HR: 11:00h
AN: AE12A-03    [Abstracts]
TI: Negative Cloud-to-Ground Lightning Properties From High-Speed Video Observations
AU: * Saba, M M
EM: msaba@dge.inpe.br
AF: National Institute for Space Research - INPE, Av. dos Astronautas, 1758 - CEA/DGE, S. Jose dos Campos, SP 12224-010 Brazil
AU: Ballarotti, M G
EM: mgballa@dge.inpe.br
AF: National Institute for Space Research - INPE, Av. dos Astronautas, 1758 - CEA/DGE, S. Jose dos Campos, SP 12224-010 Brazil
AU: Pinto, O
EM: osmar@dge.inpe.br
AF: National Institute for Space Research - INPE, Av. dos Astronautas, 1758 - CEA/DGE, S. Jose dos Campos, SP 12224-010 Brazil
AB: From analysis of digital high-speed video records of 233 negative cloud-to-ground (CG) lightning flashes associated to 27 thunderstorms in southeastern Brazil, various lightning properties have been determined. The analysis of the video records showed that although 20% of them were single-stroke flashes and the average number of strokes per flash was 3.8, a significant variation was observed in these parameters from storm to storm. In a smaller subset (138 flashes), we found 51% to have multiple terminations on ground. They produced 235 different strike points; therefore, the average number of strike points per CG flash was 1.70. Considering that in this study the missing of strokes is practically negligible, we can say from the average multiplicity and from the average number of strike points per flash, that each ground contact point is, in average, struck 2.2 times. 41% of the new strike points were produced by the second stroke in the flash, and 91% of the changes in channel geometry occurred after there had been just one stroke in the previous channel. 608 time intervals between strokes of 186 negative multiple-stroke flashes presented a geometric mean value of 61 ms. Although time intervals preceding subsequent strokes that create a new termination tend to be greater than intervals between subsequent strokes that follows the previously formed channel, the difference was not statistically significant. Almost 50% of the observed strokes, independently of its order, are followed by some kind of continuing current: long, short or "very short continuing current". We term "very short continuing current", those with durations less than 10 ms which are termed "questionable" in previous studies. A strong positive correlation between the number of subsequent strokes in a flash and the flash minimum duration may indicate that some processes in the cloud do not permit multiple strokes occur under a certain minimum time duration. Some of these estimates, like the average number of strikes per ground contact, were only possible to be obtained due to the simultaneous accurate stroke counting and accurate visualization of their channels given by a high-speed camera.
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: Fall Meeting 2005