Induction effects on ionospheric electric and magnetic fields

Abstract

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, -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.

New method for solving inductive electric fields in the non-uniformly conducting ionosphere

“…These will certainly include the Westward Travelling Surge (WTS) and -band models already studied in a more approximate way by Vanhamäki et al (2005). These models provide a realistic potential electric field and conductance distributions that are based on measurements.…”

“…These local "hot-spots" tended to occur in those areas where the field-aligned currents (FAC) were largest, so in these areas the inductive processes could well contribute to the ionosphere-magnetosphere coupling. Vanhamäki et al (2005) also concluded that at ionospheric altitudes the secondary contribution from ground induction is always very small and smoothly distributed, and in practice negligible when compared to the larger and more concentrated primary contibution from ionospheric self-induction. However, the calculation method used by Vanhamäki et al (2005) was rather approximate, giving only order of magnitude estimates.…”

“…Vanhamäki et al (2005) also concluded that at ionospheric altitudes the secondary contribution from ground induction is always very small and smoothly distributed, and in practice negligible when compared to the larger and more concentrated primary contibution from ionospheric self-induction. However, the calculation method used by Vanhamäki et al (2005) was rather approximate, giving only order of magnitude estimates. The induced electric fields in the ionosphere were calculated as vacuum fields, i.e.…”

“…Recently Vanhamäki et al (2005) showed by approximate calculations that inductive electric fields associated with some very dynamic ionospheric phenomena, including Westward Travelling Surge (WTS), -bands and Giant Pulsations, are locally very significant. They calculated the inductive fields caused by self-induction in the ionosphere (primary process) and also by the ground-induced currents flowing in the conducting ground (secondary process).…”

Ionospheric Electrodynamics Modeling

“…We can, therefore, treat the ionospheric electrodynamics as steady state, with divergence-free current density J and an electrostatic electric field E. (Vanhamäki et al [2005] have illustrated how nonelectrostatic effects can sometimes be significant for very rapidly varying fields.) With the use of Ohm's law in the frame of the moving neutrals, E and J can be written as…”