Abstract
The spatial and temporal variation of the geomagnetic field component annual means has been analyzed. The data used in this study consist of the annual means of the vector magnetic field components measured at nearly one hundred magnetic observatories widely distributed about the Earth. The data that have been analyzed are for the time interval 1961–1977.
Spherical harmonic models for each year within the indicated time interval have been computed for filtered first, second, and third time derivatives of the field using filtered first, second, and third time differences of the annual means as input data. A set of 48 magnetic observatories selected to minimize noise was used for the analysis. Coefficients corresponding to both internal and external sources were included in the models.
The geomagnetic jerk of 1969 was found to be due to internal sources. External current systems were found to be responsible for a significant portion of the first, second and third time differences of the annual means of the geomagnetic field. While most of the effect of the external current systems can be modeled by degree one spherical harmonics, higher degree spherical harmonics are also important for modeling the field due to external sources. The time variation of the external sources included harmonics of the sunspot cycle.
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© 1989 Kluwer Academic Publishers
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McLeod, M.G. (1989). Geomagnetic Secular Variation. In: Lowes, F.J., Collinson, D.W., Parry, J.H., Runcorn, S.K., Tozer, D.C., Soward, A. (eds) Geomagnetism and Palaeomagnetism. NATO ASI Series, vol 261. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-0905-2_2
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DOI: https://doi.org/10.1007/978-94-009-0905-2_2
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