Publication Date:
2019-05-08
Description:
This study compares waveforms recorded by “broadband” very low frequency/low-frequency/medium-frequency (VLF/LF/MF) electric field change sensors (bandwidth ~0–2.5 MHz) and very high frequency (VHF) sensors (bandwidth 186–192 MHz) during the initiation of 20 negative cloud-to-ground lightning flashes. In the first 2 ms of each flash, initial breakdown (IB) pulses are detected with the VLF/LF/MF sensors. Comparison shows that all classical IB pulses are accompanied by VHF pulses, where classical IB pulses are defined herein as bipolar with duration 〉10 μs and amplitude 〉25% of the largest IB pulse amplitude in the flash. There are on average 47% of IB pulses (of all amplitudes and durations) that are accompanied by VHF pulses within ±1 μs. There are also many VHF pulses with no associated IB pulses. These observations indicate that the initial in-cloud lightning channel extension process (es) occurs very fast and at multiple length scales, since substantial electromagnetic radiation is emitted in the VLF/LF/MF and VHF bands. ©2019. American Geophysical Union. All Rights Reserved.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
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