Motional induction in North Atlantic circulation models

Motionally induced voltage differences provide one of the few observation methods sensitive to fluctuations of large-scale ocean transports. However, uncertainties of interpretation have impeded widespread oceanographic use of voltages measured on open-ocean cables. To resolve these uncertainties, we have developed a numerical simulation of the flow-induced voltages in general circulation models. The model includes the effects of flow meandering, the spatial and temporal variations of seawater temperature and salinity, three-dimensional Earth models with realistic sediment conductances, and the full physics applicable to the large-scale, long-period circulation when self-induction may be neglected. For the oceanographic input, we used the World Ocean Circulation Experiment Community Modeling Effort's model, which simulates the wind-driven and thermohaline circulation in the North Atlantic using mean monthly winds and realistic topography with resolution permitting mesoscale eddies. The results are in good agreement with the experimental cable calibration results from the Straits of Florida and with the Mid-Ocean Dynamics Experiment. We find less influence of large-scale electric current loops on the seafloor horizontal electric field than has previously been feared, our results supporting a local relationship of the seafloor electric field and ocean transport and the interpretation of seafloor horizontal electric field measurements in terms of local transport over much of the North Atlantic basin.