Fig. 4. Temporal variation of nongyrotropic electrons at multiple energy and pitch angle bins and the resonant current (Event 1).

a Amplitude of wave component of the magnetic field (B_w) and the electric field (B_w) in the field-aligned coordinate (FAC) x-y plane. Moving-average values from all four spacecraft measurements with a window of 90 ms, which is comparable with the window for the analysis of electron data (3 temporal bins (see Methods, subsection Electron and ion measurements by FPI)), are shown. b–g $\zeta$-t spectra of normalized differential energy fluxes of electrons (energy bin: 320.9–419.7 or 419.7–549.8 eV and pitch angle (PA) bin: 123.75°–135.0°, 135.0°–146.25°, or 146.25°–157.5°). h the resonant current (J_res) (x and y components in the wave field-aligned coordinate (wFAC)). Vertical gray dashed lines indicate the interval analyzed for Fig. 3. Vertical blue dotted and red dotted lines indicate the intervals shown in Fig. 5.