SIO 210 Talley Topic 4: Pacific circulation: wind driving

Lynne Talley, 2000
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Reading and study questions

Reading (on reserve):

Tomczak and Godfrey text: ch. 8 (pp. 113-121, 130-141) and ch. 9 (pp. 149-166)
Pickard and Emery text: 7.62, 7.65

Talley, L. D., 1995. Some advances in understanding of the general circulation of the Pacific Ocean with emphasis on recent U.S. contributions. U. S. National Report, 1991-1994, Contributions in Ocean Sciences. American Geophysical Union. 1335-1352.

Reid, J.L., 1997. On the total geostrophic circulation of the Pacific Ocean: flow patterns, tracers, and transports. Prog. in Oceanogr., 39, 263-352.

Study questions:

North Pacific circulation

1. Name the major surface currents north of about 15 N in the Pacific.

2. What drives the large gyres of the North Pacific? Describe the dynamic topography distribution that is associated with the gyres. Describe the vertical structure of the subtropical gyre. (What happens to its structure with depth?)

3. Where is the Kuroshio? Where does it become the Kuroshio Extension? How deep does the Kuroshio Extension reach? What is the circulation just to the south of the Kuroshio Extension? Does the Kuroshio Extension transport vary with longitude?

4. How does water get from the surface to below the surface in the subtropical gyre? (What is subduction?) Why is there a tongue of high tritium and low salinity extending westward along the southern limb of the subtropical gyre?

5. What is Subtropical Mode Water, where is it found, and what is a possible mechanism for forming it?

6. What is the surface structure that separates waters of the subtropical and subpolar gyres? What is its importance for fisheries?

7. Where does the densest ventilation in the North Pacific occur? What processes are important in this ventilation? How is this relatively dense ventilation recognized on maps of oxygen and salinity?

8. What is the direction of mean flow through Bering Strait? How deep is the strait?

9. What is the source of the deep water in the North Pacific?

10. What evidence is there for large-scale vertical mixing between the surface/intermediate/deep layers?

General wind-driven circulation ideas

1. What are the common elements of the surface circulation found in each of the five ocean basins? What are the elements common to the two northern hemisphere oceans? What distinguishes these from the three southern hemisphere oceans? What is special about the Indian Ocean?

2. Name the major surface western boundary currents, indicate which way they flow and what gyre circulation they are a part of. What are typical maximum velocities and dynamic height differences for these boundary currents?

3. What horizontal and vertical structure is typical of the subtropical gyre?

4. How deep are the western boundary currents and the Antarctic Circumpolar Current?

5. How deep is the typical wind-driven gyre, excluding the western boundary current?

6. In which parts of the ocean is it currently assumed that the Sverdrup balance is approximately correct? Where is it clearly incorrect?

7. How deep is the directly wind-driven layer? How deep is the surface mixed layer in the North Pacific? How deep is it in the North Atlantic? Why are they so different in the subpolar regions of these two oceans?

Study calculations

1. If the Kuroshio Extension velocity is 10 cm/sec averaged from top to bottom, and the current width is 100km, assuming a depth of 5 km, what is its volume transport? Express transport in Sverdrups. What is its approximate mass transport assuming a constant density?

2. If the Bering Strait velocity is 5 cm/sec averaged from top to bottom, what is its approximate transport? (Make a very rough calculation, with rough values fo the width and depth.)

3. If the California Current velocity is 10 cm/sec over a depth of 200 m, with a width of 100 km, what is its approximate transport?

4. Calculate the approximate heat transport associated with the shallow part of the Kuroshio and its return flow. Assume that 50 Sv flows northward in the Kuroshio at 22C, and returns southward in the interior at 18C. Use a density of 1025 kg/m^3 and a specific heat of 3850 J/(kg C).

Further reading and figure sources

Bingham, F.M. and L.D. Talley, 1991. Estimates of Kuroshio transport using an inverse technique. Deep-Sea Res., 38, S21-S43.

Dodimead, A.J., F. Favorite and T. Hirano, 1962. International North Pacific Fisheries Commission, Bulletin Number 13: Salmon of the North Pacific, Part II.

Favorite, F., A.J. Dodimead and K.Nasu, 1976. International North Pacific Fisheries Commission, Bulletin Number 33: Oceanography of the subarctic Pacific region, 1960-71.

Fine, R.A., J.L. Reid and H.G. Ostlund, 1981. Circulation of tritium in the Pacific Ocean. J. Phys. Oceanogr., 3-14.

Hasunuma, K. and K. Yoshida, 1978. Splitting of the subtropical gyre in the western North Pacific. J. Oceanogr. Soc. Japan, 34, 160-172.

Joyce, T.M., 1982. Hydrographic sections across the Kuroshio extension at 165\(deE and 175\(deW. Deep-Sea Res., 34, 1331-1352.

Kawai, H., 1972. Hydrography of the Kuroshio extension. In: Kuroshio, physical aspects of the Japan Current, H. Stommel and K.Yoshida, editors, U. Washington Press, Seattle, pp. 235-352.

Masuzawa, J., 1969. Subtropical mode water. Deep-Sea Res., 16, 463-472.

Mizuno, K. and W.B. White, 1983. Annual and itnerannual variability in the Kuroshio current system. J. Phys. Oceanogr., 13, 1847-1867.

Niiler, P.P., W.J. Schmitz and D.-K. Lee, 1985. Geostrophic volume transport in high eddy-energy areas of the Kuroshio Extension and Gulf Stream. J. Phys. Oceanogr., 15, 825-843.

Nitani, H., 1972. Beginning of the Kuroshio. In: Kuroshio, physical aspects of the Japan Current, H. Stommel and K.Yoshida, editors, U. Washington Press, Seattle, pp. 129-164.

Nitani, H., 1975. Variation of the Kuroshio south of Japan. J. Oceanogr. Soc. of Japan, 31, 154-173.

Reid, J.L., 1982. On the use of dissolved oxygen concentration as an indicator of winter convection. Naval Research Reviews, 34, 28-39.

Reid, J.L., 1986. On the total geostrophic circulation of the South Pacific Ocean: flow patterns, tracers and transports. Prog. in Oceanogr., 16, 1-61.

Reid, J.L., 1997. On the total geostrophic circulation of the Pacific Ocean: flow patterns, tracers, and transports. Prog. in Oceanogr., 39, 263-352.

Roemmich, D., S. Hautala and D. Rudnick, 1996. Northward abyssal transport through the Samoan passage and adjacent regions. J. Geophys. Res., 101, 14039-14055.

Roemmich, D.L. and T. McCallister, 1989. Large scale circulation of the North Pacific Ocean. Prog. in Oceanography, 22, 171-204. (read for general ideas; please don't worry about the method - section 4).

Talley, L. D., 1993. Distribution and formation of North Pacific Intermediate Water. J. Phys. Oceanogr., 23, 517-537.

Talley, L.D. and T.J. Joyce, 1992. The double silica maximum in the North Pacific., J. Geophys. Res., 97, 5465-5480.

Talley, L. D. and G. C. Johnson, 1994. Deep, zonal subequatorial currents. Science, 263, 1125-1128.

Tsuchiya, M., 1982. On the Pacific upper-water circulation. J. Mar. Res., 40 (Suppl.), 777-799.

Yuan, X. and L.D. Talley, 1992. Shallow salinity minima in the North Pacific. J. Phys. Oceanogr., 22, 1302-1316.

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.