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Abstract: A negative lightning flashwith 16 leader-return stroke sequences, triggered in the summer of 2013 using the classical rocket-and-wire triggering technique, was examined with simultaneous two-dimensional (2D) imaging of very high-frequency (VHF) radiation sources, channel-base current measurement, broadband electric field waveforms and high-speed video images. A total of 28.0 C negative charge was transferred to
ground during the whole flash, and the charge transferred during the initial stage was 4.9 C, which is the
weakest among the triggered lightning flashes at the SHandong Artificially Triggering Lightning Experiment
(SHATLE). The peak current of 16 return strokes ranged from 5.8 to 32.5 kA with a geometric mean of 14.1 kA.
The progression of upward positive leader and downward negative (dart or dart-stepped) leaders was
reproduced visually by using an improved short-baseline VHF lightning location system with continuous data
recording capability. The upward positive leader was mapped immediately from the tip of the metal wire
during the initial stage, developing at a speed of about 104 m/s without branches. The upward positive leader
and all the 14 negative leaders captured by the 2D imaging system propagated along the same channel with
few branches inside the cloud, which might be the reason for the relatively small charge transfer. The 2D
imaging results also show that dart leaders may transform into dart-stepped leaders after a long time interval between successive strokes.