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- Title
Characterizing Radio Frequency Magnetic Radiation of Initial Upward Leader Stepping in Triggered Lightning With Interferometric Lightning Mapping.
- Authors
Fan, Yanfeng; Lu, Gaopeng; Zhang, Yang; Lyu, Weitao; Zheng, Dong; Fan, Xiangpeng; Li, Xiao; Zhang, Yijun
- Abstract
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. Key Points: B‐field signals with frequency range extending to 1.2 MHz reveal the radiation of upward positive leader during the quiet stageNew measurements indicate common stepping feature of upward positive leader during the initial stage of negative triggered lightningBreakdown processes emitting VHF radiations detected by interferometric technique correspond to the onset of individual magnetic pulses
- Subjects
GUANGDONG Sheng (China); MAGNETIC field measurements; LIGHTNING; MAGNETIC sensors; RADIATION sources; RADIATION; RADIO frequency; SOLAR photosphere
- Publication
Geophysical Research Letters, 2020, Vol 47, Issue 22, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2020GL089392