Rocket-triggered lightning and new insights into lightning

The rocket-and-wire technique has been routinely used since the 1970s to artificially initiate (trigger) lightning from natural thunderclouds for purposes of research and testing. Leader/return stroke sequences in triggered lightning are similar in most (if not all) respects to subsequent leader/return-stroke sequences in natural downward lightning and to all such sequences in object-initiated lightning. The initial processes in triggered lightning are similar to those in object-initiated (upward) lightning and are distinctly different from the first leader/return-stroke sequence in natural downward lightning. The results of triggered-lightning experiments have provided considerable insight into natural lightning processes that would not have been possible from studies of natural lightning due to its random occurrence in space and time. Among such findings are the observation of an UCL in a dart leader/return-stroke sequence, identification of the M-component mode of charge transfer to ground, the observation of a lack of dependence of return-stroke current peak on grounding conditions, discovery of X-rays produced by lightning dart leaders, new insights into the mechanism of cutoff and reestablishment of current in the lightning channel, direct measurements of NOx production by an isolated lightning channel section and the characterization of the electromagnetic environment within tens to hundreds of metres of the lightning channel. Triggered-lightning experiments have contributed significantly to testing the validity of various lightning models and to providing ground-truth data for the US National Lightning Detection Network (NLDN). Triggered lightning has proved to be a very useful tool to study the interaction of lightning with various objects and systems, particularly in view of the fact that simulation of the lightning channel in a high-voltage laboratory does not allow the reproduction of many lightning features important for lightning protection and it does not allow the testing of large distributed systems such as overhead power lines.