VHF broadband interferometer observations and micro-structure of lightning discharge

Lightning Research Group of Osaka University (LRG-OU) has been developing and improving the VHF broadband digital interferometer (DITF), which locates the impulsive VHF radiation sources caused by lightning discharges with extremely high time resolution in three-dimension. As a result of the VHF observations during the ´06-´07 monsoon season in Darwin, Australia, cloud flashes accompanied by K-processes are clearly visualized in three-dimension with high time resolution. In the late stage of the cloud flashes, negative recoil streamers accompanied by K-changes propagate along the same channels as that of preceding negative breakdowns in the early stage. The speeds of the negative recoil streamers are two orders of magnitude faster than the preceding negative breakdown. The negative recoil streamers are supposed to initiate from the tips of positive breakdowns which has progressed along the same path as previous negative breakdown in opposite direction.