Fig. 4.

Van Allen Probe B observations of a the dynamic power spectrum of the magnetic field variations in the azimuthal component with selected peak frequency indicated by black dots, b the selected peak frequency, c mass density at the satellite position, d electron density at the satellite position, and e average plasma mass, during 02:00–09:30 UT on 12 September 2017. In b–e, colors indicate results of different eigen-frequencies, that is, fundamental (f₁): red, second harmonic (f₂): orange, and third harmonic (f₃): green. f–j Same as in a–e but for the Arase observations during 03:00–11:00 UT on 12 September 2017