Title: Crustal contribution to the spatial spectrum of geomagnetic secular variation.
Abstract: This paper deals with the secular change of the induced crustal magnetic field, inferred from a global model of crustal susceptibility distribution and the inducing core field of IGRF 1965 and IGRF 1980. The difference between the spatial spectra of the calculated crustal model fields in the two epochs gives an estimate of the crustal part in the geomagnetic secular variation. Its distribution is approximately uniform over a wide range of spherical harmonic degrees. Thus the spatial spectrum of the secular variation to be observed at the Earth's surface should consist—like that of the internal field itself—of a linearly decreasing core field part and a quasi-white part of crustal origin. The transition from the core to the crustal section appears at the degree of about 16.