资源环境科技发展态势分析平台

We present sub-microsecond-scale, high-speed video camera observations of three negative stepped leaders in cloud-to-ground flashes with return-stroke peak currents (estimated by the U.S. National Lightning Detection Network) of -17, -104, and -228 kA. The camera frame exposure times for these observations were 1.8, 1.0 and 0.74 µs, respectively. The 0.74 µs exposure time is the shortest reported to date. We observed the temporal and spatial evolution of space leaders from their inception to their attachment to the pre-existing leader channel (PELC). For stepped leaders that led to return strokes having higher peak currents, the space leaders appear to have incepted at farther median two-dimensional distances from their respective PELC-attachment points. These median distances were 6.1, 16.6, and 17.6 m, respectively, for the three strokes. Our observations indicate that space leader characteristics are likely influenced by stepped-leader line-charge-density, which is expected to be higher in strokes with higher return-stroke peak currents.