A note on the secular variation of the geomagnetic field

Details A note on the secular variation of the geomagnetic field A note on the secular variation of the geomagnetic field

Aug 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982pepi...29..119m&link_type=abstract

Physics of the Earth and Planetary Interiors, vol. 29, Aug. 1982, p. 119-134.

Physics

8

Geomagnetism, Magnetic Variations, Periodic Variations, Secular Variations, Data Processing, Dynamo Theory, Fourier Analysis, Linear Filters

Scientific paper

Data processing methods used by Alldredge (1976, 1977) and Courtillot and Le Mouel (1976) to study secular variations of the geomagnetic field are analyzed. Variations that appear to have periods of 13-30 years may be due to geomagnetic signals of longer periods, and the remainder of these variations may be of external origin. In order to attenuate low frequencies with periods of the order of 1000 years while studying a frequency band with periods in the order of 10 years by Fourier analyzing data, the data should first be filtered. To estimate spectra of the data, this principle still applies. The data processing methods used are shown to be linear and to constitute time-varying linear filters. Estimations of the temporal Fourier spectrum for the vertical magnetic field are given. It is shown how Courtillot and Le Mouel observations indicate that their spectra of annual means of geomagnetic data are aliased in the 5-2 year period range, and that spectra within the 10 year to 2 month range correspond to the random walk. A filtering method which reduces leakage is presented, and all of these filter methods will hopefully assist in future field variation studies.

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