Current and Electromagnetic Field of M Component in Triggered Lightning

Based on data obtained in the triggered lightning at Conghua, Guangzhou during the period of 2008—2010, the characteristics and correlations of base current and electromagnetic field of M component are analyzed.Lightning M components are transient enhancements in the continuing current and in the associated channel luminosity after the return stroke. A typical M component is characterized by a more or less symmetrical current pulse at the channel base. The M component characteristics of each charge is examined using multiple station measurements of electric and magnetic fields at distances of 80 m, 2 km and 9 km from triggered lightning channels, respectively. Different bandwidth between the current and the electromagnetic field could lead to the differences between different data waveform, affecting the accuracy of the extracted parameters. Furthermore, the relation between the current and the close electromagnetic field is complex since it includes the static field, the induction field and radiation field. The ranging from 500 Hz to 20 kHz band pass filter is designed to filter these data, in order to obtain the valid data within the bandwidth of the M component.Results show that the geometric mean values of duration, 10%—90% rise time, decline time and half-peak width for electric field waveform of M component are 0.49 ms, 0.12 ms, 0.28 ms and 0.15 ms, respectively. The geometric mean values of duration, 10%—90% rise time, decline time, half-peak width and peak for current waveform of M component are 0.53 ms, 0.11 ms, 0.31 ms, 0.17 ms and 0.34 kA. The geometric mean values of duration, 10%—90% rise time, decline time, half-peak width and peak for magnetic field waveform of M component are 0.65 ms, 0.16 ms, 0.37 ms, 0.21 ms and 2.76×10^-5 T.In addition, the following relationship exists between the current, electric field and magnetic field waveform of M component. The correlation coefficient of duration, 10%—90% rise time, decline time, half-peak width, peak between the electric field and current are 0.64, 0.69, 0.39, 0.77 and 0.86, respectively. The coefficients between the magnetic field and current are 0.62, 0.86, 0.55, 0.76 and 0.93, respectively.In summary, there is a relatively strong correlation between the peaks of current and electromagnetic field waveform, and their geometry is comparable. As a result, the current waveform of M component can be calculated by the electromagnetic field data.