Observations of the initial stage of a rocket‐and‐wire‐triggered lightning discharge

Zhang, Yang; Krehbiel, P. R.; Lu, Wei; Zheng, Dong; Xu, Liangtao; Huang, Zhongwei

doi:10.1002/2017gl072843

Cited by 26 publications

(45 citation statements)

References 24 publications

(58 reference statements)

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“…The VHF signals from each antenna were recorded continuously for 2 s with 16-bit resolution at a sampling rate of 200 MHz. The time series of VHF signals were postprocessed utilizing the generalized cross-correlation time delay algorithm (Stock et al, 2014) and applied to sequences of overlapping data segments from the time series waveforms (Zhang et al, 2017). Figure 2 gives the synchronized measurements during the initial phase of the selected triggered lightning flash.…”

Section: Measurements and Datamentioning

confidence: 99%

“…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).…”

Section: Introductionmentioning

confidence: 99%

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

Fan

Zhang

et al. 2020

Geophysical Research Letters

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In summer of 2019, the bandwidth of magnetic field sensor with relatively high sensitivity was extended to 1.2 MHz during the triggered lightning experiment of Field Experiment Base on Lightning Sciences, China Meteorological Administration (CMA-FEBLS) in Conghua, Guangdong Province. The measurements with the new magnetic fields reveal the presence of microsecond-scale magnetic pulses during the entire duration of upward positive leader (UPL), including the quiet stage when only few signals can be discerned in previous observations, which indicates that the UPL generally propagates in a stepwise manner during the initial stage of triggered lightning. Synchronous mapping observations from the broadband VHF interferometer shows that the VHF radiation corresponds to the onset of individual magnetic pulses, indicating that the VHF signals are radiated by the breakdown processes of individual stepping, and these breakdown events launch the meter-scale current pulses as the radiation source of individual magnetic pulses. Plain Language Summary The magnetic field sensor with high sensitivity has demonstrated its capability to resolve the weak discharging processes during the initial upward leader of rocket-triggered lightning. However, the bandwidth of the magnetic sensor used in previous measurements was usually below 500 kHz, which restricts the identification of more impulsive discharging processes with microsecond time scale. In order to improve the understanding on the development of initial upward leader in triggered lightning, new measurements were conducted by extending the upper bandwidth of magnetic sensor to 1.2 MHz and comparing with the very high-frequency (VHF) interferometric mapping observations. Benefitting from the extension of bandwidth to higher frequency, the microsecond-scale magnetic pulses associated with the upward positive leader are unambiguously resolved during the "quiet" stage for the first time, when few signals could be discerned in previous measurements. Many of these pulses cannot be resolved in the measurement of channel-base current and fast/slow electric fields. Consequently, the measurements with the improved sensor help to reveal more features for the development of upward leader during the initial stage of triggered lightning. By comparing with the synchronous VHF signals, it is found that the VHF radiation and mid-/low-frequency magnetic field manifest different discharging processes of the upward leader.

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Section: Measurements and Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Fan

Zhang

et al. 2020

Geophysical Research Letters

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“…Upward flashes can be divided into two types ( self‐initiated and nearby‐lightning‐triggered type, Wang et al, ), but the initial current pulses and its associated E field changes are only observed in the upward flash of nearby lightning‐triggered type (Guimaraes et al, ; Visacro et al, ), which suggests that these current pulses are attributed to the approach of horizontally propagating negative part of bipolar leaders in the cloud. In contrast, the initial current pulses are commonly observed in rocket‐triggered lightning, but there is no observation of very high frequency (VHF) radiation related to downward negative leaders by lightning mapping array or broadband VHF interferometer, even though the negative leaders emitted strongly at VHF (Hill et al, ; Sun et al, ; Zhang et al, ). The observation indicates that the initial current pulses are related to upward positive leaders rather than the induction effect of downward negative leaders.…”

Section: Introductionmentioning

confidence: 99%

“…Besides, for the triggered lightning, the time windows for the launch attempt to avoid the ambient lightning, and the current measurements do not observe the variations caused by the attachment of positive and negative leaders, which further eliminates the influence of downward negative leaders. Triggered lightning provides a good opportunity to acquire the lightning current waveform at the channel base with a shunt or current transformer and the electromagnetic signals at close range (Jiang et al, ; Qie et al, , ; Yang et al, ; Zhang et al, ; Zheng et al, ). Since the initial stage of triggered lightning contains some weak discharge processes (Miki et al, ), the current magnitudes of which are on or below the order of milliampere, it is difficult to acquire the current and electromagnetic fields associated with these weak discharge processes for the limited resolution and sensitivity of measuring systems.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of Electromagnetic Signals During the Initial Stage of Negative Rocket‐Triggered Lightning

Fan

Jiang

et al. 2018

JGR Atmospheres

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With the measurements in SHandong Triggering Lightning Experiment and GuangdongComprehensive Observation Experiment on Lightning Discharge in China, we examine the electromagnetic signals associated with the upward positive leaders during the initial stage of negative triggered lightning. The magnetic field (B field) signals measured at close range (<100 m) for both sites can be divided into two categories (i.e., impulsive and ripple pulses) according to the discernibility of separation between individual pulses. The impulsive pulses are well simulated by using the transmission line model, which suggests that these pulses are generated by leader current pulses propagating downward along the steel wire. Because the length of extended leader channel ahead of the wire is not negligible during the stage of ripple pulses, the waveform of impulsive current pulses is changed after traveling through the high impedance leader channel. Taking the filtered current pulse as the input variable, the waveform of ripple pulse can be simulated properly, which indicates that ripple pulses are caused by the attenuation of impulsive current along prolonging leader channel. In addition, the paper analyzes the fast electric field (E field) changes measured at 60-m range from the launching site during the initial stage by using the transmission line model and shows that the polarity of E field change at a given range is determined by the inception height of upward leader, namely the surface E field change caused by the individual charge transfer of initial upward leader also involves the problem of reverse distance as present for a vertical dipole. Plain Language SummaryLightning can occur at a predictable time and place by using the technique of rocket-triggered lightning, which launches a small rocket trailing a grounded steel wire toward the charged thundercloud overhead. Therefore, the technique facilitates the research of lightning discharges and their electromagnetic effects. At the beginning of triggered lightning, a sustained train of current pulses can be measured at the base of discharge path, and the synchronous electromagnetic field signals can also be recorded by the electric and magnetic sensors deployed around the rocket launching site. The paper focuses on the characteristics of electromagnetic signals measured at close range (<100 m) during the SHandong Triggering Lightning Experiment and Guangdong Comprehensive Observation Experiment on Lightning Discharge (two experimental sites of triggered lightning in China) campaign. The main contributions of this article include two aspects: first, we clarify the relationship between the electromagnetic signals and current pulses during the initial stage of triggered lightning; second, we demonstrate the influences of the triggering height on the polarity of electric field waveform.

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“…Detailed information about the current measurement system can be found in the studies by Zhang et al (2016Zhang et al ( , 2017. A positive current value corresponds to negative charge moving downward or positive charge moving upward.…”

Section: 1029/2018rs006552mentioning

confidence: 99%

Characteristics and Discharge Processes of M Events With Large Current in Triggered Lightning

Zhang

Zheng

et al. 2018

Radio Science

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Observations have been obtained of M events during triggered lightning flashes with a broadband very high frequency interferometer and measurements of electric field changes, channel‐base current, and high‐speed video. The current characteristics of 239 M events in 18 triggered lightning flashes are analyzed, and the discharge processes leading to large M currents are investigated. Sixty‐eight of the M events (28%) had peak currents exceeding 1 kA. The geometric average values of peak current, duration, 10–90% rise time, half peak width, charge transfer, interval from return stroke to M and background current are 2.358 kA, 0.627 ms,0.078 ms, 0.165 ms, 0.417 C, 2.172 ms, and 579 A, respectively. Compared to other M events, the M events with large peak current occurred closer in time to the preceding return stroke, and their corresponding current changes were more rapid. Three cases associated with the initiation processes of M events reveal that some large M events were initiated by fast positive streamers propagating away at a velocity of about 107 m/s followed by a possible recoil event, or by a dart leader while the channel of continuing current generated by previous leader still existed. It is found that a fast current pulse with 10–90% rise time of less than 300 μs is a necessary, but not sufficient, condition for the occurrence of large M events. The fast current pulse often corresponded to a low/close junction site.

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Observations of the initial stage of a rocket‐and‐wire‐triggered lightning discharge

Cited by 26 publications

References 24 publications

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

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

Characteristics of Electromagnetic Signals During the Initial Stage of Negative Rocket‐Triggered Lightning

Characteristics and Discharge Processes of M Events With Large Current in Triggered Lightning

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