Skip to main content

Advertisement

We’d like to understand how you use our websites in order to improve them. Register your interest.

A numerical study on magnetic polarity transition in an MHD dynamo model

Abstract

Magnetic polarity transitions in a Takahashi-Matsushima-Honkura dynamo model are analyzed. Distinctive differences in behavior of the axisymmetric poloidal magnetic field are found among a polarity reversal and excursions, including short polarity events. At the beginning of magnetic polarity transitions, the magnetic field with the reversed polarity is generated by anti-cyclonic convection columns deep within the outer core. In the case of excursion, it is soon advected by the radial flow toward a shallow interior of the core, and the transition can be detected at the core surface. However, the same process retrieves the original polarity from the deep interior, and the reversed field eventually vanishes. In the case of polarity reversal, on the other hand, the reversed polarity field is persistently generated deep within the core. It is then advected toward a shallow interior of the core, while the generation process of the reversed field occurs successively. The reversed polarity field near the core surface is collected by the downwelling flow associated with convection columns, as is the case for the original polarity field. The polarity reversal is completed by the advection process, the duration of which is consistent with the flow speed in the core.

References

  1. Bouligand, C., G. Hulot, A. Khokhlov, and G. A. Glatzmaier, Statistical palaeomagnetic field modelling and dynamo numerical simulation, Geophys. J. Int., 161, 603–626, 2005.

  2. Brown, L. L., B. S. Singer, J. C. Pickens, and B. R. Jicha, Paleomagnetic directions and 40Ar/39Ar ages from the Tatara-San Pedro volcanic complex, Chilean Andes: Lava record of a Matuyama-Brunhes precursor?, J. Geophys. Res., 109, B12101, doi:10.1029/2004JB003007, 2004.

  3. Christensen, U. R. and J. Aubert, Scaling properties of convection-driven dynamos in rotating spherical shells and application to planetary magnetic fields, Geophys. J. Int., 166, 97–114, 2006.

  4. Christensen, U. R., P. Olson, and G. A. Glatzmaier, Numerical modelling of the geodynamo: A systematic parameter study, Geophys. J. Int., 138, 393–409, 1999.

  5. Clement, B. M., Dependence of the duration of geomagnetic polarity reversals on site latitude, Nature, 428, 637–640, 2004.

  6. Coe, R., L. Hongre, and G. A. Glatzmaier, An examination of simulated geomagnetic reversals from a palaeomagnetic perspective, Philos. Trans. R. Soc. Lond. A, 358, 1141–1170, 2000.

  7. Glatzmaier, G. A. and P. H. Roberts, A three-dimensional self-consistent computer simulation of a geomagnetic field reversal, Nature, 377, 203–209, 1995.

  8. Gubbins, D., The distinction between geomagnetic excursions and reversals, Geophys. J. Int., 137, F1–F4, 1999.

  9. Gubbins, D. and K. Zhang, Symmetry properties of the dynamo equations for palaeomagnetism and geomagnetism, Phys. Earth Planet. Inter., 75, 225–241, 1993.

  10. Guillou, H., B. S. Singer, C. Laj, C. Kissel, S. Scaillet, and B. R. Jicha, On the age of the Laschamp geomagnetic excursion, Earth Planet. Sci. Lett, 227, 331–343, 2004.

  11. Kageyama, A., T. Sato, and the Complexity Simulation Group, Computer simulation of a magnetohydrodynamic dynamo II, Phys. Plasmas, 2, 1421–1431, 1995.

  12. Kono, M. and P. H. Roberts, Recent geodynamo simulations and observations of the geomagnetic field, Rev. Geophys., 40, 1013, doi:10. 1029/2000RG000102, 2002.

  13. Kutzner, C. and U. R. Christensen, From stable dipolar towards reversing numerical dynamos, Phys. Earth Planet. Inter., 131, 29–45, 2002.

  14. Kutzner, C. and U. R. Christensen, Simulated geomagnetic reversals and preferred virtual geomagnetic pole paths, Geophys. J. Int., 157, 1105–1118, 2004.

  15. Li, J., T. Sato, and A. Kageyama, Repeated and sudden reversals of the dipole field generated by a spherical dynamo action, Science, 295, 1887–1890, 2002.

  16. McMillan, D. G., C. G. Constable, R. L. Parker, and G. A. Glatzmaier, A statistical analysis of magnetic fields from some geodynamo simulations, Geochem. Geophys. Geosyst., 2, doi:10.1029/2000GC000130, 2001.

  17. Merrill, R., M. McElhinny, and P. McFadden, The Magnetic Field of the Earth, Academic Press, San Diego, 1

  18. Mochizuki, N., H. Tsunakawa, H. Shibuya, T. Tagami, A. Ozawa, J. Cassidy, and I. E. M. Smith, K-Ar ages of the Auckland geomagnetic excursions, Earth Planets Space, 56, 283–288, 2004.

  19. Mochizuki, N., H. Tsunakawa, H. Shibuya, J. Cassidy, and I. E. M. Smith, Palaeointensities of the Auckland geomagnetic excursions by the LTD-DHT Shaw method, Phys. Earth Planet. Inter., 154, 168–179, 2006.

  20. Mochizuki, N., H. Tsunakawa, H. Shibuya, T. Tagami, A. Ozawa, and I. E. M. Smith, Further K-Ar dating and paleomagnetic study of the Auckland geomagnetic excursions, Earth Planets Space, 59, this issue, 755–761, 2007.

  21. Oda, H., M. J. Dekkers, C. G. Langereis, L. Lourens, and D. Heslop, A paleomagnetic record of the last 640 kyr from an eastern Mediterranean piston core and a review of geomagnetic excursions in the Brunhes, EOS Trans. AGU, 95, GP41B-08 (Abstract), 2004.

  22. Olson, P. and U. R. Christensen, Dipole moment scaling for convection-driven planetary dynamos, Earth Planet. Sci. Lett, 250, 561–571, 2006.

  23. Olson, P., U. R. Christensen, and G. A. Glatzmaier, Numerical modeling of the geodynamo: Mechanisms of field generation and equilibration, J. Geophys. Res., 104, 10383–10404, 1999.

  24. Sarson, G. R. and C. A. Jones, A convection driven geodynamo reversal model, Phys. Earth Planet. Inter., 111, 3–20, 1999.

  25. Singer, B. S., M. K. Relle, K. A. Hoffman, A. Battle, C. Laj, H. Guillou, and J. C. Carracedo, Ar/Ar ages from transitionally magnetized lavas on La Palma, Canary Islands, and the geomagnetic instability timescale, J. Geophys. Res., 107, 2307, doi:10.1029/2001JB001613, 2002.

  26. Takahashi, F. and M. Matsushima, Dynamo action in a rotating spherical shell at high Rayleigh numbers, Phys. Fluids, 17, 076601, 2005.

  27. Takahashi, F., J. S. Katayama, M. Matsushima, and Y. Honkura, Effects of boundary layers on magnetic field behavior in an MHD dynamo model, Phys. Earth Planet. Inter., 128, 149–161, 2001.

  28. Takahashi, F., M. Matsushima, and Y. Honkura, Dynamo action and its temporal variation inside the tangent cylinder in MHD dynamo simulations, Phys. Earth Planet. Inter., 140, 53–71, 2003.

  29. Takahashi, F., M. Matsushima, and Y. Honkura, Simulations of a quasiTaylor state geomagnetic field including polarity reversals on the Earth Simulator, Science, 309, 459–461, 2005.

  30. Takahashi, F., M. Matsushima, and Y. Honkura, Scale variability in convection-driven MHD dynamos at low Ekman number, Geophys. J. Int., 2007 (submitted).

  31. Wicht, J., Inner-core conductivity in numerical dynamo simulations, Phys. Earth Planet. Inter., 132, 281–302, 2002.

  32. Wicht, J., Palaeomagnetic interpretation of dynamo simulations, Geophys. J. Int., 162, 371–380, 2005.

  33. Wicht, J. and P. Olson, A detailed study of the polarity reversal mechanism in a numerical dynamo model, Geochem. Geophys. Geosyst., 5, Q03H10, doi:10.1029/2003GC000602, 2004.

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to Futoshi Takahashi.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Takahashi, F., Matsushima, M. & Honkura, Y. A numerical study on magnetic polarity transition in an MHD dynamo model. Earth Planet Sp 59, 665–673 (2007). https://doi.org/10.1186/BF03352729

Download citation

Key words

  • Dynamo
  • magnetic polarity transition
  • advection
  • stretching