The mechanisms of stepped and dart leaders in cloud-to-ground lightning strokes

Abstract

Recent observations indicate the rather complete neutralization of volume space charges by induced positive corona streamers. New photographic observations of high-tension power lines in rain and snow storms reveal strong and heavily branched corona streamers from such hydrometeors. A study of uniform field streamer breakdown in midgap in clean gases, just published, has provided additional information essential to the delineation of the processes active in the forging of the channel of the cloud-to-ground stroke. On the basis of these findings, consistent sequential qualitative analysis is presented resolving the following moot questions: 1. How is the negative charge stored on raindrops in cubic kilometers of cloud volume drained and channeled to yield a pilot leader channel some meters in diameter? 2. How is this hydrometeor-supported discharge able to leave the cloud base and forge into clean, initially un-ionized air to give a stepped leader? 3. What causes stepping? 4. How is the channel several kilometers in length maintained conducting for the tens of milliseconds needed for it to reach ground? 5. How is it that the stepped leader of some meters diameter leads to a return stroke channel with the most intense luminosity millimeters in diameter and the larger luminous conducting envelope no more than 4 cm in diameter? 6. Why is the pilot leader channel zigzagged? 7. What starts the dart leader stroke and how is the channel maintained conducting for the tenths of seconds between successive strokes?