Figure 3: Relative wavelet power of residual electron fluxes.

(a-e) Relative wavelet power at the energy channels 2.0, 2.3, 2.9, 3.6 and 4.5 MeV, respectively. Residual flux is defined as (j−j₀)/j₀ with j the spin-averaged differential flux from the REPT instrument and j₀ the 1,000 s running averaged j, which reflects the oscillation of electron flux at each energy channel. Relative wavelet power is defined as the wavelet power of residual flux normalized by the maximum power with oscillation period <1,000 s. The obtained relative wavelet power (colour-coded scale) of the twin spacecrafts is plotted alternatively to characterize the oscillation of the outer radiation belt electron fluxes. The superposed dotted and dot-dashed lines represent the drift periods of electrons with the equatorial pitch angles 0° and 90° at the corresponding energy channels in the dipole field. The vertical-dashed line denotes the beginning of ULF wave enhancement induced by the solar wind dynamic pressure variation.