The Effect of Electromagnetic Attenuation on the Spatial Spectrum of the Geomagnetic Field

Abstract

A comparison of the mean energy densities in the different spatial harmonics of the geomagnetic field with the corresponding scale times derived from the secular variation reveals a correlation which may be explained by greater attenuation of faster varying harmonics due to the finite electrical conductivity between the source level in the core and the surface of the earth. The conductivity required for the mantle alone to produce this effect is an order of magnitude too high to allow the observed sudden onset of some events in the surface field. It is found that the correlation may equally well be explained by a layer of core material ~ 10 km thick screening the principal motions responsible for the secular variation. Surface field events with rise times up to several years must then involve a disturbance of this layer or be transported across it as a hydromagnetic wave disturbance. Show more