Barotropic ocean velocity observations from an electric field float, a modified RAFOS float

Abstract

A seldom observed characteristic of ocean motion is depth-averaged velocity, or transport per unit width. One approach to observing this quantity is to measure the ambient horizontal electric field of the ocean with electric field sensors added to a RAFOS float. The Electric Field Float (EFF) is a RAFOS float modified by the addition of a compass, electrode arms, amplifiers, and a microprocessor. The float's velocity is determined by the acoustic ranging of the RAFOS subsystem. The velocity determined by the electrode system is the electric field (EF) observed by the electrode array divided by the vertical component of the Earth's magnetic field, F/sub 2/. The difference between the RAFOS and EF velocities is v~*, a conductivity weighted, vertically averaged velocity which is generally equal to the vertically averaged velocity (v~) to within 10%. An EFF launched off Monterey Bay, California, observed a velocity at 800-m depth of about 33 cm s/sup -1/ to the NW of which about 2 cm s/sup -1/ was contributed by the barotropic flow. As expected, the barotropic velocity closely paralleled the depth contours. The 2-h average EF velocities exhibited the expected CW/ACW asymmetry in the internal wave band.