Spatial Observations of Schumann Resonance at the Ionospheric Altitudes

Abstract

Based on power spectrum analysis as well as impedance function calculation, we confirm that the Aureol-3 satellite in-situ measurements of ELF/VLF electric and magnetic field fluctuations are the results of the fractional transmission into the ionosphere of Schumann resonances from the Earth-ionosphere cavity. Compared with ground-based Schumann resonance observations, the Aureol-3 observed Schumann resonances exhibit some particular features. The horizontal electric component presents distinct resonance spectral structures and peak at eigen-frequencies of Schumann resonances while the three magnetic components usually peak at frequencies departing from the eigen-frequencies. The first-order power maxima of electric and magnetic components also appear at different frequencies, 7.8Hz for the former and 10.0Hz for the latter. The dominant magnetic field components of Schumann resonance in the ionosphere result in a quasi-linear magnetic polarization in horizontal direction other than the elliptical one in the Earth-ionosphere cavity. The experimental wave impedance forms a somewhat indistinct sinusoid with frequency, decreasing with increased frequency and higher altitude, consistent with theoretical calculation. Although nonlinear interactions between Schumann resonances and ionospheric density fluctuations has been proposed to interpret the characteristics of Schumann resonance observed by the Aureol-3 satellite, some other mechanisms, such as instabilities in the ionosphere, wave coupling between different modes, should be included to better understand the spatial observations of Schumann resonance at the ionospheric altitudes.