Observation and Analysis of Polarity Reversal for the Burst-type Magnetic Pulses during the Propagation of Upward Positive

In order to understand the propagating process of upward positive leader and related burst-type electromagnetic pulses, in this paper we analyze three cases of downward propagation of positive leader channels obtained by SHATLE (SHAndong Triggering Lightning Experiment) on August 23, 2014.The results show that the reversals in the polarity of magnetic pulses observed in the stage of initial continuous current are related to the variation of projection direction of positive leader head relative to the observation position.Thereby it can be inferred that the burst-type magnetic pulses are emitted by small spatial scale discharge process of positive leader head.For the cases analyzed in this paper, the discharge scale is about 2 m, and the maximum discharge intensity reaches 2.49 kA.The radiation mechanism for these magnetic pulses is different to the radiation mechanism for the magnetic pulses generated by the initial pulse current in the channel measured at the initial stage of rocket-triggered lightning, which may be related to the stepped propagation of positive leader.