Current and Close Electromagnetic Fields of Artificially Triggered Lightning in Shandong, China

Shandong artificially triggering lightning experiment (SHATLE) has been continuously conducted since the summer of 2005 in Binzhou, Shandong. Eight negative lightning flashes including 32 return strokes were successfully triggered from 2005 to 2007. The discharge current and close electromagnetic fields at 50 (m) and 550 (m) distances were documented simultaneously. The whole discharge process of the triggered lightning flashes lasted from 518 (ms) to 1900 (ms). The range of current peak value for 14 recorded strokes in 3 triggered flashes was varying from 5.8 kA to 45.7 (kA) with an average value of 18.6 (kA), similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 30.7 (¿s), which is much larger than the usual result. The peak current of stroke I_p (kA) and the neutralized Charge Q (C) has a relationship of I_p=18.5Q^0.65. The radiation field of return stroke is 5.4 kV.m^-1 and 0.45 (kV/m) at 60 (m) and 550 (m), respectively. The radiation field decreases as r^-1.119 with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4×10⁸ (m/s), with a variation range of (1.1-1.6)×10⁸ (m/s). Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning.