THE LUMINOUS DEVELOPMENT OF FLORIDA TRIGGERED LIGHTNING

Abstract

During the past few years, various types of time-resolved photographic recordings of rocket-triggered lightning flashes have been made at the Kennedy Space Center (KSC), Florida. These recordings have included visible and near ultraviolet streak records of all phases of the discharges. The initial leaders photographed have been almost exclusively upward propagating, positive polarity leaders. In general, the evolution of an upward propagating positive leader evidences an increasing propagation speed with height and a corresponding decrease in channel tortuosity. The near ultraviolet photography of positive leader steps almost always reveals a corona "brush" extending 5-10 m outward from the step stem in the direction of propagation. In contrast, the two cases of negative leaders photographed with the same near ultra violet system show no such corona f ea tu re. In addition, the first highly time-resolved recordings of return stroke and M-component channel cross-sections have recently been obtained; two such examples are presented. A preliminary analysis of channel diameter indicates that the return stroke channel reaches a diameter of approximately 5 cm in less than 3 s after which the growth of the channel is quite gradual, reaching 7 cm after 200 s. The initial growth of the M-component channel is, in contrast, very gradual but steady from an initial size of about 1 cm and to a size of 6 cm after 200 s.