1063-1088.
Dynamic height:
Pickard and Emery, chapter 6.255
Forcing - review mechanisms discussed by Hendershott
(Tomczak and Godfrey, chapters 3 and 4)

Further reading

Fofonoff, N.P., 1962. Physical properties of seawater. In The Sea: Ideas and observations on progress in the study of the seas, Vol, 1: Physical Oceanography. M.N. Hill, ed., Wiley, Interscience, new York, pp. 3-30.

Fofonoff, N.P., 1985. Physical properties of seawater. J. Geophys. Res., 90, 3332-3342.

Gill text, pp. 39-45

Mantyla, A., 1987. Standard seawater comparisons updated. J. Phys. Oceanogr., 17, 543-548.

UNESCO tables, 1983. (Fofonoff and Millard) Includes fortran code (see bottom of study questions to get source code online).

Jackett, D. and T. J. McDougall, 1995. Neutral density. International WOCE Newsletter, 19, 30-33.

Other sources for viewgraphs

Gordon, A.L., 1986. Interocean exchange of thermocline water. J. Geophys. Res., 91, 5037-5046. 339-359.

Hellerman, S. and M. Rosenstein, 1983. J. Phys. Oceanogr., 13, 1093-1104.

Hsiung, J., 1985. Estimates of global oceanic meridional heat transport. J. Phys. Oceanogr., 15, 1405-1413.

Schmitt, R., P. Bogden, C. Dorman, 1989. Evaporation minus precipitation and density fluxes for the North Atlantic. J. Phys. Oceanogr., 19, 1208-1221.

Schmitz, W. J., 1995. On the interbasin-scale thermohaline circulation. Rev. Geophys., 33, 151-173.

Stommel, H. P. Niiler, and D. Anati, 1978. Dynamic topography and recirculation of the North Atlantic. J. Mar. Res., 36, 450-468.

Talley, L.D., 19484. Meridional heat transport in the Pacific Ocean. J. Phys. Oceanogr., 14, 231-241.

Wijffels, S. E., R. W. Schmitt, H. L. Bryden and A. Stigebrandt, 1992. Transport of freshwater by the oceans. J. Phys. Oceanogr., 22, 155-162.

Worthington, L.V., 1981. The water masses of the world ocean: some results of a fine-scale census. In Evolution of Physical Oceanography, MIT Press, 42-69.

Wyrtki, K., 1975. Fluctuations of the dynamic topography in the Pacific Ocean. J. Phys. Oceanogr., 5, 450-459.

Study questions:

Seawater properties

1. What is the difference between accuracy and precision?

2. What properties of seawater determine its density?

3. What is the pressure at the bottom of the ocean relative to sea surface pressure? What unit of pressure is very similar to 1 meter? What unit is similar to 100 meters?

4. What is the appropriate temperature scale to use for heat content?

5. What happens to a parcel of water (or any fluid or gas) when it is compressed adiabatically? What two quantities do physical oceanographers use to account for compression in comparing parcels of water from different depths?

6. Is cold water more or less compressible than warm water?

7. What is salinity and why do we use a single chemical constituent (which one?) to determine it? What other physical property of seawater is used to determine salinity? What are the problems with both of these methods?

8. Why do we use different reference pressure levels for potential density? (see answer to 6)

9. What is a neutral surface? neutral density?

10. What are the significant differences between freezing pure water and freezing seawater? What happens to the salt in frozen seawater?

11. Fresh water has a density maximum at a temperature above the freezing point, which allows ice to float. Is this also true for sea water? Why does ice formed from sea water float?

12. Why is there a sound speed minimum in the middle of the water column?

Typical profiles and vertical structures

1. How deep is a typical mixed layer if mixed by wind? How deep can it reach if driven by cooling?

2. How do vertical temperature and salinity profiles differ between the subtropical and subpolar regions?

3. What appears to be a minimum number of layers with which the ocean can be described, based on salinity and oxygen?

4. What is the volumetrically most common water on earth and where is it found?

5. Is the North Atlantic Ocean saltier or fresher on average than the Pacific?

Dynamic height

1. Why is it so difficult (e.g. expensive) to determine the circulation below about 1000 meters?

2. What are the common methods for measuring currents in the ocean?

3. How are temperature and salinity information used to calculate currents? What is the biggest drawback to this method? Why aren't direct current measurements used more frequently?

4. What dynamic height difference over 100 km is associated with a current speed of 100 cm/sec?

5. What dynamic height difference is associated with a transport of 100 Sverdrups? (1 Sverdrup = 10**6 m**3/sec)

Forcing

1. What are the two principle driving forces for the general circulation?

2. How is wind forcing communicated to the general circulation: What is the direct response of the ocean to the imposed surface stress? How deep does this response extend? How is the forcing communicated deeper in the water column?

3. For a wind stress of 1 dyne/cm**2, what is the vertically-integrated Ekman transport at 40N? If the wind stress changes from eastward at 1 dyne/cm**2 at 40N to westward at 1 dyne/cm**2 at 20N, what is the order of magnitude of the vertical velocity? Is the vertical velocity up or down? (In calculating this, don't worry about the effect of the changing latitude on the Ekman transport, and assume the change in stress is linear with distance.)

Fortran computer algorithms for properties of seawater.

You can type them in yourself from the UNESCO tables or get them through netscape to the anonymous ftp site on nemo.ucsd.edu:

Netscape instructions

netscape to ftp://nemo.ucsd.edu
click into the subdirectory pub/user_software (in anonym ftp, cd pub/user_software)
retrieve the files: README, ppsw.f and all other files ending in .f

Anonymous ftp instructions

ftp nemo.ucsd.edu
login anonymous
cd pub/user_software
mget *
quit