- Article
- Published:
The time-varying geomagnetic field of Southern Africa
Earth, Planets and Space volume 55, pages 111–116 (2003)
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
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.
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.
Bloxham, J. and D. Gubbins, The secular variation of Earth’s magnetic field, Nature, 317, 777–781, 1985.
Bullard, E. C., The secular change in the Earth’s magnetic field, Mon. Notices Royal Astronom. Soc, Geophys. Suppl, 5, 248–257, 1948.
Courtillot, V. and J.-L. Le Mouël, Geomagnetic secular variation impulses: A review of observational evidence and geophysical consequences, Nature, 311, 709–716, 1984.
De Michelis, P., L. Cafarella, and A. Meloni, Worldwide character of the 1991 jerk, Geophys. Res. Lett., 25, 377–380, 1998.
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.
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.
Haines, G. V., Spherical cap harmonic analysis, J. Geophys. Res., 90, 2583–2591, 1985a.
Haines, G. V., Spherical cap harmonic analysis of geomagnetic secular variation over Canada 1960–1983, J. Geophys. Res., 90, 12563–12574, 1985b.
Kotzé, P. B., Spherical cap modelling of Ørsted magnetic field vectors over southern Africa, Earth Planets Space, 53, 357–361, 2001.
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.
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.
MacMillan, S., A geomagnetic jerk for the early 1990s, Earth Planet. Sci. Lett., 137, 189–192, 1996.
McLeod, M. G., On the geomagnetic jerk of 1969, J. Geophys. Res., 90, 4597–4610, 1985.
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.
Malin, S. R. C. and B. M. Hodder, Was the 1970 geomagnetic jerk of internal or external origin?, Nature, 296, 726–728, 1982.
Mizuno, H., Abrupt change in secular variation rate of geomagnetic north component observed in Japan, J. Geomag. Geoelectr, 32, 413–420, 1980.
Stewart, D. N. and K. Whaler, Geomagnetic disturbance fields: An analysis of observatory monthly means, Geophys. J. Int., 108, 215–223, 1992.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Kotzé, P.B. The time-varying geomagnetic field of Southern Africa. Earth Planet Sp 55, 111–116 (2003). https://doi.org/10.1186/BF03351738
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1186/BF03351738