Correlation between Frequency-Divided Magnetic Field and Channel-Base Current for Rocket-Triggered Lightning

Different discharge processes of triggered lightning can radiate electromagnetic signals with different frequency bands. During the triggered-lightning experiment conducted at the Field Experiment Base on Lightning Sciences of China Meteorological Administration (CMA-FEBLS), three magnetic field (B-field) antennas with different frequency responses were deployed at about 80 m from the rocket-launching site. By using the synchronous observations, the quantitative relationship between the close-range B-field measurement and the channel-base current at different stages of triggered lightning were established in the investigation. The initial continuous current (ICC) waveform can be reconstructed by numerically integrating the B-field signals measured with the dB/dt antenna. However, the slow variations of ICC cannot be retrieved by the B-field signals measured with the LF-MF antenna because the antenna bandwidth cannot cover a frequency below 500 Hz. The B-field signals of the return stroke measured with the low-sensitivity antenna can be simulated by the MTLL return-stroke model, and the B-field signal shows a fairly good consistency with the return-stroke current. The analyses suggest that the current waveform of the natural return stroke that occurred within 1.5 km can be retrieved, or at least its peak value can be estimated by using the B-field measurements.