High‐speed video observations of rocket‐and‐wire initiated lightning

We present observations of a rocket‐and‐wire triggered lightning flash obtained with high‐speed video cameras recording 5400 and 50000 frames per second (frame times 185 μ s and 20 μ s) with time‐synchronized current and electric field measurements. Transient leader channels were observed with precursor current pulses occurring before the development of the sustained upward positive leader that initiated the initial continuous current. The sustained upward positive leader stepped with a constant speed of 5.6 × 10 4 m s −1 over its initial 100 m. The wire destruction occurred discontinuously over a time of 7 ms about 45 ms after sustained upward leader inception, with a small change in channel current. Downward leaders, upward connecting leaders, and filamentary streamers were imaged in the bottom 50 m of the channel. We present the first images of a negative step forming in lightning, apparently involving a space stem similar to steps in meter‐length negative laboratory sparks.