Large‐scale electric field measurements on the Earth's surface: A review

Abstract

There exist only a few reported measurements of quasi‐stationary (near dc) electric potentials over very large spatial scales (hundreds of kilometers or more) on the Earth's surface. Such measurements have typically been made using unpowered submarine telecommunications cables. The measurements pose unique experimental challenges and require careful procedures to avoid data contamination by electrode contact potentials and local ground currents. In addition, there are possible interpretational problems from pervasive, poorly understood, low‐frequency electric fields induced by ocean water motion through the Earth's stationary magnetic field. Nevertheless, estimates of the magnitude of the electric field computed from large‐scale potential difference measurements, made principally to date in the Pacific Ocean, can be used to place a limit on the size of the toroidal magnetic field at the core‐mantle boundary under certain conditions on the Earth's electrical conductivity profile. Thus, large‐scale electric potential measurements can serve as an adjunct probe of the Earth's dynamo process in addition to measurements of the poloidal magnetic field and its secular changes made at and above the surface of the Earth. A review of all of these data suggests that the toroidal and poloidal magnetic fields at the top of the core are comparable in magnitude.

Motional induction in North Atlantic circulation models

“…For an introduction to recent work in this field, see Luther and Chave [1993]. For voltages across longer distances, up to basin-wide scales, the modern possibilities include both retired and in-service analog and fiber optic telecommunication cables [e.g., Larsen, 1992;Lanzerotti et al, 1993]. In-service or discontinued military surveillance cables may also become available.…”

Geoelectric power spectra over oceanic distances

“…At Point Arena, a separate telecommunications ground rod is installed for the measurements. An AT2•T computer-based data acquisition system records the geoelectric potential between HI and CA at 2s intervals, together with local measurements of the three components of the geomagnetic field [see, e.g., Lanzerotti et al, 1993]. The GP cable has been grounded to the old TPC-1 ground bed in the Philippines; the ground bed at Guam is that presently used for the active cables at that telecommunications station.…”

“…[1983]. Results in magnetospheric/ionospheric, oceanic, and solid Earth studies are included in several publications over the last decade [e.g., Medford et al, 1982;Lanzerotti et al, , 1993Thomson et al, 1986; Chave et al, 1992; and references therein]. This paper describes some initial results obtained from simultaneous measurements of the geoelectric potential over large (1000's of km) distances using two separate Pacific cables.…”

GeO-TOC Project-Reuse of Submarine Cables for Seismic and Geoelectrical Measurements.

“…A submarine telecommunication cable acts as a sensor on a planetary scale to measure geopotential variations (Lanzerotti, 1993). If the quasi-stationary or DC potential difference is measured, it might provide information on the dynamo process in the Earth's core (Runcorn, 1954).…”