The paper makes a new contribution to the problem of separation of magnetovariation fields, observed over a limited area of the Earth's surface, into parts of external and internal origins. It is shown that there are important advantages in making such separations in the wavenumber domain, making use of the orthogonality of external and internal parts. The method uses a unified potential both for the adjustment of data to minimize their curl, and in the separation process. The technique is tested by combining the analytically calculated fields of line currents above and below the plane of "observation", separating them and comparing the separated field components with the known original fields. While the precision is limited by known effects of the limited area covered by the data, satisfactory correlation coefficients are obtained between separated and original fields. The new separation technique is finally applied to a magnetovariation event recorded in a recent array study in western Canada, and it is shown that a prominent anomaly is caused by internal currents.The interpretation of time-varying magnetic fields recorded at the Earth's surface involves the problem of separation of the observed field components into parts due to external and internal currents. Global data are usually expressed in spherical harmonics for this purpose (CHAPMAN and BARTELS,1940) but for fields recorded over a limited area numerical integration is very often employed (VESTINE, 1941;PRICE and WILKINS, 1963;WEAVER, 1964;PORATH et al., 1970). Such numerical calculations are usually carried out in the space domain. The use of the wave number domain has two notable advantages: computing time is saved through the fast Fourier transform (FFT), and the results are ready for application of the induction equations in more easily soluble form. WIESE (1965) was the first to separate internal and external fields in the wave number domain, using a formulation which differed from this study in two respects. Working before the development of the FFT, Wiese considered only the real part of the Fourier transform, whereas the FFT provides the full complex values; and where the two horizontal components gave different estimates of parameters he used mean values. This is an ad hoc procedure without formal theoretical basis.This paper presents a unified technique of potential field analysis in the

No abstract

No abstract

No abstract