Fig. 2.

a–d Van Allen Probe B observations during 02:00–09:30 UT on 12 September 2017. The top three panels display the dynamic power spectra of the magnetic field variations in the radial, azimuthal, and compressional components measured by EMFISIS. In b, a harmonic structure of wave power enhancement is labeled f₁ (fundamental mode), f₂ (second harmonic mode), and f₃ (third harmonic mode). The bottom panel shows the plasma wave spectrogram for the electric field measured by EMFISIS. A white/black line delineates the local cyclotron frequency of electrons (f_ce). e–h Arase observations during 03:00–11:00 UT on 12 September 2017. The format is the same as a–d except that the magnetic field data are obtained by MGF and the plasma wave spectrogram for the electric field is obtained by PWE-HFA and PWE-OFA