Comparative Analysis on Characteristics and Mechanism for Two Types of M-component in Triggered Lightning

Parameters such as amplitude, rise time, half-peak width and charge transfer is obtained by analyzing channel base current data from triggered lightning, which is acquired by GCOELD (Guangdong Comprehensive Observation Experiment of Lightning Discharge) during 2008 and 2013. Geometric mean value of amplitude, rise time, half-peak width and charge transfer from 31 samples are 301 A, 341 μs, 662 μs and 0.207 C, among which geometric mean value of amplitude is close to the result from Shandong Articicially Triggering Lightning Experiment, while rise time and half-peak width are close to results in Florida. From the histogram for parameter distribution, M-component is mostly within 400 A, the rise time is lower than 400 μs, the half-peak width is less than 1 ms, and the charge transfer is from 0.1 C to 0.3 C. Whereas, histogram of amplitude, rise time, half-peak width and charge transfer indicates portion of M-component has unusual characteristics. Combined with previous research, it's concluded that M-component can be divided into two types, by amplitude lower/higher than 1 kA. Geometric mean value of amplitude, rise time, half-peak width and charge transfer is analyzed, respectively. Two types of M-component show obvious differences, for instance, the amplitude of Type 2 M-component is almost 10 times the value of Type 1 M-component, while the rise time and half-peak width is approximately quarter of the corresponding parameter for Type 1. In general, Type 2 M-component has higher amplitude, shorter rise time and narrower half-peak width than Type 1. The relationship between M amplitude and the lag between return stroke and M-component for Type 1 and Type 2 are compared, and lags of Type 2 M-components are shorter than 50 ms, shorter than lags of Type 1 M-components as a whole. It possibly indicates that the lower the amplitude of M-component is, the longer the lag is. With M-component two-wave model, the electric field are calculated. By configuring incident wave velocity and reflected wave velocity to various values, it's found that the result is consistent with measured electric field, but the incident velocity is always smaller than reflected velocity for both Type 1 and Type 2. The ratio between incident wave velocity and reflected wave velocity for Type 1 is larger than that of Type 2. Based on analysis for M-component characteristics and M-component classification, two types of M-component may correspond with streamer occurred by breakdown in channel branch into main channel and breakdown within part of the lightning channel, indicating Type 1 M-component has some differences with Type 2 M-component in mechanism.