Fig. 2: Superbolt’s electric power from space and ground-based measurements.

a–f Show electric power spectral density and squared electric field (intensity) versus time for six different superbolts measured either (a–d) in burst mode in space (PSD in mV²/m²/Hz) or (e, f) on the ground (PSD in V²/m²/Hz). The specifics of the events are in Supplementary Tables 2 and 3. Panel a1, b1, c1, d1, e1, f1 show the evolving power spectral density. Panel a2, b2, c2, d2, e2, f2 show the evolving wave electric field intensity. Panel a3, b3, c3, d3, e3, f3 show the average of the PSD over 1 s (in V²/m²/Hz). Dashed vertical lines in the line plots (a2–f2) show times of all WWLLN-detected lightning during that time interval. Circles in the line plots (a2–f2) indicate an estimate of the median squared electric field in space based on WWLLN-measured lightning energy (computed from ref. ²²). The non-superbolt median squared electric field estimates (green circles) are found to be >3 orders of magnitude less than the superbolt estimates (green circle with a red contour), confirming that the detected space-based signals correspond to the WWLLN superbolt, and are not caused by other lightning. Continuous signal at ~20 kHz (e1–f1) is due to a powerful VLF ground transmitter and should be disregarded. The sharp rising tone just prior to the main whistler profile in (a1, c1, d1), best seen in (d1) at t = 0.4 s for frequencies within 10² and 10⁴ Hz, is an anti-aliasing filter effect with a fold over of the power above the top frequency.