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Ann. Geophys., 22, 101-113, 2004
www.ann-geophys.net/22/101/2004/
© European Geosciences Union 2004
Fast computation of the geoelectric field using the method of elementary current systems and planar Earth models
A. Viljanen1, A. Pulkkinen1, O. Amm1, R. Pirjola1, T. Korja2,*, and BEAR Working Group3
1Finnish Meteorological Institute, Geophysical Research Division, P.O.B. 503, FIN-00101 Helsinki, Finland
2Geological Survey of Finland, P.O.B. 96, FIN-02151 Espoo, Finland
3Contact person: T. Korja
*now at: University of Oulu, Department of Geosciences, P.O.B. 3000, FIN-90014 Oulu, Finland
Abstract. The method of spherical elementary current systems provides an accurate
modelling of the horizontal component of the geomagnetic variation field. The
interpolated magnetic field is used as input to calculate the horizontal
geoelectric field. We use planar layered (1-D) models of the Earth's
conductivity, and assume that the electric field is related to the local
magnetic field by the plane wave surface impedance. There are locations in
which the conductivity structure can be approximated by a 1-D model, as
demonstrated with the measurements of the Baltic Electromagnetic Array
Research project. To calculate geomagnetically induced currents (GIC), we
need the spatially integrated electric field typically in a length scale of
100km. We show that then the spatial variation of the electric field can be
neglected if we use the measured or interpolated magnetic field at the site
of interest. In other words, even the simple plane wave model is fairly
accurate for GIC purposes. Investigating GIC in the Finnish high-voltage
power system and in the natural gas pipeline, we find a good agreement
between modelled and measured values, with relative errors less than 30% for
large GIC values.
Key words. Geomagnetism and paleomagnetism (geomagnetic
induction; rapid time variations) – Ionosphere (electric
field and currents)
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