Practical Model Applicable to Investigating the Coast Effect on the Geoelectric Field in Connection with Studies of Geomagnetically Induced Currents

The horizontal geoelectric field induced at the Earth’s surface during temporal variations of the geomagnetic field drives Geomagnetically Induced Currents (GIC) in groundbased conductor networks, such as electric power transmission grids. Usually studies of the geoelectric field in connection with GIC research employ the assumption of a onedimensional (1D) Earth conductivity structure. At ocean-land interfaces the conductivity contrast in the horizontal direction is large making the 1D assumption invalid in coastal areas. Geoelectromagnetic induction literature contains many publications dealing with complicated 2D or 3D Earth models. However, these studies mainly aim at the investigation of the Earth’s structure and often do not provide an easy theoretical discussion and clear numbers to be used in practical power engineering investigations of GIC in networks located at coasts. Regarding GIC applications, James Gilbert introduces a two-dimensional (2D) Earth conductivity model for studying the “coast effect” near an