Characteristic Analysis of Continuing Current Process and M-component in Artificially Triggered Lightning

The continuing current (CC) process of cloud-to-ground lightning is a discharge process in which charges continuously transfer to ground along the lightning channel after return stroke. The magnitude of CC is small, but the duration of CC is commonly long, so CC often causes lightning disaster. It's very hard to get current data due to the randomness of lightning. Artificially triggered lightning, in which the time and location of triggered lightning can be controlled, is an effective way to measure current of lightning. Artificially trigged lightning is different from nature lightning which only has CC after return stroke, yet artificially trigged lightning has CC and initial continuous current (ICC) process both. Only the CC is analyzed using simultaneous observations of current, electric field change and chnnel luminosity by coaxial shunt, fast and slow antenna, and high-speed camera in Guangzhou Field Experiment Site for Lightning Research and Testing, Conghua, Guangdong, China. Then, photoelectric character and characteristic parameters of 14 CC and 43 M-components after return strokes of triggered lightning observed in summer in 2008 and 2011 are analyzed. The relationship between some characteristic parameters of CC and M-component is analyzed, too.The current waveforms of CC after return strokes are continuous and change slowly. Usually, there are current pulses ranging in size superimposed on CC waveforms. The slow electric field waveforms of CC are slowly changing, too. The lightning channel below the cloud is always luminescent during CC. The current waveforms, fast and slow electric field waveforms and channel luminosity variation waveforms of M-components are approximate symmetrical. The geometric mean of duration, charge transferred to ground, average current and action integral for CC are 22 ms, 6.0 C, 273 A, 4187 A²s, respectively. The geometric mean of magnitude, charge transferred, half peak width, rise time (10%-90%), duration, preceding CC level, inter-pulse interval, action integral for M-components are 409 A, 205 mC, 520 μs, 305 μs, 1.6 ms, 310 A, 6.5 ms, 465 A²s, respectively. There are very remarkable positive correlations between the duration of continuing current and number of M-components, and between the duration of continuing current and inter-pulse interval of M-components. The correlation coefficients are 0.83 and 0.75, and both pass the significant verification of 0.01 level.