A Spherical Cap Harmonic Model of the Crustal Magnetic Anomaly Field in Europe Observed by Magsat

Abstract

The geomagnetic field observed in current-free regions above the Earth’s surface may be expressed as the gradient of a scalar potential satisfying Laplace’s equation. Spherical cap harmonic analysis enables solution of Laplace’s equation, subject to boundary conditions appropriate to geomagnetic field analysis, in a region bounded by a spherical cap. Magsat data within a spherical cap of half-angle 35° centred on latitude 45°N, longitude 10°E have been analysed for their crustal content. The resulting estimates of the crustal vector field have been used to derive a spherical cap harmonic model of the crustal scalar potential. The model contains 256 parameters and portrays wavelengths of 1000 km and above. Vector anomaly maps derived from the model show several prominent features of which the largest is that in the Kursk region of the USSR. The model has been used to correct both the vector and total intensity data on to a 2° by 2° grid at an altitude of 400 km. Anomaly maps produced by contouring the grid averages are in good agreement with those derived from the model. The major difference is for the vertical component of the anomaly field over the Kursk region of the USSR. This is a high-amplitude short-wavelength feature which the model smooths.