Simulated electron precipitation structures after subtracting initial flux distribution from final flux distribution. Simulation parameters: Electromagnetic wave frequency ω/(2π) = 19.8 kHz; wave amplitude δb = 200 pT; semi-band width 500 Hz; N₀ = 1000 counts/s; and equatorial pitch angles α_eq = 0.1–0.2 rad (a), 0.2–0.3 rad (b), 0.3–0.4 rad (c), 0.4–0.5 rad (d), 0.5–0.6 rad (e), 0.6–0.7 rad (f).