Observations of the magnetic pulses in rocket-triggered lightning with sensitive magnetic sensor

With the observations in SHandong Triggering Lightning Experiment (SHATLE) and Comprehensive Observation Experiment on Lightning Discharge (GCOELD) in China, we investigate the magnetic pulses associated with the upward positive leaders during the initial stage of negative triggered lightning. The initial magnetic pulses (IMPs) measured at the very initial stage are corresponding to the sustained upward positive leaders, and can be divided into two categories (i.e., impulsive and ripple pulses) according to the discernibility of separation between individual pulses. The IMPs are generated by leader current pulses propagating downward along the steel wire. For the magnetic pulses measured during the stage of initial continuous current or called magnetic pulse bursts (MPBs) since these pulses last longer than IMPs, they are commonly observed both in SHATLE and GCOELD, even though the associated signals of electrical fields are not obvious. The heights of rocket upon the inception of the MPBs are at least about 268 m in our observations, and the average inter-pulse intervals are affected by the height significantly. The cases with higher height usually have shorter inter-pulse intervals. In comparison with the IMPs, the inter-pulse intervals of the MPBs contain more small time scale (<;20 μs) cases, since the speed of upward leaders show an accelerating tendency with height and time. MPBs are derived from the breakdown near the leader tip.