The Perturbation of Alternating Geomagnetic Fields by Three-dimensional Island Structures

Abstract

Summary The perturbation of alternating geomagnetic fields by island-type structures in three dimensions is considered. Two different structures are studied for sinusoidally time-varying source fields of three different frequencies. The general model is that of a semi-infinite conducting half-space with regions of different conductivities. A single-island model and a two-island model are considered. The equations and boundary conditions are solved by a numerical method and the results are compared between models. Contour plots of the amplitudes of the E and H components over the surface of the conducting region are compared near the islands. Profiles of the amplitudes of the E and H components are also given so that the values of the contours may be specified. Profiles of phase are given so that the sign of the observed E and H components at any particular instant in time may be compared. The distortion of the current lines and associated fields by island structures is illustrated in the results. Also, phase changes of the components due to the island structures are evident. The results indicate that a second smaller island near a larger island considerably modifies the fields associated with the larger island.