Nature of the geoelectric field associated with GIC in long conductors such as power systems, pipelines, and phone cables

Electric fields can be resolved into scalar potential and vector potential terms that are respectively irrotational and solenoidal: E=-∇φ-∂A^s/∂t. It is shown that these parts can be uniquely identified with different sources: a distribution of charge and a changing magnetic field. Examining induction in a uniform and non-uniform earth shows that the geoelectric field affecting long conductors is principally due to an induced electric field associated with magnetic field changes. Potential gradients are a secondary effect that results from charge accumulation at conductivity boundaries. The electric field experienced by a long conductor at the Earth´s surface extending from point a to point b can be represented by a voltage source V_ab=∫_a^bE.dl where, because of the vector potential part of the electric field integration has to be done along the path of the conductor