Reconstructing initial continuous current waveform in rocket-triggered lightning with close magnetic measurement
We present a new method that remotely measures the initial continuous current in classical rocket-and-wire triggered lightning using a compact dB/dt sensor deployed at 78 m distance from the channel base. The current waveform retrieved from the numerical integration of close magnetic signals perfectly shows the general feature and all the slow variations (such as M-components) embedded in the channel-base current measured with a shunt. This method was applied to several rocket-triggered lightning flashes in 2014, including one flash containing a long continuous current similar to that occurring in natural lightning. In comparison with the shunt measurement, the new method has the advantage of significantly reduced noise (with the lower detection threshold as small as a few mA). Our method could be applied to remotely probe the initial continuous current in upward lightning from high objects and altitude-triggered lightning, as well as continuing current in natural cloud-to-ground lightning strokes at a sufficiently close range.