Notes on Global Mean-Square Values of the Geomagnetic Field and Secular Variation

Abstract

The spatial power spectrum of the geomagnetic field was analyzed by calculating the spectrum for the X, Y and Z components separately. Based on different slopes of the power spectrum lines it was concluded that the dipole field originates partly from the surface layer of the outer core partly from the inner core. The dipole field from the inner core is axially symmetric.
A new method was introduced for separating the drifting and non-drifting parts in the spatial power spectrum of secular variation. Equations were derived which connect the non-drifting part with the energy density spectrum.
The non-drifting part has been rather stable since 1965. In the drifting part the harmonic constituents n=1 and n=4 have increased roughly by a factor five during the last 20 years.