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VHF Radio Spectrum of a Positive Leader and Implications for Electric Fields
Author(s) -
Pu Yunjiao,
Cummer Steven A.,
Liu Ningyu
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2021gl093145
Subject(s) - electric field , lightning (connector) , cutoff , physics , broadband , cutoff frequency , interferometry , radio frequency , computational physics , environmental science , optics , telecommunications , computer science , power (physics) , quantum mechanics
Abstract Electric fields associated with a developing natural lightning leader are difficult to measure. This work demonstrates a new approach to indirectly probing the electric fields in the streamer zone of a lightning leader. Using a 10–250 MHz broadband lightning interferometer, very high frequency (VHF) radio emissions from the tip of a positive cloud‐to‐ground (CG) leader were measured and localized. We specially use a normalized spectral analysis to avoid the challenge of absolute system calibration to show that the positive leader spectrum exhibits a clear cutoff frequency at 80 MHz. Compared with theoretical predictions, this cutoff frequency corresponds to a streamer growth rate of 1.7 × 10 8 s − 1and an average electric field of 0.9 times the conventional breakdown fieldE kin streamer bursts from the positive leader. Implications for the detectability of positive leaders through VHF emissions and for the production of X‐rays by positive leaders are analyzed.