High-Speed Video and Lightning Mapping Array Observations of In-Cloud Lightning Leaders and an M Component to Ground: IN-CLOUD LIGHTNING LEADERS

High-speed video (46,000 frames per second) and lightning-mapping-array (LMA) data are correlated to determine three-dimensional properties of in-cloud lightning leaders (altitudes ranging from 2.78 to 3.81km) observed in a rocket-and-wire triggered lightning flash. Three positive leaders were observed with speeds ranging from 6.1x10(4) to 1.0x10(5)m/s, one of which branched within the camera frame. The upper branch was then traversed twice by attempted negative leaders propagating toward the main channel to ground (speeds of 2.4x10(6) and 1.1x10(7)m/s). Both attempted negative leaders terminated abruptly at the branch point of the remnant channel. In the remnants of a separate positive leader channel, a bidirectional leader initiated, which resulted in an M component whose luminosity and current were measured at ground. Analysis shows that the luminosity wave associated with the entire M component process (propagating 8.8km from initiation to ground) is highly dispersive, with calculated group velocities ranging from 1x10(7) to 5x10(7)m/s over the dominant signal bandwidth of DC (0Hz) to 2kHz. Plain Language Summary In this paper, we present analysis of high-speed video and radio observations of lightning processes within the cloud generally obscured from sight. The analysis provides a three-dimensional reconstruction of lightning leaders which either breaks down air to create a path for electrical flow (i.e., stepped leaders) or reignites an old leader path to renew electrical flow (i.e., dart leaders). Analysis is presented for three stepped leaders that carry positive charge away from groundone of the observed positive stepped leaders is seen to branch within the camera field of view. Then, analysis is presented for two dart leaders, which attempted to reach ground level but were suddenly terminated when they reached the observed branch point of an old leader path. Lastly, analysis is presented for a dart leader that extended bidirectionally, one end of which connected to an active lighting channel to ground (i.e., a lighting path with current flowing to ground). This results in a brightening of the lightning channel and a momentary surge of current transferred to ground known as an M component. High-speed footage of the M component shows that multiple waves of light traverse the lightning channel in both directions.