Height-based characterization of structure-initiated upward positive leader speeds using high-speed photogrammetry

Upward lightning from ten towers in Rapid City, South Dakota has been observed using high-speed cameras since 2008. In this study, two methods will be used to determine two dimensional upward leader speeds. The first is the Point-by-Point Method measuring leader progression between consecutive images with speed averaged over the entire leader path. Secondly, Bin Average Method, measures leader speeds using progressive images as well, but speeds are averaged in 500m height bins starting from the tower tip. This second approach is to determine if speeds increase or decrease with height above tower tip. It is hypothesized that upward leader speeds decrease during approach to cloud base and transition to horizontal propagation. Preliminary data suggest a trend towards fluctuations of speed as the leader nears cloud base with a gradual decline in velocity. Many studies have examined leader propagation speeds using high-speed cameras, but most focused on downward leaders. Upward leader speeds from triggered lightning have been analyzed; however they were completed using the Point-by-Point Method with incremental and average speeds being reported. This study's intent is to expand understanding of natural upward lightning leader characteristics and to gain further insight into leader physics.