Energy spectra averaged over the time intervals defined in Fig. 2, shown in two panels a and b for clarity. The spectra for B1 to B5 are displayed as open circles and squares, representing STEP and EPT measurements, respectively, while the spectra for S1, S2, D1, and D2 are displayed as dashed lines. The black horizontal bars at the top indicate the energy ranges covered by STEP and EPT. Other horizontal bars mark the valley and peak of the spectral bumps in corresponding colors.