Lightning electric field characteristics of first and subsequent return strokes to a tall tower

Abstract

Simulation of electric fields associated with lightning return stroke (RS) currents of flashes to a tall structure (the Toronto 553-m CN Tower) is based on the modeling of current distributions along both the tall structure and the lightning RS channel using the modified transmission line model (MTL). The main peculiarity of the developed MTL model is that it accounts for multiple current reflections within the Tower [8-10] as well as within the continuously growing RS channel [5]. In this paper, previously obtained current distributions [5] are used to calculate vertical electric fields (2 km away from the Tower) for various: (a) parameters (peak and maximum steepness) of first and subsequent RS current pulses injected at the Tower's top; (b) values of RS front velocities; (c) values of the channel current decay factor in the MTL model. Calculated electric field waveforms and ratios of peak values (for subsequent and first RS) are discussed and compared with observed data.