Cloud‐to‐ground lightning in southeastern Brazil in 1993: 1. Geographical distribution

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 1‐year continuous lightning data set is the first obtained in Brazil. It has been analyzed for geographical distribution of total flash density, percentage of positive flashes, negative and positive flash densities, and negative and positive flash peak currents. The dependence of the flash density and peak current on latitude, altitude, and soil resistivity was investigated. Negative flash peak current was found to be inversely correlated with latitude, but no other significant correlation was found for flash density and peak current with these parameters. Positive flashes were found to be contaminated by intracloud flashes. The maximum total, negative, and positive flash densities were 15.5, 9.1, and 7.7 flashes/km2 per year, respectively. The average percentage of positive flashes was 36.5%. The geometric means of negative and positive peak current were 30.9 kA and 17.8 kA. The high density, high percentage and low average peak current of positive flashes found in this study are probably a result of such a contamination. Neglecting positive flashes below 15 kA, assuming that they correspond to intracloud flashes erroneously identified by the system, the maximum positive and total flash densities would be 3.9 flashes/km2 per year and 11.7 flashes/km2 per year. The percentage and geometric mean peak current of positive flash would be 23% and 38.7 kA, respectively. The results are discussed in the context of other similar measurements made at different parts of the world.