Cloud‐to‐ground lightning in southeastern Brazil in 1993: 2. Time variations and flash characteristics

Abstract

About 1.1 million cloud‐to‐ground lightning flashes were recorded by a lightning positioning and tracking system in southeastern Brazil in 1993. The data have been analyzed in terms of their monthly, seasonal (summer/winter), and diurnal (local time) variations. The monthly variation shows a double peak characteristic of tropical lightning activity. The seasonal variation indicates that most flashes occur in the spring and summer seasons, with less than 25% occurring in the autumn and winter. The lightning flash polarity and multiplicity were found to be very similar in the summer and winter seasons. Radiation field and direct current lightning data were obtained in towers located in the same region of the network to verify the multiplicity data obtained by the network. The results indicate that the multiplicity obtained by the system is much lower than that obtained by radiation field measurements of close lightning in the same region of Brazil. The lightning flash peak current were found to be larger in the summer than in the winter, in contrast with results obtained in other parts of the world. The diurnal variation of the negative flashes shows in the summer and winter seasons the same behavior, with a peak around 1500–1800 LT, associated with the maximum convective activity in the afternoon. The diurnal variation of positive flashes, in turn, shows this behavior only in the winter. In the summer, it shows a maximum around 1400–1500 LT, with a secondary peak at 1900 LT. However, considering only positive flashes with peak currents higher than 15 kA, the diurnal distribution in the summer is similar to that for negative flashes. This fact indicates that the positive flashes with a peak current less than 15 kA are probably intracloud flashes erroneously identified by the network. The results are discussed in association with the findings presented in paper 1 [Pinto et al., this issue] and compared with results obtained in other parts of the world.