Idone/Abstract The objective of this research is the acquisition and analysis of highly time-resolved photographic records of triggered lightning flashes to be obtained during the summer of 1997 at Camp Blanding, Florida. The data acquired will allow study of 1) the channel creation process, 2) the development of the return stroke and dart-leader diameter with time, and 3) the evolution of channel microscale tortuosity. These experiments will yield unique data sets that are fundamentally new and that could be critical in the testing of newly emerging models of different phases of the lightning discharge. The recordings proposed would be made from two separate sites. A distant site (~ 1 km away) would be used to provide an overall record of the luminous lightning components propagating along most of the channel below cloud base. A "near photographic site (80 m away) is also proposed to record new details of the evolution of lightning channels during the course of the discharge. The totality of photographic records obtained would correlate with and complement other data sets to be acquired simultaneously by other researchers participating in this campaign. The distant-site recordings would document the creation of the lightning channel by the initial leader process using a near-UV photographic system; this provides a superior rendering of the initial phase of the discharge. The near-site experiments would provide highly time-resolved imagery of the cross-sections of lightning channels for the same strokes, these records being attained from a vertical section only 8 mm in extent. These close-up recordings would yield a direct measurement of the luminous channel diameter as small as 6mm with a time resolution of 0.9 ms. Once 10-20 return stroke images are obtained, attempts would be made to image the cross-sections of downward propagating dart-leaders or dart-stepped leaders from a channel section aloft as the dart-leader luminous diameter has not been examined directly before. Framing photographs (4000 fr/sec) of the same field of view would document the movement and geometric variation of the channels on the microscale (~2 cm). It is anticipated that the field observations could be acquired in a single field campaign during the first summer of support. The remainder of the project would be devoted to analysis of the photographic data in its own right along with use of these results in collaborative analyses with other researchers.
