Complicated aspects of a CG lightning flash observed in winter storm in Japan

Abstract

We have observed a complex winter lightning flash by multiple instruments, including a high-speed video camera NAC, an optical imaging system LAPOS3 (Lightning Attachment Process Observation System), and a lightning mapping system FALMA (Fast Antenna Lightning Mapping Array). The lightning flash lasted for about 0.34 seconds with a large horizontal extent of about 40 X 40 km. In the initial stage, two positive return strokes (RSs) with remarkably different electric field change (E-change) waveforms were located with a horizontal distance of about 13.3 km. An upward positive leader (UPL) was triggered following the second positive RS from the tip of a tall tower. The UPL exhibited not only characteristic progression modes but also needle discharges. The results show a relation between the formation of needle discharges and the previous luminosity variation events (LVEs) of UPL. After the UPL entered the cloud, a negative leader connected with the UPL channel and resulted in a return stroke type of discharge that produced an E-change waveform similar to a large bipolar event (LBE) pulse. About 0.22 s after the UPL initiation, four negative RSs, with two of them producing complicated E-change waveforms, were located at about 5.2 km from the tower. The results indicate that such unusually complicated RS E-change waveforms are produced by the discharges along some floating channels of their preceding discharges around the cloud-base.