Measurement of continuing charge transfer in rocket-triggered lightning with low-frequency magnetic sensor at close range

Based on the magnetic fields recorded with a compact low-frequency (LF) magnetic sensor deployed at 78 m distance from the channel base, we reconstruct the time-resolved current waveform for the continuously discharging processes in classical rocket-and-wire triggered lightning flashes, including the initial continuous current (ICC) and long continuing current. Both the overall feature and the millisecond-scale slow variations (e.g., initial current variation, ICC pulses and M-components) embedded in the channel-base current as measured with the conventional methods (such as the shunt or Pearson coil) can be retrieved through the numerical integral of close LF magnetic signals. Despite the artifact caused by the magnetic fields radiated by the fast in-cloud processes, the new approach has the advantage of significantly reduced noise in comparison with the measurements of conventional methods, and it is likely applicable to remotely measure the initial continuous current in upward lightning from high objects and altitude-triggered lightning, as well as long continuing current in natural cloud-to-ground (CG) lightning strokes that occur at sufficiently close range (e.g., within 100 m).