On December 13, 1989, a coordinated campaign was conducted in Brazil to study the electrical signatures associated with a large storm system over the South American continent. Balloon-borne VLF electric field data showed more than a hundred lightning-related stratospheric vertical electric field (sferics) signatures during approximately 6 hours. The sferic signatures were characterized by a rapid transient with peak amplitudes exceeding 7 V/m which would be expected by the removal of positive charge below followed by a slow recovery. This signature indicates that the lightning strokes experienced by the balloon were either cloud discharges or positive ground discharges. The peak amplitudes indicate that the positively charged region is of the order of tens of Coulombs. The recovery curves are quite variable, reflecting the complex nature of the propagating phenomena in the atmosphere. A lightning position and tracking system (LPATS) network recorded 326 ground strokes at distances less than 100 km of the balloon. In contrast with previous observations during the summer in the northern hemisphere it was found that most lightning flashes (60%) were positive. In addition, only a small fraction of them occurred simultaneously with a balloon sferic signature, indicating that most balloon sferics were a result of cloud discharges.

An analysis of wind and temperature data during the event showed that the predominance of positive ground flashes is apparently not supported by the tilted dipole hypothesis, being necessary to search for other mechanisms to explain it. Although this observation cannot be considered as usual in this region, it clearly indicates that the flash polarity should depend on many factors besides the season. These factors should be probably related to the geographical location and the meteorological environment. ¿ American Geophysical Union 1992