The Seafloor Electric Field as a Barotropic Velocity Sensor

By contrast to our knowledge of baroclinic motions, only limited information is available about the distribution and statistics of the subinertial barotropic velocity field in the world ocean. This paper proposes that measurement of the seafloor horizontal electric field using inexpensive free-fall recorders deserves more serious consideration for study of the low frequency barotropic field. We will validate the theoretical relation of the horizontal electric field to the seawater conductivity-weighted, vertically-integrated (CWVI) water velocity by comparing a six element current meter mooring to nearby electric field data collected in 1986-1987 during BEMPEX. We will show that low coherence between the electric field and the mooring-derived CWVI water velocity occurs only where the coherence between individual current meters is itself low, suggesting the presence of short vertical scale components that are not resolvable by the mooring.