Introduction

Positive flashes are defined as those transporting positive charge from cloud to Earth. It is thought that less than 10 percent of global cloud-to-ground lightning is positive. The first well-documented study of positive lightning was due to K. Berger and co-workers, who presented the detailed statistical characteristics of 26 positive lightning discharges observed on Monte San Salvatore in Switzerland (Berger et al. 1975). It is interesting to follow the evolution of the views of Berger and co-workers regarding these discharges. Initially, Berger and Vogelsanger (1969) and Berger et al. (1975) considered the discharges as downward positive flashes that involved long, upward-connecting, negatively charged leaders. Later, Berger (1977) expressed his uncertainty in identifying those discharges as either downward or upward positive flashes. Finally, Berger and Garbagnati (1984) assigned all 67 positive flashes observed on Monte San Salvatore to the upward discharge category, perhaps as an indication that such flashes were not expected to occur in the case of objects of moderate height (less than 100 m or so) located on flat terrain.

Interestingly, Berger and Garbagnati reported on five upward positive and seven downward positive discharges from tower measurements in Italy, the lightning type (upward or downward) being identified solely on the basis of the recorded current waveforms.