Low‐frequency, motionally induced electromagnetic fields in the ocean: 2. Electric field and Eulerian current comparison

Abstract

The theoretical relationship between the motional horizontal electric field (HEF) and the seawater conductivity‐weighted vertical average of horizontal water velocity is validated at subinertial frequencies with seafloor point measurements of HEF and moored measurements of horizontal water velocity collected in 1986–1987 in the central North Pacific during the Barotropic, Electromagnetic and Pressure Experiment (BEMPEX). The comparison is limited principally by inaccurate estimation of vertically averaged water velocity due to weak vertical coherences among the current meters and excessive rotor stalls at the deepest instruments. In the BEMPEX area, conductivity weighting results in only a trivial baroclinic contribution to HEF, so that HEF is an accurate measure of the vertically averaged water velocity (or, transport divided by depth) at periods greater than approximately 5 days. Furthermore, the actual transport divided by the depth is nearly identical to the barotropic (approximately depth‐independent) component of motion. The magnetic field at the seafloor is found to have no detectable relationship to horizontal water currents at subinertial frequencies.