Recent Update on Lightning Parameters for Downward and Upward Flashes Observed at Tokyo Skytree

Abstract:
Direct observation of lightning current is a fundamental approach to evaluating lightning parameters, which are among the most basic factors for the lightning protection design of various grounded objects. However, for a tall grounded structure, upward lightning flashes initiated from the top of the structure have usually been observed, and the direct observation results of downward flashes have been limited. Tokyo Skytree is a free-standing independent broadcasting tower, which a height is 634m-ASL, located on a flat terrain about 8 km inland in Tokyo, Japan (35.71ºN, 139.81ºE). The authors have conducted lightning current observation with the Rogowski coils at the tower since 2012. At Tokyo Skytree, we have confirmed 39 downward-initiated lightning flashes and 73 upward-initiated lightning flashes to the tower as of the end of December 2023 for 12 years. The cumulative frequency distribution of some lightning parameters of the return stroke of the lightning current waveform has been accumulating since 2012 at the tower. In this paper, we overview the recent result of lightning current observation. It consists the evaluation of the lightning current parameters for return strokes of both downward and upward flashes and initial continuous current (ICC) obtained at Tokyo Skytree.