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Earth, Planets and Space
Fig. 3 | Earth, Planets and Space

Fig. 3

From: Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents

Fig. 3

Geomagnetic ΔB x (north) and ΔB z (vertical) components from Addis Ababa and Adigrat. On 31 May 2013 there is a sudden commencement occurring at 16:19 UT starting a geomagnetic storm. The individual (left axes) and cumulative (right axes) Fourier spectra of the filtered data are presented in the last four panels. Also shown is the percentage of total energy content for each component and station, filtered below the cut-off frequency \(f_{\text{c}} = f_{\text{Nyquist}} /8 = 1.04\,{\text{mHz}}\) (or period: 16 min)

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