Statistical analysis of lightning current parameters: Measurements at Morro do Cachimbo Station

Most of the available data concerning lightning current parameters were obtained by means of measurements made in temperate regions in the Northern Hemisphere. Considering the influence of regional aspects on such parameters, the need for references concerning lightning protection practices specifically in tropical zones requires dedicated data. An experimental investigation program has been carried on in Brazil since 1971 in order to provide data for characterization of local lightning current parameters. The authors of the present work are involved in that research. With such purpose, they have evaluated a significant amount of data, obtained by means of measurements taken at an instrumented tower located at "Morro do Cachimbo'' Station, in Southeastern Brazil. The lightning current wave registers correspond to 157 strokes, which were measured during 13 years at the station. In this paper, the authors present a statistical evaluation of measured current waves, with particular interest in front wave parameters. The considered parameters (peak current, front duration and front steepness) are compared with those traditionally presented in literature. The cumulative frequency distributions and the correlation coefficients between parameters were determined. One main result was derived from this work, concerning the negative downward discharges: the median (and average) value of current peak measured at tower basis was found to be around 50% and 30% higher, respectively for the first and subsequent strokes, than the usual Berger references measured at tower top.