Fig. 2: Spectral analysis of the magnetic field perturbations measured by VAP and ERG.

a Normalized power spectra of the perturbations of the magnetic field radial component of the magnetic field B_r (black, thin for VAP-A and thick for VAP-B) and the electric field azimuthal component E_a (red) measured by VAP-A. b Bandpass filtered (1.5 ± 0.5 mHz) perturbations of B_r (red), field-aligned magnetic field B_p (green) and E_a (blue). c Bandpass filtered (1.5 ± 0.5 mHz) perturbations of the azimuthal magnetic field B_a (red) and the radial electric field E_r (blue). d Bandpass filtered (1.5 ± 0.5 mHz) perturbations of B_r (red), B_p (green) and radial ion velocity V_r (blue) (see the Methods section, data usage). The background in b–d represents electron density with dark color (colorless) for high (low) density inside (outside) the plasmasphere. e Bandpass filtered (1.5 ± 0.5 mHz) perturbations of B_r measured by VAP-A (red) and VAP-B (blue). f Normalized power spectra of the perturbations of B_r (black), B_a (red), and B_p (blue) measured by ERG. The vertical line indicates a peak at 1.4 mHz. g Radial profile of the plasmaspheric electron density. h–j Bandpass filtered (1.4 ± 0.5 mHz) perturbations of B_r, B_a, and B_p, respectively between 13:30 and 14:30 UTC. The thick vertical line indicates crossing of the magnetic equatorial plane by ERG with the left side in the southern hemisphere (inside plasmapause) and the right side in the northern hemisphere (outside plasmapause).