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

Abstract

Different discharge processes of triggered lightning can radiate the 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 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. 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 the frequency below 500 Hz. The B-field signals of return stroke measured with the low sensitivity antenna can be simulated by the MTLL return stroke model, and the B-field signal shows fairly good consistency with return stroke current. The analyses suggest that the current waveform of 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.