Earth Planets Space, Vol. 58 (No. 6), pp. 785-791, 2006
I. Wardinski and M. Mandea
Section 2.3, Earth's Magnetic Field, Geoforschungszentrum Potsdam, Germany
(Received June 10, 2005; Revised February 3, 2006; Accepted February 6, 2006; Online published June 2, 2006)
Monthly means of three geomagnetic components (X-northern, Y-eastern and Z-vertical downward) from 154 observatories over the interval 1960-2002 have been analysed to determine the annual and semi-annual variations. The method applied is a multi-taper analysis, which gives a robust estimate of the power spectral density of the temporal variation of the field components. The main objective is to investigate the geographic dependence of the annual and semi-annual variations. Surprisingly, these variations in the vertical downward component are not homogeneously distributed all over the globe, having mainly a longitudinal dependency. The results of the analysis are briefly discussed with regard to possible mechanisms responsible for these variations and to mantle conductivity.
Key words: Geomagnetic field variation, multi-taper method, time series analysis.