High-Speed Video Observations of Needles in a Positive Cloud-to-Ground Lightning Flash

Abstract

High-speed video data were used to analyze the initiation and propagation of 36 needles and their associated 306 flickering events observed in a single-stroke positive cloud-to-ground (+CG) flash. The needles occurred during the return-stroke later stage and the continuing current, within approximate 10 ms after the onset of the +CG return stroke. They initiated near the lateral surface of the predominantly horizontal channel and extended almost perpendicular to that channel. Flickering events are recoil type streamers (or leaders) that retrace the channels created by needles. Flickering events can be repetitive and are classified into four categories based on different scenarios of their occurrence. Needles are caused by the radial motion of negative charge from the hot core of the positive-leader channel into the positive corona sheath surrounding the core, when the core is rapidly recharged (its radial electric field reversed) by the return-stroke process and during the following continuing current.