Spherical cap modelling of Orsted magnetic field vectors over southern Africa

Abstract

Vector magnetic field observations by the Orsted satellite during geomagnetic quiet conditions around January 1, 2000, have been employed to derive a spherical cap harmonic model (Haines, 1985) over the southern African region between 10 degrees and 45 degrees South in latitude and between 10 degrees and 45 degrees East in longitude. In the process a total of 9283 vector (27949 components) Orsted observations have been used to derive a spherical cap model with minimum wavelength resolution approximately 1200 km. This model is compared with the global Orsted magnetic field model (Olsen et al., 2000a) in terms of a fit to observatory and repeat station data over the southern African subcontinent where the Hermanus Magnetic Observatory conducts field surveys at regular 5 year intervals.