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Ann. Geophys., 23, 1735-1746, 2005
www.ann-geophys.net/23/1735/2005/
© European Geosciences Union 2005
Induction effects on ionospheric electric and magnetic fields
H. Vanhamäki, A. Viljanen, and O. Amm
Finnish Meteorological Institute, Space Research Unit, P.O.Box 503, FI-00101 Helsinki, Finland
Abstract. Rapid changes in the ionospheric current system give rise to induction
currents in the conducting ground that can significantly contribute to
magnetic and especially electric fields at the Earth's surface. Previous
studies have concentrated on the surface fields, as they are important in,
for example, interpreting magnetometer measurements or in the studies of the Earth's
conductivity structure. In this paper we investigate the effects of induction
fields at the ionospheric altitudes for several realistic ionospheric current
models (Westward Travelling Surge, Ω-band, Giant Pulsation). Our main
conclusions are: 1) The secondary electric field caused by the Earth's induction is
relatively small at the ionospheric altitude, at most 0.4 mV/m or a few percent of
the total electric field; 2) The primary induced field due to ionospheric
self-induction is locally important, ~ a few mV/m, in some "hot spots",
where the ionospheric conductivity is high and the total electric field is
low. However, our approximate calculation only gives an upper estimate for
the primary induced electric field; 3) The secondary magnetic field caused by
the Earth's induction may significantly affect the magnetic measurements of low
orbiting satellites. The secondary contribution from the Earth's currents is
largest in the vertical component of the magnetic field, where it may be
around 50% of the field caused by ionospheric currents.
Keywords. Geomagnetism and paleomagnetism (geomagnetic
induction) – Ionosphere (electric fields and currents)
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