Large‐scale electric and magnetic fields generated by the oceans

Abstract

The magnetostatic equations are used to derive a consistent set of equations capable of describing the global‐scale, low‐frequency electric and magnetic fields induced by the motion of the ocean through the geomagnetic field. The equations are solved numerically with realistic 2° × 2° topography in a global domain with ocean flow simulated by a detailed ocean circulation model. Estimates of the annual mean and the first annual harmonic of the electric potential, the vertical component of the oceanic magnetic field, and the vertically integrated electric current density stream function are obtained. With the idea of using electric and magnetic fields to deduce large‐scale oceanic flow, emphasis is placed on the geographical location of interesting features. The fields are not found to be basin‐wide but rather are found to be localized and strongest in shallow regions. The magnetic fields generated by ocean currents are of the order of 1 nT, and while these can be measured by magnetometers, they would be difficult to detect owing to contamination from other sources of magnetic variation. In finding the electric field, electric currents cannot be neglected where ocean currents cut across isobaths. However, in regions where the ocean flow is aligned with the isobaths, measurement of electric fields is sufficient to find the ocean flow.