[1] Based on analyses of high-speed video recordings of cloud-to-ground lightning in Brazil and the USA, the characteristics of positive cloud-to-ground (+CG) leaders are presented. The high frame rates permitted the average, 2-dimensional speeds of development along the paths of the channels to be resolved with good accuracy. The values range from 0.3 to 6.0 Â 10 5 ms À1 with a mean of 2.7 Â 10 5 ms À1. Contrary to what is usually assumed, downward +CG leader speeds are similar to downward ÀCG leader speeds. Our observations also show that the speeds tend to increase by a factor of 1.1 to 6.5 as they approach the ground. The presence of short duration, recoil leaders (RLs) during the development of positive leaders reveal a highly branched structure that is not usually recorded when using conventional photographic and video cameras. The existence of the RLs may help to explain observations of UHF-VHF radiation during the development of +CG flashes. Citation: Saba, M. M. F.,

[1] From analysis of digital high-speed video records of 233 negative cloud-to-ground (CG) lightning flashes associated with 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 containing 138 flashes, 70 (51%) had multiple terminations on the ground. As 138 flashes produced 235 different strike points, 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, on average, struck 2.2 times. The 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 follow the previously formed channel, the difference was not statistically significant. A strong positive correlation between the number of subsequent strokes in a flash and the flash minimum duration may indicate that some processes concerning the time requisite for the channel decay and for the positive leader in the cloud to provide more charges for the next stroke do not permit multiple strokes to occur under a certain minimum time duration.

[1] The magnitude of the return stroke peak current preceding continuing current (CC) in ground flashes was investigated. This study was performed using a high-speed camera (1,000 frames/s), an electric field flat-plate antenna and data provided by the Brazilian Lightning Detection Network (RINDAT). The observation of 454 negative strokes followed by CC with durations from 4 ms to 542 ms revealed that negative strokes combining both peak current greater than 20 kA and CC greater than 40 ms are highly unlikely to occur. However, this was found to be possible for positive strokes. In addition, we found that on average the longer the CC, the lower the return stroke peak current preceding it. Therefore, the average detection efficiency of RINDAT was found to decrease from 62% for negative strokes followed by very-short CC (less than 10 ms) to 36% for strokes followed by long CC, with an intermediate value of 57% for strokes followed by short (from 10 to 40 ms) CC. Citation: Saba, M. M. F., O. Pinto Jr., and M. G. , Relation between lightning return stroke peak current and following continuing current, Geophys.

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A study of cloud‐to‐ground lightning characteristics based on high‐speed camera observations of 455 flashes related to 40 thunderstorms is presented. The Brazilian Lightning Location Network (RINDAT) was used to calculate the polarity and the distance of the flashes to the camera. In some cases, a fast electric field flat antenna was also used to calculate the time difference between strokes on a microsecond‐scale. Some general features of the data set are briefly presented. This paper is focused on two specific characteristics observed in video records with a frame a rate of 1,000 frames/s: (i) six strokes presenting two ground terminations that were simultaneously connected for some milliseconds, (ii) and a high number of continuing current occurrences with durations less than 10 ms.