EVALUATION OF PEAK CURRENT POLARITY RETRIEVED BY THE ZEUS LONG RANGE LIGHTNING MONITORING SYSTEM CARLOS A. MORALES Departamento de Ciências Atmosféricas Universidade de São Paulo, São Paulo, Brazil

This study presents the first assessment of a newly developed polarity retrieval scheme augmenting a Very Low Frequency (VLF) long-range lightning detection network (named ZEUS). The polarity scheme uses the Extremely Low Frequency (ELF) in conjunction with the VLF waveform. The measured ELF signal is compared with simulated ELF signal to extract the polarity sign. This comparison also produces correlation coefficients that are used to assign four confidence index categories on the polarity sign. In this paper we present polarity results for a period (November 26 to December 15 2004) of ZEUS network operation. Assessment of the polarity measurements is conducted through comparisons against the Brazilian lightning network–RINDAT that uses a well established lightning location technology. Contingency test analysis shows that the algorithm performance is consistent with the assigned confidence level: e.g., at medium confidence level the algorithm has a 5% bias, while at high level perfect agreement is shown with RINDAT. Peak current strength was found not to influence the accuracy of the polarity retrieval.