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Unusual behaviour of the IGRF during the 1945–1955 period
Earth, Planets and Spacevolume 52, pages1227–1233 (2000)
The International Geomagnetic Reference Field (IGRF) for 1900–2000 is testedin this paper. A peculiar behaviour is found in the time variations of higher-degree coefficients of the IGRF models. During the 1945–1955 period the spherical harmonic coefficients g n m and h n m with n > 7 show unusual jumps, while their variations before and after this period are quite smooth. These irregular variations have little effect on the main features of the surface magnetic pattern. However, when we extrapolate the field pattern downward through the insulating mantle to the core-mantle boundary (CMB), the contributions of the higher-degree coefficients become more important and are likely to affect the shape of the geomagnetic energy spectrum, distribution of magnetic flux, and magnetic determination of the conducting core radius. It seems necessary to re-examine and revise these coefficients in the IGRF models.
Baldwin, R. T. and R. A. Langel, Tables and maps of the DGRF 1985 and IGRF 1990, in IAGA Bulletin, 54, 183 pp., 1993.
Barraclough, D. R., International Geomagnetic Reference Field revision, Nature, 318, 316, 1985.
Barraclough, D. R., International Geomagnetic Reference Field: the fourth generation, Phys. Earth Planet. Int., 48, 279–292, 1987.
Barton, C. E., International Geomagnetic Reference Field: the seventh gen eration, J. Geomag. Geoelectr., 49, 123–148, 1997.
Benton, E. R., R. H. Estes, R. A. Langel, and L. A. Muth, Sensitivity of selected geomagnetic properties to truncation level of spherical harmonic expansions, Geophys. Res. Lett., 9, 254–257, 1982.
Bloxham, J. and D. Gubbins, The secular variation of Earth’s magnetic field, Nature, 317, 777–781, 1985.
Bloxham, J. and A. Jackson, Fluid flow near the surface of Earth’s outer core, Rev. Geophys., 29, 97–120, 1991.
Bloxham, J. and A. Jackson, Time-dependent mapping of the magnetic field at the core-mantle boundary, J. Geophys. Res., 97, 19537–19563, 1992.
Cain, J. C., Z. Wang, D. R. Schmitz, and J. Meyer, The geomagnetic spectrum for 1980 and core-crustal separation, Geophys. J., 97, 443–447, 1989.
Chapman, S. and J. Bartels, Geomagnetism, 1049 pp., Oxford University Press, London, 1940.
Ducruix, J., V. Courtillot, and J.L. LeMouel, The late 1960s secular impulse, the eleven year magnetic variation and the electrical conductivity of the deep mantle, Geophys. J. R. Astr. Soc., 61, 73–94, 1980.
Hide, R., How to locate the electrically conducting fluid core of a planet from external magnetic observations, Nature, 271, 640–641, 1978.
Hide, R. and S. R. C. Malin, On the determination of the size of the earth’s core from observations of the geomagnetic secular variation, Proc. R. Soc. Lond., A347, 15–33, 1981.
Hulot, G., J. L. Le Mouel, and J. Wahr, Taking into account truncation problems and geomagnetic model accuracy in assessing computed flows at the core-mantle boundary, Geophys. J. Int., 108, 224–246, 1992.
IAGA Commission 2 Working Group 4, International Geomagnetic Refer ence Field 1965.0, J. Geophys. Res., 74, 4407–4408, 1969.
IAGA Division 1 Study Group on Geomagnetic Reference Field, Interna tional Magnetic Reference Field 1975, J. Geomag. Geoelectr., 27, 437–439, 1975.
IAGA Division 1, Working Group 1, International geomagnetic reference field: DGRF1965, DGRF1970, DGRF 1975 and IGRF 1980, EOS Trans. Am. Geophys. Union, 62, 1169–1170, 1981.
IAGA Division 1, Working Group 1, International geomagnetic reference field revision 1985, J. Geomag. Geoelectr., 37, 1157–1163, 1985.
IAGA Division 1, Working Group 1, International geomagnetic reference field revision 1987, J. Geomag. Geoelectr., 39, 773–779, 1987.
IAGA Division 5, Working Group 8, International Geomagnetic Reference Field, 1991 revision, J. Geomag. Geoelectr., 43, 1007–1012, 1991.
IAGA Division 5, Working Group 8, International Geomagnetic Reference Field, 1995 revision, Geophys. J. Int., 125, 318–321, 1996.
IAGA Division 5, Working Group 8, International Geomagnetic Reference Field 2000, Geophys. J. Int., 141, 259–262, 2000.
Langel, R. A., The main field, in Geomagnetism, edited by J. A. Jacobs, Vol. 1, pp. 249–512, Academic Press, London, 1987.
Langel, R. A., International geomagnetic reference field: the sixth genera tion, J. Geomag. Geoelectr., 44, 679–707, 1992.
Langel, R. A. and R. H. Estes, A geomagnetic field spectrum, Geophys. Res. Lett., 9, 250–253, 1982.
Langel, R. A. and R. H. Estes, Derivation of proposed International Geomagnetic Reference Field models for 1945, 1950, 1955, and 1960, Phys. Earth Planet. Int., 48, 293–305, 1987.
Langel, R. A., D. R. Barraclough, D. J. Kerridge, V. P. Golovkov, T. J. Sabaka, and R. H. Estes, Definitive IGRF models for 1945, 1950, 1955, and 1960, J. Geomag. Geoelectr., 40, 645–702, 1988.
Lowes, F. J., Mean square values on sphere of spherical harmonic vector field, J. Geophys. Res., 71, 2179, 1966.
Lowes, F. J., Spatial power spectrum of the main geomagnetic field and extrapolation to the core, Geophys. J. R. Astr. Soc., 36, 717–730, 1974.
Macmillan, S. and C. E. Barton, Magnetic field maps for IGRF 1995, J. Geomag. Geoelectr., 49, 149–156, 1997.
Malin, S. R. C., B. M. Hodder, and D. R. Barraclough, Geomagnetic secular variation: A jerk in 1970. Publicado en volumen commemorativo 75 aniversario del observatorio del Ebro, (75th anniversary volume of Ebro observatory), edited by J. O. Cardus, pp. 239–256, Tarragona, 1983.
Olson, P. and J. Aurnou, A polar vortex in the Earth’s core, Nature, 402, 170–173, 1999.
Pais, A. and G. Hulot, Lengthof day decade variations, torsional oscillations and inner core superrotation: evidence from recovered core surface zonal flows, Phys. Earth Planet. Int., 118, 291–316, 2000.
Sabaka, T. J., R. A. Langel, R. T. Baldwin, and J. A. Conrad, The geo magnetic field 1900–1995, including the large-scale field from magnetospheric sources, and the NASA candidate models for the 1995 revision, J. Geomag. Geoelectr., 49, 157–206, 1997.
Verosub, K. L. and A. Cox, Changes in the total magnetic energy external to the earth’s core, J. Geomag. Geoelectr., 23, 235–242, 1971.
Voorhies, C. V. and E. R. Benton, Pole-strength of the Earth from MAGSAT and magnetic determination of the core radius, Geophys. Res. Lett., 9, 258–261, 1982.
Zmuda, A. J., The International Geomagnetic Reference Field, 1965.0, in IAGA Bulletin, 28, World Magnetic Survey, IUGG, Paris, 1971.