Abstract
Nighttime hourly mean values of D, H and Z (or X, Y and Z in a few cases) from 113 observatories for the interval 1964.0 to 1966.0 have been analyzed to determine the semi-annual variation. Results from the 84 observatories with dip latitudes between ±60° have been subjected to spherical harmonic analysis to determine the coefficients of the internal and external parts. Only those coefficients that are found to be significantly different from zero at the 5 per cent level have been included.
One of the main objectives is to obtain a reliable estimate, with confidence limits, of the internal/external ratio at a very low frequency for constraining estimates of the deep conductivity of the mantle. It is shown that a model that includes only the principal P 01 term can lead to a seriously misleading internal/external ratio.
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Akaike, H., A new look at the statistical model identification, IEEE Trans. Autom. Contr., AC-19, 716–723, 1974.
Anderssen, R. S., On the solutions of certain overdetermined systems of linear equations that arise in geophysics, J. Geophys. Res., 74, 1045–1051, 1969.
Banks, R. J., The overall conductivity distribution of the earth, J. Geomag. Geoelectr., 24, 337–351, 1972.
Black, D. I., Lunar and solar magnetic variations at Abinger: their detection and estimation by spectral analysis via Fourier transformation, Phil. Trans. R. Soc. London, A268, 233–263, 1970.
Butcher, E. C. and D. M. Schlapp, The annual variation of the night-time values of the geomagnetic field, Geophys. J. Int., 111, 151–158, 1992.
Campbell, W. H., Secular, annual, and semi-annual changes in the baseline level of the Earth’s magnetic field at North American locations, J. Geophys. Res., 85, 6557–6571, 1980.
Campbell, W. H., Annual and semiannual variations of the geomagnetic field at equatorial locations, J. Atmos. Terr. Phys., 43, 607–616, 1981.
Fukushima, N. and T. Nagata, Morphology of magnetic disturbance, Ann. Geophys., 24, 1–11, 1968.
Gupta, J. C. and S. Chapman, Some statistics concerning the daily geomagnetic character figure Cp, Pure Appl. Geophys., 68, 103–113, 1967
Harwood, J. M. and S. R. C. Malin, Sunspot cycle influence on the geomagnetic field, Geophys. J. R. Astr. Soc., 50, 605–619, 1977.
Hibberd, F. M., The geomagnetic Sq variation—annual, semiannual and solar cycle variations and ring current effects, J. Atmos. Terr. Phys., 47, 341–352, 1985.
Malin, S. R. C., Worldwide distribution of geomagnetic tides, Phil. Trans. R. Soc. London, A274, 551–594, 1973.
Malin, S. R. C. and A. M. Işkara, Annual variation of the geomagnetic field, Geophys. J. R. Astr. Soc., 47, 445–457, 1976.
Malin, S. R. C. and D. M. Schlapp, Geomagnetic lunar analysis by least squares, Geophys. J. R. Astr. Soc., 60, 409–418, 1980.
Malin, S. R. C. and D. E. Winch, Annual variation of the geomagnetic field, Geophys. J. Int., 124, 170–174, 1996.
Malin, S. R. C., M. K. Tunçer, and O. Yazici-Çakim, Systematic analysis of magnetic observatory data—1. A proposed method, Geophys. J. Int., 126, 635–644, 1996.
McCreadie, H. and E. C. Butcher, Preliminary analysis of annual and semiannual variations of the geomagnetic field, Explor. Geophys., 24, 151–156, 1993.
McIntosh, D. H., On the annual variation of magnetic disturbance, Phil. Trans. R. Soc. London, A251, 525–552, 1959.
McLeod, M. G., Magnetospheric and ionospheric signals in magnetic observatory monthly means: electrical conductivity of the deep mantle, J. Geophys. Res., 99, 13577–13590, 1994.
Rangarajan, G. K. and B. N. Bhargava, Long term changes in the amplitude and phase of the semiannual and annual variations in low latgitude geomagnetic field, J. Geomag. Geoelectr., 39, 437–446, 1987.
Rastogi, R. G., Geomagnetic field variations at low latitudes and ionospheric electric fields, J. Atmos. Terr. Phys., 55, 1375–1381, 1993.
Rastogi, R. G., S. Alex, and A. Patil, Seasonal variations of geomagnetic D, H and Z fields at low latitudes, J. Geomag. Geoelectr., 46, 115–126, 1994.
Russell, C. T. and R. L. McPherron, Semi-annual variation of geomagnetic activity, J. Geophys. Res., 78, 92–108, 1973.
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Malin, S.R.C., Winch, D.E. & Işıkara, A.M. Semi-annual variation of the geomagnetic field. Earth Planet Sp 51, 321–328 (1999). https://doi.org/10.1186/BF03352236
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DOI: https://doi.org/10.1186/BF03352236