Spatiotemporal response of a conducting sphere under simulated geomagnetic storm conditions

A theoretical study of satellite-based geomagnetic induction signals from uniform and heterogeneous spheres is undertaken using existing analytic and semi-analytic harmonic solutions. Transient responses to ring current excitations are computed using inverse Fourier and Laplace methods. A wide range of simulated storm excitations from impulse to step-on are considered. The early-time radial and late-time polar responses are diagnostic of the electrical conductivity of the sphere. The early-time diagnostic is likely more useful because of better signal to noise characteristics. Induction signals from deeply buried heterogeneities are likely to be contained in the late-time responses and their extraction will require new statistical approaches that average over many storms and incorporate multi-satellite and ground-based observations. The spatiotemporal induction response shows an interesting crossover during which time the rapidly-evolving polar component starts to decays while the slowly-evolving radial component continues to grow. At the crossover time, the intensity of the field is independent of colatitude, an effect which could be sought in satellite induction data.