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Time dependency of fluid flow near the top of the core

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Abstract

Fluid flow in the core is assumed to consist of a slowly varying (on time scales > magnetic diffusion time) part and a smaller, rapidly varying part as in the theory of the hydromagnetic dynamo put forward by Braginsky (1965). On the basis of this theory, geomagnetic secular variation models for the last 150 years are used to determine a rapidly varying, axisymmetric, poloidal motion of the fluid near the top of the core as a function of latitude in regions away from the equator. Approximations made in estimating this motion fail near the equator, thus restricting the estimates to latitudes ≥40°. Amplitude of the oscillating part of the axisymmetric poloidal flow is found to be ≤1 km/yr in the northern hemisphere, and nearly 3 km/yr in some parts of the southern hemisphere. The nature of temporal variation of this component differs significantly between the northern and southern hemispheres during the period under consideration.

References

  1. Backus, G. E., Kinematics of the geomagnetic secular variation in a perfectly conducting core, Phil. Trans. Roy. Soc. Lond. A, 263, 239–266, 1968.

  2. Backus, G. E. and J. L. Le Mouël, The region on the core-mantle boundary where a geostrophic velocity field can be determined from frozen flux magnetic data, Geophys. J. R. Astron. Soc., 85, 617–628, 1986.

  3. Benton, E. R. and M. A. Celaya, The simplest, unsteady surface flow of a frozen-flux core that exactly fits a geomagnetic field model, Geophys. Res. Lett., 18, 577–580, 1991.

  4. Bhattacharyya, A., An estimate of the radial gradient of the toroidal magnetic field at the top of the Earth’s core, Phys. Earth Planet. Inter., 90, 81–90, 1995.

  5. Bloxham, J., On the consequences of strong stable stratification at the top of Earth’s outer core, Geophys. Res. Lett., 17, 2081–2084, 1990.

  6. Bloxham, J. and A. Jackson, Simultaneous stochastic inversion for geomagnetic main field and secular variation, 2. 1820–1980, J. Geophys. Res., 94, 15,753–15,769, 1989.

  7. Bloxham, J. and A. Jackson, Fluid flow near the surface of Earth’s outer core, Rev. Geophys., 29, 97–120, 1991.

  8. Bloxham, J. and A. Jackson, Time-dependent mapping of the magnetic field at the core-mantle boundary, J. Geophys. Res., 97, 19,537–19,563, 1992.

  9. Braginsky, S. I., Theory of the hydromagnetic dynamo, Sov. Phys. JETP, 20, 1462–1471, 1965.

  10. Glatzmaier, G. A. and P. H. Roberts, Intermediate dynamo models, J. Geomag. Geoelectr., 45, 1605–1616, 1993.

  11. Gubbins, D., Finding core motions from magnetic observations, Phil. Trans. Roy. Soc. Lond. A, 306, 249–256, 1982.

  12. Honkura, Y. and M. Matsushima, Time-dependent pattern of core motion inferred from fluctuations of standing and drifting non-dipole fields, J. Geomag. Geoelectr., 40, 1511–1522, 1988.

  13. Honkura, Y. and T. Rikitake, Core motion as inferred from drifting and standing non-dipole fields, J. Geomag. Geoelectr., 24, 223–230, 1972.

  14. Hulot, G., M. Le Huy, and J. L. Le Mouël, Secousses (jerks) de la variation sulaire et mouvements dans le noyau terrestre, C. R. Acad. Sci. Paris, 317, 333–341, 1993.

  15. Jackson, A., Time-dependency of tangentially-geostrophic core surface motions, Phys. Earth Planet. Inter., 103, 293, 1997.

  16. Jackson, A., J. Bloxham, and D. Gubbins, Time-dependent flow at the core surface and conservation of angular momentum in the coupled coremantle system, in Dynamics of Earth’s Deep Interior and Earth Rotation, edited by J. L. Le Mouël, D. E. Smylie, and T. Herring, pp. 97–107, AGU Geophysical Monograph 72, IUGG Volume 12, 1993.

  17. Jault, D., C. Gire, and J. L. Le Mouël, Westward drift, core motions and exchanges of angular momentum between core and mantle, Nature, 333, 353–356, 1988.

  18. Kelly, P. and D. Gubbins, The geomagnetic field over the past 5 million years, Geophys. J. Int., 128, 315–330, 1997.

  19. Langel, R. A., The main field, in Geomagnetism, 1, edited by J. A. Jacobs, pp. 249–512, Academic, London, 1987.

  20. Lloyd, D. and D. Gubbins, Toroidal fluid motion at the top of Earth’s core, Geophys. J. Int., 100, 455–467, 1990.

  21. Matsushima, M., Fluid motion in the Earth’s core derived from the geomagnetic field and its implication for the geodynamo, J. Geomag. Geoelectr., 45, 1481–1495, 1993.

  22. Matsushima, M. and Y. Honkura, Fluctuation of the standing and drifting parts of the Earth’s magnetic field, Geophys. J., 94, 35–50, 1988.

  23. Matsushima, M. and Y. Honkura, Large scale fluid motion in the Earth’s outer core estimated from non-dipole magnetic field data, J. Geomag. Geoelectr., 41, 963–1000, 1989.

  24. Matsushima, M. and Y. Honkura, Reexamination of fluid motion in the Earth’s core derived from geomagnetic field data-Is the -effect really strong in the core?, J. Geomag. Geoelectr., 44, 521–553, 1992.

  25. Rikitake, T., Non-dipole field and fluid motion in the Earth’s core, J. Geomag. Geoelectr., 19, 129–142, 1967.

  26. Roberts, P. H. and S. Scott, On the analysis of the secular variation, 1, A hydromagnetic constraint: Theory, J. Geomag. Geoelectr., 17, 137–151, 1965.

  27. Voorhies, C. V., Geomagnetic estimates of steady surficial core flow and flux diffusion: Unexpected geodynamo experiments, in Dynamics of Earth ’s Deep Interior and Earth Rotation, edited by J. L. Le Mouël, D. E. Smylie, and T. Herring, pp. 113–125, AGU Geophysical Monograph 72, IUGG Volume 12, 1993.

  28. Voorhies, C. V. and G. E. Backus, Steady flows at the top of the core from geomagnetic field models: The steady motions theorem, Geophys. Astrophys. Fluid Dyn., 32, 163–173, 1985.

  29. Whaler, K. A., Does the whole of the Earth’s core convect?, Nature, 287, 528–530, 1980.

  30. Yukutake, T. and H. Tachinaka, Separation of the earth’s magnetic field into the drifting and the standing parts, Bull. Earthq. Res. Inst., Univ. Tokyo, 47, 65–97, 1969.

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Correspondence to A. Bhattacharyya.

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Bhattacharyya, A. Time dependency of fluid flow near the top of the core. Earth Planet Sp 50, 813–825 (1998) doi:10.1186/BF03352174

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Keywords

  • Southern Hemisphere
  • Secular Variation
  • Outer Core
  • Core Surface
  • Truncation Level