On geomagnetically-induced currents in the finnish 400 kV power system by an auroral electrojet current

The auroral electrojet current flowing in the ionosphere is modeled by a horizontal east-west line current of infinite length. The Earth is described by a simple two-layer model. An expression for the Earth-surface electric field, which is connected with a geomagnetic disturbance in and near the auroral zone, is given. This electric field is considered as external from the viewpoint of the Finnish 400 kV power system, and the resulting geomagnetically induced currents (GICs) in the system are computed. In the north, i.e. near the electrojet, GICs may have values on the order of hundreds of amperes. A comparison to GICs produced by an `equivalent´ spatially constant external electric field is presented. It is noted that sometimes the location of the electrojet is further south. This possibility is studied by letting the line current have several different locations above the Finnish power grid