Quantitative relationship between current pulses and associated low-frequency magnetic fields during initial stage of rocket-triggered lightning

The quantitative relationship between the channel-base current and the associated low-frequency magnetic field (B-field) during the early stage of rocket-triggered lightning was examined based on field experiments and numerical simulation. There is a good correlation between the current pulse and the corresponding B-field pulse in terms of amplitude and duration. In specific, the duration of current pulse is approximately proportional to that of the corresponding B-field pulse for precursors and initial upward leaders; as for the pulse amplitude, the linear correlation is more apparent for the initial upward leaders when compared to the precursors, with the ratio of B-field pulse and current pulse between 1.7 and 2.0, which is always greater than that (0.97–1.32) for the precursors. A response function is established to show the quantitative relationship in the time domain between the current pulse and the associated B-field pulse, which is considered as the convolution of the current pulse and the response function. Meanwhile, the current waveform can be obtained if the measured B-field pulse is de-convolved with the response function. The simulation results are in good agreement with the measurement, which proves that our approach is accurate and efficient to quantify the relationship between the current and the B-field pulse of the initial leader discharges.