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The time-varying geomagnetic field of Southern Africa

Abstract

The geomagnetic field at any given epoch is a function of space coordinates, varying differently at each location with time. It has been known that secular change is a comparatively local phenomenon and that it does not proceed in a regular way all over the Earth, giving rise to regions where the field changes more rapidly than elsewhere, like for instance southern Africa. The Hermanus Magnetic Observatory routinely executes geomagnetic repeat surveys, which includes South Africa, Namibia, Zimbabwe and Botswana. Spherical cap modelling of field survey and observatory secular variation data at 5 year intervals between 1975 and 2000 shows that a geomagnetic jerk occurred between 1980 and 1985 over southern Africa. The secular variation models are based on 70 repeat station data central differences as well as the 3 magnetic observatories at Hermanus, Hartebeesthoek and Tsumeb (Namibia) and include terms up to spatial degree 3 and temporal degree 2. Although each model allows for 48 coefficients, only 42 were found to be statistically significant.

References

  1. Alexandrescu, M., D. Gibert, D. Hulot, J.-L. Le Mouël, and G. Saracco, Detection of geomagnetic jerks using wavelet analysis, J. Geophys. Res., 100, 12557–12572, 1995.

    Article  Google Scholar 

  2. Alexandrescu, M., D. Gibert, D. Hulot, J.-L. Le Mouël, and G. Saracco, Worldwide wavelet analysis of geomagnetic jerks, J. Geophys. Res., 101, 21975–21994, 1996.

    Article  Google Scholar 

  3. Bloxham, J. and D. Gubbins, The secular variation of Earth’s magnetic field, Nature, 317, 777–781, 1985.

    Article  Google Scholar 

  4. Bullard, E. C., The secular change in the Earth’s magnetic field, Mon. Notices Royal Astronom. Soc, Geophys. Suppl, 5, 248–257, 1948.

    Article  Google Scholar 

  5. Courtillot, V. and J.-L. Le Mouël, Geomagnetic secular variation impulses: A review of observational evidence and geophysical consequences, Nature, 311, 709–716, 1984.

    Article  Google Scholar 

  6. De Michelis, P., L. Cafarella, and A. Meloni, Worldwide character of the 1991 jerk, Geophys. Res. Lett., 25, 377–380, 1998.

    Article  Google Scholar 

  7. Efroymson, M. A., Multiple regression analysis, in Mathematical Methods for Digital Computers, edited by A. Ralston and H. S. Wilf, pp. 191–203, John Wiley, New York, 1960.

    Google Scholar 

  8. Golovkov, V. P., T. I. Zvereva, and A. O. Simonyan, Common features and differences between ‘jerks’ of 1947, 1958 and 1969, Geophys. Astrophys. Fluid Dyn., 49, 81–96, 1989.

    Article  Google Scholar 

  9. Haines, G. V., Spherical cap harmonic analysis, J. Geophys. Res., 90, 2583–2591, 1985a.

    Article  Google Scholar 

  10. Haines, G. V., Spherical cap harmonic analysis of geomagnetic secular variation over Canada 1960–1983, J. Geophys. Res., 90, 12563–12574, 1985b.

    Article  Google Scholar 

  11. Kotzé, P. B., Spherical cap modelling of Ørsted magnetic field vectors over southern Africa, Earth Planets Space, 53, 357–361, 2001.

    Article  Google Scholar 

  12. Le Huy, M., M. Mandea, G. Hulot, and J.-L. Le Mouël, On the characteristics of successive geomagnetic jerks, Earth Planets Space, 50, 723–732, 1998.

    Article  Google Scholar 

  13. Le Huy, M., M. Mandea, J.-L. Le Moüel, and A. Pais, Time evolution of the fluid flow at the top of the core, Earth Planets Space, 52, 163–173, 2000.

    Article  Google Scholar 

  14. MacMillan, S., A geomagnetic jerk for the early 1990s, Earth Planet. Sci. Lett., 137, 189–192, 1996.

    Article  Google Scholar 

  15. McLeod, M. G., On the geomagnetic jerk of 1969, J. Geophys. Res., 90, 4597–4610, 1985.

    Article  Google Scholar 

  16. McLeod, M. G., Geomagnetic secular variation, in Geomagnetism and Paleomagnetism, edited by F. J. Lowes, D. W. Collison, J. H. Parry, S. K. Runcorn, D. C. Tozer, and A. Soward, pp. 19–30, Kluwer Acad., Mass., 1989.

    Google Scholar 

  17. Malin, S. R. C. and B. M. Hodder, Was the 1970 geomagnetic jerk of internal or external origin?, Nature, 296, 726–728, 1982.

    Article  Google Scholar 

  18. Mizuno, H., Abrupt change in secular variation rate of geomagnetic north component observed in Japan, J. Geomag. Geoelectr, 32, 413–420, 1980.

    Article  Google Scholar 

  19. Stewart, D. N. and K. Whaler, Geomagnetic disturbance fields: An analysis of observatory monthly means, Geophys. J. Int., 108, 215–223, 1992.

    Article  Google Scholar 

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Correspondence to P. B. Kotzé.

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Kotzé, P.B. The time-varying geomagnetic field of Southern Africa. Earth Planet Sp 55, 111–116 (2003). https://doi.org/10.1186/BF03351738

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Keywords

  • Secular Variation
  • Earth Planet Space
  • Repeat Station
  • Magnetic Observatory
  • Geomagnetic Jerk