Optical and current measurements of lightning attachment to the 356-m-high Shenzhen meteorological gradient tower in southern coastal area of China

Abstract

This paper presents in detail the instrumentation for coordinated optical and current measurements of lightning discharges to a 356-m-high meteorological tower and the observation results. The tower, which is located at Shenzhen, a lower latitude coastal city in south China, was equipped with a non-inductive current shunt at its top and a high-speed camera and electromagnetic field sensors at 440 m away from the tower base. A total of 24 discharges to the tower were well documented in the period of April to June of 2019. Three of them were analyzed in detail with the focus being given to the feature of upward leaders initiated from the tower: Case 1 - a connecting upward positive leader (connecting UPL) induced by a downward negative in a downward negative discharge, Case 2 - an upward positive leader (UPL) in the initial stage of an upward negative discharge, and Case 3 - an upward negative leader (UNL) in the initial stage of an upward positive discharge. All the three leaders had a stepping feature during their initial stages, each step producing an isolated but oscillated current pulse with a time scale of 1 mu s. The connecting UPL had 5 steps during its initial 2.6 ms, with a step interval ranging in 0.1 similar to 1.5 ms and a current pulse peak in 1 similar to 5 kA. The UPL had also 5 steps but during its initial 200 mu s, with a step interval ranging in 20 similar to 50 mu s, a step length in 0.8 similar to 2.2 m, a current pulse peak in 0.5 similar to 2.2 kA, and a leader average speed in 0.4 similar to 1.1 x 10(5) m/s. The UNL had 8 steps during its initial 104 mu s, with a step interval ranging in 13.6 similar to 22 mu s, a step length in 3.9 similar to 7.1 m, a current pulse peak in 2.3 similar to 12.5 kA, and a leader average speed in 1.9 similar to 6.6 x 10(5) m/s.