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

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 × 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 Echange 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.