Modling And Characteristic Analysis On Far-Field Waveform Of Compact Lightning

In this paper, we have studied the validity range of parameters for the Bouncing-Wave Model on the basis of corresponding experimental results. From modeling the CID with Bouncing-Wave Model and comparing modeling results with measurements, we estimated that the effective current reflection coefficients at channel ends (additionally accounting for current attenuation along the channel) should be in the range of 0 to -0.5, the current wave propagation speed should range from 0.3*10^8 to 3*10^8 m/s, and the channel length is less than 1000 m. In these calculations, we assumed that the current wave had a typical risetime of 6 μs and a total duration of 30μs. We also examined the influence of current risetime on far-field waveforms, and it was found to be typically in the range from about 2 to 8.5 μs.On base of the modeling results of the Bouncing-Wave Model, we studied the validity range of parameters for Hertzian Dipole Approximation. We found that Hertzian Dipole Approximation is consistent with Bouncing-Wave Model for a considerable range of combinations of propagation speed and channel length. On this basis, we inferred the discharge electric parameters of CID using Hertzian Dipole Approximation.Considering the production envirment of large bipolar events (LBEs) occurred in winter thunderstorms in Japan, we extended the Bouncing-Wave Model to the case in the presence of tall grounded object for different physical process, and simulated the far field waveform characteristic of large bipolar events (LBEs) occurred in winter thunderstorms in Japan, and compared the field-to-current conversion factors(FCCFs) of LBEs with that of the lightning cloud-to-ground (CG) return stroke (RS)in summer thunderstorm. Because the physical process of LBEs may be very similar to the typical lightning RS (RS-like process), or caused by an initial continuous current pulse (ICC-like process) in upward lightning flashes,we simulated far field waveform of LBEs both for RS-like process and ICC-like process. We assume the lightning channel length of LBEs ranges from 500 m to 1000 m, and the height of tall object struck by LBEs is from 100 m to 300 m. By using the bouncing-wave model,we found that only when the injected current waveform of LBEs is characterized with a symmetric Gaussian pulse, the simulated far field waveform of LBEs both for RS-like process and ICC-like process is similar to the experimental results. When LBEs strike tall objects with heights from 100 m and 300 m,the FCCFs of LBEs are positively correlated with its channel length and derivatives of injected current waveform, and the FCCF for RS-like process is about similar to that for ICC-like process. However, the FCCFs of LBEs are very different from lightning RS in summer thunderstorm, that is to say, the FCCFs developed for the well-known lightning RS in summer thunderstorm are not suitable for LBEs.