Collaborative Research: CEDAR--High Time-Resolution Sprite Imaging

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The scientific objective of this study is to determine the processes involved in the formation of sprites, how sprites fit into the larger field of streamer development, and the consequences of sprites on the middle atmosphere. To accomplish this goal, the project will use ground-based high speed cameras to image their spatial and spectral development with unprecedented high temporal resolution. Sprites are large (~50km vertical scale size) luminous events seen above thunderstorms often extending to ionospheric heights. Most sprites are associated with positive cloud to ground lighting strikes, and the optical emissions last only from a few milliseconds to a few 10's of milliseconds. Sprites start at 70 - 80 km altitude with downward propagating streamer heads. In some events upward moving streamer heads are also observed, but upward moving streamers always start later than the downward streamers and further, they start from a lower altitude and from existing bright spots in the sprite body. Previously funded research has shown sprite development to have essentially two phases: an active initial phase characterized by fast moving streamer heads followed by a decay phase in which there is little spatial activity. This analysis work will continue under this project and be augmented by observations taken with new high-speed imagers to record sprites with high temporal and spatial resolution. Slit less spectroscopy will also be used to obtain sprite spectra with ~500m altitude, 0.1 ms (or possibly less) temporal and 10 nm spectral (400-800 nm) resolution. For high spatial resolution a telescope will be used to obtain 3m spatial and possibly 100 s temporal resolution. The program will include use of a roving ground station to allow for triangulation. One field campaign per year will be undertaken. The observations are expected to provide new images with unprecedented temporal, spatial, and spectral resolution, which will aid in providing realistic estimates of the amount of energy and charge deposited into the mesosphere by sprites. The broader impacts of the project includes support of one full-time graduate student who will receive training in both observational and theoretical work suitable for a Ph.D. thesis. Undergraduate cadets from the Air Force Academy will participate in gathering and analysis of the basic data. The project may indirectly extend the use of high frame rate imagery to the ionosphere, thermosphere, and mesosphere community. The observations will be made available to the sprite community, thus providing fundamental observational constraints on the various sprite and streamer theories available.