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Spherical cap harmonic analysis of magnetic variations data from mainland Australia

Abstract

Spherical cap harmonic analysis (SCHA) has been applied to geomagnetic data from an array of magnetometers deployed across the Australian mainland during 1989–90 in order to examine features of the ionospheric Sq current system. The external contours, corresponding to ionospheric currents, are generally in good agreement with the data in that the direction of current flow is perpendicular to the measured horizontal magnetic field. The derived internal (induced) current systems are less reliable but exhibit fairly consistent behaviour on some occasions. As the Sq current system whorl passes over Australia, the reversed internal current whorl lags by a bit less than an hour. When the external system moves off the continent into the Indian Ocean, the derived internal system sometimes appears to remain over the continent for about two hours but this is found to be caused by the large coastal effect in the west. The variations obtained from the analysis at particular sites are compared with the original data and give generally good agreement. Internal and external variations at several sites are derived and behave as expected to some extent. In particular we find that the internal component of the vertical element adds to the external component on the west coast but subtracts from it on the east coast. Further analyses are performed using data from the CM4 model. The SCHA gives a separation of internal and external components in good agreement with the original for the horizontal CM4 magnetic fields while the agreement is not so good for the vertical component.

References

  • Chamalaun, F. H. and C. E. Barton, Electromagnetic Induction in the Australian Crust: Results from the Australian-Wide Array of Geomagnetic Stations, Explor. Geophys., 24, 179–186, 1993a.

    Article  Google Scholar 

  • Chamalaun, F. H. and C. E. Barton, The large scale conductivity structure of Australia, J. Geomag. Geoelectr., 45, 1209–1212, 1993b.

    Article  Google Scholar 

  • De Santis, A. and J. M. Torta, Spherical cap harmonic analysis: a comment on its proper use for local gravity field representation, J. Geod., 71, 526–532, 1997.

    Article  Google Scholar 

  • De Santis, A., J. M. Torta, and F. J. Lowes, Spherical cap harmonics revisited and their relationship to ordinary spherical harmonics, Phys. Chem. Earth (A), 24, 935–941, 1999.

    Article  Google Scholar 

  • Düzgit, Z. and S. R. C. Malin, Assessment of regional geomagnetic field modelling methods using a standard data set: spherical harmonic analysis, Geophys. J. Int., 141, 829–831, 2000.

    Article  Google Scholar 

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

    Article  Google Scholar 

  • Haines, G. V. and J. M. Torta, Determination of equivalent current sources from spherical cap harmonic models of geomagnetic field variations, Geophys. J. Int., 118, 499–514, 1994.

    Article  Google Scholar 

  • Lowes, F. J., A problem in using spherical cap harmonic analysis to separate internal and external fields, IUGG Birmingham Abstracts, Week B, p. 324, 1999.

    Google Scholar 

  • Matsushita, S. and H. Maeda, On the geomagnetic solar quiet daily variation field during the IGY, J. Geophys. Res., 70, 2535–2558, 1965.

    Article  Google Scholar 

  • Sabaka, T. J., N. Olsen, and R. A. Langel, A comprehensive model of the quiet-time, near-Earth magnetic field: phase 3, Geophys. J. Int., 151, 32–68, 2002.

    Article  Google Scholar 

  • Sabaka, T. J., N. Olsen, and M. E. Purucker, Extending comprehensive models of the Earth’s magnetic field with Ørsted and CHAMP data, Geophys. J. Int., 159, 521–547, 2004.

    Article  Google Scholar 

  • Stening, R. J., The shape of the Sq current system, Ann. Geophys., 26, 1767–1775, 2008.

    Article  Google Scholar 

  • Stening, R. J. and T. Reztsova, The daily variations of the vertical (Z) element of the geomagnetic field around the coast of mainland Australia, Earth Planets Space, 59, 579–584, 2007.

    Article  Google Scholar 

  • Thébault, E., J. J. Schott, M. Mandea, and J. P. Hoffbeck, A new proposal for spherical cap harmonic modelling, Geophys. J. Int., 159, 83–103, 2004.

    Article  Google Scholar 

  • Thébault, E., J. J. Schott, and M. Mandea, Revised spherical cap harmonic analysis (R-SCHA): validation and properties, J. Geophys. Res., 111, B01102, doi:10.1029/2005JB003836, 2006.

    Google Scholar 

  • Torta, J. M. and A. De Santis, On the derivation of the earth’s conductivity structure by means of spherical cap harmonic analysis, Geophys. J. Int., 127, 441–451, 1996.

    Article  Google Scholar 

  • Torta, J. M., J. J. Curto, and P. Bencze, Behavior of the quiet day ionospheric current system in the European region, J. Geophys. Res., 102, 2483–2494, 1997.

    Article  Google Scholar 

  • Torta, J. M., L. R. Gaya-Piqué, and A. De Santis, Spherical cap harmonic analysis of the geomagnetic field with application for aeronautical mapping, in Geomagnetics for Aeronautical Safety, edited by J. L. Rasson and T. Delipetrov, 291–307, Springer, 2006.

    Chapter  Google Scholar 

  • Winch, D. E., The Sq overhead current system approximation, Planet. Space Sci., 14, 163–172, 1966.

    Article  Google Scholar 

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Correspondence to R. J. Stening.

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Stening, R.J., Reztsova, T., Ivers, D. et al. Spherical cap harmonic analysis of magnetic variations data from mainland Australia. Earth Planet Sp 60, 1177–1186 (2008). https://doi.org/10.1186/BF03352875

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  • DOI: https://doi.org/10.1186/BF03352875

Key words

  • Spherical cap harmonic analysis
  • Sq currents
  • induced currents
  • Australia