Submicrosecond structure of magnetic-field waveforms of different types of return strokes

Optical observations show that the geometries of the lightning current channels belonging to different types of cloud-to-ground (CG) lightning strokes substantially differ [1, 2, 3]. The positive CG stroke channels are quite smooth [4, 5]. The lightning channel geometry of negative CG strokes depends primarily on the order of the stroke in the flash. The channels of first negative CG strokes are branched. Subsequent negative CG strokes copying the channel of the first stroke are similar to that of the first stroke but without branches. The newly created subsequent stroke channels are usually also branched. The channels of other subsequent strokes belonging to the same flash and sharing the same channel sometimes slightly differ, probably due to temporal changes of the lightning channel geometry during the development of the flash [6]. We performed a superposed epoch analyses of return stroke waveforms in order to reveal waveform properties typical for different types of return strokes. We examine the possibility to identify the type of return strokes without optical observations. This analysis can have implications for lightning protection and lightning test standards.