Modelling the electric field at the seafloor due to a non-uniform ionospheric current

Electric fields occurring at the seafloor during geomagnetic disturbances drive geomagnetically induced currents (GIC) in submarine cables, possibly leading to problems in the operation of the equipment and systems connected to the cable. To be able to estimate the GIC risk on the cables, it is necessary to know the magnitude of the electric field at the seafloor, which can be conveniently determined from the magnetic data recorded at the surface. In this paper, we consider the theoretical models associated with non-uniform source fields existing at high latitudes. The case of a two-dimensional ionospheric current distribution is summarized together with numerical examples, and formulas for the general three-dimensional ionospheric-magnetospheric current system are derived in detail. The seawater is modelled by a highly conducting surface layer, and the basement is characterized by a surface impedance. In the 2D case, the expression for the seafloor electric field is either an inverse Fourier transform over the wave number or a spatial convolution. Corresponding formulas are also obtained in the 3D case, and both expressions are then double integrals. Three-dimensional numerical computations are therefore much more difficult, and they will be the topic of a future paper. This paper demonstrates the applicability of the method to the estimation of the impact of geomagnetic disturbances on submarine cables. (C) 2002 Elsevier Science B.V. All rights reserved.