Strokes of upward illumination occurring within a few milliseconds after typical lightning return strokes



[1] Correlated data for natural cloud-to-ground lightning flashes were obtained with a high-speed video camera (54000 frames per second), five stations of electric field change antennas, and a seven-station VLF/LF LIghtning NETwork (LINET), along with operational lightning and electric field networks at Kennedy Space Center, Florida. Four observed flashes at 25–55 km distance had return-stroke-like upward illumination (UI) from the ground just after (within 2 ms of) a return stroke (RS), but in a separate channel connection to ground (0.7 to 2.5 km apart). The UI events were visible for short duration (0.5 ms or less) and short length (to 1.7 km altitude or less), and they had slow propagation speed (1.6–2.6 × 107 m s−1) and no apparent connection to the RS channel. In one case, the RS was no longer visible to the ground when the UI began 1.30 ms later, although mid-level channel was still distinct. In another case, the main RS had dimmed over the 0.52 ms interval before the UI but was still visible. The remaining two cases had the entire length of the prior RS channel no longer visible (for 40 and 240 μs) before the UI began (1.32 and 1.87 ms later). Electric field change data for the UI events resemble those of weak return strokes. These events were not located by the operational ground-strike and VHF detection systems; all four UI events were detected by LINET as negative ground strokes with small (less than 7 kA) peak current magnitude.