Induced geoelectric field: influence of polarization in coast effect and proximity effect

During a magnetic storm, the induced geoelectric field drives induced currents that couple with artificial metallic networks such as power lines, pipelines, telecommunication cables and railway lines with the consequent risk, in case of strong events, of possible blackouts, damages and impairments of those systems. It is known that magnetic storms are global phenomena and their effects in specific regions with specific ground conductivity may be different; in particular, when a magnetic storm involves regions composed of two adjacent media characterized by very large difference of conductivity between them (e. g. sea and land) the induced geoelectric field is largely influenced by this conductivity contrast and depends, primarily, on its orientation with respect to the discontinuity line. By representing the source as an incident plane wave normally directed with respect to the air-land/sea interface, two kinds of polarizations are usually considered in literature: H/E polarization i.e. with the incident magnetic/electric field parallel to the discontinuity. In this paper, we wish to study a more general case i.e. when the source is characterized by an electric field forming a generic angle with the discontinuity line so that the resulting field is a combination of both H and E polarizations; to do this, and by adopting a 2D approach based on the generalized thin sheet model, the paper combines, published formulas for H polarization while new approximated analytic formulas for E polarization are derived. Moreover, we express the induced geoelectric field as a function of a generic direction which represents the layout orientation of a potentially affected plant (power line, pipeline…); this is important, because that is the first step necessary to evaluate the level of geomagnetically induced currents (GIC) in the plant itself. In conclusion, the novelty of this approach is that the resulting induced geoelectric field on the Earth’s surface can be expressed using only analytical formulas; a further advantage of the proposed approach to the problem is that it is quite simple and particularly suitable for the evaluation of GIC in terrestrial conductor networks.