Comparing high-speed video and Lightning Mapping Array observations to investigate the influence of ground strikes on lightning flash characteristics

This study presents exploratory observations for a set of 28 cloud-to-ground flashes recorded on highspeed video, each with a time resolution of 10,000 frames per second. The high time resolution, along with precise GPS timing, allows a detailed comparison of the videos with corresponding data from the Oklahoma Lightning Mapping Array (LMA). The LMA detects VHF radiation sources throughout the flashes, complementing the videos to provide a more complete visual understanding of flash development. We indentify several interesting effects and phenomena related to the ground strike, and highlight the differences in flash development between cloud-to-ground flashes recorded on video and nearby intracloud flashes. Observations start with initial breakdown patterns in the flashes, contrasting initial structure of video cloud-to-ground flashes with that of the intracloud flashes. An initial descending discharge pattern is likely to terminate with a ground strike. The opposite initial pattern, a rising succession of source points, was observed in both some video recorded cloud-to-ground flashes and most nearby intracloud flashes. For cloud-to-ground flashes with an initial rise, abrupt changes in flash development can occur after the ground termination on video. In some cases, breakdown starts suddenly at new altitudes or locations, often associated with the beginning of new large-scale branches. The density of radiation source points can also change following a ground strike on video, often switching from dense, well-defined branching to sparser, more scattered discharge during the continuing current phase. Nearby intracloud flashes typically featured simultaneous defined and scattered breakdown, each developing in a separate layer.