A study of cloud-to-ground lightning flashes initiated by fast positive breakdown

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Sabri M.H.M.
Ahmad M.R.
Al-Kahtani A.A.N.
Kadir M.Z.A.A.
Baharin S.A.S.
Lu G.
Zhang H.
Williams E.
Cooray V.
Nordin F.H.
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Elsevier Ltd
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In this paper, we examine the initiation event of two tropical negative cloud to ground (CG) lightning flashes within reversal distance (<8 km) detected on 12 (CG1) and 24 (CG2) November 2019, respectively. The CG flashes were recorded using a fast antenna (FA), slow antenna (SA), magnetic field (B-field), and very high frequency (VHF) sensors located at two observation stations (ST1 and ST2) 13.26 km apart. The key finding is that CG1 flash was initiated by a short VHF pulse followed by a VHF burst (fast positive breakdown) while CG2 flash was initiated by a VHF burst (fast positive breakdown) not preceded by a short VHF pulse. The VHF burst was a precursor for initiation of a narrow bipolar event (NBE)-like pulse and initial electric field changes (IECs). Based on the VHF interferometer map, the VHF sources of NBE-like pulses have been propagated upward predominantly vertical. The initiation altitude, total length of the VHF sources propagation, estimated velocity of NBE-like pulse for CG1 flash were 4.5 � 0.5 km, 1.9�3.8 km, and 2.4 � 108 to 4.8 � 108 ms?1, respectively, and for CG2 flash were 5.1 � 0.8 km, 0.2�3.0 km, and 2.7 � 107 to 4.1 � 108 ms?1, respectively. It is evident that IECs process has been initiated during fast positive streamers propagation. It can be suggested that the IECs process resulted from charge transfer during a fast positive breakdown. The durations and magnitudes of IECs for CG1 flash were 248.5 ?s and 27.97 V/m, respectively, and for CG2 flash were 265.8 ?s and 2.31 V/m, respectively. � 2022 Elsevier B.V.
Charge transfer; Clouds; Interferometers; Lightning; Cloud-to-ground lightning flash; Electric field change; Fast breakdown; Frequency source; High-frequency pulse; Initial breakdown pulse; Initial electric field change; Interferometer narrow bipolar event; Narrow bipolar events; Very high frequency; Antennas; altitude; cloud to ground lightning; electric field; interferometer