METEOROLOGICAL CONDITION INFLUENCING LIGHTNING CHARACTERISTICS HITTING TOKYO SKYTREE

摘要

This paper describes observation of lightning currents at Tokyo Skytree, which is a 634-m high freestanding broadcasting tower stands in the eastern area of central Tokyo on Kanto Plain. Direct observation of lightning current by using a pair of Rogowski coils started in the end of February 2012, and high-speed cameras were set 6 months later. Both 19 downward and 23 upward lightning flashes were observed at Tokyo Skytree from 2012 to 2014. This paper reports on updated lightning parameters, such as current and charge transfer of return strokes of downward and upward lightning. This report also describes the relationship between occurrence of downward/upward lightning and meteorological conditions. The authors investigated their meteorological conditions by data assimilation with Numerical Weather Forecasting and Analysis System (NuWFAS) developed by CRIEPI, and obtained altitudes of -10°C temperature level, where the lower charge centre frequently exists in thunderclouds. During 2012 to 2014, downward flashes to the tower occurred when the altitude of -10°C temperature level was higher than 5.5 km except at 2 cases. In contrast, except at 3 case, upward flashes occurred when the -10°C temperature level was lower than 5.5 km.