Fast computation of the geoelectric field using the method of elementary current systems and planar Earth models

摘要

The method of spherical elementary current systems provides an accuratemodelling of the horizontal component of the geomagnetic variation field. Theinterpolated magnetic field is used as input to calculate the horizontalgeoelectric field. We use planar layered (1-D) models of the Earth'sconductivity, and assume that the electric field is related to the localmagnetic field by the plane wave surface impedance. There are locations inwhich the conductivity structure can be approximated by a 1-D model, asdemonstrated with the measurements of the Baltic Electromagnetic ArrayResearch project. To calculate geomagnetically induced currents (GIC), weneed the spatially integrated electric field typically in a length scale of100km. We show that then the spatial variation of the electric field can beneglected if we use the measured or interpolated magnetic field at the siteof interest. In other words, even the simple plane wave model is fairlyaccurate for GIC purposes. Investigating GIC in the Finnish high-voltagepower system and in the natural gas pipeline, we find a good agreementbetween modelled and measured values, with relative errors less than 30% forlarge GIC values.Key words. Geomagnetism and paleomagnetism (geomagneticinduction; rapid time variations) – Ionosphere (electricfield and currents)