A comparative study of negative cloud-to-ground lightning characteristics in Sao Paulo (Brazil) and Arizona (United States) based on high-speed video observations

There are only a few prior reports that detail accurate measurements of the number of strokes in natural negative cloud-to-ground (CG) lightning flashes. These are known as ``accurate-stroke-count{''} studies, and they have been performed using various instruments and techniques. Here, we will examine the lightning characteristics produced by warm-season thunderstorms in two different climate regimes (southern Arizona, United States, and Sao Paulo, Brazil) using the same instrumentation. The lightning parameters were obtained from high-speed video recordings and time-correlated data provided by lightning locating systems (LLS). The use of these instruments has allowed us to measure the number of strokes in each flash and their polarity, the interstroke intervals, the number of different ground contacts, and the durations of the continuing currents. Altogether 209 negative flashes were recorded on video in the United States and 223 in Brazil (containing a total of 1681 strokes), and the majority of these flashes had at least one stroke reported by a LLS. Statistical analyses of these data sets as a whole did not show any significant differences in the characteristics of negative CG flashes from warm-season thunderstorms in both locations. The mean values for all data are as follows: video multiplicity, 3.9; single-stroke flashes, 19.5%; flash duration, 226.5 ms; interstroke interval, 61.5 ms; long continuing current, 17.5%; multigrounded flashes, 49.5%. Those characteristics were very similar to the well-accepted values for negative flashes in other regions. However, there were large storm-to-storm variations. (AU)