MOTIONALLY-INDUCED ELECTROMAGNETIC-FIELDS GENERATED BY IDEALIZED OCEAN CURRENTS

Using the induction equation, we investigate the generation of electro magnetic fields by the motional electromagnetic induction due to ocean currents. In this paper, solutions are presented for a linear inducti on equation for the magnetic flux density vector which contains prescr ibed time-independent ocean current and conductivity fields. Once the magnetic Bur density is known, the electric held and electric current density are easily obtained by differentiation. Solutions are given fo r several examples of idealized flow which include: 1) Vertically and horizontally sheared plane-parallel flow with depth-dependent conducti vity; 2) A simple Stommel circulation gyre; and 3) Symmetric gyres. Th e results indicate that typical ocean current features induce magnetic fields with magnitudes reaching 100's of nT within the water and abou t 1-10 outside of the water. For the case of a field of gyres, the oce an-induced magnetic fields decay away from the ocean on spatial scales set by the horizontal scale of the ocean feature. At the altitudes of magnetic field satellite surveys, ocean-induced magnetic fields may r etain values of a few nT, which are strong enough to be detected. Thus it is concluded that satellite observations of the earth's main magne tic field and, in particular, the observed temporal variations, could be affected by the ocean circulation.