Lifetime and structures of TLEs captured by high-speed camera on board aircraft

Temporal development of sprite streamer is the manifestation of the local electric field and conductivity. Therefore, in order to understand the mechanisms of sprite, which show a large variety in temporal and spatial structures, the detailed analysis of both fine and macro-structures with high time resolution are to be the key approach. However, due to the long distance from the optical equipments to the phenomena and to the contamination by aerosols, it's not easy to get clear images of TLEs on the ground. In the period of June 27 - July 10, 2011, a combined aircraft and ground-based campaign, in support of NHK Cosmic Shore project, was carried with two jet airplanes under collaboration between NHK, Japan Broadcasting Corporation, and universities. On 8 nights out of 16 standing-by, the jets took off from the airport near Denver, Colorado, and an airborne high speed camera captured over 60 TLE events at a frame rate of 8000-10,000 /sec. Some of them show several tens of streamers in one sprite event, which repeat splitting at the down-going end of streamers or beads. The velocities of the bottom ends and the variations of their brightness are traced carefully. It is found that the top velocity is maintained only for the brightest beads and others become slow just after the splitting. Also the whole luminosity of one sprite event has short time duration with rapid downward motion if the charge moment change of the parent lightning is large. The relationship between diffuse glows such as elves and sprite halos, and subsequent discrete structure of sprite streamers is also examined. In most cases the halo and elves seem to show inhomogenous structures before being accompanied by streamers, which develop to bright spots or streamers with acceleration of the velocity. Those characteristics of velocity and lifetime of TLEs provide key information of their generation mechanism.