Interferometric directions of lightning sources at 34 MHz

We present a new technique for measuring the VHF radio centroid of nearby lightning flashes at 5‐μs intervals. Its ability to provide continuous positions during long ( 100 μs) emissions is, we believe, new and reveals new information about the discharge process. The new technique solves many of the data‐handling problems in old techniques. We have built and demonstrated this technique in one angular coordinate of the lightning flash. We present data from five flashes showing complex positional and motional patterns. The breakdown phase consists of many impulses. The average speed from impulse to impulse lies in the range of 10–100 km s −1 . During individual impulses, speeds measure from one to several tens of thousands of kilometers per second. At times of strong VLF bursts there is usually a similar VHF burst. Its speed is like the speeds of individual impulses. We identify VLF‐associated VHF burst sources with the main electrical current flow in lightning flashes. We identify the motion from one impulse to another in the breakdown phase as being caused by avalanching electrons accelerating along paths soon to become the discharge paths within thunderclouds. The high speeds in impulses represent the gross current flow in breakdown channels not yet large enough to create large VLF emissions or flashes.