A seven-year study about the negative cloud-to-ground lightning ash characteristics in Southeastern Brazil

Abstract A seven-year study of negative cloud-to-ground (CG) lightning ash characteristics in southeastern Brazil is presented. The study is based on approximately 10 million ashes recorded by a Lightning Position and tracking system lightning detection network from November 1988 to December 1995. The data set is the longest ever obtained in the tropics using an almost constant network conÿguration. It provides a unique opportunity to study the long-term annual, monthly, and local time distributions of the number, intensity (peak current) and multiplicity of negative CG ashes in the tropics. The annual distribution of the number of ashes has variations as large as 80%. The variations does not show any clear relationship with any meteorological parameter, possibly indicating the complex interactions of di erent processes responsible for the lightning activity. The monthly and local time distributions seem to follow closely the related distributions of air temperature. The annual distribution of peak current shows an average value of 40:4 kA and has a signiÿcant decrease from 1991 to 1994, apparently related to an El Niño seasonal e ect. The monthly distribution of peak current shows lower values in the winter, in contrast with the results recently reported for the United States, and seems to be related to the monthly distribution of the number of ashes. The local time distribution of the peak current seems also to be related to the local time distribution of the number of ashes; however, the dependency is less evident. The annual distribution of multiplicity has a systematic decrease during the period, with no apparent relationship with any of the variables studied. The monthly distribution of multiplicity is consistent with the hypothesis that the multiplicity is related to the average height of thunderstorms. The local time distribution of multiplicity, in turn, shows a sunrise/sunset e ect. The results are compared to similar ones obtained in other regions of the world