Electromagnetic induction effects by the solar quiet magnetic field at satellite altitude

We show that magnetic fields induced by a near-earth ionospheric source can produce, at a satellite altitude of 400 km, an induced magnetic anomaly fi eld with an amplitude of 2-3 nT at dawn and dusk local times and 3-4 nT at noon local time. Our results are based on an earth model which has an upper 4 km thick shell with a laterally varying electrical conductivity represen ting the distribution of continents and oceans. The upper shell overlies a one-dimensional mantle with a radially varying electrical conductivity. In some regions, the induced anomaly field does not change sign between dawn a nd dusk and appears static when sampled by a satellite such as MAGSAT. This induced anomaly field could explain some of the weak oceanic static anomal ies observed in satellite global magnetic anomaly maps.