Measurements of x-ray emission from rocket-triggered lightning

[1] We report measurements of the x-ray emission from rocket-triggered lightning, made during the summer of 2003, using four instruments placed between 15 and 40 m from the lightning channels. X-rays were measured 0–80 ms just prior to and at the beginning of 73% of the 26 return strokes observed. The emission was composed of multiple, very brief bursts of x-rays in the 30–250 keV range, with each burst typically lasting less than 1 ms. The x-rays were primarily observed to be spatially and temporally associated with the dart leaders with a possible contribution from the beginning of the return strokes, with the most intense x-ray bursts coming from the part of the lightning channel within 50 m of the ground. Because triggered lightning strokes are similar to subsequent strokes in natural lightning, it is likely that x-ray emission is a common property of natural lightning.