Leader Charges, Currents, Ambient Electric Fields, and Space Charges Along Downward Positive Leader Paths Retrieved From Ground Measurements in Metropolis

An approach for retrieving the leader channel charge density, leader current, ambient electric field, and space charge along a leader channel path from ground observations with a complicated ground condition was presented. With this approach, properties of two downward positive leaders (DPL1 and DPL2) struck at high-rise buildings were studied based on electric and optical measurements made on the roof of a 100 m high building in Guangzhou, China. It shows that the leader-produced electric field on the roof of the 100 m high building was about 4 times of that on flat ground. The 2-D speed for both leaders showed a general increasing trend as the leader going down, in the range of 1.8 to 32.3 × 10⁵ and 1.7 to 46.9 × 10⁵ m/s, respectively. The channel line charge density for both leaders showed firstly a sharp increasing trend and then a decreasing trend as the leader going down, in the range of 0.4 to 8.6 and 0.4 to 15.2 mC/m, respectively. The current of the two leaders varied in the range of 0.7 to 5.4 and 0.7 to 4.6 kA, respectively. The ambient electric field (downward is positive) for both leaders showed an alternating polarity along the leader path, in the range of −120 to +176 and −250 to +180 kV/m, respectively. The space charge for both leaders showed also an alternating polarity along the leader path, in the range of −12.3 to +4.2 and −13.9 to +7.8 nC/m³, respectively, which may reflect the in-cloud electric structure and the corona charge distribution between the cloud and ground.