Correlating the Characteristics of the CN Tower Lightning Return-Stroke Current with Those of Its Generated Electromagnetic Pulse

Simultaneous measurements of the lightning return-stroke current derivative at the Canadian National (CN) Tower and the corresponding lightning electromagnetic pulse (LEMP) 2 km north of the tower have been performed since 1991 using broadband, high-resolution measurement systems. The recent installation of global positioning systems for time synchronization of CN Tower lightning measurement stations has enabled the correlation of the wavefront characteristics (peak, maximum derivative, and 10-90% rise time) of the return-stroke current with those of its LEMP. The characteristics of the tower's lightning electric and magnetic fields have also been correlated with each other. The current and field correlation analysis is based on August 19, 2005, CN Tower lightning return-stroke data. In addition to the strong linear correlations of the wavefront characteristics of the electric and magnetic field waveforms, an excellent linear correlation has been established between the magnetic field and current wavefront peaks. Also, a good linear correlation has been found between the magnetic field wavefront maximum derivative and that of the current. These findings are of interest in lightning detection methodology. For example, the current wavefront maximum derivative can be estimated from the detected magnetic field after taking into consideration the propagation effect on its derivative. Although weakly correlated, a general trend of increase in the magnetic field peak and maximum rate of rise has been observed as the current maximum rate of rise and peak increase, respectively. It is hoped that the field-current relationships developed in this paper, using the recent CN Tower lightning return-stroke data, will contribute to solving the inverse-source problem, one of the challenging problems in lightning research, where lightning current characteristics are estimated based on the characteristics of the measured LEMP.