Measurements of Magnetic Pulse Bursts During Initial Continuous Current of Negative Rocket‐Triggered Lightning

Abstract

During the SHandong Triggering Lightning Experiment (SHATLE) in summer of 2014 and 2015 and the Guangdong Comprehensive Observation Experiment on Lightning Discharge (GCOELD) campaign in 2018, we have conducted the observations of the magnetic pulse bursts (MPBs) during the initial continuous current in negative rocket-triggered lightning. The MPBs are commonly recorded at the main site of SHATLE (970 m from the rocket launch site), but the synchronous magnetic field (B-field) measurements at the close site of SHATLE (78 m from the rocket launch site) show the slow variations with small MPBs superposing on them. Note that both the charge transfer and the relative brightness increase notably during the appearance of the MPBs. After shifting up the operation frequency of the magnetic sensor, the MPBs can be observed at close distance (80 m from the rocket launch site) obviously in GCOELD. Observations show that the radiation sources of MPBs originate from the breakdown in the vicinity of the leader tip, but the sources of the initial magnetic pulses (IMPs) measured at the very initial stage of triggered lightning are from the radiation of the whole steel wire. The continuous current measured at the channel base during the MPBs cannot reflect the characteristics of breakdown current, because the current is attenuated and dispersed when propagating along the high-impedance leader channel. The average peak current associated with the MPBs is estimated to be on the order of kiloamperes.

A Comprehensive Study on the Improved Radio-Frequency Magnetic Field Measurement for the Initial Upward Leader of a Negative Rocket-Triggered Lightning Flash

“…The duration and inter-pulse interval of MPBs are approximately 4.7 and 25.9 µs (see Table 3), respectively. The statistical results are very similar to those of the upward leader in natural lightning [29], which means that MPBs are likely related to the stepwise progression of the upward positive leader [30,31]. The superposition of radiation from two different sources causes the chaotic waveform of MPBs measured at the close site.…”

Characterizing Radio Frequency Magnetic Radiation of Initial Upward Leader Stepping in Triggered Lightning With Interferometric Lightning Mapping

“…However, the impulsive feature gradually transforms to ripple pulses along with the extension of leader channel. During the ICC stage, impulsive MPBs are recorded by the magnetic sensors at two sites, and the MPBs are derived from the discharging processes in the vicinity of the UPL (Fan et al, 2019). Due to the extension of the bandwidth of magnetic field sensor to the relatively high frequency, the magnetic pulses associated with the UPL at the quiet stage are unambiguously discerned at the close site for the first time.…”

“…Actually, only some small variations are recorded by the fast antenna during the stage (Jiang et al, 2013; Rakov et al, 2003). In addition, Fan et al (2019) confirmed that MPBs are commonly observed during the ICC of triggered lightning, and these pulses are driven by the discharging processes in the vicinity of the UPL. Previous observations have showed the advantages of high sensitivity of the magnetic sensor.…”

“…The broadband interferometer consisted of three broadband VHF discone antennae (25-90 MHz), which were placed at the vertices of an equilateral triangle with side length of 20 m (Zhang et al, 2017). There was another magnetic sensor with 3-dB bandwidth of 6-340 kHz as used by Lu et al (2014) and Fan et al (2018Fan et al ( , 2019 deployed at about 1.9-km range. Figure 1 gives the layout for the triggered lightning experiment in summer of 2019.…”

“…By the aid of the high‐speed video observation, it can be concluded that the propagating manner of the UPL is stepped during the initial stage of triggered lightning (Biagi et al, 2011; Jiang et al, 2013). As the leader channel extends, the electromagnetic pluses associated with the sustained UPL change to ripple‐like deflections, and then the measurements show a signal quiet period that lasted about several to dozens of milliseconds (Fan et al, 2018, 2019; Lu et al, 2016). These observations suggest that the UPL might propagate continuously during the signal quiet period, but many VHF radiations can still be observed during the period by using the interferometer (Sun et al, 2014; Zhang et al, 2017).…”