On the Occurrence of Positive Ground Flashes in Summer Thunderstorms in Brazil

This paper, reports the results obtained by a lightning position and tracking system network during a coordinated campaign conducted in Brazil on December 13, 1989 to study a large storm system. The results are supported by synoptic, radiosonde, radar and satellite data. It was found that most lightning flashes (60%) were positive, in contrast with previous observations during the summer in the northern hemisphere. An analysis of wind and temperature data showed that the predominance of positive ground-flashes can not be supported by the tilted dipole hypothesis, being necessaxy to search for other mechanism to explain it. Although tlis observation can not be considered as usual in this region, it clearly indicates that the flash polarity should depend on many factors besides the season. These :eactors should be probably related to the geographical location and the meteorological environment.