Return-stroke current measurement at the Canton Tower and preliminary analysis results

Abstract

The lightning current on the 600-m high Canton Tower was measured directly for the first time, using a Rogowski coil installed at a height of 492 m above ground level. Return-stroke current measurements for three single-stroke downward negative flashes and two multiple-stroke upward negative flashes were presented and preliminarily analysed by combining the associated return-stroke luminosity and data of the lightning location system (LLS). The 10-90% rising time and the full width at half maximum (FWHM) of the first-stroke current were within a range of 6.0 to 9.3 μs and 68.1 to 96.9 μs, respectively. Subsequent-stroke currents were characterized by distinct sharp double peaks, and the typical 10-90% rising time of the initial peak was about 0.4 to 0.5 μs. The FWHM of the subsequent-stroke current ranged from 6.1 to 39.3 μs with AM (GM) value of 18.1 (15.0) μs. An approximately quadratic relation was found between the maximum peak current and the initial peak luminosity for subsequent strokes in the same upward flash. A total of 88% (14/16) of the subsequent strokes were misclassified as intracloud (IC) events by the LLS. The LLS-inferred peak current was overestimated by a larger factor for subsequent strokes than the first strokes.